Research On Multi-site Damage In Aircraft Structure

Multi-site damage formed on structure due to the action of fatigue load in long-term use of aircraftwould reduce the residual strength rapidly and brought possible severe accidents. Consequently, it wasmore necessary to do research on prediction of multi-site damage, which was investigated in this thesisfrom three aspects: crack-tip interaction factor, multiple crack propagation and residual strength.Firstly, the interactions among multi-cracks were discussed on Multi-site damage and mutualinfluence about collinear multiple cracks were divided into five modes, whose interaction factor wascalculated so as to obtain the laws of crack interaction.Secondly, the fatigue tests on typical specimen with multi-row rivet holes were carried out inorder to gain the data about residual strength and crack propagation, which were verified with FEM andprobabilistic models. The results indicated that FEM and probabilistic models had sufficient accuracyand consideration of excessive safety.Finally, the analyses on residual strength and crack propagation were made based on previousmodels. Then the influences about three different sequences of crack growth were taken intoconsideration, and it was worth notice that net section yield criterion and plastic zone criterion wereused in calculating residual strength and crack growth, the results showed that sequence of crackgrowth had more effect on crack propagation than residual strength. Besides adopting plastic zonecriterion, crack grew more rapidly.Depending on all above studies, the prediction and evaluation on crack propagation life, residualstrength, and interaction among cracks could be made to assure the safety of aircraft structures.