Investigation on crashworthiness of ultrafine grained A356 sheets and validation of Hall-Petch relationship at high strain-rate deformation

High crushing force and good energy absorption are the essential requirements for structural materials subjected to dynamic loading. In the present work, commercial A356 material is subjected to cryorolling and post-cryoroll annealing to produce sheets of different grain sizes and the influence of microstructural change on dynamic behavior of the material is studied. Dynamic tests are done in a crossbow test equipment at an average strain rate of 250 s−1. Quasi-static tests are done at an initial strain rate of 0.005 s−1 to compare the dynamic performance of the material with its static/quasi-static behavior. It is found that strength and ductility of cryorolled material at dynamic loading condition is lesser than that in quasi-static loading. Upon annealing, the material performance of the material is found to be better at high strain-rate deformation than that at quasi-static condition. A detailed analysis on the deformation behavior and fracture mechanism of the material at high strain-rate is carried out. Further, the existence of Hall-Petch relationship at high strain-rate deformation is evaluated. The material's strengthening factor is found to hold good agreement to the Hall-Petch relationship with a grain boundary strengthening coefficient of 112 MPa at dynamic loading.