Advances in Acoustics and Vibration II

In this work, we propose to follow the progression of different gearbox defects under the effect of variable load and speed. The non-stationary vibration signals are obtained by using a physical model of a spur gear transmission. In order to detect the presence of the fault characterized by transient signals which are usually masked by other vibration signals and noise. We can use the Improved Complete Ensemble empirical mode decomposition with adaptive noise (ICEEMDAN) to decompose the non-stationary vibration signals into many components that represent mechanical behaviour of the machine, transient component and noise. The ICEEMDAN method is based on the estimation of the local mean and the white noise is not used directly. this method eliminates the mode mixing introduced by EMD and reduces the amount of noise contained in the modes given by using EEMD and gives better results than EEMD. To analyze IMFs given by ICEEMDAN method we can use statistical methods like kurtosis which is very used to detect impulsion in the signal. In this work, we also use a statistical method, the L-Kurtosis, as an indicator to compare the IMFs given by ICEEMDAN, the results given by this indicator are compared to the results given by the Kurtosis.

The diagnosis of rotating machinery such as planetary gearbox running under operating condition is a complex task. Depending on their nature, the defects can be classified into teeth, geometrical or bearing defects. This paper studies the dynamic behavior of a back-to-back spur planetary gear running in stationary condition in the presence of teeth defects. This damage is the pitting and it is located in one tooth of the sun gear. An experimental test is performed by the measurement of the instantaneous accelerations on a test gear. The tests are carried out under a fixed load and speed. The presence of the tooth pitting defect activates repeated-like transient in ring’s vibration displacement because of phase change and amplitude reduction of the mesh stiffness when the damage tooth comes into contact. The Fast Fourier Transform (FFT) is used to transform the time signal into the frequency domain for signature analysis. The acceleration spectra show the influence of damage both in frequency and amplitude. The frequency of pitting which is the frequency of rotation of the test sun and the frequency of rotation of the motor appears along of frequency bandwidth. Moreover, the impulses of the defect tooth with the planets become important in amplitude.

This work provide more new knowledge about rolling bearings lubricated with axle gear oils. Extensive tests were performed and a considerable amount of experimental results of power loss in rolling bearings, difficult to find in literature, were obtained. Five fully formulated axle gear oils with different base oil, viscosity and different formulations and additive packages were selected. Their chemical and physical properties were measured. Thrust ball bearings lubricated with axle gear oils were tested using a modified Four-Ball Machine where the four-ball arrangement was replaced by a rolling bearing assembly. These tests were performed under a constant temperature of 70 $$^{\circ }$$ C and under the following operating conditions: speed between 75 and 1200 rpm and two axial loads (4000 N and 7000 N). The rolling bearing friction torque was measured and the effect of speed, temperature and axial load have been evaluated. Based on experimental results, a rolling bearing torque loss model was calibrated using SKF model for ball contacts. The model allows a better understanding of the behaviour of the rolling bearing geometries and of the influence of oil formulation on rolling bearing friction torque. The rolling bearing power loss model will be relevant for the global axle differential power loss model predictions.

Among the problems encountered in rotordynamics, the phenomena of instability generally due to the hydrodynamic bearings and interns damping, the gyroscopic effect due to the discs and shafts, the excitations due to the unbalance as well as the nonlinear phenomena related on the bearings which support the rotor and the elements carried by the rotor.The objective of this paper is to investigate the effects of damping and rigidity of hydrodynamic bearing on the stability of a Lalanne-Ferraris rotor. This study was conducted with respect to the stability criterion seen in a natural frequencies’ equation. The process begins with the establishment of the characteristics of rotor elements. This is to assess the expressions of the kinetic and deformation energies, as well as the corresponding virtual work for rotor components: disk, shaft, unbalance and hydrodynamic bearing. The Rayleigh-Ritz method and Lagrange’s equations were used to determine the equations of motion. A computational program in FORTRAN is elaborated to solve the characteristic equation in free vibration. The roots are pairs of complex conjugate quantities. In forced vibration, the resolution of the linear algebraic system is conducted by the Gauss-Jordan direct method. Also a computational program in FORTRAN is elaborated. A numerical example of Lalanne and Ferraris rotor is computed. According to the results presented herein, the presence of damping for certain values of rigidities was found to be a possible source for instability of the rotor at defined speeds.

