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This proceedings gather a selection of peer-reviewed papers presented at the 8th International Conference on Fracture Fatigue and Wear (FFW 2020), held as a virtual conference on 26–27 August 2020. The contributions, prepared by international scientists and engineers, cover the latest advances in and innovative applications of fracture mechanics, fatigue of materials, tribology, and wear of materials. In addition, they discuss industrial applications and cover theoretical and analytical methods, numerical simulations and experimental techniques. The book is intended for academics, including graduate students and researchers, as well as industrial practitioners working in the areas of fracture fatigue and wear.





The Folded Wiener Process for Non-negative Non-monotone Degradation Processes

The Wiener process is very largely and successfully adopted for modelling degradation phenomena that can exhibit negative increments. However, so far as the observed degradation phenomenon is intrinsically non-negative, as generally occurs, its use may lead to incongruous results, unless (based on the parameter setting) the probability that the considered Wiener process takes negative values is negligible for any time of interest. To overcome such a limitation of the Wiener process, a new Markovian degradation process, called the folded Wiener process, is here proposed that can be used to describe intrinsically non-negative, non-monotone, degradation phenomena. In fact, under the folded Wiener process, the degradation increment over future time intervals is constrained to be no less than the opposite of the current degradation level, so that the total amount of degradation accumulated up to any time $$ t $$ t is necessarily non-negative. The main features and properties of the folded Wiener process are then presented and discussed, and closed form expressions for the mean and variance functions of the process are also provided. Finally, to show the feasibility of the proposed folded Wiener process, an applicative example is developed by using real data.

Massimiliano Giorgio, Gianpaolo Pulcini

Crowd Management for Power Generation: A Critical Analysis on the Existing Materials and Methods. (Structural Modal Analysis)

Energy harvesting by means of different materials and mechanisms is considered an important topic of interest in past decades. Materials such as piezoelectric, electromagnetic and electrostatic in nature are generally used to harvest energy in many of the sensing applications. Mechanisms based on simple deformation, vibration and magnetism are used to harvest energies in power generation applications. The published research shows that the harvested energy from these materials and mechanisms are still far away from practical feasibility and optimisation. However, not a single review article is available which can provide a critical analysis on the existing materials and methods with regards to the mentioned feasibility and optimisation. In this paper, a review attempt has been made to describe the mentioned analysis. All the past research is described in two categories: Energy Harvesting through Materials and Energy Harvesting through Mechanisms. The materials used for energy harvesting contain characteristic to release electric charge under the influence of an external excitation. Several materials such as Multiwalled Carbon Nano Tubes (MWCNT), Polyvinylidene Fluoride (PVDF), Polydimethyl siloxane (PDMS) and ZirconateTitanate (PZT) with slight change in their internal properties and efficiencies are used to harvest charge. In contrast to the materials, several mechanisms are also in use to produce useful energy from available external forces. Their mechanics is principally based on phenomena like structural vibrations, electromagnetic induction, and magnetism. This review concludes that a methodology of energy harvesting which can utilise any random load and converts into maximum useful energy is still not present.

Abdulaziz O. Alnuman, Muhammad A. Khan, Andrew Starr

Damage Evaluation of Free-Free Beam Based on Vibration Testing

Damage can be detected by vibration responses of a structure. Damage changes the modal properties such as natural frequencies, mode shapes, and damping ratios. Natural frequency is one of the most frequently used damage indicators. In this paper, the natural frequency is used to monitor damage in a free-free beam. The modal properties of the intact free-free beam are identified based on 15 accelerometers setup. A finite element model is used to model the free-free beam. Three models are considered: beam (1D), shell (2D) and solid (3D). The numerical models are updated based on the first seven bending natural frequencies. The free-free beam is damaged by a rectangle cut. The experiment is re-setup and the model properties of the damaged beam are re-identified. The cuttings are modeled in the numerical model. The first seven numerical bending natural frequencies of the damaged beam are compared with the experimental ones. The results showed that the 1D beam element model has the highest differences, while the 2D and 3D models have approximately the same results. Therefore, the 2D representation can be used to model the damaged beam for fast computation.

Duong Huong Nguyen, Viet Long Ho, Thanh Bui-Tien, Guido De Roeck, Magd Abdel Wahab

A Comparative Study on Indentation and Flattening Contacts

This work presents a comparative analysis of elastic-plastic flattening and indentation contacts by using finite element analysis. The similarity and difference between the two types of single asperity contacts are investigated. Five elastic-ideally plastic materials, whose yield strengths covering a typical range of steel materials used in engineering, are selected as materials of deformation body. The numerical simulation covers a wide range of contact deformation. The results are normalized such that to be valid either for macro contacts or for micro contacts. The contact force and radius are obtained and compared. The similarity of the two contact types is found when the contact deformation is relatively small, even when the contact approaches to the fully plastic deformation. When the interference is large enough, the two contacts behaviors are significantly different. Two prediction formulas for upper limit interference of similarity of contact force and radius are given.

Qingming Deng, Xiaochun Yin, Magd Abdel Wahab

Impact of Abrasive Blasting Media on the Strength of Steel Sheets Adhesively Bonded Joints

This paper concerns a comparative study assessing the impact of various mechanical surface treatment methods on the strength of adhesively bonded joints. The surface treatment methods used were glass-bead blasting and steel shot blasting. The joints used sheet components of S235JR steel, bonded with one of two epoxy adhesives. Several configurations of adhesive joints were tested, based on specific blasting medium variants. The study included the analysis of substrate surface topography (Hommel-Etamic T8000 RC 120-400) and strength tests (Zwick/Roell Z150). The results show that the highest joint strength was developed by the assemblies with steel shot blasted adherends, which in addition exhibited the highest levels of surface roughness.

Anna Rudawska, Jakub Szabelski, Magd Abdel Wahab, Izabela Miturska

Determination of the Effective Stiffness of Half-Open Cross-Section Bars and Orthotropic Steel Deck of a Truss Bridge Using Model Updating

Vibration-based model updating is widely accepted as an effective technique to construct a baseline model for structural health monitoring. In this paper, the effects of half-open cross-section and orthotropic deck on the global vibration behaviour of a truss bridge are considered. To do that, an FE model using ANSYS is built with variations of half-open cross-section area of bars and the stiffness of the orthotropic steel deck. The cross-section area of bars are assigned a reduced coefficient, less than and equal to one. Based on a vibration test, a hybrid optimization algorithm, known as Hybrid Particle Swarm Optimization and Gravitational Search Algorithm (PSOGSA), is applied to reduce the differences in frequencies and mode shapes between measurements and FE simulations. Finally, the effective coefficients of the cross-section as well as the stiffness of steel deck are obtained from the updated model.

Viet Long Ho, Guido De Roeck, Thanh Bui-Tien, Magd Abdel Wahab

A Study On Optimal Design of Longitudinal Shape For Improving Small-Overlap Performance

This paper presents a study on the optimal design of longitudinal shape for improving the small-overlap performance, based on a computer-based crash simulation model. The small-overlap frontal impact (SOFI) event was simulated using explicit finite element method. The models were developed for the simulation according to the Insurance Institute for Highway Safety IIHS real test conditions with the Flat 150 mm radius rigid barrier and 25% overlap. Several different cross sections of longitudinal members were subjected to dynamic compression load, which occurs in small overlap frontal impact. The different shapes of longitudinal structure were compared initially to obtain the cross section that fulfills the small overlap performance criteria. The evaluated performance parameters included the absorbed crash energy, crush force efficiency, ease of manufacture and cost. Once the cross section was selected, the design was further enhanced for better crashworthiness performances by investigating the effect of material characterization, increasing the wall thickness and by introducing a trigger mechanism. Real experiments were also performed for …. The results of this study showed that the multi edges profile with 2 mm wall thickness and steel material was a good candidate for energy absorption in SOFI condition.

