Influence of Constant Amplitude and Variable Amplitude Loading on Crack Initiation and Microcrack Propagation in Al 2024-T3

摘要

The influence of constant amplitude and variable amplitude loading on the formation and on the propagation characteristics of microcracks was studied. The fatigue life of notched and unnotched specimens was compared. A concept based on fracture mechanics and taking into account the crack geometry and stress distributions was elaborated to describe the propagation characteristics of the microcracks. Up to the time of crack initiation, the microscopic plastic deformations occurring within a low-amplitude fatigue cycle are increased if preceded by large-amplitude fatigue cycles. The effect on the crack opening behavior is decisive for crack propagation.