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This volume contains the proceedings of the 13th International Conference on Damage Assessment of Structures DAMAS 2019, 9-10 July 2019, Porto, Portugal. It presents the expertise of scientists and engineers in academia and industry in the field of damage assessment, structural health monitoring and non-destructive evaluation. The proceedings covers all research topics relevant to damage assessment of engineering structures and systems including numerical simulations, signal processing of sensor measurements and theoretical techniques as well as experimental case studies.



Structural Health and Condition Monitoring


Machine Learning Techniques for Structural Health Monitoring

Structural Health Monitoring has become a hot topic in recent decades as it provides engineers with sufficient information regarding the damages on civil infrastructure by analysing data obtained from the monitoring sensors installed in the structures. Commonly, the process of implementing a damage identification strategy for aerospace, civil and mechanical engineering infrastructure is referred to as Structural Health Monitoring (SHM). The development of smart sensors and real-time communication technologies via Wireless Sensor Networks (WSN) has empowered the advancement in SHM. Recently, statistical time series models have been widely used for structural damage detection due to the sensitivity of the model coefficients and residual errors to the damages in the structure. Increasingly Machine Learning (ML) algorithms are employed for damage detection tasks. This research sheds light on the methodologies to predict the structural damage on concrete structures with the help of sensor technology by effectively combining data science and ML strategies. Experimental test results publicly available are used, where the tests have been performed with varying stiffness and mass conditions with the assumption that these sources of variability are representative of changing operational and environmental conditions in addition to changes caused by damage. To enhance the accuracy of damage detection, instead of the traditional time series analysis, ML is used for learning from prior experience. To detect the existence and location of the damage in the structure, we use supervised learning, and for measuring the severity of the damage, unsupervised learning is used. Accuracy results are obtained with three well-known ML algorithms (KNN- k Nearest Neighbour, SVM-support vector machine and RFC random forest classifier). In this study, the Random Forest Classifier algorithm generated good predictions on damaged and undamaged conditions with good accuracy, when compared to the KNN algorithm and Support Vector Machine algorithm under the supervised mode of machine learning. The utilisation of sensor technology effectively combined with aspects of Artificial Intelligence (AI) such as Machine Learning has the potential to implement a more efficient SHM system.

Bibin Kurian, Ranjith Liyanapathirana

Bridge Monitoring Using Geophones: Test and Comparison with Interferometric Radar

More than 30% of European highway bridges present structural criticalities. Their continuous health monitoring is a priority. Conventional sensors are accurate and reliable, but they are often too expensive for continuous monitoring. Possible low-cost alternative equipment are the geophones, that are able to detect the displacement of structures by integrating in time their response. They can be easily installed and can provide continuous health monitoring by transmitting the data to a remote server.The aim of this paper is to assess the capability of a geophone sensor to provide continuous, accurate and reliable data about the dynamic loads of a bridge. In order to validate its performance, it has been experimentally compared with an interferometric radar. As preliminary test the geophone has been fixed to a horizontal steel plate. The radar has been positioned under the steel plate in order to detect the same displacement component. The steel plate has been excited with controlled pulses. Finally a network of geophone sensors, provided with its control and transmission electronics, has been installed on a well-known bridge in Florence, Italy (the “Amerigo Vespucci” bridge). The interferometric radar has been installed under the deck close to an abutment. The obtained results both in controlled environment and in the in-field test are in good agreement, although the geophone appears less sensible to impulsive stimulus than the radar.

Gabriele Corsi, Ferdinando Frediani, Lapo Miccinesi, Michelangelo Micheloni, Massimiliano Pieraccini

A Damage Detection Method by Transient Damping Feature Based on Monitoring Data

This paper introduces the details of a transient damping feature extracting method based on the bridge monitoring data with the aid of the frequency slice wavelet transform (FSWT) which is a time-frequency space analysis tool and its application to damage detection of the bridges. The proposed method via the state representation methodology (SRM) algorithm has been verified by the state probably density distribution using the vibration signal from a laboratory bridge monitoring system. As a result, the system state vector as a non-parametric state variable will be able to apply to assess the state change (damage) of the bridge structures by expression of the state probably density distribution.

Ayaho Miyamoto

Finite Element Modelling and Damage Detection of Seam Weld

Seam welds are widely used in assembled structures for connecting components. However, the dynamic effects of a seam weld are often difficult to characterise in numerical models for several reasons: (1) it is often not wise to build a fine mesh on the seam line which will add considerable computational cost for a structure with many welds, (2) the mechanical properties of weld materials are not well known; (3) sometimes some geometric information about welds is not known beforehand. In this work, the finite element model of a welding connection part is developed by employing CSEAM element in NASTRAN and its feasibility for representing a seam weld is investigated. Based on this result, a damage detection method by updating the properties of the built CSEAM elements is also proposed for welding quality assurance. The damage takes the form of a gap in the weld which causes a sharp change of model strain energy at the edges of the gap for certain vibration modes. Specifically, the model strain energy shape is used as the objective function. A Kriging model is introduced for efficiency and simulation of a T-shaped welded plate structure to demonstrate the effectiveness of this method.

Xiuming Yang, Huajiang Ouyang, Xinglin Guo, Dongsheng Li

Detection of Multiple Cracks Using an Energy Method Applied to the Concept of Equivalent Healthy Beam

We introduce herein the concept of global stiffness of a damaged beam, and the Equivalent Healthy Beam (EHB) as a damage model. This model simplifies the process of assessing multiple cracks in beams. It consists of a thinner beam with constant cross-section, but with unchanged mass, which stores in each vibration mode identical energy as the damaged beam. Hence, the model has similar frequencies as for the damaged beam. We estimate the amount of the stored energy from the beam deflection under dead mass. Each additional crack provokes a deflection increase, and consequently the beam stores less energy. The resulted EHB becomes therefore thinner. We performed simulations for beams with transversal cracks which are present on the opposite beam faces. By iteratively removing one crack relative to the other, we obtained the values of the deflections and the eigenfrequencies for the first vibration modes. Comparing the separate frequency drop due to cracks with the effect of the concomitantly acting cracks, we demonstrated the superposition principle applies successfully for most locations of the multiple cracks. As an exception, for nearby-located cracks the principle does not apply. In such a case, a bigger frequency drop is noticed.

Gilbert-Rainer Gillich, Alexandra Teodora Aman, M. Abdel Wahab, Cristian Tufisi

Study Regarding the Effect of Crack Branching on the Eigenfrequencies of Beams

The paper presents a study regarding the vibration behavior of Euler-Bernoulli beams which have cracks with complex shapes. The aim is to show that diverse orientations of the crack branches occurring in a given region of the structure produce different changes of the eigenfrequencies for the different vibration modes, dependent on the position and propagation angle of the crack. The research is conducted employing the finite element analyses, which are used to describe the dynamic response of a structure affected by a transversal open crack followed by two branches, each oriented at a different angle. These cracks are traditionally referred to as Y-shaped crack. We calculated the relative frequency shifts for the first six transverse vibration modes and extracted the damage signature for the considered branched crack location. The damage signatures can be used as patterns in damage detection procedures, transforming the procedure of detecting the crack position and severity from the eigenfrequency changes in an inverse problem.

Cristian Tufisi, Gilbert-Rainer Gillich, Codruta Oana Hamat, Tiberiu Manescu

The Application of Spatial Filtration for Damage Detection in Structures with Multiple Poles

For many years, modal analysis and its results has been used to detect and locate damage. Also modal filtration, which is related to modal analysis, was recently applied for this purposes. Especially the method, which involves the detection of peaks that appear on the badly filtered output characteristics of the spatial filter. This poor filtration results from the fact that the spatial filter is tuned for the object in the reference (undamaged) state, and the filtered characteristics are recorded on the structure in the current (possibly damaged) state. Modal filter coefficients are the coordinates of a reciprocal modal vector which main property is orthogonality for all modal vectors except the one for which filter has been set. When the damage occurs, the modal vectors change, and the orthogonality of the reciprocal modal vector ceases to occur. Then the modal filter does not work properly. There are therefore additional peaks on the filtered characteristics and their presence is a symptom of damage.The question arises how the method will work for the system, which contained double or multiple poles. In such a case, badly filtered peaks could be located at the same frequency as the main peak resulting from the natural frequency to which the filter was set. This can lead to failure in damage detection. Therefore, appropriate simulations have been carried out, the results of which will be presented in the article.

Krzysztof Mendrok

Experimental Validation of Damage Indices Based on Complex Modes for Damage Detection in Vibrating Structures

Commonly, the damage detection techniques for structures prone to earthquakes are based on the changes of modal parameters between different structural states, namely before and after a seismic event. Recently, in this context, damage indices based on measures of the imaginary part of complex mode shapes turned out to be an interesting alternative as compared to the direct use of the modal parameters. In fact, numerical simulations proved that the increase in mode shapes complexity comes from the energy dissipated along with damage occurrence. In literature, several indices have been suggested on purpose. However, such indices, for being successful in damage detection, should possess at least two properties with respect to the damage severity: monotony, to guarantee solution uniqueness, and sensitivity, to cope with incipient damage. The present work aims to investigate experimentally the behavior of one of these indices that has been proved the most effective by previous numerical studies. To this end, the results provided by a laboratory physical model subjected to base motion have been used. The damage severity was graded by stepping the amplitude of the base motion so that quasi-linear conditions of the overall structure response can be preserved. The model response was processed via the joint use of the Empirical Mode Decomposition and the Complex Plane Representation methods. The resulting damage index was used to validate the numerical results of previous studies; it was found that numerical and experimental values of the damage index are well comparable.