The objective of this paper is to use the Independent Component Analysis technique (ICA) in the Operational Modal Analysis (OMA) in order to determine the modal parameters of a half car model with four degrees of freedom. The ICA method is a major technique of the Blind Source Separation (It considers the studied system as a black box and knowing only its responses it can estimate its modal parameters) which is based on the inverse problem. In our case, this technique can be used to reconstruct the modal responses of the half car model knowing only its vibratory responses. In this paper, these vibratory responses are numerically computed using the Newmark approach and they constitute the observed signals for the ICA algorithm. So that based only on the knowledge of these responses, the ICA estimates the modal characteristics (modal responses, eigenfrequencies) of the studied half car model. Finally, the modal responses of the studied system obtained by the classical modal analysis are compared with those estimated by the ICA technique using some performance criteria which are the Modal Assurance Criterion (MAC number) and the relative error. The obtained results show a good agreement between the theoretical and estimated modal characteristics.

We consider the problem of detecting the presence of sound-hard cracks in a non homogeneous reference medium from the measurement of multi-static far field data. First, we provide a factorization of the far field operator in order to implement the Generalized Linear Sampling Method (GLSM). The justification of the analysis is also based on the study of a special interior transmission problem. This technique allows us to recover the support of the inhomogeneity of the medium but fails to locate cracks. In a second step, we consider a medium with a multiply connected inhomogeneity assuming that we know the far field data at one given frequency both before and after the appearance of cracks. Using the Differential Linear Sampling Method (DLSM), we explain how to identify the component(s) of the inhomogeneity where cracks have emerged. The theoretical justification of the procedure relies on the comparison of the solutions of the corresponding interior transmission problems without and with cracks. Finally we illustrate the GLSM and the DLSM providing numerical results in 2D. In particular, we show that our method is reliable for different scenarios simulating the appearance of cracks between two measurements campaigns.

Gearboxes have been investigated and monitored for decades since they present one of the important transmission power systems which have been used in navy, air and automotive sectors. One of the most adopted one is the planetary gearbox since it has an important reduction ratio within compact space. The dynamic behaviour of a such one is very complicated because it possesses several gears in mesh and differs from other types of gearboxes by the fact that planet gears can occupy different positions in one period carrier rotation which leads to an important influence on the overall vibration signal acquired by a transducer mounted one the external housing. Consequently, in a measured vibration spectrum, the pass planet frequency component is identified and its energy level is considered only as the pass planet energy. However, there is another phenomenon that increases the level of the pass planet frequency component which is the due to the rotation of planets. In this work, a comprehensive monitoring of a staged planetary gearbox is presented. The unbalance phenomenon is investigated in every stage. Then, an experimental validation is provided in order to support our hypothesis claiming that the phenomenon depends on the parity of the number of planets.

Most engineering system, machines and products have moving parts and in order to achieve a desired performance, they require the manipulation of their mechanical or dynamic behavior from the early stage of design. Also, the dynamic interaction between the moving object and the structure should be properly considered at this level. The objective of the presented paper is to propose a new methodology for the pre-design of a mechatronic system, considering the vibrational behavior using the object oriented modeling language Modelica with Dymola environment. In fact, we study the dynamic behavior of a supporting flexible beam structure (simply supported at both ends) traversed by moving masses at variable speeds, based on the object-oriented modelling paradigm developed in Modelica. An analytical approach is adopted, providing a compromise between the results accuracy and the computation time. To illustrate the methodology, the bridge crane system is used as a supporting study. This machine is commonly used in industrial facilities. The effects of varying the different parameters on the dynamic response of the system are investigated. This methodology would be useful for a designer to have an overview about the system response and the interaction between the different subcomponents in the conceptual design phase.

