Anomalous Hardening of Submicron Porous Silver at High Strain Rates

Microscratch hardness measurements were conducted on porous silver membranes using a sphero-conical Rockwell indenter over a strain rate range of 10-1-10+4 s-1. At high strain rates, the porous silver has a strain-rate sensitivity of hardness that is enhanced in comparison to its dense counterpart. The enhancement is found to increase for strain rates greater than 10+2 s-1 wherein strain rate exponents are measured as high as 0.25. The increase appears attributable to the free volume available for deformation within the porous structure. This result represents up to a five-fold increase in the exponent value in comparison to tensile tests conducted at strain rates less than 10-1 s-1.