F. Iezzi, C. Valente, F. Brancaleoni

Application of Modulation Transfer Effect to Damage Detection

The paper presents investigation of modulation transfer effect. This effect - originally observed in the early nineteen thirties in Luxembourg and in Gorky for radio waves propagation in ionosphere - was manifested by modulation transfer of a weaker wave in presence of a strong amplitude-modulated wave. The research are focused for both, application to damage detection and analysis of possible sources of modulation transfer. The different nonlinear model are analyzed to find the potential source of non-linearities responsible for sidebands transfer form low to high frequency. The models include hysteretic stiffness and quadratic damping. In experimental part of the work, modulated low-frequency signal was used as excitation of cracked beam. Simultaneously the high frequency acoustic wave has been introduced to the structure. This combination of excitations induced a modulation transfer from low-frequency to high-frequency wave in presence of structural damage. Surface bonded piezoceramic transducer and electromagnetic shaker were used to excite the structure. Laser vibrometry was used to acquire the response of the structure. The experimental work presented focuses on the analysis of modulation intensities and damage-related nonlinearities. The paper demonstrates that the method can be used for fatigue damage detection.

Jakub Górski, Andrzej Klepka

Application of Wavelet Analysis for Crack Localization and Quantification in Beams Using Static Deflections

Wavelet analysis has been proven to be an efficient tool for identifying singularities in signals, such as the effect of damage in structural deflections. This paper establishes a new approach applying this technique to identify cracks in beams using static measurements. The deflection difference of the beam before and after damage is a piecewise polynomial with discontinuities at crack locations. The crack positions can be identified at apexes of the continuous wavelet transform coefficients. At damage locations, a damage index can be defined from the y-intercept of the linear regression between the logarithms of wavelet coefficients and their corresponding scales. By normalizing itself to the internal bending moment at the damage location, the damage index becomes damage location independent. Through a numerical model, a reference map between the crack depth and the damage index can be established and further used for damage severity assessment.

Qiaoyu Ma, Mario Solís

Using Enhanced Cepstral Analysis for Structural Health Monitoring

Mel-Frequency Cepstral Coefficients (MFCCs) have been proved to be viable to detect damage-induced shifts in the frequency content of structures subjected to external forces. Nevertheless, the Melodic (Mel) Scale is a perceptual feature, roughly based on human perception and originally formulated to resemble the biological mechanisms of the auditory apparatus. Thus, its straight application to non-auditive acquisition systems may be misleading. However, the intrinsic basilar assumption – that is, a nonlinear, non-constant spacing between filters in the frequency domain – is promising for the time-frequency analysis of structural dynamic behaviour. Here, an ensemble of related techniques, developed departing from the original approach, is described; different features, filter types and filter spacing have been investigated. Candidates are compared to each other and benchmarked against the previous approaches present in Literature on the challenging Case Study of the Fossano Bell Tower, considering realistic damage scenarios.

M. Ferraris, M. Civera, R. Ceravolo, C. Surace, R. Betti

Operational Modal Analysis of Y25 Bogie via Stochastic Subspace Identification for the Condition Monitoring of Primary Suspension Systems

Railway vehicle suspension systems are vital to the vehicle safety and ride comfort, which is further driven by high speed operations. Condition Monitoring (CM) based online measurement is an efficient and achievable method to ensure the suspension systems working under normal function. In this paper, a potential method, which can achieve online CM of railway vehicle primary suspension, denoted as Average Correlation Signals based Stochastic Subspace Identification (ACS-SSI) was explored through simulation and experimental studies. Particularly, the dynamic performance of an Y25 bogie were investigated under the operational condition and the main focus was on the modes related to the suspension system. Firstly, ACS-SSI was presented briefly. Then, the employed test rig, an advanced dynamic test cell in the Institute of Railway Research (IRR) at University of Huddersfield, was introduced and the theoretical modal parameters of the tested bogie associating with the primary suspension system were calculated based on a multi rigid body model in the SIMPACK. The theoretical natural frequencies of bounce, roll and pitch modes are 11.07 Hz, 13.93 Hz and 15.19 Hz, respectively. Finally, ACS-SSI was adopted to identify modal parameters of the bogie using the collected responses on the four corners of the bogie frame. The pitch mode was identified successfully, which can illustrate the condition of the suspension system. Therefore, it can draw the conclusion that ACS-SSI has the potential to achieve suspension online monitoring.

Fulong Liu, Jiongqi Wang, Miaoshuo Li, Fengshou Gu, Andrew D. Ball

A Comparative Study on Data Manipulation in PCA-Based Structural Health Monitoring Systems for Removing Environmental and Operational Variations

Vibration-based structural health monitoring (VSHM) methodologies provide a robust, data-driven, system for damage diagnosis. However, there are a few challenges that are currently being investigated to ensure the systems are more reliable for decision-making. The features selected from the vibration responses are not only sensitive to damage but also to environmental and operational variations (EOV). This paper aims to investigate the use of a principal component analysis (PCA) based system for VSHM. In particular, the aim is to compare different approaches, using the same dataset, to explore the effect that data manipulation has on the damage detection capabilities of such a system when it is corrupted by EOV. The data that was used for this study was first taken from a simulated five degree of freedom spring-mass-damper system and secondly from an in-operation Vestas V27 wind turbine with damaged and undamaged scenarios. The simulated system was subjected to varying temperatures and involved four states; one healthy state followed by three states with increasing damage, represented by the reduction of a spring stiffness. Each combination of data manipulation was compared to determine their performance and limitations on removing EOV for reliable damage diagnosis.

Callum Roberts, David Garcia, Dmitri Tcherniak

Damage Localisation in Thin Plates Using the Inverse Finite Element Method

This work investigates the use of the inverse Finite Element Method (iFEM) for damage localisation by reconstructing the damaged strain field of the structure. The iFEM is a proven technique for reconstructing the displacement field of a structure using surface strain measurements from discrete locations on the structure. This new approach divides a large structure into square grid cells with strain sensors located only at the boundaries of these cells. Presence of a crack in a cell causes perturbations in the strain measurements at the boundary. The iFEM reconstructed strain field will show a higher strain magnitude in those cells affected by damage in comparison to healthy, unaffected cells of the structure. Using such a relative rather than absolute measure of strain for damage localisation helps to reduce the number of strain sensors required for the Structural Health Monitoring (SHM) of large structures.

Rinto Roy, Marco Gherlone, Cecilia Surace

Damage Localization and Quantification in Structures Using Residual Force Indicator

This paper presents damage identification and assessment methodology based on the changes in dynamic parameters of structures. According to continuum damage mechanics, the damage is represented by a reduction in stiffness. A Residual Force Method (RFM) and modal strain energy change ratio (msecr) were studied in this paper to predict the damage location. In order to demonstrate the accuracy of this method, three examples are included using free-free beam, truss structure and 3-dimensional frame structure. Single and multiple damages are considered for all structures to investigate the accuracy of these indicators. The obtained results show that RFM is capable of detecting the location and severity of diagnostic even in large-scale structures with a large number of elements.

M. Slimani, S. Tiachacht, S. Khatir, A. Behtani, L. Mansouri, A. Bouazzouni, M. Abdel Wahab

Damage Detection in Truss Structures Using Transmissibility Combined with Optimization Techniques

The paper presents an effective approach based on Modal Assurance Criterion (MAC) formulation, transmissibility function and Particle Swarm Optimization (PSO) for damage assessment in truss structures. The Finite Element Method (FEM) is used to build the structures using Matlab. The main purpose of this study is to apply the transmissibility technique as an objective function based on MAC formulation to predict the damage location and severity. The objective function used in the proposed approach is based on transmissibly using MAC formulation (TMAC). The results show that the present methodology can reliably identify damage scenarios with higher accuracy even in case of complex structures.

Roumaissa Zenzen, Samir Khatir, Idir Belaidi, M. Abdel Wahab

Bolted Joint Monitoring Using the Elastic Wave Propagation

The paper presents an analysis of wave propagation through the contact zone in pretensioned bolted lap joints. A mathematical Schoenberg’s model of wave propagation through the interface between two elastic media was discussed. The experiment was carried out using piezoelectric transducers. A single lap joint with different preload levels was examined. The value of the bolt load was measured by a force washer transducer. In the first step, an indicator based on the signal energy was tested. It has been shown that the visible trend is observable only for selected frequency and small range of bolt load. For this reason, advanced signal processing techniques were used for quantitative comparing the recorded signals. The presented experimental results are consistent with the theoretical prediction and they can be used to monitor the bolted joint state in a wide range of the pretension force.

Rafał Kędra, Magdalena Rucka

A Generic Framework for Application of Machine Learning in Acoustic Emission-Based Damage Identification

Advanced non-destructive monitoring scheme is necessary for modern-day lightweight composite structures used in aerospace industry, due to their susceptibility to barely visible damages from minor impact loads. Acoustic emission (AE) based monitoring of these structures has received significant attention in the past few years primarily due to their possibility of use in operating structures under service loads. However, localization and characterization of damages using AE is still an open area of research. The exploration of the space of signal features collected by a distributed sensor network and its reliable mapping to damage metrics (such as location, nature, intensity) is still far from conclusive. This problem becomes more critical for composite structures with complex features/geometry where the localized effects of discontinuity in geometric or mechanical properties do not make it appropriate to rely on simple signal features (such as time difference of arrival, peak amplitude, etc.) to identify damage. In this work, the AE signal features (which are spatially and temporally correlated) have been mapped to the damage properties empirically with a training dataset using metamodeling techniques. This is used in the online monitoring phase to infer the probabilistic description of the acoustic emission source within a hierarchical Bayesian inference framework. The methodology is tested on a carbon fibre composite panel with stiffeners that is subjected to impact and dynamic fatigue loading. The study presents a generalized machine learning-based automated AE damage detection methodology which both localizes and characterizes damage under varying operational loads.

Abhishek Kundu, Shirsendu Sikdar, Mark Eaton, Rukshan Navaratne

Selection of Small Sensor Arrays for Localization of Damage in Complex Assemblies Using Vibro-Acoustic Signals

A procedure is proposed to suggest a good placement of sensors to form an array of a pre-defined size in order to localize damage in complex assemblies using the Time-Reversal MUltiple SIgnal Classification (TR-MUSIC) algorithm. The technique takes into account the amount of information that can be obtained from each possible sensor location and the difference in information provided by each possible sensor location. The proposed procedure is successfully validated on the numerical example of an aluminium framework and on the experimental example of an aluminium framework covered by a honeycomb panel.