To solve problems of higher computational burden in standard collaborative optimization (CO) approach during the processing of design problem of the multi-physics systems with multiples disciplines, a Dynamic Relaxation Coordination based Collaborative Optimization (DRC-CO) method is presented. The main concept of DRC-CO method is to decompose the global design problem into one optimization problem at the system level and several autonomous sub-problems at disciplinary level. At the system level, the dynamic relaxation coordination aims to solve the inconsistency between all disciplines, which leads the optimization process converging to the feasible optimum efficiently. To demonstrate the efficiency and accuracy of the proposed DRC-CO method, a safety isolation transformer is considered. The obtained results of the engineering multi-physics system show the effectiveness of the proposed DRC-CO process compared to Single Level Optimization (SLO) and standard CO methods. The obtained optimal configuration of the safety isolation transformer in terms of total mass using DRC-CO method (2.30 kg) is close to the result obtained from SLO method (2.31 kg) with an absolute percentage error is less than 0.5%. Moreover, our approach requires 3 system iterations to find realizable designs. However, an important number of disciplinary design problems were evaluated at the disciplinary level optimizer.

The prediction of the gear behavior is becoming major concerns in many industries. For this reason, in this article, an electro-mechanical modeling is developed in order to simulate a gear element driven by an asynchronous motor. The electrical part, which is the induction motor, is simulated by using the Kron’s model while the mechanical part, which is the single stage gear element, is accounted for by a torsional model. The mechanical model that simulates the pinion-gear pair is obtained by reducing the degree of freedom of the global spur or helical gear system. The electrical and mechanical state variables are combined in order to obtain a unique differential system that describes the dynamics of the elecro-mechanical system. The global coupled electro-mechanical model can be characterized by a unique set of non-linear state equations. The contribution of this work is to apply the control based on observers in order to supervise the electrical and mechanical behavior of the electro-mechanical system from only its inputs and its measurements outputs (sensors outputs). Some simulations on pinon/motor angular speed, electromagnetic torque, currents, are presented, which illustrate the system evolution (i.e., the electrical and mechanical quantities) and the good performances of the proposed observers.

A mechatronic system consists in a close intersection between mechanics, electronics, control engineering and software engineering. Typically, the controller design and the system design are developed and optimized contemporaneously. However, a poorly designed mechanical system will not at any time be able to hand out a good performance by adding a good controller. Furthermore, to design complex systems, the designers have to follow the traditional point-based development model where one solution is iteratively modified until it fits the specifications. The main problem with the point-based development model lies in the several resets and modifications that return to the previous steps to satisfy the requirements that meet those of the current stage. Therefore, in this paper, we propose to use Set Based Concurrent Engineering to develop a complex system after that we propose to carry a preliminary optimization of the parametric model of the system in the preliminary design before adding the control system. This approach is shown with a simulation model using Modelica for a case study in the automotive field of an Electronic Throttle Body (ETB).

The present study investigates the modeling of the vibration energy localization from a nonlinear quasi-periodic system. The periodic system consists of n moving magnets held by n elastic structures and coupled by a nonlinear magnetic force. The quasi-periodic system has been obtained by mistuning one of the n elastic structures of the system. The mistuning of the periodic system has been achieved by changing either the linear mechanical stiffness or the mass of the elastic structures. The whole system has been modeled by forced Duffing equations for each degree of freedom. The forced Duffing equations involve the geometric nonlinearity and the mechanical damping of the elastic structures and the magnetic nonlinearity of the magnetic coupling. The governing equations, modelling the quasi-periodic system, have been solved using a numerical method combining the harmonic balance method and the asymptotic numerical method. This numerical technique allows transforming the nonlinearities present in the governing equations into purely polynomial quadratic terms. The obtained results of the stiffness and mass mistuning of the quasi-periodic system have been analyzed and discussed in depth. The obtained results showed that the mistuning and the coupling coefficients have a significant effect on the oscillation amplitude of the perturbed degree of freedom.

In this paper, the low melting point metal Phase Change Material (PCM) heat sink for coping with ultrahigh thermal shock (1 W/cm2) is developed numerically. Sodium hydrate-based PCP is selected as the best Phase Change Material candidate from the point of view of thermal performance based on an approximate numerical analysis. Plate fin structure is investigated. The effects of fin number, heat flux, filling factor of PCM and fin width are parametrically studied; the influence of the structural material is briefly discussed. For arbitrarily given heating condition, the optimal geometric configuration of the heat sink is suggested and corresponding thermal performance is provided. The proposed low melting point metal PCM heat sink can cope with very large thermal shock with maximum device temperature, under the ambient temperature, which is extremely difficult to deal with otherwise by conventional PCMs. The conclusions drawn in this paper can serve as valuable reference for thermal design and analysis of PCM heat sink against ultra-high thermal shock. The results indicated that PCM-based heat sinks with fins are viable option for cooling plate structure with respect the number of fins, the power level of the heat source.

