Investigating the effect of cold expansion process on the fatigue behavior of aluminum alloy 7075-T6 in double-lap shear joints

In this paper, the effect of cold expansion process on the fatigue behavior of 7075-T6 aluminum alloy has been investigated both by numerical modeling and conducting experimental tests. In the experimental part, one batch of the specimens without cold expansion and two other batches after being subjected to cold expansions of 1.5% and 4.7% were subjected to cyclic loading in a double-lap shear joint. In the numerical part, finite element simulations of the cold expansion process and loading of the joint were performed and the effect of this process on the stress distribution and the location of the critical zone of the fatigue crack initiation were surveyed. Tangential stresses at different angles around the hole were extracted from the finite element analysis, and after determining the angular position of the surfaces with maximum stresses, crack initiation location in the thickness direction is predicted with an acceptable approximation. The S–N diagrams obtained from the experiments show that the cold expansion process increases fatigue life, and this increase is much more pronounced in lower loads. Also by increasing the percentage of cold expansion from 1.5% to 4.7%, this increase is more appreciable.