Philip Becht, Elke Deckers, Claus Claeys, Bert Pluymers, Wim Desmet

Efficient Algorithm for Frequency Estimation Used in Structural Damage Detection

In damage detection processes, the accuracy of estimating the eigenfrequencies of structures is crucial because the frequencies are not highly sensitive to damage. This paper analyses the accuracy of the Discrete Fourier Transform when estimating the frequency and amplitude of sine waves, identifies its limitations and proposes an algorithm to significantly improve the attained results. Standard methods used to evaluate the eigenfrequencies fail because the results depend on the position of the spectral lines, which are related to the acquisition time. Frequently, interpolation involving the amplitude peaks displayed on several spectral lines located around the maximizer is employed to improve the frequency readability. The estimated results are improved indeed, but the achieved precision still depends on the acquisition time. We develop an algorithm that uses the maximizer of signals with different time lengths, which are obtained from the original acquired signal by cropping. The three selected maximizer are used for parabolic interpolation input data. The maximum of the regression curve represents a precise estimate of the amplitude, associated with the true frequency of the targeted harmonic component. The efficiency of the algorithm is demonstrated for harmonic and multi-harmonic signals.

Gilbert-Rainer Gillich, Dorian Nedelcu, Cristian-Tatian Malin, Istvan Biro, M. Abdel Wahab

Damage in Civil Engineering


Modal Property Extraction Based on Frequency Domain Stochastic Subspace Identification

Structural integrity can be investigated through observing modal properties (e.g., natural frequencies, mode shapes, and damping ratios) determined by system identification methods. To understand the dynamic behavior of a structure over time, automated modal tracking techniques are developed to reduce human-computer interaction. Moreover, modal tracking using earthquake responses is essential since the magnitudes of ambient vibrations are less effective for structural responses as well as for identification. Therefore, this study is focused on performance evaluation of the automated frequency-domain stochastic subspace identification (SSI) under both ambient and seismic excitations. The method first divides the measurements into sequential portions and then employs the refined frequency domain decomposition (rFDD). A peak-picking method is subsequently applied to extracting modal candidates with respect to natural frequencies in accordance with the rFDD results. The sequential portions of measurements are also used to construct the accumulated frequency-domain Hankel matrix, and the Hankel matrix is utilized for the frequency-domain SSI. Finally, the modal properties of the stable structural modes are selected from quick stabilization diagrams. In the numerical example, the proposed method is applied to a constant-stiffness structure with 500 sets of ambient excitation events in order to examine the stability and accuracy. Moreover, the proposed method is investigated for a continuously degraded structure using 500 sets of ambient excitation events of which the structure encounters an aging problem. Additionally, seismic excitation events are also examined using the proposed method. As a result, the proposed method is capable of extracting modal properties of structures under different types of excitations with high accuracy and shows consistency in modal tracking.

Jau-Yu Chou, Chia-Ming Chang

Damage Assessment of a Cloister Vault

Vibration-based damage identification methods are fundamental tools for the condition assessment of historical constructions prone to earthquakes. However, despite the substantial advances in the field, several issues must still be deepened to broaden the application range of such tools and to assert their effectiveness. This is particularly true for the vaulted systems considering their modal characteristics. This study deals with the damage detection of a cloister vault of the Middle Age castle sited in Bussi sul Tirino (Abruzzo, Italy), an area of moderate seismicity, which was significantly damaged by an earthquake in 2009. Due to the impossibility to have experimental measures related to the non-damaged initial state, an a priori numerical model of the undamaged vault is set up using the geometrical and mechanical properties measured on site. Ambient noise measurements were then carried out to identify the dynamic behaviour of the cloister vault in the current situation, where seismic damage is present. The a priori model is then updated on the basis of the modal parameters identified by the ambient noise measurements. The differences between the a priori and updated models are analysed to identify the presence of damage. The results found allow for discriminating the real structural damage suffered by the vault.

A. Di Primio, N. Fiorini, D. Spina, C. Valente, M. Vasta

Ensemble Technique for Machine Learning with Application to Monitoring of Heritage Structures

Recent studies have demonstrated the effectiveness of machine learning techniques in the context of Structural Health Monitoring (SHM), where they can be applied to distinguish operational and environmental changes of dynamic features from those related to the evolution of damage. For instance, the combination of these techniques with the cointegration, a theory usually employed in econometric studies, has led to promising results, even in the detection of damage in complex monumental buildings. Several algorithms, including Support Vector Machine and Relevance Vector Machine, can be used for implementation of the multivariate regression required in the method. The choice of the algorithm to apply and the parameters to set can drastically influence the results and can lead to a wrong perception of the structural health. This paper proposes a combinatorial selection of machine learning algorithms and their settings to define the most performing among several optimal results. The ranking problem is solved by using the Plackett–Luce (PL) model-based strategy. The final aim is to obtain the damage indicator as indifferent as possible to harmless environmental and operational variations but still sensitive to structural changes, suitable to investigate the dynamic response of a structure. Data recorded by the dynamic monitoring system installed on the Sanctuary of Vicoforte, which contains the largest masonry oval dome in the world, and a calibrated finite elements model of this structure are used to simulate a damaged condition, in order to demonstrate the proposed strategy for SHM.

Giorgia Coletta, Gaetano Miraglia, Rosario Ceravolo, Cecilia Surace

Sensitivity to Damage of the Forced Frequencies of a Simply Supported Beam Subjected to a Moving Quarter-Car

The vibration of bridges under operational conditions can be measured via accelerometers to extract their dynamic features. These features can then be monitored in time, although only a reduced number of cause-effect scenarios can be verified on the field. Therefore, theoretical models of the bridge are often employed for covering a wider range of scenarios. For instance, a variety of damage conditions can be introduced in a calibrated bridge model to obtain the associated frequencies, which can be subsequently compared to frequencies measured on-site for assessing the bridge condition. It must be noted that these frequencies may be influenced by factors other than damage, i.e., environmental effects due to temperature changes and operational effects due to traffic. During the forced vibration of a bridge caused by a moving vehicle, the frequencies governing the bridge response depend on the mass and stiffness ratios of the vehicle to the bridge. Therefore, records in free vibration are usually preferred or alternatively, the influence of operational loads is removed from forced vibration records before assessing whether damage has occurred or not. This paper shows that forced vibration stores relevant information about damage beyond the frequency changes derived from free vibration. Eigenvalue analysis is employed to investigate how forced frequencies change with the positions of a crossing vehicle and damage. The vehicle is modelled using a quarter-car and the bridge as a simply supported finite element beam, where damage is introduced via localized stiffness losses.

Arturo González, Miguel Casero, Kun Feng

Physical and Virtual Implementation of Closed-Loop Designs for Model Updating

A recently proposed virtual implementation of output feed-back based on signal processing eliminates the practical overhead associated with physical operation in closed loop. Additionally, the virtual implementation facilitates realization of multiple closed-loop systems from a single test in open loop, allows for complex gains, and removes the constraint of closed-loop stability. Care must, however, be exercised in the design of the closed-loop systems, as the errors in these are governed by the intrinsic approximations in the open-loop identification. The present paper offers an examination of this item when the closed-loop systems are designed for parameter estimation in updating of numerical models of structural systems. The differences between physical realization and the proposed virtual implementation are discussed, and the pivotal points outlined are demonstrated in the context of a numerical examination with a structural system.

M. S. Jensen, T. N. Hansen, M. D. Ulriksen, D. Bernal

On Gain Design in Virtual Output Feedback for Model Updating

The set of equations to be solved for parameter estimation in model updating has no unique solution when, as will often be the case in structural applications, the dimensionality of the model exceeds the number of target parameters estimated from experiments. One approach for enlarging the target space is to create closed-loop systems that, in addition, can be designed with pole sensitivities favorable for updating the model. The present paper will focus on designing gains for model updating using a recently proposed virtual implementation of output feedback, which allows computation of several closed-loop systems from a single open-loop realization and removes the constraint of closed-loop stability. The gains are designed through an eigenstructure assignment procedure, in which the model parameters of interest in the updating are divided into two different classes; one where the pole sensitivities with respect to the parameters are to be enhanced and one where they are to be reduced. A numerical example with a structural system is presented that demonstrates the merit of the proposed gain design procedure.

Martin D. Ulriksen, Dioniso Bernal

Damage Assessment in Beam-Like Structures Using Cuckoo Search Algorithm and Experimentally Measured Data

This paper presents an approach for damage identification in a steel structure using Cuckoo Search (CS) algorithm. CS is an evolutionary algorithm based on global search techniques, which provides a higher opportunity for seeking the best solution and avoid local minima. A steel beam calibrated on experimental modal analysis is applied to assess the efficiency of the proposed algorithm. While a finite element (FE) model is created using MATLAB to estimate structural dynamic behavior, measurement is carried out using excitation sources of a hammer. Dynamic characteristics are selected as an objective function to minimize the discrepancy between the results of numerical model and measurements. The results show that the proposed algorithm can accurately identify damage location and extents in the considered structure.

H. Tran-Ngoc, S. Khatir, G. De Roeck, T. Bui-Tien, M. Abdel Wahab

State Evaluation of Centrifugal Compressor Unit Based on Parameter Distribution

To evaluate the state of centrifugal compressor unit, this paper presents a method based on Logistic Regression Model and Gaussian Model. First, the improved failure mode and effect analysis (FMEA) is used to select important unit parameters on the basis of subsystem of centrifugal compressor unit. And weights of selected important parameters are determined by means of analytic hierarchy process (AHP). Thus, the state evaluation index is established. Then, the distribution models of the parameters in state evaluation index are determined according to its characteristics. Meanwhile, the corresponding parameter distribution model is constructed based on the alarm range of each parameter. Finally, the quantitative evaluation model of centrifugal compressor unit is established using the evaluation value of each parameter distribution model instead of the expert experience score. We applied the model to a motor-driven centrifugal compressor unit in a gas transmission station, and the evaluation result demonstrates the model can evaluate the state of compressor unit accurately.