Piezoelectric energy harvesting from ambient energy sources, particularly vibrations, has attracted considerable interest throughout the last decade. Sensitivity analysis is a promising method used for many engineering problems to assess input-output systems based on vibration. In this paper, the formulation of first order sensitivity (FOS) of complex Frequency Response Functions (FRFs) is developed to evaluate the output responses of piezoelectric energy harvesters. The adapted approach for the FOS is the finite difference method, which consists in computing an approximation of the first derivation. Furthermore, the main goal is to study the influence of the variation of the load resistance from the short circuit (load resistance tends to zero) to open circuit (load resistance tends to the infinity) conditions on the tip displacement and the voltage FRFs of a Bimorph Piezoelectric Energy Harvester (BPEH). The determination of FRFs of the harvester are derived using Finite Element Modelling for a bimorph piezoelectric cantilever beam based on Euler-Bernoulli theory, which is composed of an aluminum substrate covered by two PZT-5A layers. The results show a high sensitivity of the FRFs of the BPEH to the load resistance at the natural frequencies. For each excitation frequency, the sensitivity near the resonance frequencies decreases from the short circuit conditions to the open circuit conditions.

The plastic ball grid array (PBGA) package has become a major packaging type in recent years, due to its high capacity for the input/output counts. However, vibration loading is encountered during the service life of PBGA. This study investigates the effect of vibration loading on the solder ball response. A two-dimensional finite element model of the printed circuit board (PCB) and PBGA component assembly is released using COMSOL Multiphysics software. The natural frequencies and modes were calculated. Forced vibration analysis was performed around the first natural frequency to determine the solder joints having highest stress and strain concentration under harmonic excitation. It showed that the interface between solder ball and the PCB is the most vulnerable part. Displacement and Von Mises stress variation were calculated in the most critical point. It was found that the height amplitude of displacement and Von Mises stress may conduct to decrease the solder interconnects lifetime. Moreover, resonance may conduct to the failure of the solder joints.

This paper proposed a design technique to dampen water-hammer surges into an existing steel piping system based on replacing a short-section of the transient sensitive region of the main piping system by another one made of polymeric material. The flow behavior was described using a one dimensional unconventional water hammer model based on the Ramos formulation to account for pipe-wall deformation and unsteady friction losses. The numerical solver was performed using the fixed gird Method of Characteristics. The effectiveness of the proposed design technique was assessed with regard to water-hammer up-surge scenario, using a high- or low-density polyethylene (HDPE or LDPE) for the replaced short-section. Results demonstrated that the utilized technique provided a useful tool to soften severe water-hammer surges. Additionally, the pressure surge softening was slightly more important for the case of a short-section made of LDPE polymeric material than that using an HDPE polymeric material. However, it was observed that the proposed technique induced an amplification of the radial-strain magnitude and spread-out of the period of wave oscillations. It was also found that the amortization of pressure amplitude, and reciprocally the radial strain magnitude, was strongly dependent upon the short-section size and material.

This paper presents a parametric study of the microphones distribution effect in the identification of the boundary acoustic sources acting in the acoustic cavities through the knowledge of the acoustic energy densities measurement. An energetic approach, also called the simplified energy method (MES) was developed to predict the energy densities distribution for the acoustic applications. MES can also be applied to structures to determine energy densities. This energy method can solve inverse problems in order to localize and quantify the structural and the acoustic boundary sources at medium and high frequency ranges, thanks the inverse formulation of this energetic approach (IMES). The main novelty of this paper is to study the performances of this inverse energetic approach in the quantification and localization of the boundary acoustic sources acting in the acoustic cavities. Numerical investigation concerning 3D acoustic cavity was performed to test the validity of the presented technique using different number of acoustic sources and distance between the microphones repartition and the cavity walls. The numerical results show that the inverse simplified energy method (IMES) has an excellent performance in identifying and detecting the boundary acoustic sources at medium and high frequency ranges from the knowledge of the acoustic energy densities measurement.