Nguyen Phu Thuong Luu, Ly Hung Anh

Investigation of Flow Forming Process and Heat Treatment Effects on 2024 Aluminium Tubes

The aim of this study is to investigate mechanical and microstructural properties of 2024 aluminium tubes (2024 AA) which are produced by flow forming technique and make comparisons between the flow formed 2024 AA, full annealed (2024-O) and solution heat treated then artificially aged (2024-T6) temper aluminium tubes. For this purpose, 70% reduction rate was applied on the 2024-O tempered samples by the flow forming process. The 2024-T6 samples demonstrated higher mechanical properties than 70% thickness reduced 2024 AA due to formation of Al2Cu precipitation. However, it was found that the mechanical properties of the flow formed 2024 AA was almost two times higher than that of the 2024-O sample. Furthermore, grain orientations of these three samples were investigated by the optical microscope. Although any grain orientations were not seen in 2024-O and 2024-T6 aluminum samples, severely grain orientations were observed after the flow forming process.

Acar Can Kocabıçak, Aptullah Karakaş, Güneş Aydın, Senai Yalçınkaya

Application of Improved Artificial Neural Network to Stiffness Reduction Analysis of Truss Joints in a Railway Bridge

Railway bridges are susceptible to the problems of fracture and fatigue because they endure millions of stress cycles under moving train load during their service life. This may lead to stiffness reduction in truss joints of the truss bridges and reduce the operational effectiveness of the bridge. In this paper, a hybrid algorithm based on Artificial Neural Network (ANN) coupled with an evolutionary algorithm, i.e. Genetic Algorithm (GA) is proposed to analyze the stiffness reduction of truss joints in a railway bridge. GA is employed to determine training parameters and overcome the local minimum problems of ANN. Natural frequencies are selected as input data, whereas output data is damage characteristics (locations and levels) of truss joints. The results demonstrate that ANN-GA determines vibration behavior and damages of the considered structure accurately, comprising single stiffness reduction of truss joints as well as multiple stiffness reduction scenarios.

H. Tran-Ngoc, L. Nguyen-Ngoc, H. Ho-Khac, A. Le-Thuc, Guido De Roeck, Thanh Bui-Tien, Magd Abdel Wahab

Flow Forming Process for Annealed AISI 5140 Alloy Steel Tubes

Flow forming process performed on annealed AISI 5140 steel material which called “preform” by 50% reduction ratio in this experimental study. The mechanical properties such as tensile strength, yield strength and hardness and microstructures were investigated in order to see the effect of flow forming process on the tested materials. The changes of these properties were evaluated in terms of microstructural observation and hardness tensile measurement. The hardness distribution and microstructural characterization were investigated throughout the wall thickness of the workpiece. The experimental results indicated that the hardness differences occurred because of the roller force effect on the outer surface was more than the force on the inner surface of the workpiece and faster coolant rate. In addition, severely grain orientations were observed, hardness, yield and tensile strength of the workpiece enhanced significantly because of dislocation generation and pile-up during plastic deformation. Although the yield and tensile strength increased, elongation properties reduced after the flow forming operation. Besides, the homogeneous grains orientations were observed throughout the wall thickness of the workpiece due to application the flow forming.

Aptullah Karakaş, Acar Can Kocabıçak, Senai Yalçınkaya, Yusuf Şahin

Hydrogen Degradation Effects on Crack Propagation in High-Strength Steels: A Fully Coupled Approach

This study presents a fully coupled cohesive zone model (CZM)-based computational framework to simulate crack propagation in high strength steels. The model comprises initially zero thickness, cohesive-interface elements with the constitutive response described by a hydrogen-degraded Park-Paulino-Roesler (PPR) model. The linear dependence on hydrogen concentration according to a phenomenological decohesion model is chosen for the critical cohesive traction. Moreover, the value of the cohesive energy of the traction separation law (TSL) is adopted from the experimental data of hydrogen-charged specimen. The computational framework accounting for both hydrogen enhanced localized plasticity (HELP) and hydrogen enhanced decohesion (HEDE) mechanisms is employed to simulate crack growth in a C(T) specimen made of AISI 4130 high-strength steel. The parameters included in the PPR model are satisfactorily calibrated with experimental data for the uncharged and hydrogen-charged specimens. It has been concluded that the lattice hydrogen has the dominating factor in the hydrogen degradation compared with trapped hydrogen.

B. Sobhaniaragh, S. H. Afzalimir, C. Ruggieri

Sensitivity of Damping for Diagnostics of Damage in Structure

Available researches on the sensitivity of damping capacity of specimens and structures as applied for the diagnostics of damage are quite conflicting. Certain of researchers revealed sufficiently high sensitivity of damping capacity for the reliable diagnostics of damage, but others declared that the change of damping due to damage is negligibly small. In the presented study this contradiction was attributed to the fact that the change of damping capacity of damaged structures is the function of great number of factors. The influence of these factors on the change of damping of damaged structure was investigated with the developed fracture mechanics-based procedure. In such a way, the sensitivity of damping for the diagnostics of crack in a beam-like structure in the case of bending and axial vibrations was investigated. In particular, it was revealed that the sensibility of damping to crack is dependent on structure’s stiffness and on damping capacity of structure in the undamaged state. In addition, the intensity of stress in the damaged area should be sufficiently high to induce the dissipation of energy of vibration. As a result, a simple formula was developed to estimate the sensitivity of damping capacity as applied for the damage detection.

A. Bovsunovsky, E. Soroka

Effect of Cross-Over Fraction on Objective Function Value in Genetic Algorithm Optimization of Machining Parameters in Diamond Turning of Aluminum Alloy (RSA-431) for Optical Applications

The ever-escalating industrial production competition, coupled with the use of highly automated industrial machinery has seen the emergence of artificial intelligence-based process optimization models that are perceived as being reliable. In this present study, the effect of cross-over fraction parameter on objective function value in genetic algorithm optimization of machining parameters is assessed. Single point diamond turning is carried out on RSA 431. Primary cutting parameters namely; cutting speed, feed rate and depth of cut are optimized in this study for minimum surface roughness. A genetic model fitness function was developed using multiple regression modelling in Excel environment to establish the quality of each population member. Validation of the resultant model is achieved through determination of its prediction accuracy. The results indicate the presence of a linear relationship between the cross-over fraction parameters. The linear model has a prediction accuracy of 95.05% indicating its effectiveness in predicting objective function value.

Funsho Oyekunle, Khaled Abou-El-Hossein

A Heat Transfer Finite Element Model for Wire-Arc-Additive-Manufacturing Process

This paper presents a part of work to develop a suitable numerical tool to define printing strategy for Wire-Arc-Additive-Manufacturing (WAAM) process. Based on previous research work, A three dimensional metallo-thermo-mechanical model on welding process are transplanted through Abaqus CAE and user subroutines for the simulation of WAAM process. A test plate manufactured by WAAM processing is used as the validation of the simulation. In this paper, heat transfer modelling for WAAM process is presented, which includes two key issues, namely a modified Goldak model for heat source and interval layer forced cooling parameters. The modified Goldak model is capable to simulate energy input of filler material correctly. The inter layer idle time and forced cooling flux are very crucial to the geometry, and the quality of the fabricated part by WAAM process. The ambition of this project is to use desired properties as input parameters of the simulation tool and obtain output parameters to define the optimized strategy for WAAM process.

