Strain rate and triaxiality effects on the dynamic ductile damage of DOMEX 355MC

The effect of strain rate on the ductile fracture of DOMEX 355MC, a high strength low alloy steel, is investigated using notched specimens loaded in uniaxial tension at quasi-static and high strain rates. The high strain rate tests are conducted on a tensile Split Hopkinson Bar (SHB), which incorporates a novel mechanism for tensile loading using an otherwise standard gas gun. Furthermore, the Tensile SHB uses a novel “fir-tree” gripping system which permits rapid changing of specimens, minimises slack between specimens and the bar and prevents slippage. The experiments were simulated in explicit FEA using a material model that incorporates temperature and rate sensitive plasticity, to identify the local strain at fracture. The intent of the simulations is to extend the pragmatic approach of Wierzbicki and co-authors [Int. J. Mech. Sci. 46 , 81 (2004); Study on the effect of the third stress invariant on ductile fracture, Tech. Rep. 151, 2006; Int. J. Plast. 24 , 1071 (2008)], who studied the effect of triaxiality and Lode angle on strain at fracture at quasi-static rates, to a higher strain rates. The experiments conducted had a Lode angle of approximately 1 prior to the onset of necking. The strain at fracture for DOMEX 355MC decreased as strain rate increased, for the range of strain rates and Lode angles which were studied.