PORES COLLAPSE AND SPALL FRACTURE: A DIRECT OBSERVATION USING FAST ULTRA-HIGH SPEED X-RAY PHASE CONTRAST IMAGING

Plate-impact experiments have been performed at the ID19 beamline of the European Synchrotron Radiation Facility on porous plates printed using SLM technique out of AlSi10Mg and Ti6Al4V. The samples contain a large population of voids with different sizes varying from 5 to 120 μm. The tests have been conducted with a meso-scale gas-launcher at different impact velocities ranging from 150 to 650 m/s. The targets have been analyzed by X-ray tomography before and after testing, to obtain a 3D reconstruction of the porous microstructure of the samples. In-situ radiography has allowed to obtain time-resolved measurements of the shape and size evolution of voids. The tests have been monitored with a PDV system which was synchronized with the radiographies to correlate the velocity of the free surface of the target with the initial collapse of the pores and the later spall fracture. Finite element simulations of the experiments, with explicit representation of the porous microstructure have been performed. The analysis of experiments and calculations has provided new insights on the effect of porosity on the void collapse and spall fracture of porous metallic materials fabricated using additive manufacturing.