Influence of stress condition on adiabatic shear localization of tungsten heavy alloys

Dynamic deformation and failure behavior of a tungsten heavy alloy (93W) under complex stress condition are studied using a split Hopkinson pressure bar (SHPB) apparatus. Cylindrical, step-cylindrical and truncated-conic specimens are used to generate different stress condition in an attempt to induce strain localization in the alloy. The microstructure of the specimens after tests is examined by optical microscopy and scanning electronic microscopy (SEM). It is found that in all the specimens, except the cylindrical ones, intense strain localization in the form of shear bands is initiated at stress concentration sites. In order to analyze the stress condition of different specimen geometry, finite element simulations are also presented. The Johnson-Cook model is employed to simulate the thermo-viscoplastic response of the material. It is found that dynamic deformation and failure modes are strongly dependent on the geometry of the specimens. The stress condition controlled by specimen geometry has significant influence on the tendency for shear band formation. The adiabatic shear band has general trends to initiate and propagate along the direction of maximum shear stress. It is suggested that further studies on the control of the stress condition to promote shear band formation be conducted in order to improve the penetration performance of the tungsten heavy alloy.