Effects of microstructure and shock loading conditions on the damage behavior of polycrystalline copper

A suite of plate-impact experiments have been conducted to determine the dominant factors in dynamic damage evolution in uniaxial strain tensile (spall) experiments. The first group of experiments addresses the effect of microstructure by using copper samples with varying grain sizes while maintaining similar loading conditions (peak compressive stress ∼ 1.5GPa). In a second set, the density of grain boundaries in copper samples and the compressive stress (∼ 1.6GPa) were held constant while the tensile loading characteristics were tailored by controlling the geometry of flyers and targets. For similar loading conditions, the damage fields were observed to depend on the grain size: void growth and coalescence were observed to dominate the damage behavior in samples with either small (30μm) or large grain size (200μm); whereas in samples with intermediate grain size (60 and 100μm), most of the damage was restricted to individual voids. For the second portion of the study the characteristics of the damage fields were observed to strongly depend on the characteristics of the tensile pulse. In this case, an increasing large plastic dissipation, in the form of grain misorientation, and more advanced stages of damage were observed in the samples deformed at lower tensile stress rates