Damage evolution in ductile materials at high rates of tensile strain

The study of ductile fracture at high rates of strain is important for the analysis of many impact events and metal forming operations. Ductile fracture occurs through the nucleation, growth and eventual coalescence of voids. Previously, the evolution of void damage with deformation has been determined at quasi-static loading rates. Until recently, no method has existed to perform similar tests at higher strain rates.; For this research, leaded brass was used as a model material to investigate high strain rate damage evolution. A novel momentum trapping technique, recently applied to Carleton's tensile split Hopkinson bar, allowed tests of constant strain rate to be interrupted at various levels of strain. This modified Hopkinson bar was used to test uniaxial and notched specimens. Image processing techniques were applied with quantitative stereology methods to evaluate the resulting damage in the test specimens. In this manner the damage was determined as a function of applied strain and stress-state at strain rates in excess of {dollar}rm10sp3 ssp{lcub}-1{rcub}.{dollar} Plate impact tests were also performed at the Ernst Mach Institute in Freiburg, Germany. Plates which did not spall were quantitatively investigated to evaluate the distribution of damage over their cross-section.; It is concluded that interrupted split Hopkinson bar testing provides a viable means of evaluating damage evolution in ductile materials in the 10{dollar}sp3{dollar} to {dollar}rm10sp4 ssp{lcub}-1{rcub}{dollar} strain rate regime. The damage study indicated that: (i) the rate of void evolution increases with triaxiality; (ii) the evolution of void aspect ratio is inversely proportional to triaxiality; and (iii) void nucleation strain is a function of triaxiality. Plate impact tests near spall exhibited damage levels similar to those of the Hopkinson bar tests, supporting a critical void volume fraction criterion for void coalescence.