A Numerical Study of MSD in Aircraft Lap Joints

Abstract

Many military aircraft have reached or exceeded their original design life, and have been subject to significant increase in maintenance and repair cost due to multiple site damage (MSD). In order to assessing the effects of MSD on the structural integrity of aircraft lap joints, the wing lap joint of certain model military aircraft with MSD was analyzed using special code FRANC2D/L. The rivet holes along the top row of the outer skin of lap joint were considered as the independent structural unit for the simulated MSD cracks. The stress intensity factors (SIFs) at each crack tip with different distribution loads at the rivet holes were computed and show that the analysis results have good coherence with the available literature data. It also shows that the SIF at each crack tip s a function of crack length can be calculated by the crack growth simulation capability of FRANC2D/L. The SIF values are not sensitive to the rivet load distribution manner, which has seriously influence on MSD crack growth direction. Rivet loading can be best molded quadratic load distribution over one half of rivet hole relative to uniform load distribution and point load. As a result of this analysis, it is postulated that for MSD in aircraft lap joints, compliance measurements may provide a useful tool for assessing the structural integrity of the lap joints.