A three-dimensional elastic-plastic contact code based on semi-analytical method is presented and validated. The contact is solved within a Hertz framework. The reciprocal theorem with initial strains is then introduced, to express the surface geometry as a function of contact pressure and plastic strains. The irreversible nature of plasticity leads to an incremental formulation of the elastic-plastic contact problem, and an algorithm to solve this problem is set up. Closed form expression, which give residual stresses and surface displacements from plastic strains, are obtained by integration of the reciprocal theorem. The resolution of the elastic-plastic contact using the finite element (FE) method is discussed, and the semi-analytical code presented in this paper is validated by comparing results with experimental data from the nano-indentation test. Finally, the resolution of the rolling elastic-plastic contact is presented for smooth and dented surfaces and for a vertical or rolling loading. The main advantage of this code over classical FE codes is that the calculation time makes the transient analysis of three-dimensional contact problems affordable, including when a fine mesh is required.

Two-dimensional materials, such as graphene and MoS2, are films of a few atomic layers in thickness with strong in-plane bonds and weak interactions between the layers. The in-plane elasticity has been widely studied in bending experiments where a suspended film is deformed substantially; however, little is known about the films' elastic modulus perpendicular to the planes, as the measurement of the out-of-plane elasticity of supported 2D films requires indentation depths smaller than the films' interlayer distance. Here, we report on sub-ångström-resolution indentation measurements of the perpendicular-to-the-plane elasticity of 2D materials. Our indentation data, combined with semi-analytical models and density functional theory, are then used to study the perpendicular elasticity of few-layer-thick graphene and graphene oxide films. We find that the perpendicular Young's modulus of graphene oxide films reaches a maximum when one complete water layer is intercalated between the graphitic planes. This non-destructive methodology can map interlayer coupling and intercalation in 2D films.

a b s t r a c tThis paper describes the mechanical behavior of the 6061-T6 aluminium alloy at room temperature for various previous thermal histories representative of an electron beam welding. A fast-heating device has been designed to control and apply thermal loadings on tensile specimens. Tensile tests show that the yield stress at ambient temperature decreases if the maximum temperature reached increases or if the heating rate decreases. This variation of the mechanical properties is the result of microstructural changes which have been observed by Transmission Electron Microscopy (TEM).

A n erpm'mental study of metallic contatninant e,@!cls on sufacesurface defect-such as large inclusion-is beco~ning indentation i n EHL contacts is presented. Partic/es (,re initially uncommon. In the same time, the increase of the contact sphhcal and are composed of M-50 high-carbon steel poruder. Their rec~uirements-in terms higher temperature and diameter ranges from 3 2 to 40 Fm. A n original lzcbricrition system lower amount of oil available-reduce the EHL film thickness. As a consequence, the proportion of rolling bearing with a controlled leuel of contamination was built. Tlte contaminant failures initiated from the surface increases. It is well known distribution and concentration are measured on-line by nil automatic that solid particles in suspension in oil may pass through an particle counter. Tesls are conducted on a truo-disk nrnchine with EHL contact and dent the contacting surfaces. on conditions. may lravel througll lhe EHL the bearing element as well as grinding furrows o r contact only one time, the lubn'cantflow bkng used only once. The improper surface finishing, may be at the origin of a rolling oil is a synthetic one qualiJied under the MI[,-Ld-23699 sj>eci$cation.bearing failure surface initiated. A n optical profilometer is used to describe the indent rqogruphy andOperating oils contain many contaminants prior to the first a CCD video camera to count the number of dents.The test bench is described and the experimental procedure is presented. Specific tests were perjormed to qunlifjr the contanrination bench. The combined qfects of particles concentration ccnd tesf duration on dent distribution ruere studied. Some reszclts o,?. the shape and concentration of indents verstis operating mnrlitiotzs are presented. It is shown that over the range of test conditions considered, the number of indents on the racnuays can be esfittrnturl from the particle concentration i n the oil bulk. This leads to /he conclusion that the particle mtty ratio is close to one, i.e., the concentration of particles inside the EHL contact is close to tlrose i n the Irulk.

In age-hardening alloys, high-temperature processes, such as welding, can strongly modify the precipitation state, and thus degrade the associated mechanical properties. The aim of this paper is to present a coupled approach able to describe precipitation and associated yield stresses for non-isothermal treatments of a 6061 aluminium alloy. The precipitation state (in terms of volume fraction and precipitate size distribution) is modelled thanks to a recent implementation of the classical nucleation and growth theories for needle-shaped precipitates. The precipitation model is validated through small-angle neutron scattering and transmission electron microscopy experiments. The precipitation size distribution is then used as an entry parameter of a micromechanical model for the yield strength of the alloy. Predicted yield stresses are compared to tensile tests performed with various heating conditions, representative of the heat-affected zone of a welded joint.

Tests have been performed on a two-disk machine in order to evaluate the role of inclusions, surface roughness and operating conditions on rolling contact fatigue of AISI 52100 and M50 bearing steels. Important parameters-such as nature and location of inclusions, small and large wavelengths of surface roughness, normal loading or sliding conditions-on crack initiation and propagation stages have been identified. The operating conditions have been selected to encompass typical jet engine applications. Tests have been carried out up to 4.2 GPa, for two different surface finishes. Surface distress and sub-surface damage which could result in catastrophic failure have been observed. Indeed, surface initiated deep spalling (observed at 3.5 GPa for unpolished surfaces and under rolling plus sliding conditions) as well as sub-surface initiated deep spalling (at 4.2 GPa for polished specimens) have been observed. Sub-surface micro-cracks were detected early and followed during some interrupted tests by the means of an ultrasonic echographic device. Results of our experiments are analyzed and discussed in relation to the rolling contact fatigue theories.

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Cold spray is a rapidly developing coating technology for depositing materials in the solid state. In this work, the cold spray particle deposition process was simulated by modeling high-velocity impacts of spherical particles onto a flat substrate under various conditions. For the first time, we proposed the coupled Eulerian–Lagrangian (CEL) numerical approach as a means of solving the high-strain rate deformation problem. Using this approach, we observed a compressive stress region at the interface between the particles and the substrate induced by large plastic strains in the materials. Due to the high contact pressure (about 1 GPa) and the short contact time (about 40 ns), the high-strain rate (106 s-1) plastic deformation region was only a few micrometers deep and was localized mainly at the bottom of the particle and substrate surface. The ability of the CEL method to model the cold spray deposition process was assessed through a systematic parametric study including impact velocity, initial particle temperature, friction coefficient, and materials combination. The higher the impact velocity, the higher the initial kinetic energy, leading to more substantial plastic deformations and significant temperature increases in the substrate. The initial particle temperature has a greater influence on the equivalent plastic strain than on the temperature increase in the substrate. Friction has a limited effect on the temperature distribution and increase in the substrate, and the equivalent plastic strain increases only slightly as the friction coefficient rises. Four combinations of particle/substrate materials (Cu/Cu, Al/Al, Cu/Al, and Al/Cu) were considered in our study. Obviously, the particle's material had a greater influence on the deposition process and on the deformation than the substrate material. Concerning the particle's material, a higher-density material, such as Cu, has a higher initial kinetic energy, which has the advantage of increasing the contact area and contact time, resulting in better bonding between particles and substrate. Compared to other numerical methods (Lagrangian, arbitrary Lagrangian–Eulerian (ALE), and smooth particle hydrodynamics (SPH)), the CEL approach is globally more accurate and more robust in high-strain rate deformation regimes.