Structural Fatigue Life Prediction Methods, Based On The Residual Strength Degradation Model Of Composite Repair

In recent years the composite materials are more and more widely used, so a lot of researchers have carried out the research on the repair technology of the composites. But these researches are limited in the static loading. Based on the residual strength degradation model the author performs the research on the fatigue life prediction method of the composite adhesive bonding repair. In phenomenological view, several residual strength degradation equations of composite laminates are proposed. According to the test data the parameters in those equations are fitted so the degradation law of each strength of the composite laminate is derived. Because of the complexity of the stress distribution in the repaired structure, based on the residual strength degradation model the author introduce into the local stress-strain method to set up the fatigue life prediction model for the composite repaired structure. The fatigue failure criteria of the unidirectional laminate is established based on the residual strength degradation model and the plastic formula of anisotropy materials proposed by Hill. 3D FEM model is set up to simulate the repaired structure, stress distribution of the structure is reckoned out, and the dangerous locations are located. According to the fatigue life prediction model proposed formerly, the fatigue life of the structure is predicted, and the degradation law of the ultimate strength of the repaired structures is achieved as well. Finally, the results of the research are summarized and the feasibility and rationality are discussed. Based on residual strength model, the author introduces the local strain-stress method to predict the fatigue life of the repaired structure. The calculating result shows that, the influence of the complex stress distribution of repaired composite structure on fatigue life can be well reflected in this method.