Experimentally, errors on measurement points’ coordinates, among others, could affect identification results. These errors can be committed by engineer or result from measuring tools and conditions. Resulting coordinates’ variability is modeled in this work by uncertainties and is included into an experiment-based identification process to identify, in a wave propagation framework, the wavenumber and the wave attenuation of a honeycomb sandwich beam. The proposed process combines a Variant of the Inhomogeneous Wave Correlation (V-IWC) method and a sample-based uncertainty propagation method: the Latin Hypercube Sampling. Vibratory fields, which are used as inputs of the identification process, are computed experimentally. Both deterministic and statistical investigations of identified wavenumber and damping are performed. Results prove the efficiency of the proposed V-IWC method on wide frequency ranges and the robustness of identification against uncertainties. Moreover, if some measured vibratory fields do not match associated measurement points’ coordinates, no damping sensitivity to such uncertainty is detected.

This study presents an analysis of the mechanical and vibration behavior of a flax fibre reinforced composites with and without an interleaved natural viscoelastic layer. Two types of elastic and viscoelastic cross ply laminates [02/902]s and [02/902/NR]s have been characterized experimentally using different mechanical and vibrational tests. The elastic laminate is composed of natural long flax fibre and greenpoxy resin while the viscoelastic laminate is composed of a natural viscoelastic layer and two elastic composites. First, both types of specimen composites were studied using uni-axial tensile tests under the same conditions. A comparison between the two composites behaviors has been realized. Then, Acoustic Emission (AE) has been often used for the identification and characterization of micro failure mechanisms and damage in laminates. Finally, experimental vibration analyses were carried out on the composites with and without an interleaved natural viscoelastic layer. Throughout a series of resonance vibration tests, the evolution of the Young modulus and the modal damping were evaluated. The effect of the viscoelastic layer on the mechanical and vibration behavior of the elastic composite has been investigated and analyzed. It has been shown that the viscoelastic layer improves with a significant way the modal properties of the flax fibre reinforced composite.

The domestic windows in the exterior building facade play a significant role in sound insulation against outdoor airborne noise. The prediction of their acoustic performances is classically carried out in laboratory according to standard ISO 10140. In this work, a 3D elasto-acoustic finite element model (FEM) is proposed to predict the sound reduction index of three different glazing configurations of domestic window follows the ISO recommendations for acoustic measurements, which are compared to laboratory measurements. Two acoustic cavities with rigid-boundaries on both sides of the window are used to simulate respectively the diffuse sound field on the source side and the pressure field on the receiver one. By using a simplified FEM for the double-glazed windows, the sound reduction index is calculated from the difference between the source and receiving sound pressure levels in the one-third octave band from 100 to 500 Hz. Although the comparison between numerical and experimental results shows a relatively good agreement which highlights the interest of this kind of approaches to avoid expensive experiments, many improvements should be taken to ameliorate the model such as the different components of the frame and the design of the two rooms to avoid the problematic of multi-resonant frequency ranges.

This paper aims to present an efficient cultural algorithm to solve the target optimization problem of vibration-based damage detection. The modal flexibility error residual is employed as objective function to be minimized. Cultural algorithms are inspired from the cultural evolutionary process in nature and use social intelligence to solve optimization problems. A cultural algorithm is composed of a belief space which consists of different knowledge sources, a population space and a set of communication protocols that enables interaction of these two spaces. Cultural algorithm offers powerful tools to solve various optimization problems as a result of its robustness as well as computation effectiveness. In this work, cultural algorithm is applied to generate solutions using three knowledge sources namely situational knowledge, normative knowledge, and domain knowledge. The core idea of using domain knowledge source is to speed up the convergence of the algorithm and thus, reducing its computational cost. The performance of the proposed algorithm is demonstrated through a numerical example, with different damage scenarios and noise levels. Comparison of the proposed algorithm with other basic and state-of-the-art algorithms reveals its superiority in accurately detecting the sites and the extents of structure damages in spite of contaminated vibration data by noise.

