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