Quasistatic cracking of materials with high fracture toughness and low yield stress

Abstract

Cracks in large structures of materials of relatively high fracture toughness and low yield stress propagate before disseminated yielding occurs, whereas in geometrically similar small structures of materials with the same mechanical properties disseminated yielding precedes cracking. The size parameter which controls the cracking-yielding transition is ER /σ 2 y , where E is the Young modulus, R fracture toughness and σ y yield stress. The paper describes a laboratory-size testing rig which enables the large structure fracture mode of materials with large ER /σ 2 y to be simulated using small laboratory test pieces in conventional testing machines so that the appropriate fracture toughness can be determined. Some experimental results are quoted for thin warm mild steel and aluminium alloys. The rig also has interesting possibilities in producing stable cracking in d R /d Å negative materials, where Å is the time rate of change of crack area.