In this paper, we present an effective methodology for assessing the vibrational properties of real-life bells, using reverse engineering techniques. When struck by a clapper, bells vibrate in rather complicated ways, which result in complex sounds. Typically, to obtain pleasant sounds, bell founders tune the first five partials (vibration modes) according to specific frequency ratios, while also trying to control the amount of beats, which also affect the musical quality. In practice, many musically important aspects are strongly related to fine details of the bell geometry. In this work, we use scanning imaging technology to obtain precise 3D geometry bell data, and then assess the bell tuning features by combining the acquired 3D geometrical data with Finite Element modal computations. Our numerical results are compared with experimentally identified bell modes, attesting the feasibility and effectiveness of the proposed approach. This analysis strategy is particularly suited in the context of cultural heritage preservation, by providing new and comprehensive ways to characterize and describe historical bells. Moreover, it can also shed light when addressing bell casting and tuning techniques throughout times.

Vibrations, considered one of the major problems in the engineering applications, are analyzed to predict their detrimental effects on the equipment and structures. The metal mesh isolator has become widely applied to mitigate the disturbing vibration due to its special production techniques. The metal mesh isolator is a kind of novel style porous damping material that is manufactured via a process of wire-drawing, weaving and compression molding. The influencing laws of the manufacturing parameters including the relative density and the working condition together with the excitation direction dependence should be taken into account in the characterization of the metallic wires material. In this paper, the mechanical properties of three models with different relative density will be investigated under different preload masses and for three acceleration levels. A number of experiments can be examined by changing the direction of excitation in order to describe the compression and non-compression molding direction effect on the dynamic behavior. A modal analysis is performed using the rational fraction polynomial method to determine the stiffness and the damping ratio from the measured transmissibility data. According to the reported experimental results, the major factor affecting the mechanical characteristics (stiffness and damping) is the sliding friction that exists at the contact-points between wires.

The purpose of this paper is to numerically investigate the impact of replacing existing cast iron pipes of an actual branched network with High-Density Polyethylene HDPE pipes on damping and dispersing pressure waves created by water hammer phenomenon. A transient solver based on the Kelvin-Voigt formulations was developed. The numerical model takes into consideration the pipe wall viscoelastic behavior of polymeric pipes. The numerical resolution method of characteristics MOC with specified time intervals was adopted to solve the nonlinear, hyperbolic, partial differential equations that govern the unsteady flow generated in the network. The reliability of the numerical model was validated with experimental results from the literature. Flow disturbances in the branched network were generated due to the simultaneous fast closure of both downstream valves. Three different configurations of control strategies were suggested. The proposed strategies were based on implementing one or two high-density polyethylene (HDPE) pipes in the sensitive regions where the highest pressure perturbations took place. A comparison between the performances of the different control strategies was performed. Obtained results showed that even with one HDPE pipe implemented in the network, the positive and negative pressure peaks were reduced remarkable. Furthermore, the results have also shown that the risk of cavitation has been completely avoided using the control strategies.

“Smart Materials” become more and more used due to their physical properties compared to other materials. Shape memory alloys (SMA) could be classified as one of them. Such material is characterized by the ability to remember its original shape after deformation. SMA provides high structural performance. However, this kind of material increases the cost of structures. Thus, optimization techniques have been applied in order to obtain minimum the volume structure. As SMA requires a global optimization tool, the evolutionary algorithms such as particle swarm optimization (PSO) is well suited. In deterministic optimization, the uncertainties of the system parameters are not taken into consideration. As a result, the optimal design obtained does not ensure the target reliability level. Thus, reliability based design optimization (RBDO) method was applied to provide an enhanced design. However, classical RBDO leads to high computational time. So, the purpose of this paper is to optimize SMA structure taking into consideration uncertainties in the structural dimensions. Therefore, a proposed RBDO methodology based on safety factors derived from Karush Kuhn Tucker (KKT) methodology coupled with PSO is developed. Compared to deterministic optimization, the proposed method guarantees the target reliability level of the structure but requires little extra computational effort.

