Numerical study of the critical impact velocity in shear

The phenomenon of critical impact velocity (CIV) in shear is studied in this paper. Deformation trapping due to thermoplastic instability caused by the propagation of plastic waves are the main physical reasons for CIV in shear. A simple analytical approach is offered on how to estimate the value of CIV. A numerical study of impact shearing of a layer with a small geometric imperfection has been performed by the FE code ABAQUS, and available experimental results verified for VAR 4340 steel, approximate to 50 HRC, obtained by direct impact on modified double shear (MDS) specimen. In particular, the numerical study was focused on the effect of the imposed velocity on the spatial deformation of the layer. Seventeen velocities were assumed in FE calculations from quasi-static to 160 m/s. Two modes of shear deformation of the layer were found: in the first mode all plastic deformation concentrates in the middle of the layer, and in the second near the surface where the shear velocity is imposed. CIV could be defined as a transition between those two modes. It has been shown that impact velocities higher than CIV lead to a substantial reduction in the total energy of strain localization. Overall good correlation with experimental results and physical intuition has been satisfactorily achieved. (C) Elsevier, Paris.