Shear localization as a damage mechanism in pore collapse under shock compression

Abstract

The effect of porosity in shock-compressed materials is widely studied in the literature, accounting for its contribution to the materials' compressibility and to shock attenuation. Yet, the role of porosity in damage or failure under shock compression is limitedly addressed. In this work, shear localization resulting from pore collapse is studied, in potential relation to damage and failure under shock compression. Ti-6Al-4V specimens, with cylindrical and spherical pores, were manufactured using additive manufacturing (AM), and a soft catch set-up was used to enable post-mortem analysis of the impacted specimens. Under plate impact experiments, at shock pressures of 3–8 GPa, the 1–2 mm voids demonstrated collapse, followed by the evolution of shear bands (SB), emanating from the pore's surface. Samples with multiple pores were also tested to examine the interaction of shear bands between adjacent pores, to coalesce to larger damage surfaces. Varying the impact velocity and corresponding impact pressures, protracted states of SB evolution were studied. Numerical simulations using a material damage model reproduced many of the experimentally demonstrated phenomena. The presented results suggest evidence that shear localization around pores could be a damage mechanism under shock compression, identified as a threshold effect, making it a significant mechanism to be well characterized. The applicability of this mechanism is examined in relation to damage behavior under shock compression, extrapolating the experimental findings to μm-sized pores at high pressures.