Yuan Li, Zeyang Qiu, Ling Fan, Xiaolu Tan, Tianyou Qiu

Crack Identification in Multi-Span Beams on Elastic Foundation by Using Transfer Matrix Method

In this study, an analytical based approach is proposed for detection of cracks in multi-span Euler-Bernoulli beams on Winkler foundation. Transfer matrix method (TMM) is used for both forward and inverse problems. The crack is modeled by means of a linear rotational spring. For the forward problem, natural frequencies of intact and cracked multi-span beam models are calculated via TMM for two different support arrangements and the results are compared with those obtained using finite element method (FEM). In the inverse problem, the crack location and crack length are calculated based on the natural frequencies obtained from FEM simulations using plots of rotational spring flexibilities versus crack location. The predicted crack properties are tabulated with actual data. It is seen that considering elastic foundation slightly decreases the accuracy of crack depth prediction for multi-span beams. However, the accuracy of localization of crack is not affected by Winkler foundation.

Baran Bozyigit, Irem Bozyigit, Yusuf Yesilce, M. Abdel Wahab

Non Destructive Inspection of Corrosion in Rock Bolts Using an Ultrasonic Waveguide Approach

Rock bolts are used frequently to consolidate and stabilize the rock mass in mining and civil engineering structures. Since their installations decades ago, there are concerns that corrosion might have set in, increasing the risk of a lack of holding strength.In this study, preliminary measurements in rock gallery sites have shown that ultrasonic wave guide technic is able to determine the length of rock bolts. Then tests were undertaken on 4 m long bolts with different defects imbedded in a concrete block. They all respectively had different artificial defect to simulate corrosion or fracture in terms of cross-section reduction, length of loss of contact and crack. Besides depth of the defect, the following variables were added: the loss of contact length, the position of the defect and the length of bolt, with measurements taken for different conditions.Based on a physical model for the wave energy propagation and reflection, an inspection method was developed to evaluate the effects of corrosion on section reduction, cracks and loss of contact. Results show a good correlation of the wave energy propagation model to the reflections of the different types of defects. Corrosion type defects (modelled by tapered reduction) were discriminated from crack defects through a signal analysis technic. Also, a reflection from a major defect was differentiated from an end of bolt reflection using the propagation model. Finally, a third approach was developed to identify the presence of a “ghost defect” and to determine its length of loss of contact and its influence on the end of bolt reflection. A thorough inspection method to determine anchor bolt corrosion has been put forth encompassing several inspection parameters.

André Taras, Kaveh Saleh

Effects of Measuring Techniques on the Accuracy of Estimating Cable Tension in a Cable-Stay Bridge

Nowadays, many methods have been employed to estimate the cable tension in a cable-stayed bridge. In these methods, the non-destructive test has a widespread application thanks to its feasibility and effectiveness. The vibration-based approach determines the cable tension based on natural frequency. In fact, there are many factors that can influence the tension values. Some of them are derived from objective factors, others from subjective factors. In this paper, a subjective issue, so-called measurement technique, is studied. A cable, without fillings between the HDPE duct and strands, is the main object of this study. In the first step, some scenarios related to the placement of sensors are conducted. The former considers the tension between different positions of sensors, directly and indirectly contact conditions with strands, under the ambient and pulling-rope excitation. The latter takes into account the directions, out-of-plane and in-plane, of sensor placement on the strands or HPDE duct. In the next step, the relationship between the force and frequency is utilized to identify the mean tension of the cable. In the finally step, results of cable tension estimation are compared with the real-time monitoring and finite element (FE) simulation. From the comparison, the effects of measuring technique in situ are discussed in the conclusion.

Viet Long Ho, Thanh Nam Hoang, Guido De Roeck, Tien Thanh Bui, M. Abdel Wahab

Finite Element Analysis of Pile Foundations Under Surface Blast Loads

Recent terrorist attacks on important buildings raised the significance of analysis of structures under blast loads in order to seek mitigations measures to have safer structures under such threats. Most of recent studies consider the superstructure only since it is the major part affected by the blast loads. However, the foundations may be affected severely as well. This can make the superstructure repair is impractical or inefficient. In this research, detailed finite element analysis using ABAQUS was used to study the effect of blast loads on the response of soil and nine reinforced concrete piles buried in the soil and connected by a 10 m × 10 m × 1.0 m reinforced concrete raft. The piles have a 0.6 m diameter and a length of 20 m. Drucker-Prager Cap model was used to model the soil behavior. The model accounts for soil hardening and softening and stress path dependence. The raft and piles were modelled using 8-node solid elements with reduced integration. The concrete damage plasticity model was used to model the reinforced concrete material for the pile and raft. The blast load was considered through several explosive weights of TNT at a height of 0.66 m above ground surface. The effect of standoff distance was studied through five different distances from the raft edge. Finally, observations and recommendations were provided to enhance the response of pile foundations under blast loads.

Yasser E. Ibrahim, Marwa Nabil

Recurrence Analysis for Damage Detection and Localization in Beam Structure

In the paper, application of the Recurrence Plots (RP) method to damage detection and localization in the beam structure is proposed. The RP is a well-established method of nonlinear data analysis dedicated to investigation into changes in dynamic behaviour of mechanical systems during their normal work. Interpretation of information provided by the recurrence plots can be supported by the estimation of the measures of Recurrence Quantification Analysis (RQA).The main emphasis of the paper is put on damage detection and localization in the aluminium beam subjected to burst random excitation provided by the electrodynamical shaker. In order to simulate the damage, the notch of known parameters and position was introduced to the system. System responses in the form of time series measured by vision methods (fast cameras) were analysed with the application of the RP and RQA methods. Obtained results proved high sensitivity of the applied methods to changes in dynamical system properties resulting from damage initialization.

Joanna Iwaniec, Krzysztof Mendrok, Ángel J. Molina-Viedma, Łukasz Pieczonka

Fault Detection for a Satellite-like Structure Using Sine Sweep Vibration Test Data

Sine sweep vibration test is one of the most important means for verifying the dynamic environmental adaptation and assessing the structural dynamic characteristics of a satellite structure, which should be generally carried out on the ground before launching. Many vibration-based techniques have been investigated and applied to civil structures and mechanical systems. However, very few studies have been reported on their applications to satellite structures. This paper makes fault detection of a satellite-like structure using sine sweep date. Firstly, the time and frequency domain acceleration responses on some specified points are measured to form the fault detection indicators respectively, which are derived from the variational modal decomposition technique. Then the indicators of three-dimensional tests are combined based on Dempster-Shafer’s evidence theory. Finally, the proposed method is implemented in an experimental study on a two-story satellite-like structure. The result proves the effectiveness and feasibility of the proposed method. In addition, the effect of selection of data segments on the detection results is also discussed.

Gao Haiyang, Guo Xinglin, Xie Yicun, Yang Yanjing, Ouyang Huajiang

Debonding Detection in Reinforced Concrete Beams with the Use of Guided Wave Propagation

One of the most frequent damage of the reinforced concrete structures is debonding between steel bar and concrete cover. In the case of debonding occurrence not only the strength of the structure decreases, but also it is more vulnerable to corrosion damages. For this reason fast and effective methods of debonding detection in an early stage of its development need a significant boost. The paper presents analytical and experimental investigation of debonding detection in reinforced concrete beams using non-destructive method based on guided waves propagation. Concrete beams of rectangular cross-section consisting of four steel rebars with pre-existing debonding are investigated. Lack of adhesive connection between one rod and concrete cover is provided by introducing cellophane film of a small thickness (90 μm). The research is focused on detection of debonding with variable length on the basis of time-domain signals captured by piezoelectric sensors. Presented method of damage detection takes advantage of the time of flight of the reflections registered at the ends of the specimens.

Beata Zima

On the Model Order in Parameter Estimation Using Virtual Compensators

Processing signals from open-loop system realizations can replace real-time operation using actuators in the design of closed-loop eigenstructures. One merit of the signal processing-based implementation is that it, in principle, allows virtual compensators of user-defined model order since the closed-loop systems are not to be realized during physical testing. The present paper explores the implication of the virtual compensator order in terms of the Fisher information on unknown parameters to be estimated in a model updating context. A numerical example with a structural system of engineering interest is presented that demonstrates the basic points outlined in the paper.

Tommi Navntoft Hansen, Martin Skovmand Jensen, Martin Dalgaard Ulriksen, Dionisio Bernal

Smart Acoustic Band Structures

Smart acoustic band structures exhibit very interesting and non-standard physical properties due to the periodic nature of their certain characteristic on different scale levels. They manifest mostly in their frequency spectra as so-called frequency band-gaps or stop-bands, what has a great impact on the behaviour of these structures in relation to the propagation of vibro-acoustic signals that can be transmitted through the structures in some precisely defined frequency bands. Properties of acoustic band structures are directly linked to their geometry on the level of the unit cell, which parameters determine structural dynamics of such structures on the macroscopic scale. Here the piezoelectric transducers play a significant role. The combined exploitation of active properties of acoustic band structures equipped with active piezoelectric elements, in order to filter or damp transmitted vibro-acoustic signals, allows for very effective their applications. In their paper, the authors present certain results of certain computer simulations by the time-domain spectral finite element method, related to 1-D smart active and passive acoustic band structures supplemented with experimental measurements.

