On the mechanism of mixed fatigue-tensile crack growth

Abstract The fracture instability associated with alternating periods of fatigue and tensile crack growth was investigated in the 7178 aluminium alloy. This instability commenced when the maximum stress intensity factor K max in the fatigue cycle first exceeded the fracture toughness K Ic and resulted in a tensile component or crack jump. Each crack jump occured within a single fatigue cycle and appeared to be analogous to the pop-in event in fracture toughness tests. The condition for the reestablishment of fatigue cracking after each jump is described and this emphasizes the importance of crack front length in the growth and stability of cracks. The effective K max values for both the fatigue-tensile and the tensile-fatigue transitions were found to be constant, the value for the tensile-fatigue transition being the lower.