Analysis of multiple site damage in lap joints

This thesis presents fracture and stress analyses of mechanics problems related to multiple site damaged(MSD) aircraft fuselage and riveted lap joints. The main purposes of this thesis are to develop an effective fracture criterion to guide the growth of the MSD cracks and to find out what are the important factors that affect the fatigue life of a rivetted lap joint.; Chapter 2 addresses the effect of the MSD crack on the structure integrity. Several levels of approximation are investigated for accounting for the effect of small fatigue cracks on the residual strength of aircraft sheet materials and fuselage lap joints containing major cracks. A version of the Dugdale model is proposed which accounts for strain hardening of the sheet in an approximate way and which incorporates a criterion for crack advance leading to crack growth resistance. This model builds upon the model proposed by Nilsson and Hutchinson (1994) and accounts for the detailed interaction between the major crack and the small damage cracks. A simpler version of the model uses the damaged-reduced local strength of the sheet or joint in assessing the effect of the major crack on residual strength. The simpler approach thus bypasses the necessity of a direct determination of the highly complicated details of the interaction of the small cracks in a lap joint with a major crack.; Chapter 3 studies the cold-driving rivetting process. Primary efforts are made to understand the overall stress changing during the riveting process and the factors that affect the residual clamping stress in the joint after the rivetting process.; Chapter 4 studies effect of factors associated with the rivet on the growth of small fatigue cracks at the rivet holes. Based on results from Beuth (1992), a simple computational model is created for studying effects such as friction and plasticity. The effect of frictional sliding between riveted skins on the crack growth and the fatigue life of the joint is investigated.