Wiktor Waszkowiak, Arkadiusz Żak, Magdalena Palacz, Marek Krawczuk

Damage in Machineries


Development of a Novel Solution for Leading Edge Erosion on Offshore Wind Turbine Blades

In recent years, wind energy has become a leading source of renewable energy as the world strives to remove its reliance on fossil fuels. With the growing demand for wind energy, wind farms have begun to move offshore and the size of the average wind turbine has increased (up to 10 MW). However, as a result of these advances, additional challenges are presented – one of the most significant being leading edge erosion on wind turbine blades. This erosion requires additional maintenance, while lowering a turbine’s annual energy production by up to 25%, which needs to be eliminated, or significantly reduced, if offshore wind energy is to become competitive within global energy markets. To this end, in this paper, the methodology proposed in LEAPWind, a new collaborative European research project, which aims to prevent blade leading-edge erosion by employing advanced composite materials and innovative manufacturing processes has been presented. An advanced thermoplastic-epoxy composite material is used to manufacture a leading edge component for a wind turbine blade. The critical technical stages, including material identification and characterisation, component design and manufacture have been discussed. Additionally, the details relating to de-risking of the novel technologies through mechanical and rain erosion testing, and full-scale operational trials on a 2.1 MW wind turbine, located in an onshore wind farm in Portugal, has been included. The results of this study, will not only have social and economic benefits, but also a significant environmental impact as it will allow for the manufacture of a more sustainable wind turbine blade.

William Finnegan, Tomas Flanagan, Jamie Goggins

Fault Diagnosis of Shaft Misalignment and Crack in Rotor System Based on MI-CNN

Focusing on the difficulty in distinguishing the shaft misalignment and crack in a rotor system, a fault diagnosis method based on multi-input convolutional neural network (MI-CNN) is proposed in this paper. The time-domain vibration signals are directly taken as the input of a one-dimensional convolutional neural network, which are collected on the test bench in the conditions of health, shaft misalignment, crack and misalignment-crack coupling of the rotor system. Kernels of different sizes are adopted to extract the signal features of diverse dimensions at different input ends to fully use the information of the raw vibration signals, and then the extracted features from each input end are fused adaptively. Finally, the classification of shaft misalignment and crack of the rotor system is completed by softmax function. The results show that the intelligent diagnosis of shaft misalignment and crack in the rotor system can be realized effectively by the proposed method, and eventually the recognition rate reaches 99.42%, which has better accuracy and stability compared with other intelligent algorithms. The study achievements can provide a basis for intelligent fault diagnosis of rotating machinery.

Wang Zhao, Chunrong Hua, Danyang Wang, Dawei Dong

Development and Tuning of a Simplified 1D Model for Generation of Transient States in Large Turbomachinery

The Machine Learning methods require a large data sets for model training and it often causes a problem in a real application. Usage of a model based approach to generate the data can be a way to generate data in various degrees of malfunctions, e.g. with different sizes of unbalance.The aim of this paper is to demonstrate the applicability of a 1D rotor-bearing model to reproduce the unbalance conditions during rotors coast-down operation. The model parameters adjustment case study is focused on an application of the model in order to reproduce rotor unbalance conditions of a 200 MW steam turbine. The rotor coast-down operation is considered to reduce external forces related to start-up or steady-state rotor operation. This allows to reduce and in turn clearly isolate unbalance conditions. The developed 1D model consists of first-principle rotor motion equations along the hydrodynamic bearing-support and foundation equations. The gray-box approach was applied to reduce the number of parameters required to be adjusted during system identification process. The rotor geometry and related mass-stiffness parameters were derived from the bearing-rotor assembly drawings while other phenomenological parameters were adjusted based on the measurements to obtain a good correlation with amplitude of vibrations at measurement locations along the shaft line.

Tomasz Barszcz, Piotr Czop, Mateusz Zabaryłło

Static Strength Analysis of Centrifugal Compressor Balance Plate Based on Finite Element Method

After the centrifugal compressor balance disc is installed in the final stage impeller, the rotor system can be protected because the axial force of the rotor is offset by the axial thrust generated by the pressure difference between the two sides. The balance plate plays an important role in the safe operation of the centrifugal compressor rotor system, and its strength is the guarantee for the safe operation of the centrifugal compressor. In order to analyze the reliability of the balance disc, this paper uses the static finite element method to analyze its strength. Considering the influence of centrifugal force, the stress and strain distribution of the balance plate under different rotating speeds are obtained, which plays a certain reference role for the design of the balance plate. The stress and strain distribution of the balance disc under the single action of centrifugal force is studied, and the influence of rotating speed on the strength of the balance disc is obtained.

Yuan Li, Zeyang Qiu, Yu Zhang, Zhenyu Ding, Ling Fan

Modulation Signal Bispectrum Analysis of Motor Current Signals for Condition Monitoring of Electromechanical Systems

Induction motor is one of the most widely used prime drivers and electric energy consuming devices in industry. Accurate and timely diagnosis of faults in motors will help to maintain their operating under optimal status and avoid excessive energy consumption and severe damages to systems. In this study, instantaneous motor current and voltage signals (IMCVS) is analyzed by an advanced Modulation Signal Bispectrum (MSB) method to achieve accurate demodulations of Frequency Modulation (FM) and Amplitude Modulation (AM) by minimizing noise influence and enhancing modulation characteristics simultaneously. Firstly, the modulation effects due to motor faults and downstream mechanical components were modelled, thus finding the interaction between AM and FM effect and hence developed a scheme to use the signature of AM and FM jointly for accurate fault diagnosis. Then experimentations were carried out to verify the performance of the proposed scheme in detecting and diagnosing common mechanical faults including Shaft Misalignments(SM), Motor Rotor Broken Bar (BRB), Stator Resistance Imbalance (SRI) and compound BRB with SRI

Funso Otuyemi, Haiyang Li, Fulong Liu, Jiongqi Wang, Fengshou Gu, Andrew D. Ball

Diagnosis for Timing Gears Noise of a Diesel Generating Set

There is an abnormal noise generated from the timing gears while practicing for the commissioning of a diesel generator set. As the load increases, this phenomenon becomes more apparent. In order to find the cause of the noise, a fault diagnosis model is established which considers not only the gears but also the effects of the associated structures. After eliminating the possible reasons such as the defects of timing gears, the abnormality of the valve system, fuel system controllers and generator, the injector problem is suspected to cause the fault. To verify this conjecture, the fuel injection pumps of the diesel generator set are inspected and the second injector is found to be blackened with some carbon deposition. By replacing the injector, the noise is gone. Hence, the fault diagnosis model can provide a new tool for future diagnosis of gear fault.

Wanyou Li, Chongpei Liu, Yunbo Hu, Shuwen Yu, BingLin Lv, Yibin Guo

Adaptive Feature Selection for Enhancing Blade Damage Diagnosis on an Operational Wind Turbine

Monitoring wind turbine blades (WTB) is an important aspect when assessing the health of wind turbines. Structural Health Monitoring (SHM) systems enable continuous monitoring of the condition of WTB during operation. When SHM is coupled with advanced data analysis techniques, damage detection can be improved by customizing the methodologies to the structure being monitored. The work presented in this manuscript introduces an SHM methodology based on a Semi-supervised damage detection algorithm that uses preliminary findings to reinforce the selection of features used to identify damage. The methodology proposes a novel technique for feature extraction by sorting the acceleration values in each vibration response. Then, an adaptive feature selection algorithm is applied to identify the most sensitive characteristics of the feature for damage detection. This technique enhances the correlation between measurements of the same blade status and therefore the performance of the proposed SHM methodology. The methodology was implemented on real acceleration measurements on an operational Vestas V27 WTB. The results were compared with those from an alternative Semi-supervised methodology that considers only the measurements from the undamaged WTB. The comparison of the results demonstrated that the proposed adaptive feature selection algorithm enhances damage diagnosis.

Artur Movsessian, David Garcia, Dmitri Tcherniak

Condition Monitoring of Wind Turbines Using Adaptive Control Charts

Due to the harsh working environments, variable speeds and alternating loads, wind turbines are likely to breakdown or suffer damage. Effective condition monitoring methods for wind turbines are essential for maintenance decisions which aim to reduce O&M costs. A typical supervisory control and data acquisition (SCADA) system records comprehensive wind turbine condition parameters, which would be fault informative. Thus, a framework for condition monitoring of wind turbines is introduced based on adaptive control charts and SCADA data. The adaptive exponential weighted moving average (AEWMA) is proposed for abnormal state alarm of wind turbines. Random forest (RF) is used for feature selection and regression prediction to establish the normal condition prediction model (NCPM) of wind turbine with fault-free SCADA data. The performance and robustness of various control charts are compared comprehensively. Compared with the exponential weighted moving average (EWMA) control charts, the AEWMA control chart behaves more sensitive to the abnormal state, and thus has more effective anomaly identification ability and better robustness.

Qinkai Han, Fulei Chu

A New Intelligent Fault Diagnosis Method and Its Application on Bearings

Fault diagnosis is vital in manufacturing system, however, fault diagnosis is divided into three stages: signal preprocessing, feature extraction and fault classification, which destroys the relationship between each stage and causes a part of the loss of fault information. The feature extraction process depends on the experimenter’s experience, and the recognition rate of the shallow diagnostic model does not achieve satisfactory results. In view of this problem, this paper proposes a method, the first step is converting raw signals into two-dimensional (2-D) images, the step can extract the features of the converted 2-D images and eliminate the impact of expert’s experience on the feature extraction process. Next, an intelligent diagnosis algorithm based on convolutional neural network (CNN) is proposed, which can automatically complete the feature extraction and fault identification of the signal. The effectiveness of the method is verified by using bearing data. Test with different sample sizes and noise signals to analyze their impact on diagnostic capabilities. Compared with other mainstream algorithms, this method has a higher recognition rate and can meet the timeliness of fault diagnosis.

Yi Sun, Hongli Gao, Liang Guo, Xin Hong, Hongliang Song, Jiangquan Zhang, Lei Li

Study on Vibration Tracing and Vibration Reduction Technology of Reciprocating Compressor Pipeline

Reciprocating compressor is the core equipment for storing natural gas in gas storage. The abnormal vibration of pipeline will lead to fatigue fracture of pipeline, loose and broken connecting parts, and even lead to leakage of high temperature and high pressure, flammable and explosive gas, causing fire in gas storage. and major accidents such as explosions. In this paper, the first-level outlet safety valve pipe with abnormal vibration of a gas storage reciprocating compressor is taken as an example. Through theoretical and experimental exploration, the vibration source tracing and vibration reduction technology of reciprocating compressor are studied. Based on the finite element analysis of the cause of vibration anomaly, the double-dynamic vibration absorber with vibration reduction is designed based on the fixed-point theory. After installing the vibration absorber, the finite element analysis results reduce the pipe vibration from 16.9 μm to 11.7 μm. Finally, the vibration reduction effect of the vibration absorber is verified by finite element analysis and field test, which provides certain guidance for pipeline vibration reduction.

