Superior mechanical properties and deformation mechanisms of heterogeneous laminates under dynamic shear loading

High-strain rate response of low C steel/304 stainless steel (SS) laminates was characterized by hat-shaped specimen using Hopkinson-bar technique at a strain rate of about 7 x 10(4) s(-1). Better dynamic shear properties were observed in the laminates, compared to the plain low C steel plate and the plain 304 SS plate. The laminates were found to postpone the nucleation of adiabatic shear band (ASB) in the hard zone and to delay the propagation of ASB from the hard zone to the soft zone. The conventional maximum stress criterion on ASB nucleation was found not valid any more in the laminates. The hardness difference between the hard zone and the soft zone in the laminates was found to have great influence on the patterns of ASB evolution. Nanotwins were formed in the 304 SS and grain refinement was observed in the martensite low C steel for strain hardening under dynamic shear loading. The mechanical incompatibility across the interfaces was observed to result in strain gradient and geometrically necessary dislocations at the interfaces under dynamic shear loading, contributing to extra strain hardening. The extra hardening was also found to be triggered at the propagation tip of ASB, which helps for achieving better dynamic ductility in the laminates