Factors controlling the width of shear lips in fatigue crack growth

An analysis is made of the factors which control the width of the shear lips which are found on fatigue crack surfaces of aluminium alloy sheet material. Tests on 100-mm wide plates of 2024-T351 Al alloy in air showed that if cracks were grown at constant ΔK the shear lips reached a steady-state width which depended only on ΔK ϵff , After the beginning of a test it takes a few mm of crack growth before an equilibrium state is reached. The maximum rate of widening of shear lips depends on K μax . Most constant-amplitude (ΔS) tests do not show the steady-state shear lip width. Based on the results of the tests at constant ΔK, a method of calculating the width of shear lips as a function of a or ΔK in a constant-amplitude test is presented. The calculated values have been compared with the results from constant-amplitude tests.