The Onset of Crack Growth in Aluminium Alloy Due to Impact Tension

Abstract

The purpose of this paper is to confirm the effect of specimen length and the microstructure on the onset of precrack growth when an impact load is imposed on it. Impact, impact under static pretension and static tensile experiments were carried out using high strength aluminium alloy at 288 K and 77 K. The effect of specimen length on the critical condition for crack growth was discussed, based on the static stress intensity factor (K₁)_pre and the impact fracture stress σ_cd defined by the onset of crack growth. A linear relation between (K₁)_pre and D_f which was a summation of (K₁)_pre and σ_cd√(πa), where a was a precrack length, could be seen and this relation was independent of specimen length and temperature. Microstructural aspects near the crack tip region were also observed on the fracture surfaces. The results of microscopic deformation measured by the X-ray micro beam diffraction method and the dislocation distribution observed by TEM showed that they were almost the same at the same temperature and were independent of loading type and specimen length. Comparing above results with our previous ones for steel specimens, it is concluded that the effect of specimen length on crack growth is negligiable in the case of impact fracture when the microscopic deformation behavior at a crack tip is insensitive to a rapid stress rise, which depends on specimen length.