Mathematical Model to Predict Fatigue Crack Initiation in Corroded Lap Joints, Draft

Abstract

Abstract : This report presents the results of experimental and modeling studies to examine and simulate the effects of corrosion on the contact or faying surfaces of lap joints and on the stress and strain distribution in the lap joint. Many commercial and military aircraft have reached or exceeded their original design life, and have been subject to significant increases in maintenance and repair cost due to corrosion. While corrosion is now being recognized to having a detrimental effect on the structural integrity of aging aircraft components, the lack of predictive capability has prevented the operators of aging aircraft from successfully controlling corrosion. Specifically, there is increasing concern about the potential detrimental effects of corrosion on the structural integrity of fuselage lap joints. This corrosion can lead to a decrease in strength as a result of loss in skin thickness, early fatigue crack initiation caused by the formation of stress risers, and increased fatigue crack growth rates. The mode of corrosion in lap joints has generally been considered to be uniform loss of material by crevice and exfoliation corrosion. In fact, the effect of corrosion on fatigue crack initiation and propagation in lap joints has been largely ignored, because present non-destructive inspection techniques are considered sufficient to detect corrosion before it affects the structural integrity of the joint.