Y. Ling, J. Ni, Magd Abdel Wahab, J. Antonissen, J. Vande Voorde

Failure Analysis of a Fuel Control Tube from an Aircraft Engine

Multiple cases of fuel control pressure tube fractures from aircraft engines have been reported. The aim of the present study is to determine the cause of this tube fracture. The studied set was composed by the mentioned tube, a welded connecting pipe, where the fracture has been produced, and a union nut. The fracture has been produced in one most critical zones of the tube, in a region near to the supporting body of the union nut to the connector. Visual examination and microscopic observation through a stereo microscope of the tube fracture surface has been carried out to determine the macrofractographic features. The results revealed a plastic macrodeformation of the tube, a damaged surface and signs of a possible corrosion process. The material has been chemical, mechanical and microstructural characterized. The results confirmed that specifications were fulfilled. Fracture surface was also inspected by scanning electron microscopy to determine the microfractographic features in order to find out the failure mechanism involved in the fracture. Fatigue striations, which are typical from a progressive fracture by a fatigue mechanism have been observed. The origin of the fracture has been placed in defects located in the outer wall of the tube, leading to a final overload fracture.

María García-Martínez, María Pilar Valles González, Ana Pastor Muro, Alejandro González Meije

Detection of Damage in RC Beams Strengthened with NSM CFRP Rectangular Rod by Finite Element Modeling

The Near-Surface Mounted (NSM) reinforcement method has been shown to be one of the most important technique for the rehabilitation of damaged concrete structures or ones that are not adequate to support expected loads. However, despite decades of scientific research centered on the optimization of construction details, on models for bond behaviour and on design methods for flexural and shear strengthening, the effects of damage on FRP reinforcements have yet to be adequately investigated. In this work, the influence of different typology of damage such as loss of adhesion in the reinforcement-concrete interface, concrete’s cracking, and, finally, damages in FRP due to notches have been analysed by Finite Element Modeling (FEM). An incremental non linear analysis is developed using 3D Finite Element (FE) in the ANSYS code, considering both the static and dynamic behaviour of RC beams strengthened with one CFRP rectangular rod inserted into a groove according to NSM technique in relation to the different types of damage. Both progressive local failure and nonlinear stress–strain relationship of concrete are taken into account. For the CFRP, a model that takes into account the debonding phenomena at the interface between concrete-adhesive has been adopted. Finally, the developed theoretical model is calibrated and validated by comparison with results from experimentation and interesting aspects are remarked and discussed.

Erica Magagnini, Roberto Capozucca

Particle Swarm Optimisation-Based Support Vector Regression Model to Estimate the Powder Factor of Explosives in Groundwater Tunnel Driving

In many parts of the world, especially in arid or semi-arid areas, they find drinking water in the subsoil. One way to reach it, it is through small horizontal tunnels (Qanat) built on the mountain using explosives. Civil engineers must design projects where they estimate the budget necessary to undertake the work, taking into account the amount of explosives needed, number of blasts, duration of the civil work and powder factor among other data. However, there is not artificial intelligence-based models that help to forecast the amount of explosive needed to drill a tunnel. In this work, a hybrid regression model based on support vector machine (SVM) and particle swarm optimization (PSO) trained with real data (types of lithologies, geomechanical characteristics of the rocks and the amount of explosives used by engineers based on their previous experiences) obtained from a volcanic groundwater tunnel driving in the island of Tenerife (Spain), is proposed to predict the advance, the amount of explosives, the number of blasts and the powder factor in new tunnels or expansion of existing ones. The results show that a new, simpler regression model has been obtained that reproduces the experimental data and it will reduce the effort of the engineers in the study of a new tunnel driving work.

E. de Miguel-García, K. Martín-Chinea, J. F. Gómez-González

Study of Pre-strain Effect on Bendability in Three-Point Bending Test

The bendability of sheet metals can be estimated by the three-point bending test. Several factors and parameters such as pre-strain, can affect the bendability of sheet metals. This effect is investigated using the Gurson–Tvergaard–Needleman model through finite element method. Bending strain at the initiation of a fracture is calculated to assess bendability. Pre-strain is observed to reduce maximum force in the bending test and cause early fracturing.

M. M. Shahzamanian, Amir Partovi, P. D. Wu

Fracture Mechanics Performance of Through-Thickness Crack of Polymeric 3D Printed Components

This experimental study aims to explore the failure behavior of a pre- and post-cracked polymeric 3D printed components subjected to tensile mode. A set of through-thickness pre-cracked specimens of different cracks patterns and geometry was designed and implemented in the 3D printed parts. The specimens are then subjected to a tensile test mode. Besides, analogous intact samples were produced by 3D printing technology where the through-thickness post-cracks were created using laser cutting process of a geometry with cracks similar to those of the pre-cracked specimens. It has been observed that the pre-cracked samples initially introduced, and 3D printed cracked specimens have more resistance to fracture mechanics failure due to crack-bridging caused by the 3D printing filament profile around the crack profile. On the other hand, the samples with post-cracks made by laser cutting demonstrated a significant drop in the fracture failure resistance due to the interruption of the 3D printed filaments of the intact specimens. In conclusion, this study revealed that pre-cracked 3D printed components did not show the actual failure and fracture mechanics behavior. This is because the cracks could be introduced in the components after the additive manufacturing process during the service life and that would damage the 3D printed filament path of the components and, hence, will cause high-stress concentration that leads to unpredicted and fast failure.

Waleed Ahmed, Essam Zaneldin, Souzan Kabbani

D-Beam Theory for Functionally Graded Double Cantilever Beam Analysis

A formulation that takes advantage of both Layer-Wise and Equivalent Single Layer approaches for modeling Functionally Graded beams is presented. Such alternative formulation, referred to as D-Beam, is here applied to model the Double Cantilever Beam specimen in order to estimate the relevant fracture opening mode of metallic graded beams made up by means of Additive Manufacturing technique. Numerical results are presented.

Calogero Orlando

Numerical Treatment of Fractional Differential Models

Several fracture and fatigue problems are modelled by fractional differential equations. This paper deals with the numerical solution by a class of one and two step spline collocation methods. These methods have higher order of convergence with respect to most numerical methods for fractional differential equations. The methods are illustrated, and their convergence properties are discussed. Several numerical experiments confirm theoretical results and compare one and two step spline collocation methods.

Angelamaria Cardone, Dajana Conte, Beatrice Paternoster

Mode Shape Based Approach to Identify the Location of Crack and the Influence of Crack on Critical Speed of Gas Turbine Disc

In an aeroengine, the rotating gas turbine disc is susceptible to cracks in its service tenure due to its complex loadings and operating conditions. The appearance of crack in disc alters the stiffness near crack location which further affects vibration characteristics of the rotating disc and it is a serious reliability concern for aeroengine applications. Critical speed is one of the important design parameters which is also affected by the presence of crack on the disc. The early detection of crack is a challenging task and the variation in the vibrational behaviour under the influence of crack must be known. In the present work an attempt has been made to introduce an efficient procedure to locate the crack position on the disc and also to compare the vibrational characteristics of healthy and cracked disc under the factual operating condition specific to aeroengine. Critical speed of cracked discs is compared with that of the healthy disc to identify the influence of crack on the safe zone of operation within the permissible speed limit. In the present findings, it is appealing to note that the vibrational mode shape can be employed as an effective tool in detection of the location of the crack. The present work is expected to serve as guidelines during the design phase of gas turbine discs of aeroengine applications.