Conventional Shot-Peening is one of the popular surface enhancement processes. It consists on projecting small shots at the surfaces of the metallic components. Ultrasonic Shot-Peening is based on the same principle. The differences between both mechanisms were: the size of shot (from 0, 25 and 1 mm for Conventional Shot-Peening, and 1 to 8 mm for Ultrasonic Shot-Peening) and the velocity (from 20 to 150 m/s for Conventional Shot-Peening, and 3 to 20 m/s for Ultrasonic Shot-Peening). Another difference is the mechanism used for projecting the shots. In Ultrasonic Shot-Peening process the shots, confined in a closed chamber, are projected by sonotrode vibration on the treated specimen that is fixed on the top of this chamber. So, during the Ultrasonic Shot-Peening, the shots can be recovered after the treatment. In this paper, we propose three dimensional finite element model of Ultrasonic Shot-Peening which enable predicting the residual Stresses generated by this process on a semi-infinite target after a repetitive impacts. Moreover, this model is used to evaluate the residual stresses relaxation in AISI 316L target under cyclic tensile loading. The numerical results are validated by comparing the residual stress profile induced by the numerical model with the experimental findings.

Shot Peening is common industrial cold-working process. It is widely used in several industrial fields particularly in automotive, aerospace and marine industries. This treatment is applied to enhance the fatigue performance of metallic components by: (i) retarding the crack growth due to the induced compressive residual stresses fields and (ii) inhibiting the crack initiation through the surface work-hardening. However, this process needs to be carefully controlled in order to avoid over-peening cases. The aim of the current study is to develop a dynamic and multi-impact shot peening process’s model using the finite elements method. It is leading to predict the initial shot peening surface properties, which are classified, into three categories: (i) the outer layers compressive residual stresses, (ii) the induced plastic deformations and (iii) the superficial damage. To validate the proposed model, the obtained numerical results were compared with experimental ones analyzed by X-ray diffraction (XRD) for three materials the aeronautical-based Nickel super-alloy material Waspaloy and the AISI 316L stainless. The predictions are in good correlation and physically consistent with the experimental investigations. This proposed finite elements model is very interesting for engineering to predict the fatigue behavior of mechanical shot-peened components and to optimize the operating parameters of this process.

This attempt proposes an engineering framework to predict the AL-Si-Mg casting alloy’s High Cycle Fatigue (HCF) response considering the microstructural heterogeneities (Secondary Dendrite Arm Spacing (SDAS)) and its correlation with the casting defects effect. The developed approach is based on the evaluation of the highly stressed volume caused by local porosities and defined as the Affected Area (AA), using Finite Element (FE) analysis. Therefore, a 3D Representative Elementary Volume (REV) describing the defective material, was embedded to evaluate the cast aluminum alloy‘s High Cycle Fatigue behavior under various load conditions. Work hardening due to cyclic loading is considered by applying the Lemaitre-Chaboche model. The Kitagawa-Takahashi Diagrams were simulated, using the Affected Area Method, under fully reserved tension and torsion loadings for different SDAS values. The generated diagrams were compared to experimental data carried out on cast aluminium alloy A356 with T6 post heat-treatment with different microstructure (39–72 µm). The results show clearly that the proposed approach provides a good estimation of the A356-T6 fatigue limit and exhibits good ability in simulating the Kitagawa-Takahashi Diagrams for fine and coarse microstructures. The developed framework is practical tool able to generate the Kitagawa diagrams for fine and coarse microstructures, at different fatigue loads.

Hybridation of carbon fiber composites with flax fiber offer interesting bio-degradability, respect of the environment, reduced cost and important dynamic properties. The purpose of this work is to study the effect of hybridation on the mechanical fatigue behavior of unidirectional carbon-flax hybrid composites. Static and fatigue tensile tests were realized for different laminates made of carbon fibers and carbon-flax hybrid fibers with an epoxy resin. The carbon laminates and two different staking sequences of hybrid laminates were manufactured by hand lay-up process. Monotonic tensile tests were realized to identify the mechanical properties of composites and the ultimate loading. Then, load-controlled tensile fatigue tests were conducted on standard specimens with applied load ratio RF of 0.1. Specimens were subjected to different applied fatigue load level until the failure (60%, 65%, 75% and 85%). Damage was observed early after a few loading cycles. The decrease in the Young’s modulus was depending on the ratio of fibers on the composites. Overall, the stiffness decreases by showing three stages for all studied samples. It has been found that the stress-number of cycle S-N curves show that carbon laminates have higher fatigue endurance than hybrid composites.

