Effect of blowholes on fatigue crack initiation life of aluminum alloy lap-joint

Abstract

Blowhole (BH) contained in weld joints is known to be a cause of reduction in strength. Concerning the effect of BHs to fatigue performance of weld joints, their total number or volume are conventionally used for the mechanical design, since the available data are limited by the measuring precision and their costs. In other words, the mechanical design would be improved if the individual size or position of the BHs could be precisely determined since it would lead to a better knowledge of the material performance and therefore to a more precise maintenance of the welded components. The purpose of this study is to develop a fatigue performance evaluation method for aluminum alloy joints considering the effect of BHs. Several FE models of lap welded joints, with different BH distributions, were generated to simulate the BH effects under fatigue loading. The material model adopted for FE analyses is based on an unconventional plasticity model, calibrated to reproduce the cyclic plasticity behavior of aluminum A5083-O. The numerical local stress-strain relationship is analyzed in correspondence to the area with the higher plastic deformation. Therefore, the fatigue crack initiation life was calculated using a formula based on the experimental database. Predicted S-N curve on crack initiation life revealed that BHs in some cases would reduce the fatigue strength. Also, there was a significant correlation between the crack initiation life and the normalized distance between the toe and the BHs.