Ranjan Kumar, Vinayak Ranjan, Saikat Chaterjee, Sanjoy K. Ghoshal

Time-Delay Fractional Optimal Control Problems: A Survey Based on Methodology

We survey some representative results on time-delay fractional differential optimal control problems. In this paper we provide a review of the techniques, developed in the last decade, for the numerical solution of time-delay fractional optimal control problems. In particular, Chebyshev and Chelyshkov wavelet methods, continuous and discrete Chebyshev polynomials methods are focused on this study.

Dajana Conte, Eslam Farsimadan, Leila Moradi, Francesco Palmieri, Beatrice Paternoster

Failure Analysis of Strip Foundation on Layered Soil Under Static Loading

A soil underneath foundation structure must satisfy design criteria of bearing capacity analysis which is safety against failure and tolerable settlement. Failure analysis of bearing capacity shows differently for a strip foundation on a single layer of soil or layers of soil in a deposit. For a design criterion, the strip foundation on layer deposit can be analyzed easily by using analytical and experimental approaches. Besides, the strip foundation failure behaviour on single soil is also predictable. However, foundation failure on layered soil is difficult to analyze and predict for the complex behaviour of soil underneath the foundation by analytical or experimental method. Thus, a three-dimensional finite element of strip foundation failure is analyzed. The three-dimensional geometry model of layered soils incorporated in the geotechnical finite element of PLAXIS (V8) program with the Mohr-Coulomb soil failure criterion model were chosen in the analysis. The strip foundation bearing capacity on dense sand overlying soft clay with ratio foundation width (B) to the top layer thickness (H) subjected to vertical loading was evaluated. The shear failure mechanism of strip foundation on layered soils was investigated. The numerical analysis results were verified with theoretical analytical formula from published equations. It shows that the ultimate capacity of strip footing bearing on layered soils increase in width of footing (B). The general shear failure mechanism is observed for dense overlying soft clay in all cases except for B/H = 0.5 (B = 2 m) shows local shear failure mechanism.

Masyitah Md Nujid, Fatimah Abdul Rahman, Ng Kok Shien, Noorsuhada Md Nor, Juraidah Ahmad, Nor Faizah Bawadi, Ali Akhbar Firoozi, Eka Kusmawati Suparmanto

Evaluation of the Residual Stress Behavior of 316L Stainless Steel in Electric Generator Blades Subjected to Different Hours of Service

This work studies the stability of residual stresses on cooling blades of electricity generators made of 316L stainless steel subjected to different hours of service. New blades made by stamping were analysed and residual stresses were measured in high-stress areas by finding magnitudes of up to 400 MPa. A finite element simulation was performed to determine the magnitude of the applied stress and measurements were made at the same points on blades of 13.000, 35.000 and 60.000 h of service. It is demonstrated how the location and direction of applied load generates that residual stress decrease while the number of cycles increase, but others, coincident with the points of high applied load the residual stresses increase over time.

A. Morales-Ortiz, J. C. Arango, C. C. Palacio

Influence of Microcracks on Strength of Diamond Wire Sawn Silicon Substrates

So-called microcracks are crucial for material removal during diamond wire sawing of silicon. But they also reduce the strength of silicon substrates after sawing due to the remaining subsurface damage. In order to investigate the influence of microcracks on strength of diamond wire sawn silicon substrates, more than 180 specimens of {100}-silicon were prepared using a reproducible scratching procedure with a Vickers indenter. Subsequently, 4-point bending tests were conducted parallel and perpendicular to the scratch grooves. The results indicate a clear anisotropy in the mechanical strength, which is mainly caused by median and also affected by radial cracking. The microstructural analysis of specimens with a single scratch or multiple scratches show results as a continuous as well as straight median crack propagation at a nearly constant damage depth over the complete length of the scratch groove. Additionally, in the case of multiple scratching, periodic crack kinking towards pre-damaged zones can be observed and, thus, further emphasises the importance of considering pre-existing damage in terms of material removal mechanisms and strength analyses.

Florian Wallburg, Kevin Meyer, Michael Budnitzki, Meinhard Kuna, Felix Kaule, Stephan Schoenfelder

Residual Stress Behavior on Welding Joints in Different Steels Using X-Ray Diffraction

Residual stresses are one of the main conditioning factors of the mechanical behavior of components subjected to repair by welding. The magnitudes, directions, location and homogeneity of the residual stresses change with the chemical composition of the base material, the welding process, among other variables. Although it is inevitable to induce residual stresses during the welding process, it is possible to determinate magnitudes and directions using characterization techniques such as X-ray diffraction. In this work, the residual stress distribution measurement is carried out using a portable X-ray diffractometer in the welds of two types of steel (304 stainless steel and A36 carbon steel). On 304 stainless steel, the presence of residual compressive stresses on the base material and the thermally affected zone (HAZ) and residual stresses on tension on the weld seam were identified. For its part, for A36 carbon steel, a distribution of residual stresses in tension and random compression was evidenced in all areas of the sample due to the welding process and material formation. It is concluded that the heterogeneity in the type of residual stresses distributed over the material favors the weakening of the propagation of possible cracks that appear in the areas with residual compressive stresses and the strong influence of the chemical composition of the filler material of welding in the distribution and type of residual stresses that are induced in as a result of the joining process.

A. Morales-Ortiz, J. C. Arango, A. S. Marulanda, C. C. Palacio

Effect of Specimen Size on Localization using Digital Image Correlation

Failure of structures made of brittle materials like rock and concrete exhibits deterministic size effect on post-localization mechanical behavior. The application of advanced image-based instrumentation, along with conventional testing can provide full-field strain and its evolution that can be useful for the analysis of localized behavior of brittle materials. In this view, this study collaborates the Digital Image Correlation technique (DIC) with lateral strain-controlled uniaxial compression tests on Hawkesbury sandstone for insights into size effect on localized behavior. Full-field strain obtained from DIC is synchronized with macroscopic responses to investigate the effect of specimen size on strain localization mechanism. Results from this study demonstrate that the increase in specimen size intensifies the local scale deformation, accelerates the localization process, and increases both strain gradients across the shear band and shear band thickness. The shear band evolution analysis in this study also provides rich quantitative data useful for the development of constitutive models to capture size effect on the behavior of rocks.

Rupesh K. Verma, Giang D. Nguyen, Ha H. Bui, Murat Karakus



Prognosis of Damage Intensity on Reinforced Concrete Beam Under Cyclic Loading

Active damage such as crack initiation owing to cyclic loading in reinforced concrete beams is a pivotal global phenomenon. This damage is because the crack initiation is slowly generated in the structure and cannot be observed visually. As the cyclic load progresses, the cracks need to be classified. This paper presents the prognosis of damage intensity on reinforced concrete beams under cyclic loading. Twelve singly reinforced concrete beams were prepared for the purpose of testing. The beams were subjected to three point loading with six phases of maximum cyclic loading. The acoustic emission technique was utilised for monitoring the crack progression. For cyclic loading, the 1 Hz frequency and sinusoidal wave mode were utilised. For each phase of loading, 5000 cycles were applied. A zone intensity chart was used for classifying the cracks that occurred in the beams. The classification was constructed based on the acoustic emission signals collected from the located events and on a channel basis. The located events were concentrated on the critical sections of SEC A and SEC B. Meanwhile, for the channel basis, the closest sensor to critical sections was used from CH3. It was found that the prognosis of the active crack intensity in the beam can be identified, which closely corresponds to the load increment. This study is useful for understanding crack behaviour in a beam subjected to cyclic loading.