Yuan Li, Yang Lin, Ling Fan, Yu Zhang, Yunfeng Chang

Research on Motor Fault Warning Technology Based on Second-Order Volterra Series

As important equipment for natural gas transmission stations, electric drive centrifugal compressor units are generally in continuous high-speed operation. Long-term high-load operation is easy to induce drive motor failure, resulting in huge economic losses and casualties. Compressor group condition monitoring, maintenance and repair are all closely related to motor fault diagnosis, making compressor group fault diagnosis very important. Therefore, the study of motor abnormal fault warning technology is of great significance for the prevention of centrifugal compressor accidents. In this paper, the motor fault warning model is established based on the multi-sensor data and second-order Volterra series. The obtained prediction data is compared with the fusion data collected by the sensor to obtain a range under the normal operation of the motor, that is, the numerical set [66, 67]. Predicting the development trend of motor running based on motor monitoring data. The model is used to predict the simulation data and motor data, and the results verify the correctness of the model.

Yuan Li, Ning Ding, Zeyang Qiu, Song Yang, Yongming Wang

Topological Design of a Rotationally Periodic Wheel Under Multiple Load Cases

This paper is dedicated to designing the overall structural topology for the lightweight design of an automobile wheel. A simplified two-dimensional finite element analysis (FEA) model for the wheel is established, in which the whole wheel structure is first defined as design domain during topology optimization. A rotationally periodic constraint is introduced to design the wheel into structural topology consisting of rotationally repetitive modules. Further, compliance-based topological design under multiple load cases within single module is carried out. In order to achieve a uniform deflection and stiffness distribution around the circumference of wheel, a weighted compliance under multiple load cases is taken as the objective function. In addition, some factors significantly affecting the structural topology are discussed.

Lu Jiang, Wei Zhang, ChengWei Wu, LiPing Zhang, YiXiong Zhang, ZhenYu Liu

Effect of Loading Conditions in Fretting Fatigue on Wear Characteristics

Fretting is a phenomenon that happens when there is a small slip amplitude between two contact surfaces. Fretting can cause damages like fretting wear, fretting fatigue, and fretting corrosion. These damages can affect each other in the real case, which is ignored in most research. In this paper, the effect of loading conditions such as axial stress, tangential stress and normal load in fretting fatigue on wear characteristics is analyzed in partial slip regime. The finite element fretting model of pad-on-specimen is designed to analyze the difference in wear characteristics between fretting fatigue models with different loading conditions. The results show that by increasing axial stress, the wear depth and wear width increase near the right contact edge and decrease near the right contact edge, while with the increment of the tangential load and normal load, the wear depth and width increase near both contact edges. Moreover, by increasing the normal load, the point of maximum depth moves closer to the contact center.

S. Wang, M. Abdel Wahab

Damage Assessment in Fretting Fatigue Specimens with Micro-voids Using Critical Plane Approach

In this work, the influence of micro-voids on damage severity under fretting fatigue conditions is analysed for a regular and a random distribution of micro-voids. The finite element method is employed to obtain the stress field during a loading cycle. The well-known Smith-Watson-Topper and McDiarmid multiaxial fatigue criteria are assessed by means of critical plane analysis. Additionally, averaging methods are employed in order to consider the length scale for damage initiation. Furthermore, a direct comparison with the homogeneous case is presented. Different size and distribution of micro-voids are analysed. The numerical results show that the heterogeneity has a noticeable influence on the damage severity. In addition, the numerical model suggests that damage may firstly initiate at the upper edge of the micro-voids located close to the contact edge, generally leading to a mean increase of the damage severity. However, in some cases, the introduction of micro-voids reduces the stress intensity at the contact edge, and therefore, decreases the damage severity in the vicinity of the contact edges.

D. Infante-García, H. Miguelez, E. Giner, M. Abdel Wahab

Preliminary Evaluation of Functional Coatings for Marine Based Renewable Energy Applications

The reliability and maintenance of the tidal turbines is found to be a major problem due to cavitation erosion. The presence of hydrogen sulphide in the microbes leads to Microbially Induced Corrosion (MIC) in objects in the marine environment which can instigate biofouling to occur. Together, the synergistic effect of erosion, corrosion and fouling leads to reduced lifespan of the structural and operational components. Given the sheer scale of the marine renewable industry, which is estimated to reach around €9 billion by 2030, the effects of cavitation, corrosion and biofouling can cause large losses to the industry which will further spur significant costs in the operation of such offshore technology. This is the main driver behind developing eco-friendly multi-functional sol-gel coatings for marine renewable applications. The present research is designed to investigate the two sol-gel coatings synthesized from organically modified silicon precursor 3-methacryloxypropyltrimethoxysilane (MAPTMS) mixed with zirconium (IV) propoxide. One of the coatings was modified using 1%v/v of hexamethyl di-isocyanate (HMDI) diluted in 60% ethanol (S65) whereas the second coating left unmodified (S6) diluted in 100% ethanol. The coatings were deposited on the aluminium (Al) panel using dip coater. The structure of the coatings was evaluated using ATR-FTIR. The coating properties such as hardness, adhesion and wettability were evaluated using pencil hardness, cross-cut adhesion, and water contact angle. Subsequently, the thermal and the chemical stability of the sol-gel coatings was also evaluated.

M. Hegde, Y. Kavanagh, B. Duffy, E. F. Tobin

An Implementation of Cyclic Cohesive Zone Models in ABAQUS and Its Applicability to Predict Fatigue Lives

This paper deals with an implementation of cyclic cohesive zone models (CCZM) in ABAQUS and its application for predicting fatigue lives. Firstly, a brief introduction on cyclic cohesive zone models is given, followed by a detailed discussion of its use in ABAQUS. Two user subroutines (USDFLD and UDMGINI) are written in junction with a python script in order to predict the damage accumulation in a cyclic loading condition. This damage variable is later on used to update the parameters of a cohesive zone model, allowing the simulation of material degradation in a XFEM (with cohesive segments) element. This implementation allows the user to compute fatigue damage in a cycle-by-cycle approach, being possible to model both crack initiation and propagation phases. In this paper, we present results of low cycle fatigue using this approach. The results are then compared with literature data, providing a verification of the implementation and showing the efficiency of this methodology for dealing with fatigue problems.

K. Pereira, M. Abdel Wahab

A 3S_BN Based Approach for the Quantitative Risk Assessment of Third-Party Damage on Pipelines

Third-party damage (TPD) is identified as the greatest threat to the safe operation of pipelines in different countries. The traditional TPD risk assessment methods cannot calculate the failure probability quantitatively and ignore the conditional dependence between risk influence factors (RIFs). In view of this, a theoretical system called 3S_BN is proposed based on Statistics, Scenario analysis, Safety barrier, and Bayesian network to realize the quantitative risk analysis of TPD. According to the 3S_BN, RIFs and their causal relationships are analyzed firstly. After that, a BN model including multi-state risk is developed and historical data and experts’ opinions are used for the computation of conditional probability table. Besides, evidence theory is adopted in order to improve experts’ belief. And then, the proposed approach is verified by a fire and explosion accident. Through sensitivity analysis and posterior probability reversal, the key influence factors and possible paths of the incident are confirmed. Finally, as discussed, the model can be applied to the TPD risk management of pipelines to continuously improve the safety level of pipelines.

Xiaoyan Guo, Guozhi Zhang, Yunlong Wang, Laibin Zhang, Wei Liang

Molecular Dynamics Simulation on Intergranular Crack Propagation Along ∑3 Tilt Grain Boundary in Bcc Iron

As the major material of most machines and structures, bcc iron has a wide application in engineering. To well understand the fracture mechanism of bcc iron at atomistic scale, this work investigates the intergranular crack propagation behavior through carrying out molecular dynamics simulation, where two models containing ∑3 $$ (1\bar{1}1) $$ $$ [110] $$ and ∑3 $$ (1\bar{1}2) $$ $$ [110] $$ tilt grain boundaries are developed, respectively. For intergranular crack propagation along ∑3 $$ (1\bar{1}1) $$ $$ [110] $$ tilt grain boundary, nucleation and extension of twinning vertical to crack plane occur at crack left tip, but fast cleavage occurs at crack right tip. For intergranular crack propagation along ∑3 $$ (1\bar{1}2) $$ $$ [110] $$ tilt grain boundary, nucleation and extension of twinning inclined to crack plane occur at crack left tip, but stacking fault and phase transition from bcc to fcc occur at crack right tip. The intergranular crack propagation along ∑3 tilt grain boundary presents strong directional anisotropy.

Zhifu Zhao, Zhaoye Qin, Xueping Xu, Fulei Chu

Fatigue Crack Propagation in HSLA Steel Specimens Subjected to Unordered and Ordered Load Spectra

Prediction of fatigue crack propagation in metallic structures subjected to dynamic random load spectra, containing variable overloads and underloads, is challenging because of possible retardation and acceleration effects. In this paper, fatigue crack growth behaviour under random spectrum load is investigated on ESE(T) specimens made of DNV 460 steel, which is an HSLA steel widely used in the offshore industry. A reference spectrum composed of a sequence of random loads is transferred into various reduced and ordered spectra. Reduced spectra have been defined based on a peak-valley segmentation algorithm and on the deletion of non-damaging events. Ordered spectra consist of block loading sequences determined by rainflow counting methods. Specific control software has been developed that allows to execute the K (stress intensity factor) controlled experimental program and perform on-line crack growth measurement using a material compliance method. The different spectra are compared in terms of total crack extension and retardation in crack growth rate. Algorithms for crack growth simulation have been implemented in Abaqus using both existing and adapted plastic zone models. Numerical results are critically compared to the experimental data.

