A Modelling Approach to Tire-Obstacle Interaction

In order to improve the behavior of heavy off-road vehicles,the use of numerical simulation has become an absolutely necessarystage. The main difficulty resides in the validity of the tire-groundinteraction model, for a large range of obstacles and test courses, andat all acceptable speeds. In this paper, a new obstacle-tireinteraction model has been presented. Starting from the simple fact thatvertical tire behavior depends essentially on the air contained in thetire, this approach is based on the tire air volume optimisation. Thismodel has been investigated in the case of tire statical deflection, andgood correlation has been obtained with experimental results.     

Laser shock on a TRIP alloy: mechanical and metallurgical consequences

The present study concerns an Fe-Ni alloy (30% Ni) which was submitted to laser shocks with an energy density of 10¹⁵ and 10¹⁷ W m^–2. The main metallurgical consequence is the existence of a martensite transformation which appears in an area near to the back face of the sample. This was evidenced by microscopy and by measures of Vickers microhardness. The localization of the transformation can be explained by the reflection of the compression wave in the shape of an expansion wave. This study gives also, according to Meyer's theory, the maximum time necessary to induce the transformation, i.e. 40 ns. The mechanical consequence is the existence of tensile residual stresses at a level close to the strength limit. The stress field was determined by X-ray diffraction and by destructive methods. The shape of the stress field curve is quasi-sinusoidal with a period of about 150 mm; it is linked to the compression wave and to the expansion wave which follows the first one at the surface.