Research On Longitudinal Elastic Modulus Degradation Of Composite Under Fatigue Load

Composite material is widely applied in aviation, energy, architecture field. As the requirement of stability and low-cost of composite structure become higher, composite fatigue property becomes an important factor influences the improvement of composite. Thus it is urgent to carry out an intensive study of composite fatigue. Composite stiffness keeps degrading under fatigue load. This is due to complex damage mechanism in composite material. Stiffness degradation is an important reflection of macro-mechanics characteristic change. So it is an attractive topic of composite fatigue performance study.This article focus on composite longitudinal elastic modulus degradation law under fatigue load. First a review of typical models of the composite stiffness degradation is given. The characteristics of these models are analyzed and summarized in ways of analysis and experience. Then from the perspective of the composites fatigue failure mode, the influence factors of composite longitudinal elastic modulus fatigue degradation is analyzed. Study focus on the impact of stress level and angle on stiffness degradation. A model is proposed describing elastic modulus decrease that could predict elastic modulus degradation. In order to test the model, a series of tests are designed and performed. By testing stress and strain of different unidirectional specimen, longitudinal modulus can be obtained. The experimental results were compared with the model predictions. Model calculation and experimental results fit well, which proves the model can predict unidirectional composite longitudinal elastic modulus degradation with a certain accuracy.