Jie Zhang, Sven Trogh, Wim De Waele, Stijn Hertelé

Damage Detection in the Wind Turbine Blade Using Root Mean Square and Experimental Modal Parameters

The paper presents results of an experimental study related to a non-destructive diagnostic technique used for preliminary determination the location and size of delamination in composite coatings of wind turbine blades. The proposed method of damage detection is based on the analysis of the ten first mode shapes of bending vibrations, which correspond to displacements of rotor blades perpendicular to the rotor plane. Modal parameters depend on the physical properties of the structure. On the other hand, failures can affect these properties (e.g. locally reduce the stiffness of the structure). Monitoring of selected modal parameter can allow determination the technical condition of the structure. The main assumption of the presented method is a comprehensive analysis of the measured data by determination the root mean square value (RMS) for each measurement point from all forms of free vibration obtained from the experiment. As a result, information contained in all modes of vibrations that may indicate damage of the blade will be included in a single characteristic. The investigations were carried out on a scaled-down model of a wind turbine blade of a rotor diameter of 36 m. The modal parameters have been determined only experimentally using a Laser Doppler Scanning Vibrometer. Damage was simulated for three localizations by additional high stiffness elements fixed to the surface of the blade. The results of the research presented in this paper confirm the effectiveness of RMS calculation in detection damage using modes of vibrations.

Łukasz Doliński, Marek Krawczuk, Arkadiusz Żak

Effects of Freezing-Thawing Cycles on Mechanical Strength of Poly (Vinyl Alcohol) Hydrogels

Poly (vinyl alcohol) (PVA) hydrogels are widely used in biomimetic cartilage materials for its good biocompatibility and super shock absorbing properties. However, the small pore size, in general, a few micrometers, of pure PVA hydrogels prepared through freezing-thawing method can not provide the suitable microenvironment for the proliferation of chondrocytes, restricting the application of hydrogels in artificial cartilage. In order to solve this barrier, here, agarose is introduced as porogen to prepare the macroporous PVA hydrogels through freezing-thawing method. The obtained PVA hydrogel have the pore size of 20–200 μm, and macropores have good connectivity. The mechanical properties of the macroporous hydrogels are tested using uniaxial compression and tension experiments and the results show that the mechanical properties of macroporous PVA hydrogels are dependent on the preparation parameters, e.g. the duration of freezing, number of freezing-thawing cycles and the temperature of thawing. After optimization, the mechanical properties of the macroporous PVA hydrogels are closer to those of natural articular cartilage and the obtained hydrogels may be used as the artificial replacement materials.

Sen Wang, Heng Li, ZhiMing Qi, MengHong Yin, ChengWei Wu, Wei Zhang

Damage in Composite Materials


Delamination Buckling of FRP: Experimental Tests and Theoretical Model

In scientific literature many studies have focused on the aspects of debonding mainly due to bending and/or shear in steel/concrete beams strengthened with fiber reinforced polymers (FRPs). Few experimental investigations on delamination buckling process of fiber reinforced polymer (FRP) strip/sheet utilized as strengthening in structural damaged elements, beams or slab, have been carried out. This paper analyses about the experimental delamination buckling of two type of FRP: steel reinforced polymer (SRP) strips and basaltic reinforced polymer (BFRP) strips glued on the surface of slender homogeneous beam models. Several experimental tests have been done considering beam models made of homogeneous material marble assuming this material without tensile strength. The specimens strengthened with a double layer of FRP strips glued on both up and down surfaces were tested under increasing compressive force until the failure due to delamination buckling of strengthening. Analysis of experimental process has been developed considering an appraisal theoretical model. Finally, theoretical results with experimental data are compared and discussed.

R. Capozucca, E. Magagnini, M. V. Vecchietti

Preparation of N-Doped Carbon/Cobalt Ferrite Hybrid Nanocomposites for Lithium Ion Batteries Anodes

Transition metal oxides (TMOs) have much higher theoretical lithium storage capacities than that of the commercial graphite anode, but severe volume expansion (160–300%) and lower conductivity will result in poor cycle stability and low rate performance, which seriously hinder their applications. Developing inexpensive and efficient strategy to manufacture carbon/TMOs hybrids with good cycle stability and high rate performance is highly desired. Here, we report a facile approach to synthesize nitrogen-doped carbon/cobalt ferrite hybrids using the cheap renewable biomass, glucose and starch, as the carbon source. The resultant N-doped carbon/cobalt ferrite hybrid nanocomposites were investigated in terms of their morphology, structure, composition and electrochemical lithium storage performance. The results show that the hybrid composites possess porous structure and TMOs nanocrystals (~5.7 nm), which can not only effectively alleviate the sharp volume changes of cobalt ferrite (186%) during repeated lithiation/delithiation process, but also provide efficient electron and ion transport channels, demonstrating excellent rate performance and remarkable cycle stability. In particular, a high reversible capacity of 411 mAh/g was successfully maintained without decay over 200 cycles at a high current density of 3 A/g, exhibiting the potential as a promising lithium ion batteries anode material.

D. L. Dong, W. Zhang, J. L. Ma, C. W. Wu

Random Vibration Based Robust Damage Detection for a Composite Aerostructure Under Assembly-Induced Uncertainty

The problem of random vibration based robust damage detection for a composite aerostructure under assembly-induced uncertainty is considered. The focus is on the exploration of the performance limits and critical assessment of two unsupervised Statistical Time Series (STS) type robust methods: a Multiple Model (MM) based method and a Principal Component Analysis (PCA) based counterpart. Three progressive damage scenarios are considered, the effects of which on the structural dynamics are ‘minor’ and almost completely ‘masked’ by assembly-induced uncertainty. The assessment, based on hundreds of experiments, suggests that damage as small as 10% reduction in the tightening torque of a single bolt is detectable in a reliable way. Both methods achieve remarkably good detection performance characterized by 100% correct detection for false alarm rates of 3.5% or higher, with the MM type method exhibiting a slight edge in performance over its PCA based counterpart! Overall the unsupervised STS type robust methods are shown to effectively detect ‘minor’ damage in the presence of significant assembly-induced uncertainty!

Georgia Andriosopoulou, Andreas Mastakouris, Kyriakos Vamvoudakis-Stefanou, Spilios Fassois

Random Vibration Damage Detection for a Composite Beam Under Varying Non-measurable Conditions: Assessment of Statistical Time Series Robust Methods

The problem of vibration-response-only damage detection for a composite beam under variable and non-measurable Environmental and Operational Conditions (EOCs) is considered via three unsupervised Statistical Time Series (STS) type robust detection methods. These include three versions of a novel Functional Model (FM) based method, a Multiple Model (MM) based method, and a Principal Component Analysis (PCA) based method. Performance assessment is based on hundreds of inspection experiments under temperature ranging from 0 to 28 $$^{\circ }$$ C and tightening torque ranging from 1 to 4 Nm. The results confirm the methods’ high effectiveness, with a version of the FM based method and the MM based method achieving ideal performance, characterized by 100% correct detection rate for 0% false alarm rate.

Tryfon-Chrysovalantis Aravanis, John Sakellariou, Spilios Fassois

Damage Quantification in Composite Structures Using Autoregressive Models

When small damage is detected in its initial stage in a real structure, it is necessary to decide if the user must repair immediately or keep on safely monitoring it. Regarding the second choice, the present paper proposes a methodology for damage severity quantification of delamination extension in composite structures based on a data-driven strategy using autoregressive modeling approach for Lamb wave propagation. A pair of features is used based on the autoregressive (AR) model coefficients and residuals and a machine learning algorithm with Mahalanobis Squared Distance for outlier detection. The damage severity quantification is proposed through an experimentally identified smoothing spline trend curve between the damage index and its severity. The application of the methodology is demonstrated in a composite plate with various progressive damage scenarios. The proposed method proved to be able to identify and predict the localization and the damage index related to its respective extension of minimal simulated damage with promising accuracy.

Jessé A. S. Paixão, Samuel da Silva, Eloi Figueiredo

Meso-Scale Damage Modeling of Hybrid 3D Woven Orthogonal Composites Under Uni-Axial Compression

In this study, a detailed predictive numerical modeling technique is developed for three different kinds of hybrid and non-hybrid architectures of 3D woven orthogonal composites. A unit cell, full finite element meso model, is developed to simulate the elastic and damage progression behavior under uni-axial compression. Material systems for 3D woven Composites used in this study are Carbon/epoxy, Kevlar epoxy, and Hybrid formulation. The geometry of the constituents of the unit cell, fiber tows, and matrix, was determined through the microscopic analysis of the woven structures. The unit cell model used an idealized geometry without incorporating the fiber undulation which is a pervasive effect during the weaving process of 3D woven composites. Abaqus standard solver and a UMAT code incorporating the damage model within Abaqus was used to compute the deformation of the unit cell under in-plane compression loading. Moreover, determining the effect of void contents on the mechanical properties of the material, Balshin’s empirical equation was used to calibrate the input material parameters. The results from the numerical analysis are then compared with the experimental results and it is found that the predicted elastic modulus and compressive strength for all three types of architecture are in good agreement with the experimental results. Overall, the unit cell meso model furnished fairly accurate estimation of the compressive properties of 3D woven composites for different material systems with consideration of void contents.

Sohail Ahmed, Xitao Zheng, Tianchi Wu, Nadeem Ali Bhatti

Experimental Study on the Stiffness Evolution and Residual Strength of a Pre-damaged Structural Component Made from SMC CFRP Material

The mechanical characterisation of pre-damaged structural components made from sheet moulding compound (SMC) carbon-fibre reinforced polymer (CFRP) is still an open research question. This study shows the stiffness evolution of an automotive suspension part after damage initiation for a cyclic fully-reversed loading sequence with incrementally increased displacement amplitude. The cyclic test is followed by a quasi-static tensile test to estimate the residual strength of the component. Visual assessment of a highly stressed area is performed via 3D-DIC for the static and dynamic tests. As a result from the load and displacement measurements, the decrease in structural stiffness for the fatigue test is obtained and described by a logarithmic law. The residual strength and stiffness in the quasi-static tensile test gives insight into how pre-damaged structural parts can be used for limited durations (e.g. limp home mode in a passenger vehicle after light impact).

