Anissa Meziane

Application of the noncollinear mixing method to an interface of contact

The non-collinear mixing technique is applied on a contacting interface with friction. Two shear waves are generated with an oblique incidence on the interface of contact. The nonlinear effect of contact is activated and leads to the interaction of the incident waves, which results in the scattering of a longitudinal wave of twice the input frequency. The method is applied experimentally on an interface made of two aluminum solids. The amplitude of the longitudinal wave is obtained as a function of the compressional stress applied on this interface. A Finite Element model is proposed to study this method. The interface is modeled by unilateral contact law with Coulombs friction. This modeling enables to reproduce the generation of the longitudinal wave. The numerical results regarding to the amplitude of the longitudinal wave qualitatively agree with the experimental results.

Thermal characterisation of homogeneous materials using a weak formulation technique

A new method for the thermal characterisation of homogeneous materials is proposed. This method, specifically designed to measure the thermal diffusivity in the plane of thin specimens, is based on a low-order weak formulation (LOWF) method of the heat equation using a virtual test function. In this formulation, the spatial derivatives of temperature are coupled with an analytical expression less dependent on measurement noise. In this way, it is shown that the LOWF method leads to a robust method for the estimation of thermal diffusivity. The LOWF method is numerically tested on a two-dimensional model and validated on a homogeneous material using infrared thermography.

Ultrasonic characterization of cohesive and adhesive properties of adhesive bonds

The increasing use of adhesively bonded joints requires non-destructive evaluation methods to be developed, mostly for safety reasons. An adhesive joint can be divided into two sensitive zones that may cause mechanical failure: the body of the adhesive layer (cohesive zone) and the interphase between that adhesive and one of the substrate (adhesion zone). Weaknesses of these cohesive or adhesive zones can come, for example, from an incomplete curing of the adhesive or from inappropriate, initial treatment of the substrate surface, respectively. The present research attempts to characterize mechanical properties, which are representative of the adhesive and cohesive states of adhesively bonded assemblies, using a through-transmission ultrasonic method. To simplify the approach, the assemblies are made of two aluminum substrates and an epoxy-based adhesive layer. Six samples have been manufactured with various levels of cohesion or adhesion. Inverse problems are then solved to infer the elastic moduli of th...

Non linear analysis of vibrations generated by a contact with friction

The aim of this paper is to study vibrations generated at contact with friction for two different applications. The first one is an investigation of friction-induced vibrations of a beam-on-beam system in contact with friction. For this study the complementary use of linear and nonlinear analyses drives to the understanding of physical phenomenon induced in these vibrations. The second parts consists in investigating numerically dynamic rupture of a biomaterial interface. The numerical Finite Element model is composed of two homogeneous and isotropic elastic solids which are brought in contact with friction by remote normal compression and shear traction. The rupture is nucleated by decreasing instantaneously the friction coefficient to zero at nucleation area. The properties of the obtained ruptures (velocity, generated waves, interface state…) are analyzed.

Numerical and experimental study of the nonlinear interaction between a shear wave and a frictional interface.

The nonlinear interaction of shear waves with a frictional interface are presented and modeled using simple Coulomb friction. Analytical and finite difference implementations are proposed with both in agreement and showing a unique trend in terms of the generated nonlinearity. A dimensionless parameter ξ is proposed to uniquely quantify the nonlinearity produced. The trends produced in the numerical study are then validated with good agreement experimentally. This is carried out loading an interface between two steel blocks and exciting this interface with different amplitude normal incidence shear waves. The experimental results are in good agreement with the numerical results, suggesting the simple friction model does a reasonable job of capturing the fundamental physics. The resulting approach offers a potential way to characterize a contacting interface; however, the difficulty in activating that interface may ultimately limit its applicability.

Finite element modeling of the non collinear mixing method for detection and characterization of closed cracks

The non-collinear mixing technique is applied for detection and characterization of closed cracks. The method is based on the nonlinear interaction of two shear waves generated with an oblique incidence. This interaction leads to the scattering of a longitudinal wave. A Finite Element model is used to demonstrate its application to a closed crack. Contact acoustic nonlinearity is the nonlinear effect considered here and is modeled using unilateral contact law with Coulomb’s friction. Directivity patterns are computed using a two-step procedure. The Finite Element (FE) model provides the near-field solution on a circular boundary surrounding the closed crack. The solution in the far-field is then determined assuming that the material has a linear behavior. Directivity patterns will be used to analyze the direction of propagation of longitudinal wave(s) scattered from the closed crack. Numerical results show that the method is effective and promising when applied to a closed crack. Scattering of the longitu...

Numerical and experimental analysis of harmonic generation method for detection of closed cracks

Early detection and characterization of damages in materials are important to control the durability and reliability of parts and materials in service. In this study we considered the harmonic generation method for the detection of closed crack. Measurements were carried out on a real fatigue crack using harmonic generation method. Numerical analysis was performed using a 2D FE model describing the interaction between plane longitudinal acoustic wave and its interaction with a contact interface. Different contact interface profile had been studied, showing specific evolution of the amplitude of the second harmonic as function of applied force.

Dynamics of Rupture at Frictional Rough Interfaces During Sliding Initiation

The aim of this work is to present the results from a non linear finite element analysis in large transformations of the contact interface between two deformable bodies when sliding initiates and the roughness is introduced at the contact surfaces. The two-dimensional in-plane dynamic model consists of two different isotropic elastic media separated by an interface governed by Coulomb friction law, and subject to remotely applied normal and shear tractions (pre-stress phase). Once the ratio between the local values of tangential and normal stresses reaches the limit value, the sliding initiates and local ruptures are activated (nucleation phase). The propagation of the ruptures over the interface and the wave propagation inside the solids are analyzed. The interactions between the waves propagating into the two solids (P waves, shear waves, surface waves) give raise to different types of ruptures. They can be classified depending on their velocity front (sub-Rayleigh, sub-shear, super-shear) or on their interface states (pulse-like, crack-like). A sinusoidal roughness is introduced at the contact surfaces and the analysis is performed for different values of the roughness parameters. Depending on the relative dimension between the roughness wavelength and the width of the wave fronts, two different behaviour can be observed: i) a coupling between the wave propagating into the two bodies; ii) a decoupling of the wave propagation inside the two materials, characterized by an independent wave propagation. First the wave propagation is analyzed when a single rupture is originated in pre-sliding conditions; successively, the wave generation during sliding initiation is addressed.Copyright