The Effect Of Grain Size On Dynamic Properties Of Pure Aluminum

The damage of materials is related not only with loading conditions and temperature conditions, but also with microstructures. The grain size is the most important micro structural variable that influences the mechanical properties of polycrystalline metals. The relationship between grain size and quasi-static yield strength can be characterized by Hall-Petch equation. But the dynamic damage always differs awfully with the quasi-static damage.In this paper, pure aluminum with three widely differing grain size was subjected to dynamic deformation and damage in SHPB and SPALL experiments, to study the effect of grain size on the dynamic mechanical properties.(1) The pure aluminum specimens with grain size of 15, 60, and 500μm have been obtained by heat treatment.(2) The SHPB tests have been carried on the three grain size specimens with the strain rate of 400s^-1, 1000s^-1, and 6000s^-1. The stress-strain curves obtained in the experiments show that the dynamic yield flow stress-grain size relationships can still be fit into a Hall-Petch equation. Whereas the Hall-Petch constants vary from the quasistatic ones, and they connect with the strain and strain rate.(3) The stress-strain curves of the three grain size specimens have been fitted out using a modified Johnson-Cook constitutive equation. The fitted curves can simulate the experimental curves well.(4) Spall tests have been performed on the three grain size specimens utilizing a single-stage gas gun. The velocity curves of the free surface obtained from the tests show that complete fracture has occurred and the grain size influenced the spall properties hardly. Recovered spalled samples were analyzed using optical microscopy. It was found that the microvoids distribute both in the grain and on the boundaries, and the crack expands cross the grains.The jobs of this paper reveal some effect of grain size on dynamic behavior of pure aluminum. All the experimental results and realization in this paper provide a good exploration for future research.