Although the anisotropy of wood fibers is reasonably well established, the anisotropy of injection molded wood fiber composites is not well understood. For this, fiber distribution is an important parameter in determining the properties of the composite. This work investigates the application of ultrasonic testing in evaluating natural fiber thermoplastic composites reinforced with olive wood flour (OWF). The characterization of sound propagation speed in the composite is intended to be a tool for evaluating the bio-composite namely fiber distribution and the effects of the direction of injection during the elaboration of the composite. The quality of fiber distribution homogeneity can be assessed by mapping the returning signals of the emitted longitudinal ultrasonic wave. This study presents the measured sound speeds for a composite system of OWF and polypropylene (PP) using immersion measurements. It is known that the longitudinal wave velocity is a function of the material property, which in turn is a function of fiber content and adhesion efficiency. Therefore, the aim of this work is to study the feasibility of using the ultrasonic longitudinal sound wave and the time of flight TOF instead of the morphological analysis with the scanning electron microscope, which is much more expensive and complicate.

Ultrasonic testing is a technique frequently used in the field of nondestructive evaluation given the fact that ultrasonic waves are directly related to the mechanical behavior of materials. It is for this reason that mechanical waves are often involved in solid material testing and the evaluation of their mechanical properties. As such, ultrasonic velocity is often used to identify so-called healthy concrete in comparison to deteriorated concrete. The objective of the present study is to determine Young’s modulus of a bio composite using two methods: ultrasonic and mechanical methods. For this, a bio-composite based on polypropylene (PP) as a matrix and the olive wood flour (OWF) as a reinforcement was elaborated with extrusion using a twin extruder following by the injection in the form of 4 mm thick plate for ultrasonic control and standardized specimens for tensile testing. The longitudinal and transversal velocity of propagation of the wave in the plates is measured with the technique of immersion in water using transducer at 5 MHz center frequency in order to determinate the ultrasonic Young’s modulus. Results show that the ultrasonic Young’s modulus of the studied bio-composite is different than that mechanical Young’s modulus. The causes of this difference will be studied.

This paper investigates the characterization of the microstructure changes and the distribution of hardness and residual stress of MIG-welded high-strength low-alloy steel. Residual stresses are experimentally measured by the contour method and the experimental values are numerically treated by MATLAB to find out a representative function which is used as an input of the finite element model. The microstructure of different regions of the weld joint is also investigated and shows the grains size change in the weld. Micro-hardness distribution shows a strong influence of the bainite and ferrite grain size. Residual stresses distribution shows that high tension ferrite grained weld metal is the most critical zone for cracking growth, mainly near the pre-existing porosity. The correlation between results shows that the hardness and the residual stresses values were proportional to the percentage of bainite and inversely proportional to the ferrite grain size. A particular attention is paid in this paper to the microstructure and the hardness around porosity defect. The results highlighted the interest of respecting proper welding procedures to avoid micro-porosities and to lower tension residual stress. Ultrasonic inspection should be obligatory performed in the weld zone to detect internal defect and identify the reliability of the piece.

This paper discusses the reliability of two approaches in modeling the Flexible Polyurethane Foam (FPF) behavior. FPFs are cellular polymers characterized by highly complex mechanical behavior including nonlinearity, viscoelasticity, hysteresis, and residual deformations. The review of this topic reveals that several studies have developed models based either on hereditary or on fractional derivation formulations. However, the viscoelastic behavior of the material integrates both short and long memory effects, which needs the combination of the two mathematical approaches to cover the full behavior of such a material. This work compares the two methodologies in identifying the parameters of foam behavior using the combined model. The approaches are based on experimental observations of the FPF behavior on compression (short memory effects) and cyclic (long memory effects) loadings. The relative inefficiency of the force difference method widely addressed in modeling processes was specially discussed.