Noorsuhada Md Nor, Soffian Noor Mat Saliah, Shahrum Abdullah, Norrul Azmi Yahya, Masyitah Md Nujid

An Experimental Investigation into the Fatigue Behavior of Spot Welded Tensile Shear (TS) Specimens

The resistance spot welds (RSWs) are extensively used in many industries especially automotive industry as a joining process of sheet metals due to its flexibility and adaptability to automation. In addition to easy automation capability, there are many more advantages that this joining process offers in the attachments of thin sheet body components, such as effectiveness, low cost and reliability. Despite all the favorable properties of this manufacturing process, the spot welded sheet metals are prone to mechanical fatigue failure especially under cyclic sinusoidal loadings. Therefore, understanding and elucidating the fatigue phenomenon of the RSWs are crucial during the design phase, in terms of estimating and preventing undesired failure conditions. However, in the design procedure, there exist considerable amount of challenges to be overcome to analysis and accordingly predict the fatigue failure in the sheet metals connected by spot welds, among them it can be counted electrode wear-down, non-uniform sheet metal forms, defected or incomplete weld nuggets. Many of these faults cause non-uniform stress distributions inside the sheet metal and make it difficult to estimate fatigue failure. Thereof experimental work, in most cases, shines as a viable option in the fatigue analysis. Within the scope of this work, an attempt is made to examine the fatigue phenomenon of the spot welded sheet metals experimentally. For this purpose, tensile shear (TS) type spot welded test specimens were utilized. A series of fatigue life tests were conducted on the previously prepared samples and the deformed test specimens were examined. The experimental results were compared with those of similar research studies available in the literature. It was observed that the outcomes of the present work are reasonably consistent with the literature results.

Ahmet H. Ertas, Mustafa Akbulut

A Fatigue–Reliability Analysis of Spot Welded Modified Tensile Shear (MTS) Specimens

In sheet metal structures, generally the resistance spot welds (RSWs) are used as a joining method especially for its adaptability to automation, effectiveness, robustness and low cost. On the other hand, the spot-welded sheet metals operate, most of the time, under cyclic loading conditions, which lead to fatigue fracture in the structure. In order to predict and prevent fatigue damage in the spot-welded sheets properly, many factors which affect the quality of welds in the design phase are to be considered such as arbitrary shapes of the sheet metal, missing or incomplete spot welds, and abrasion of the welding electrodes etc. All these disadvantages cause deviations in the stress analysis and make it very hard to obtain uniform stress distributions. Hence deterministic computational approaches, even pure experimental investigations of spot welded structures, do not always result in reliable outputs. In that case, probabilistic approach appears to be a feasible alternative in the fatigue assessment of RSWs. In this study, a probabilistic fatigue analysis is carried out on spot welded modified tensile-shear (MTS) test specimens. In the probabilistic analysis a g-function was introduced for each case study. The results obtained through aforementioned method were shown to be in good agreement with the related studies in literature.

Ahmet H. Ertas, Mustafa Akbulut

A Comparative Study on Fatigue Life Prediction of Spot Welded Coach Peel (CP) and Modified Coach Peel (MCP) Type Test Specimens

Besides friction, ultrasonic and laser welding, resistance spot welding is extensively employed for joining sheet metal panels in automotive, railroad and aerospace industry as a reliable, cost-effective, and flexible manufacturing process. Structural panels attached through the spot welding usually undergo cyclic loadings in service, which cause fatigue fracture damage. In order to predict and prevent this type of failure, an in-depth assessment of the fatigue phenomenon is inevitable. In this study, a strain based model known, as Coffin-Manson is adapted to estimate the S–N diagram of various materials, for the first time, on Coach Peel (CP) and Modified Coach Peel (MCP) Type Test Specimens. The strain values used in the model are computed through the FEM analysis. The results obtained in the present work are compared with those of alternative models and experimental data available in literature. Consistencies and discrepancies among the results are presented and interpreted.

Mustafa Akbulut, Ahmet H. Ertas

Numerical Methodology to Predict Subsurface Crack Initiation from Non-metallic Inclusions Due to Rolling Contact Fatigue

Bearings used in the intermediate and high speed stages of offshore wind turbine gearboxes run in harsh working conditions and may fail prematurely due to rolling contact fatigue (RCF). The microstructural alterations linked with such premature bearing failures are often described as white etching crack failures (WEC). Understanding these white etching bearing failures requires the study of RCF phenomenon at multiple scales ranging from macroscopic to microscopic and at different stages such as crack initiation and propagation. This paper presents a 2D numerical framework to evaluate subsurface RCF crack initiation originating from non-metallic inclusions in bearings. The global finite element (FE) model simulates parts of the contact bodies such as roller elements and raceway to represent the contact zone. A submodel containing a non-metallic inclusion is derived from the global FE model of a rolling contact. The inclusion is elliptical in shape and its position, dimensions and orientation can be changed. A moving Hertzian pressure distribution is modeled to simulate the rolling pass and the stress history around the inclusion/matrix interface. A multi-axial critical plane approach is adopted to calculate fatigue initiation damage. After explaining the numerical framework, this paper highlights the functionalities based on a number of case studies, focusing on effects of normal load and surface traction between the roller and inner raceway, and on inclusion characteristics. The results give us an insight into the underlying physics behind the mechanism of subsurface initiated RCF. Investigation of the link between RCF and white etching cracking is ongoing.

Gopalakrishnan Ravi, Wim De Waele, Stijn Hertelé

Fatigue of Multiaxially Loaded Shaft-Hub Connection Under Different Load Parameters

In addition to free-surfaced components, which have predictable fatigue life, the forces in drive train systems inevitably also pass through contacting surfaces. Failures, that occur at shaft-hub connections, are caused by high stress concentration and tribological loading. In the present paper, a test rig developed in-house for combined rotating bending load and alternating torsion is introduced. Experimental results obtained from the test rig on high-cycle fatigue (107 cycles) of press-fit connections are presented. To eliminate the tribological effects, a notched specimen from the same material is examined with corresponding parameter. The phase shift as well as amplitude ratio were investigated on normalised steel 1045. Compared to the calculation standards, which are frequently used in the industry, lower fatigue limits are obtained from experimental results. For a better consideration of the multiaxial fatigue, different estimation calculations are performed. Using numerical investigations, the calculation approaches based on integral methods are applied in combination with a critical distance approach. The smallest calculation error is reached at the critical distance of 0.096 mm.

Lukáš Suchý, Alexander Hasse

Evaluation of Fatigue Strength Characteristics of Al–Mg Oxide Dispersed Aluminum Composite

Aluminum is a lightweight metal that is soft and highly malleable; thus, it offers good workability. In addition, it also exhibits corrosion resistance due to the oxide film formed on its surface. Therefore it can be adopted for various applications such as engine cylinders and, the frames and rims in a bicycle. Typically, aluminum alloys are widely used. Recently, metal matrix composites, which are composites of a base metal (such as aluminum alloys) and a reinforcing material (such as ceramics), have been employed as they are cheap and feature excellent properties that cannot be obtained via other materials. In this regard, this study aims to develop a novel composite material wherein Al–Mg oxide is dispersed in Al alloy. Fatigue tests were employed to evaluate the fatigue strength of this novel composite, and the results were compared with those of the Al/SiC composite. It was found that the Al/SiC composite material exhibited higher fatigue strength for a lower number of cycles, whereas the proposed material achieved greater fatigue strength for a higher number of cycles. Furthermore, scanning electron microscopy images of the fracture surfaces of these materials indicated that Al/SiC primarily failed due to an intergranular fracture, whereas the proposed composite failed due to a transgranular fracture. It was also observed that the fractures originated at segregated Si crystals near the surface.

