Abstract
The paper presents the attempt to predict fatigue crack growth rate in a component subjected to variable amplitude loading containing overload-underload cycles. For this goal in a deterministic approach the modified Willenborg retardation model was applied. To provide experimental data the research into fatigue crack growth for 2024-T3 aluminum alloy sheet CCT specimens under LHL type block program loading with multiple overload-underload cycles was developed. The microfractographic analysis of fatigue fractures with the use of the transmission electron microscope (TEM) made it possible to trace the effect of block program loading on the crack growth rate. The knowledge of the affection of a particular overload-underload cycle or a block of these cycles on crack rate on the basis of microfractographic analysis was utilized for assessing the equivalent loading for the LHL block program. The diagrams that presented the crack growth rate both on the surface and inside the aluminum alloy sheet was performed. The crack growth rate inside the sheet was estimated on the basis of the striation spacing analysis.