اميرمحمد فيضي

Fatigue is a critical factor in the failure of polymer matrix composites, affecting their performance and service life. This thesis investigates the effect of initial delamination on the fatigue behavior and lifespan of these materials. The primary objective of the research is to eva‎luate the impact of initial delamination on parameters such as fatigue limit, stiffness degradation, and thermal variations in composite samples using infrared thermography. For the experiments, glass-epoxy composite specimens with woven fibers were prepared in three different categories: intact samples without delamination, samples with symmetrical initial delamination, and samples with unsymmetrical initial delamination. These samples were subjected to cyclic fatigue loading, and the surface temperature changes were recorded throughout the tests using an infrared thermography camera. The analysis of thermal data and heat generation, along with the mechanical results obtained from the tests, helped to further investigate the effect of delamination on the dynamic behavior and stiffness of the samples. Furthermore, temperature changes and heat generation were used as indicators for monitoring fatigue damage and crack growth in the samples. The results of this study showed that the presence of initial delamination led to a reduction of approximately 76.8% in fatigue life and 15.8% in the fatigue limit of composite samples. Samples with initial delamination experienced faster stiffness degradation, and the temperature rise and heat generation in these samples occurred more rapidly compared to undamaged samples. This indicates a higher stress concentration and faster crack growth in the delaminated samples. The analysis of surface temperature and heat generation during loading demonstrated that these parameters can significantly aid in identifying fatigue damage and predicting useful life. Finally, a fatigue life prediction model based on entropy generation and thermal data was developed for both undamaged and delaminated samples. This model can accurately estimate the fatigue life of the samples, and the results of this research could contribute to better design and optimization of composite structures. Through non-destructive monitoring and fatigue life prediction, the safety and performance of these materials can be improved.

خستگي چندلايه‌هاي كامپوزيتي , اثر جدايش اوليه , اتلاف انرژي حرارتي , ترموگرافي مادون قرمز , مدل پيش‌بيني عمر خستگي

Laminated Composite Fatigue , Initial Delamination Effect , Thermal Energy Dissipation , Infrared Thermography , Fatigue Life Prediction Model

Amir Mohammad Feizi

Dr. Fathollah Taheri-Behrooz