Yuki Ueno, Koichiro Nambu, Masahiro Okumiya

Assessment of a Thermal Fatigue Test Conducted Under Cyclic Non-proportional Loading Using Open Source CAE and Finite Element Analysis Methods

Thermal fatigue assessment is often required for high temperature components such as those in thermal power and chemical plants. The procedures used to evaluate fatigue life consumption of a component subjected to cyclic non-steady thermal loading are rather complicated and, in many cases, difficult to carry out. In addition, experimental validation of a thermal fatigue assessment by using FEM is rarely carried out due to the high cost and length of time required to perform tests that subjected a specimen to cyclic thermal loading. The authors herein propose simplified fatigue assessment methods and undertake their experimental validation by comparing the FEA assessment with the result of a previously reported thermal fatigue test performed by JAEA (Japan Atomic Energy Agency) on a tapered cylindrical specimen. In the test considered, the loading was almost proportional, and thus the validity of these methods for general non-proportional loading remained to be solved. This paper describes the fatigue assessment of components subjected to cyclic thermal loading, in which simulation was undertaken of a previously conducted thermal fatigue test that used an axisymmetric specimen with three different types of structural discontinuities. The test was also performed by JAEA in their sodium flow test facility. The specimen was subjected to cyclic thermal loading by alternating liquid metal flows injection at different temperatures. In this study finite element analyses, non-steady-state thermal transient and stress analyses were performed using commercial FEA software (MSC.Marc) and open source FEA software (Salome-Meca, Code-Aster) to evaluate change in thermal stress, and the two FEAs were compared. The FEA results indicate non-proportional stress histories. The simplified assessment methods previously proposed for determining the pair of time steps that define the maximum stress range were applied and subsequently compared. The simplified assessments made using the methods in this study are consistent with those made based on ASME Section III Division 5.

Shosuke Miyahira, Terutaka Fujioka

Depreciation Accounting in Longevity Evaluation of Complicated Systems

Consideration is given to the systems, which consist of nonrepairable expendable items and the restorable items operating in a cyclic mode. Durability of the latter, along with the no-failure operation, maintenance ability and storage qualities is characterized by longevity, i.e. the object property to ensure safe operation until offset of the ultimate limit state providing usage of the established maintenance and repair system. Service durability also directly depends on: human errors resulting in the undeliberate result; dependent failures caused by the system latent fault, etc. The most useful technique is the operation life setting, i.e. the number of operating cycles, which the object should perform over the period of its service life. At that, the comprehensive description is given of the operation cycle, environment conditions, and qualifications of personnel. In making of the theoretical assessments to describe the materials fatigue resistance and depletion, the Weibull-Gnedenko distribution is used. In carrying out of tests, in case of revealing of the component part excessive wear (due to the safety criteria) to be checked is the deterioration rate of the devices and units mostly subjected to wear, along with the maintenance works in compliance with the article maintenance documentation. Based on all the information and analysis, the composition of the SPTA sets shall be determined proceeding from the specified values of the system reliability value. Matters related to the depreciation accounting in the complex systems longevity evaluation have been addressed. Flagship approaches to solving of the emerging problems have been outlined.

B. Avotyn’, A. Smirnov, B. Belobragin

Fatigue Assessment of Aged Steel Specimens Under Uniaxial Cyclic Loading

Corrosion degrades mechanical properties and fatigue life of structures considerably; hence reliable numerical fatigue analysis is essential for assessing the remaining life of aged steel structures. In this paper, the influence of corrosion topology and the minimum thickness location on the stress concentration over corroded specimens and, in consequence, their fatigue life was comprehensively studied. The corroded surfaces were modelled using random spatial distributions approach. The results of the numerical simulation have been compared with published fatigue test results. The comparison showed good agreement between the experimental results and the adopted approaches for fatigue life assessment.

A. Yosri, A. Zayed, S. Saad-Eldeen, H. Leheta

Estimation of Steam Turbine Shafts Fatigue Damage Caused by Torsional Vibrations

In Ukraine, 74 power units with a capacity of 150–800 MW of thermal power plants out of 102 are on the verge of exceeding the park resource (220 thousand hours). Of these, 17 power units are close to the end the park resource, and 11 units have reached their estimated resource (100 thousand hours). Statistics of power plants accidents in different countries indicates that most of them are caused by the long term accumulation of fatigue damage. Among the main causes of fatigue damage are the pulsating of high-temperature steam flows in the turbine cylinders, transverse and torsional vibrations of shafts during long-term operation etc. This causes the development of computational and experimental methods for the determination of fatigue damage of turbine units’ shafts under dynamic loads. The evaluation of fatigue damage of steam turbine K-200-130 shaft is based on the 3D finite element model. The calculations take into account experimentally determined fatigue properties of rotor steel. The fatigue damage as a result of torsional vibrations of turbine shaft caused by the abnormal operation of turbine generator is calculated. Zones of stress concentration in the rotating elements of the steam turbine type K-200-130 are established for various operating modes. The procedure to predict the effect of fatigue damage on the estimated resource of turbine unit is proposed.

O. Chernousenko, V. Peshko, B. Marisyuk, A. Bovsunovsky

Crystal Orientation Effect on the Fretting Fatigue Behavior in Ni-Based Single Crystal Superalloys

The crystal orientation effect on the fretting fatigue behavior in Ni-based single crystal superalloys (NBSX) was studied in this paper using crystal plasticity finite element (CPFE) simulation. The crystal plasticity constitutive model considering back stress was applied in the CPFE simulation, and four different crystal orientations were calculated to study the effect of crystal orientation. The CPFE simulation results showed significant differences between the four crystal orientations. The Mises stress and the cumulative shear strain under different crystal orientations was obtained. The change of stress and strain with time at different locations showed obvious difference under four crystal orientations. The simulation results showed obvious stress concentration near the contact edge, but the peak locations of cumulative shear strain would change under different crystal orientations.

Qinan Han, Jianwen Fang, Haitao Cui

Three-Dimensional Numerical Analysis of Shrink-Fitted Shafts Under Rotating Bending Fretting Fatigue Condition

The cantilever rotating bending fretting fatigue (RBFF) damage of GH4169 was investigated in this work. With the help of ABAQUS and FRANC3D, the stress distribution and the contact status in the fretting zone were studied for the different fatigue loads. Furthermore, the critical plane shear stress amplitude model, Smith-Watson—Topper (SWT) model and Ruiz-Chen model were implemented and compared for fretting crack nucleation locations. The results showed that with the increase of the fatigue loads, the contact pressures decreased and the contact area reduced at the tension side. The stick zone, slip zone and open zone were formed due to fretting contact. At the compression side, the percent of slip zone area reached 4, 15 and 60% along the top surface axis of the shaft with the fatigue load of 500, 600 and 700 MPa. However, the slip zone area reduced with larger fatigue load and were almost the same for the three fatigue loads at the tension side. Moreover, the stress distribution results showed that the negative impact of fretting were weakened with the fatigue load increasing. Finally, the critical plane shear stress amplitude model and SWT model were determined to be more accurate in crack location prediction than the Ruiz-Chen model.

