| Nowadays the issue of composite fatigue is among those primarily concerned for designing aircraft structures with long term durability and reliability. The traditional approach to design for fatigue of laminate composite has been to conduct many tests in the various service environment conditions that the structural component will subject to in a specific design. Though this approach is reasonable and robust for that specific design, however, it is time consuming, costly and needs to be repeated for designs when structural component has different stacking sequences or subject to different fatigue loading.In this research, fatigue life of laminate composite is predicted phenomenologically, dealing mainly with in-plane stresses without accounting for out-of-plane failures such as delamination. Fatigue modulus is used as a physical parameter which helps to describe the basic fatigue behaviour of unidirectional laminates and obtain expressions for cumulative damages defined by strains. Based on some typical fatigue test data for unidirectional composite laminates, a cumulative fatigue damage model is presented for predicting the fatigue life of multidirectional laminates with arbitrary stacking sequence under complicated fatigue loadings. The model is an integration of three major components: stress analysis, failure analysis and material property degradation rules. Based on the model, a computer code is developed that simulates cycle-by-cycle behaviour of composite laminates under fatigue loading.Delamination is characterized as the separating fracture at the interface between two plies of a laminated composite structure. It is widely accepted that the interlaminar stresses should be responsible for delamination. A three-dimensional finite element method is developed in order to get full stress state in the vicinity of the free edges. A simple model is utilized for evaluating fatigue life of composite laminate which is dominated by interlaminar stresses and delamination growth. |
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