Using X-microtomography and non equilibrium classical molecular dynamics, we present a study of the elementary processes of spallation of single crystal tantalum. The single crystal is illuminated by a laser pulse which induces the propagation of a strong unsustained shock. The analysed data mainly are number and shape of pores resulting from the tensile inside the material when the incident shock reflects on the opposite face. Experimental pores size distribution exhibits two power laws attributed to the growth and the coalescence stages. The average pore shape is ellipsoid with main axis along the shock axis propagation. This first part is completed by a large scale molecular dynamics simulation mimics at reduced scale the real experiment. After preliminary calculations validating the chosen potential function the formation and shock propagation is detailed. Then we extract from the simulation similar data than in experiment. The pores size distribution shows three power laws identified as the nucleation, the growth and the coalescence stages. The slopes of the two last stages are very similar to the experimental one, confirming the scale invariance of this data as suggested by their analytical form. The general pore shape also is close to the experiment shape but with a different orientation (perpendicular to the shock propagation axis).
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