The effects of periodic overloads on plastic zone and fatigue crack growth in Al 2024 –T4 using modified Wheeler model

Abstract

In this paper, the effects of periodic tensile overload on fatigue crack growth rate in CT specimens made of 2024–T4 aluminum alloy were investigated by using the modified Paris low as well as model proposed by Wheeler. Retarded crack length following overloads were studied numerically by experimental results. The coincidence between numerical and experimental data in tensile overload mode, would indicate that the model has high delicacy. The results depict that there is a direct relationship between the tensile overload and reduction in crack growth rate. However considering the larger radius of plastic zone at the crack tip and also the residual stresses generated in the process of applying three overloads on a specimen, lead to more than 26,000 cycles delayed loading in crack growth. The results show that when the sequence between periodic overloads is a half of delayed cycles in single overload, the crack growth rate is in its minimum scale.