Jingchen Wang, Yukui Gao



A Model for Prediction and Optimization of Flank Wear in End Milling of AISI 316 Stainless Steel

Controlling Tool wear is a significant issue related with material removal process in machining. This current study focuses on flank wear end milling of AISI 316 stainless steel using PVD a high-performance TiAlN multilayer coated carbide tool. Three factors (cutting speed, feed and depth of cut) and three-level factorial experiment designs with Box Behnken and statistical analysis of variance were performed in order to investigate the effect of the cutting parameters on the tool and workpiece in terms of flank wear. The results show that flank wear is statistically significant influenced by feed and cutting speed. The model for the experiment explains 75% of the variation in the tool wear and the predicted effect of speed on the tool wear. Feed rate has shown to have highest effect on the tool wear. Accordingly, ANOVA and Multiple Regression were used to develop mathematical model for response, alongside with diverse diagnostic tests were also performed to test the validity and efficacy of the proposed model.

Peter Babatunde Odedeyi, Khaled Abou-El-Hossein

Study of Sliding Wear in Rail and Wheel Steels: Effect of Hardness Ratio and Normal Load in Pin on Disc Test

Rails and wheels are one of the most expensive assets in the railways, and their life needs to be increased by existing methods such as using the optimum rail/wheel hardness ratio. This study aims to verify the synergistic effect of hardness ratio and normal load on the sliding wear resistance. For this, it was used as model system the test pin against disc. The pins were extracted from a class C steel cast wheel (AAR Standard) and the discs were extracted from premium and intermediate grade steel rails (AREMA Standard). Rails are pearlitic and the bainitic wheel is in its first life. Both are hypereutectoid steels with hardness between 321 and 392 HB. The results of the unlubricated sliding tests made possible to compare the sliding wear resistance as a function of the three normal loads (40, 80 and 120 N). The sliding wear behavior for some of the singly body wear rate cases here studied served to validate the field and laboratory tests presented in the literature. From a crossing between the results of the literature and the present study, it is recommended aiming reduction of the wear of rail and/or wheel in a unlubricated condition, to adopt the optimal hardness ratio between rail/wheel ROptimal ≥ 1.0, proposed in the field study (Steele and Reiff 1982), and/or 1.0 ≤ ROptimal ≤ 1.1 proposed by the laboratory test and mathematical model (Razhkovskiy et al. 2015).

Thiago Gomes Viana, Gustavo Tressia, Amilton Sinatora

Friction Films and Their Influence on the Antifriction Properties of New High-Temperature Nickel Composites

The article studies the tribological properties formation of new composite antifriction materials based on nickel with solid lubricant CaF2 for operation at temperatures 550–600 °C in air. It was shown the high antifriction properties are achieved due to the formation of homogeneous antiscoring friction films on contact surfaces under working conditions without liquid lubricant. It was analyzed the formed friction films are in the balance between the wear rate and the rate of new film’s areas formation at temperatures 550–600 °C. This phenomenon is explained by the formation of the oxides certain amount in combination with pure chemical elements and CaF2 solid lubricant. The contact surfaces are protected from abrasive phenomena and internal oxidation with such a chemical composition of films at 550–600 °C. Self-lubricating homogeneous antiscoring films provide the high tribological parameters. The research results allowed recommending the rational exploitation modes for new high-temperature nickel antifriction composite.

Krzysztof Jamroziak, Tetiana Roik

Proposal for New Hardness Concept Using Herbert Hardness Tester

A Herbert hardness tester uses an inverted pendulum and performs measurements under loading conditions different from those used in conventional indentation and rebound hardness tests. Hardness is conventionally measured as a resistance to monotonic deformation. In contrast, a Herbert hardness tester oscillates on a test specimen, and provides information on resistance to cyclic deformation. The original Herbert hardness tester yielded three kinds of hardness data: (1) Scale hardness (indicated by the position of the bubble in a spirit level at the end of the first swing); (2) Time hardness (based on the pendulum swing time measured using a stopwatch); and (3) Flow hardness (defined as the scale hardness/time hardness ratio, and which is an indicator of work hardening). However, this test method did not become popular due to the time and effort involved compared with other techniques. Nevertheless, the present authors have continued to work towards making improvements in hardness measurement methods based on freely damped oscillations. These improvements included the use of rotary potentiometers, laser displacement meters, and image processing. And a new concept of “Damping hardness” has also been proposed. This paper covers the following topics: (1) A new hardness measure given by the natural angular frequency/damping factor; and (2) Development of a new Herbert hardness tester incorporating a wireless acceleration sensor.

Masaaki Matsubara, Masayoshi Nakamura, Ryosuke Suzuki

Microstructure and Abrasive Wear of Particle-Filled Composites

This paper describes the influence of SiC and Al2O3 particles on the wear behaviour of epoxy including PTFE particles. Particle-reinforced epoxy composites (PRCs) covering 5 wt%SiC, 10 wt%SiC and 10 wt%Al2O3 particles plus 5 wt%PTFE were fabricated successfully by mixing technique. The tribological property of PRCs at dry sliding was studied against SiC abrasives on a conventional pin-on-disc machine using Box-Behnken method at different factors. Microstructures were examined through Scanning Electron Microscope (SEM). In addition, second order regression model of weight loss was derived from the main parameters and their interactions. SiC particles indicated a better performance than that of Al2O3 particles due to enough bonding between the fibers and the resin. Furthermore, analysis of variance showed that linear contributions were about 47.60% (load (28.36%) had a considerable effect on the mass loss, followed by speed (11.09%) and material types (8.15%) for PRCs, respectively. However, square effect was about 42.0% while two-way interactions had no effect on the mass loss.

Yusuf Şahin, H. Şahin

Experimental Characterization of Vibration on Gearing Mechanism Using Taguchi Approach

Experimental characterization of the vibration analysis were investigated in a spur gearbox using Taguchi method (TM). The influences of different parameters such as rotational speed, torque, and center distance deviation on the frequency and acceleration of the tested samples were investigated. It is shown that frequency for normal gear changed from approximately 592–1184 Hz, corresponding values of accelerations were about 0.093–0.143 m/s2, respectively. In the case of failure gear, however, frequency changed from 592 to 740 Hz, corresponding values were about 0.287–0.53 m/s2, respectively. The experimental design results exhibited that center distance deviation was the effective factor for both frequency and acceleration, followed by speed and torque, respectively. Optimized process condition was first level of speed (600 rpm), first level of torque (1000, and second level of center distance (0.0 mm).

H. I. Mirzayev, Yusuf Şahin, A. Z. Khalilov, R. S. Valili

Fretting Wear Effect on Fretting Fatigue by Findley Parameter in Mixed Slip Regime

When there is a small amplitude relative slip between two contacting parts, fretting happens. Wear, fatigue and corrosion are the three main damages caused by fretting. In reality, these three damages interact with each other, which is not emphasized in current research. Findley parameter (FP) is a commonly used parameter that can be utilized to analyze fretting wear. In this paper, the wear profile updating effect on fatigue is analyzed by FP in mixed slip regime of fretting. A finite element (FE) model of a cylinder-on-flat configuration is built to investigate the FP difference between models with and without wear profile updating. The results showed that FP in the model with wear profile updating was lower compared with the model without wear profile updating near the contact edge. It can be concluded that fretting wear shows a positive effect on fretting fatigue. Moreover, the predicted life shows a good agreement with experiments.

