Vincent Magnier

A New Contact Model for Multilayered Solids with Rough Surfaces

A new numerical model is proposed to investigate the normal contact of multilayered solids with rough surfaces. The Hankel transform and the transfer matrix technique are used to solve the problem of the deformation of a multilayered solid. Then, the normal contact of an asperity is solved with Abel transform. Using this solution, an asperity-based contact model of rough surfaces is developed considering interactions between asperities. Numerical results are presented and compared to finite element calculations. The present model provides good results. The effects of interactions and the solid layers properties are discussed.

A Multiscale Model of a Disc Brake Including Material and Surface Heterogeneities

During friction it is well known that the real contact area is much lower to the theoretical one and that it evolves constantly during braking. It influences drastically the system’s performance. Conversely the system behavior modifies the loading conditions and consequently the contact surface area. This interaction between scales is well-known for the problematic of vibrations induced by friction but also for the thermomechanical behavior. Indeed, it is necessary to develop models combining a fine description of the contact interface and a model of the whole brake system. This is the aim of the present work.A multiscale strategy is propose to integrate the microscopic behavior of the interface in a macroscopic numerical model. Semi-analytical resolution is done on patches at the contact scale while FEM solution with contact parameters embedded the solution at the microscale is used. Asperities and plateaus are considered at the contact interface. FFT techniques are used to accelerate the resolution at the micro-scale. As an example the multiscale model is applied into a complex value analysis used to identify modal coupling in NVH simulations. With this model the interaction between non uniform surface and system dynamic behavior is clearly shown. The contact surface variations clearly affect the modal coupling and therefore noise propensity.

Original Methodology Using DIC to Characterize Friction Materials Compression Behavior

Friction materials are expected to fulfill several requirements such as adequate friction coefficient, low noise, long life and low wear rate. In order to achieve these properties, friction materials are generally heterogeneous mixtures of fillers incorporated in a more or less continuous matrix. Therefore, a good understanding of the influence of row constituents (i.e., formulation, shape and size) and fabrication process on the mechanical behavior of as-produced heterogeneous materials is necessary to better customize the final products. Nowadays, the customizing process is purely empiric involving costly efforts to characterize the resulting performances. Moreover, the determination of the effect of each component is usually hampered because the behavior of row constituents can evolve during the fabrication process. An in situ compression test using X-ray laboratory tomography is performed in order to study the micro-mechanical behavior of a heterogeneous material. A DIC technique using the reconstructed images provides the displacement fields that are subsequently introduced into a FE simulation which will reproduce the material behavior. This novel methodology allows to identify the micro-constituents mechanical properties of the as-produced material as well as to optimize the numeric material constitutive law.

Numerical Chain of Forging Railway Axle and Wheel Press Fitting Operation

In today’s competitive business environment, it has become increasingly important to reduce manufacturing and raw materials costs. For this purpose, an innovative process of design and manufacturing railway axles is developed. It is based on forging hollow axle which allows a significant reduction in steel consumption. In this work, we tried to analyse how these modifications induced by this new process and design impact on the residual stress field. For this particular study, a numerical chain has been developed going from the simulation of the hot upsetting manufacturing process of the railway axle with the explicit method, to the analysis of the cutting and the press fitting assembly operation. This study consists in modelling the forging process with the dynamic FEM in order to take into account the dynamic phenomena and predict the residual stress field and the initial plastic strain. Then the evaluation of the cutting operation of the upper axle surface and finally the simulation of assembling the wheel on the axle with a static model, to better estimate the stress relaxation and redistribution.

Development of a Numerical Chain to Optimize Railway Axles with Respect to Fatigue Damage

In todays competitive business environment, it has become increasingly important to reduce manufacturing and raw materials cost. For this purpose, an innovative process of design and manufacturing railway axles is developed. It is based on forging hollow axles which allows a significant reduction in steel consumption. In this work, we tried to analyze how these modifications induced by this new process and design impact the service behavior and particularly the durability face to cyclic loadings that can lead to fatigue failure. In the present study, a numerical chain has been developed going from the simulation of the manufacturing process up to the analysis in fatigue. In the first step, the forging process is modeled in order to predict the residual stress field and the initial plastic strain. From this initial condition, the assembly operation of the wheel on the axle is simulated before the redistribution of stresses and strains under cyclic load. The final objective is to obtain the cyclic loadingpaths, in order to provide the data needed for the analysis of fatigue.