A fatigue model based on cumulative damage is developed for predicting the fatigue life of fiber-reinforced polymeric composites in offshore applications. This model incorporates applied maximum stress, stress amplitude, loading frequency, residual tensile modulus, and material constants as parameters. The model is verified with experimental fatigue data of a glass fiber/vinyl ester composite in various environments. Experiments are conducted in tension/tension stress at four levels of applied maximum tensile stress and in two frequencies while the specimens are exposed to air, distilled water, and sea water at 25 degrees Celsius. Both the residual mechanical properties at specified loading cycles and the number of cycles at which the specimens fail are measured. The results show for the material used in this study, the loss in mechanical properties (residual tensile strength and modulus) in salt water is the same as that in distilled water, and that the fatigue life in these aqueous environments is shorter than that in air. On the other hand, the S-N curves for the specimens subjected to these three environments have approximately the same slope, suggesting that the failure mechanism does not change with the exposure environment. Further, the specimens fatigued at lower frequency appear to fail at lower number of cycles than those loaded at higher frequency. Numerical analysis is carried out to determine the material constants of the composite. The fatigue model agrees well with the experimental data. The model can be used to predict the fatigue life of the polymeric composites exposed to different environments under an applied load and to predict the residual tensile modulus after a number of cycles of service at a given load.
Proceedings Title: 5th International Conference. Proceedings. International Community for Composites Engineering andCollege of Engineering University of New Orleans
Issue: No. 2
Conference Dates: July 5-11, 1998
Conference Title: Composites. Part B: Engineering
Pub Type: Conferences
E-glass/vinyl ester composite, fatigue damage, fatigue life prediction, fatigue modeling, offshore applications, polymeric composites, S-N curve strength degradation