S. Wang, Magd Abdel Wahab

Effects of Ti-6Al-4 V Surface Condition on the Performance of DFL Lifetimes

In this study, the impact of different substrate surface conditions on the performance of an epoxy-bonded dry film lubricant (DFL) and their fretting lifetimes are evaluated. Ti-6Al-4 V fretting samples with various surface preparation methods; ground (as received), grit blasted (at a range of severity levels) and shot peened samples were coated with a MoS2 loaded epoxy based DFL and implemented in fretting tests against like on like cylindrical specimen with a radii of 15 mm which were also coated. Distinct damage behaviours and coating lifetimes are observed for each of the surface preparation methods tested. Results indicate the various damage mechanisms are associated with initial substrate surface conditions which influence the stability and longevity of the system. Having established a correlation between DFL lifetime and substrate surface conditions, the next step in this work is to identify the specific surface features which promote the longevity of DFL. It must be noted that the substrate surface considered in the study is the DFL/substrate interface, i.e. the surface of the specimen prior to DFL coating, as opposed to the outer surface of the coated specimen.

E. Laolu-Balogun, S. P. Owen, S. Read, G. Pattinson, P. H. Shipway, K. T. Voisey

Predicting Rebound of Ellipsoidal Granules Using SPH

The accuracy of SPH in predicting rebound kinematics in granular flow applications involving non-spherical granules is investigated. For this, the rebound behavior of an ellipsoidal granule impacting an elastic substrate is analyzed for different impact angles and for different initial orientations of the granule. The friction modeling capabilities of SPH are investigated by comparing the rebound spin predicted by the SPH simulations (a) without any special friction model and (b) using Coulomb’s friction model, with DEM results. This study presents the potential of using SPH in analysing granular flow applications and brings to light the limitations associated with the existing friction modeling capabilities in SPH.

Dhairya R. Vyas, Sharen J. Cummins, Murray Rudman, Gary W. Delaney, Paul W. Cleary, Devang V. Khakhar

Micro-Abrasive Wear Behavior Study of an Intermetallic Material—Fe–30Al–6Cr (at.%) Under Conditions of Room and Moderate Temperatures: A Comparison

Present work focus on research of tribological resistance of an intermetallic material (Fe–30Al–6Cr—at.%), seeking correlations between wear volume, friction coefficient and temperature. Abrasive experiments were performed with specimens of an iron aluminide alloy against AISI 52100 steel ball and abrasive particles of silicon carbide in glycerin. An individual study was done with respect to their characteristics in terms of SEM-EDS analysis. Different test conditions were defined and the abrasive slurry was, continuously, supplied between the specimen and the ball. Values of tangential force and normal force were acquired simultaneously, for “ball – abrasive particles – specimen” tribological system. Systematic studies of the occurrences of the micro-abrasive wear modes, friction and wear generated during tests were done. Moderate temperature favored a larger degree of plastic deformation than removal of material, reducing the wear rate and decreasing glycerin viscosity, which facilitated the movement of the abrasive particles and, consequently, reduced the friction coefficient. Wear volume presented a rising behavior with increase in sliding distance at room and moderate temperatures. Present research explored the potential of an intermetallic material as structural material subjected to moderate temperatures.

Eduardo K. T. M. Silva, Jorge H. Luna-Domínguez, Vikas Verma, Ronaldo Câmara Cozza

Acoustic Wear Monitoring During the Milling of Tool Steel for Machining 4.0

For some years, the concept of Industry 4.0 has been a focal point of interest. Initial deliberations have often been the subject of careful academic research and visionary ideas. However, more recent developments have shown that machining 4.0 is the technology of the future in solving complex autonomous manufacturing and production issues. This technology will permeate the manufacturing sphere with the industrial concept of “Internet of Things”, powered by data and nested with machining. To efficiently digitize and automate the machining industry, it is essential to obtain data that can be precisely correlated to machining process condition. As the cutting tool is central to any machining operation, tool condition monitoring is one of the possible approaches used for data generation, production control and to optimize production economics. The research work presented herewith utilizes acoustic emission (AE) signals as a sensing method to provide adequate information on the cutting condition and wear during the end-milling operation of tool steel. A signal processing sequence consisting of feature selection, extraction and correlation process of the AE wave was performed to determine features highly correlated to the tool wear. These features were then fed to a neural network for generating prediction models for the cutting tool condition. The results identified a higher correlation between time-frequency AE features and tool wear as well as distinct time-domain features such as RMS and standard deviation.

Oluwole Olufayo, Khaled Abou-El-Hossein

Study of Wear on AISI E52100 Steel Using a Lithium Complex Grease and a Calcium Sulfonate Grease

The purpose of this work was to study the antiwear and extreme pressure properties of two synthetic greases, one of them consists of lithium complex as a thickener, it is classified in the standard ISO 6743-9 as LX and the other has calcium sulfonate as a thickener and it is classified as CS. Both greases are widely used to lubricate bearings under high loads and high speeds operating conditions. Experimental wear results in show that the two greases have similar wear protection. However, extreme pressure tests show that calcium sulfonate grease offers better performance at high contact pressures, because this can work in short times at a maximum contact pressure of 8741 MPa without the presence of the seizure wear mechanism, while the lithium complex supports lower contact pressure around 7.08 GPa with features of seizure.

J. F. Márquez-Santiago, M. Vite-Torres, E. A. Gallardo-Hernandez

Surface Roughness and Normal Force Effects on the Sliding and Rolling Behavior of POM-H Rolls

Polymer bearings are increasingly used due to their simple mass production and good tribological properties. The current contribution presents a macroscopic study of the effects of surface roughness and normal force on the sliding and rolling behavior of POM-H rolls. The counter-face roughness Ra was varied from 0.01 to 0.5 µm and the normal force from 150 up to 350 N. A polynomial regression model was used to analyze the effects of the two parameters and their interaction. The experiments showed that the coefficient of sliding friction depends strongly on the roughness with a distinct minimum at around 0.1 µm and only slightly on the normal force. In contrast, the coefficient of rolling resistance increases strongly with higher normal forces. From 150 to 350 N the coefficient of rolling resistance doubles in value. The roughness has a minor influence in rolling. The difference between sliding and rolling expresses also in the opposite interaction effects of the roughness and normal forces.

Leonhard Kilian Doppelbauer, Philipp Siegfried Stelzer, Zoltán Major

Numerical Analysis of the Wind Turbine Pitch Bearing Raceway Tribo-contact due to Cyclic Loading Under Constant Pitch Angle

Pitch control movements in wind turbines are commonly short and slow. Moreover, some operating conditions may result in no pitch movement for large time periods. Variable loads coming from wind and the own weight of the blades will turn into micro-oscillations at ball to raceway contact as consequence of ring and contact deformations. Control oscillating movements have been extensively studied in literature. However, no research has been found relating motionless operating point with wear and false brinelling damage. In the present work, a comprehensive analysis at ball-raceway contact taking a 4-point contact ball bearing of 5 MW NREL offshore reference wind turbine as case of study. A simplified finite element model allows to simulate different bearing parameters and loading conditions in order to determinate their effects on the ball and raceway contact behavior. The numerical results highlight the limitations of classic analytical contact mechanics equations which do not predict any tangential stress for non-conformal spherical bodies of same material under normal loading. Furthermore, results reveal the occurrence of micro-slip once a pressure threshold is reached and the effects of some bearing parameters such as raceway conformity or contact friction coefficient. As consequence of this analysis, it is numerically demonstrated that a cyclic normal load without any rolling can lead to local frictional wear, false brinelling or fretting corrosion damage at the bearing raceway.

David Cubillas, Mireia Olave, Iñigo Llavori, Ibai Ulacia, Jon Larrañaga, Aitor Zurutuza, Arkaitz Lopez
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