Stefan Sieberer, Susanne Nonn, Martin Schagerl

Delamination Detection via Reconstructed Frequency Response Function of Composite Structures

Online damage detection technologies could reduce the weight of structures by allowing the use of less conservative margins of safety. They are also associated with high economical benefits by implementing a condition-based maintenance system. This paper presented a damage detection and location technique based on the dynamic response of glass fibre composite laminate structures (frequency response function). Glass fibre composite laminate plates of $$200 \times 200 \times 2.64$$ mm, which had a predefined delamination, were excited using stationary random vibration waves of 500 Hz band-limited noise input at $$\approx {1.5}$$ g. The response of the structure was captured via Micro-ElectroMechanical System (MEMS) accelerometer to detect damage. The frequency response function requires data from damaged structures only, assuming that healthy structures are homogeneous and smooth. The frequency response of the composite structure was then reconstructed and fitted using the least-squares rational function method. Delamination as small as 20 mm was detected using global changes in the natural frequencies of the structure, the delamination was also located with greater degree of accuracy due to local changes of frequency response of the structure. It was concluded that environmental vibration waves (stationary random vibration waves) can be utilised to monitor damage and health of composite structures effectively.

A. Alsaadi, Yu Shi, Yu Jia

Free Vibration of Angle-Ply Laminated Micro-plates Using Isogeometric Analysis and Modified Couple Stress Theory

Based on new modified couple stress and isogeometric analysis, this paper presents a non-classical Reissner-Mindlin plate theory model for free vibration of angle-ply laminate micro-plate. This study extends the new modified couple stress for complicated geometrical structures with internal cutouts. The governing equations for size-dependent free vibration of angle-ply laminate micro-late obtained from the Galerkin weak form are solved by using isogeometric analysis. Various numerical examples are examined to verify the convergence and the accuracy of proposed model. In addition, the numerical results show the influences of material length scale parameter, fiber orientation and BCs of micro-plates. Only one material length scale parameter is investigated to predict the size effects. By increasing the material length scale parameter, the size-dependent behavior leads to an increase in non-dimensional frequencies and critical buckling loads of angle-ply laminate micro-plates.

Cuong-Le Thanh, Samir Khatir, M. Abdel Wahab

Damage Assessment of Laminated Composite Plates Using a Modified Cornwell Indicator

This paper presents an effective approach based on modal analysis for damage identification of three-layer ( $$ 0^\circ /90^\circ /0^\circ $$ ) laminated composite plates. Free vibration analysis of simply supported laminated composite plates using Finite Element Method (FEM) combined with Cornwell indicator (CI) and Modified Cornwell Indicator (MCI) is presented. The indicators are determined using modal analysis information extracted from a finite element code in Matlab and used to locate potential damage elements more effectively, after eliminating most of the healthy elements. A single and multiple damages are introduced in the laminate plate. The obtained results indicate that the proposed approach can identify the damage sites using both indicators. MCI can estimate the extent of damage with higher precision than CI.

S. Tiachacht, M. Slimani, S. Khatir, A. Behtani, L. Mansouri, A. Bouazzouni, M. Abdel Wahab

The Sensitivity of Modal Strain Energy for Damage Localization in Composite Stratified Beam Structures

In the present paper, a modal analysis of undamaged and damaged Carbon Fibre Reinforced Polymer (CFRP) beam elements with fixed and free ends and a cross-ply (0°/90°/0°) rectangular beam with clamped boundary conditions at both ends is investigated for damage identification. The presence of single and multiple damages in composite structures based on changes in the dynamic properties of the structure are considered. The Modal Strain Energy (MSE) damaged indicator based on frequency and mode shape combined with composite structure is studied. To enhance the results, the sensitivity of MSE using mode shape is investigated by varying the number of modes. The results showed that MSE using frequency much better than mode shape. Moreover, MSE with the first mode is much better than other modes.

A. Behtani, S. Tiachacht, S. Khatir, M. Slimani, L. Mansouri, A. Bouazzouni, M. Abdel Wahab

A Comparative Study of the Behavior of Glass Fiber-Reinforced Polyester Composite Laminates Under Static Loading

Glass fiber-reinforced polyester matrix composites are increasingly used because of their many advantages, namely, lightness, cost, strength, and ease of processing. Thus, they can meet sometimes special needs that conventional materials cannot meet. Nevertheless, their properties depend on the nature of the plies used, e.g. UD, mat, woven, and the stacking sequence. This work aims to study the mechanical behavior of several composites stratified under static loading and to identify the different modes of damage leading to rupture. This paper mainly studies the influence of the shape of the reinforcement on rigidity and static behavior. In addition, we are interested in the evolution of shear stress as a function of the distance between supports.

L. Mansouri, D. Arezki, S. Khatir, A. Behtani, S. Tiachacht, M. Slimani, M. Abdel Wahab

Damage Detection in Laminated Composite Plates Based on Local Frequency Change Ratio Indicator

This paper presents an application based on Local Frequency Change Ratio (LFCR) for damage assessment of three-layer (0o/90o/0o) laminated composite plates. The indicator is used to help locating single and multiple potential damaged elements. The obtained results indicate that even when increasing damaged elements, LFCR indicator can detect the damage accurately. For more accuracy to prove that the LFCR is much better to identify the damage location in laminated composite, we introduced white Gaussian noise with different levels. The obtained results indicate that even under measurement noise level 2%, the LFCR can identify the actual damage with high precision.

S. Khatir, S. Tiachacht, C. Le Thanh, T. Khatir, R. Capozucca, M. Abdel Wahab

The Impact of the Selected Exploitation Factors on the Adhesive Joints Strength

The aim of the present article is to determine the impact of the selected exploitation factors on strength of the wooden elements’ adhesive joints. Two types of adhesive joints were subject to experimental tests: butt adhesive joints and cross lap adhesive joints. Two types of adhesives were used: Prefere 6312 (a single-component PVAc adhesive for wood of D3 quality) and a two-component epoxy adhesive (Epidian 57/TFF/100:22). The exploitation factor under analysis was resistant to different temperature values above and below freezing. Six different variants of the joints’ ageing temperature value were used. The adhesive joints have been aged for 2 weeks (2 variants) and 3 months (3 variants). One ageing variant also included thermal shock (−40 °C/+60 °C), for which the ageing time was 2 months. A climatic/temperature chamber ESPEC SH 661 and a thermal shock chamber ESPEC TSE – 1 were used for ageing. Strength tests of the adhesive samples were carried out on the testing machine Zwick/Roell Z150, with accordance to the PN-EN 15870 standard. Based on the tests, it was observed that the adhesive joints of the wooden elements showed different dependencies between the strength and the ageing variant depending on the type of adhesive used. The results emphasise the importance of the temperature impact on the adhesive joints strength.

Anna Rudawska, Izabela Miturska, Jakub Szabelski, M. Abdel Wahab, Dana Stančeková, Nadežda Čuboňová, Radovan Madleňák

The Influence of the Packing Material Type on the Adhesive Joints Strength of the Paperboard Packages

This article presents selected issues related to the impact of the material factors on the adhesive joints’ strength of the paperboard packages and strength of various types of the packaging materials: Alaska Plus GC2 (grammage 235 g and 280 g) and Crescendo C1S (grammage 300 g). The bonded material consisted of different types of paperboard used in production of packages, which were subject to the surface modification process by applying a varnish coat and, in case of one material, to the lamination process. The adhesive joints were made with use of a cold adhesive produced by SALTADIS (identification number: SI 5240). It is water-soluble and may be used for a variety of industrial applications. The adhesive joints were made with use of different packaging materials and different technological modifications of these materials’ surface on an automated production line. It was in order to determine which material and which surface modification method has an impact on both the strength of the adhesive joints and the packaging material itself. Based on the packaging materials’ properties, it was observed that together with the increase of the basis weight, the material’s strength also increases. In addition, the lamination process increases the material’s strength as well.

Anna Rudawska, Arkadiusz Gola

Studies of Fibre Reinforced Polymer Samples with Embedded FBG Sensors

The paper presents analyses of fibre reinforced polymer (FRP) samples with embedded fibre Bragg grating (FBG) sensors. As a reinforcement glass or carbon fibres in a form of textiles with different grammage and bundles fibre arrangement were used. All samples were manufactured using infusion method. FBG sensors are applied for analyses of strain distribution inside sample due to static point loads. Samples internal structures were analysed using THz spectroscopy. Analyses of possibility of detection and localisation of fibre optics lying under textile or embedded into carbon/glass FRP are performed. For carbon FRP the maximal depth of inspection is determined. The THz wave propagation depth depends on conductive carbon fibres arrangement in non-conductive resin matrix.

Magdalena Mieloszyk, Katarzyna Majewska, Wieslaw Ostachowicz

The Preparation of Smart Magnetic Nanoparticles for Intracellular Hyperthermia

Magnetic induction hyperthermia is a new “green” cancer therapy method, which can destroy the tumor cells and undamage healthy cells. However, the difficulty of in vivo temperature rise control limits its clinical application. In this paper, we prepare a kind of smart magnetic nanoparticles for magnetic induction hyperthermia. The smart nanoparticles can self-control the temperature at 59.9 °C in the hyperthermia due to the low Curie temperature of nanoparticles. The formation mechanism of the smart magnetic nanoparticles is investigated. On the other hand, owing to the low thermal conductivity of the cell membrane, it is reasonable to believe that the intracellular hyperthermia is superior to extracellular hyperthermia. As such, we also discuss the feasibility of intracellular hyperthermia using the obtained smart magnetic nanoparticles. The results indicate that the temperature changes of the cell can meet the requirement of hyperthermia temperature when a single cell internalizes 2 pg of the smart magnetic nanoparticles.

XiaoGang Yu, RenPeng Yang, ChengWei Wu, Wei Zhang, DongFeng Deng, XuXin Zhang, YanZhao Li


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