Crack Growth Simulation And Fatigue Life Predication Of Panels Containing Multiple Cracks

Multiple site damage has been one of the most representative damages styles in the aircraft structures, which has badly threatened the structures integrality of aircraft. The traditional damage tolerance philosophy, which is based on a single leading crack, can't deal with MSD, so that it can't insure the structure safety. It is indispensable to develop a feasible means for determining the damage tolerance and assessing the structure fatigue life rapidly and accurately. To provide a more advanced, ideal and practical damage tolerance analysis method, the crack propagation simulation and fatigue life of the panel containing multiple cracks is obtained by finite element method in this thesis, based on the elastic-plastic and fatigue fracture mechanics.This thesis consists of two sections. The first section focuses on the fracture analysis and numerical simulation of crack propagation, to research the fracture process and the residual strength. The photos at fracture surfaces show the fracture style was shear mode, and there are opening fracture and sliding fracture styles. The cracks undergo stable tearing, linking and instable tearing. A nonlinear FEM model of panel containing multiple cracks is presented. The crack propagation is simulated using FRANC2D/L. The crack tip opening displacement criterion and the maximum circumferential direction stress criterion are used to predict the initiation and the direction of crack growth. The result indicates that the residual strength obtained by the numerical model matched favorably with the experimental values. The remainder of this thesis focuses on the fatigue experiment and life predication of panel containing multiple cracks. The tests data includes the crack growth speed, direction and fatigue life. Fatigue life is calculated using Paris formulation. The direction is predicted by the maximum circumferential direction stress criterion. The predicated life is conservative to the experiments results.Experiments and numerical simulation are used to research the fracture of panels with multiple site damage, in which every main point are studied systematically and supported by theoretical results and/or experimental results. Because of analyzing mechanical response of panel containing multiple cracks by FEM, this approach has a good capacity of predication and can be applied in engineering.