Research On Fatigue Behavior Of Glass Fiber Reinforced Polymer Composites

Glass Fiber Reinforced Polymer (GFRP) has been widely used in the fields of aeronautics, automobile, shipping and civil industry. Although the fatigue problem of the GFRP were encountered everywhere, the fatigue mechanism could not be essentially described based on its fatigue phenomena, and there was no general method for the fatigue life's prediction. In this paper, the fatigue behaviors of GFRP laminates were systematically researched by theoretical and experimental methods.The previous research results of the GFRP were reviewed and discussed firstly in this paper. Through comparing with the experimental data, the applicability of various models and their ability of dealing with practical problems were presented.Six kinds of GFRP laminates, 162 specimens totally, were tested in this research. Among of them, 50 specimens were tested for static strength and 112 for fatigue life, depending on which, the comprehensive fatigue behavior and fatigue life data of GFRP were obtained. The normalized stiffness degradation curves were provided for the same laminate under different ratio of stress to its strength and different laminates under same ratio of stress to individual strength. The reason why the stiffness is decreasing along with the cycles was given through the evolution of microcosmic damages in the material. Based on the comprehensive experimental research on the GFRP's fatigue behavior, the theoretical research was carried out as follows: Based on the definition of a condition function for the GFRP under axial loading, a theoretical model was presented to predict the S-N curve of off-axis unidirectional laminate with arbitrary angle by the S-N curves of 0o and 90o laminate; Considering the fatigue damage mechanism of GFRP laminates, a fatigue life model was presented to predict the S-N curve of arbitrary laminate with complex stacking sequence by the S-N curves of 0o and 90o laminate; A stiffness degradation model was proposed, and was proved to describe the degradation rules well.Through comparing the theoretical models with the experimental results, it shows that the predicting results of these theoretical models agree well with the experiment results. The experimental results of this research can be applied in GFRP structure design and the models could be applied in GFRP structure's fatigue analysis and life prediction.