Strain energy dissipation in the spall plane

Spall fracture in a planar impact occurs under a high triaxial stress state, TF. Under such conditions, the ductility that a ductile material can express is drastically reduced.

Experimental evidence contradicts this expectation. Jones et al. [J. App. Phys. 127, 245901, 2020] showed the occurrence of recrystallization in test driving re-compaction of the spall region, even for modest shock stresses. This result assumes the development of higher-than-expected temperatures and strain levels.

The present work aims to verify the actual behavior of the material in the spall region and quantify the strain and temperature levels achieved under planar impact conditions in OFHC copper.

The analyses were carried out by integrating observations at two different scales. At the continuum scale, numerical simulations were aimed at estimating the energy dissipated in the spalling process using cohesive elements. The results were compared with experimental pull-back signals performed on pure copper available in the literature.

At the microscale, a volume reference element was identified and modeled by the finite element method to analyze the local deformation process around the voids generated by damage into the spalling plane.

The results confirm that the local change in TF due to damage initiation causes an increase in ductility, enhanced by thermal softening due to the adiabaticity of the deformation process. Such increases can account for dissipated energy consistent with pull-back signals.