Development of a new technique for measuring damage accumulation at high strain rates

In this paper, a new experimental technique is proposed to study the effects of strain rate on ductile damage evolution in the material. In this technique, the specimen is deformed to a predesigned elongation at various strain rates using split Hopkinson tensile bar (SHTB). The deformed specimen is then subjected to quasi-static loading-unloading tensile test and its stress-strain curve is obtained. From the stress-strain curve, the elastic modulus of the material is determined for each unloading segment. The damage is computed as the reduction of elastic modulus due to void nucleation, growth and coalescence The quasi-static tests are controlled to prevent necking to occur in the specimens. The results show that the strain rate has considerable effect on ductile damage evolution in the material. In addition, this procedure is simulated using the FE code, MSC Marc software using the Bonora's damage model. The results showed that the dissipated damage function should be modified to account for strain rate effect.