Crack growth and closure behaviour of surface cracks

This paper investigated the crack growth and closure behaviour of surface cracks in AISI 4130 alloy steel under the constant amplitude loading and single-overload conditions. The compliance measurements of depth- and surface-wise crack closure were performed using the backface strain gauge and the near-tip gauge, respectively. Under the constant amplitude loading, the surface growth was faster than the depth growth, whereas at each ΔK level, the surface growth was slower because the surface-wise crack closure was stronger. Each single overload condition increased the amount of crack closure at the surface over that at the depth, thereby, lowering the growth rate at the surface. The measured crack shape developments under the constant amplitude loading and the single-overload conditions correlated well with the crack-closure inferred counterparts.