Thermomechanical Fatigue of SCS-6/(Beta)21-S (0/90)2s Composite (Final Report)

摘要

The objective of this study was to investigate the material behavior of SCS-6/Beta21-S (0/90)2s in a thermomechanical fatigue environment. Samples of the SCS-6/Beta21-S composite were subjected to in-phase and out-of-phase cyclic loading; four samples were tested under in-phase conditions and eight samples were tested under out-of-phase conditions. Stress, temperature, and total strain values were acquired during the test sequence and analyzed for indication of possible trends. Experimental results indicated in-phase specimen possessed shorter fatigue lives then their out-of-phase counterparts above the static first ply failure of the matrix. The out-of-phase specimen showed a shorter fatigue life below the first ply failure. The examination of the strain change, modulus change, fractography, and metallography of the in-phase test specimens suggests a fracture mechanism that is fiber dominated. The investigation of these parameters, for the out-of-phase test specimens, indicates the fracture mechanism may be matrix dominated. Additional analysis, using a linear life fraction model and a cumulative damage model, further suggests two parameters govern the fatigue life of SCS-6/Beta21-S. Both models indicate the maximum stress or strain parameter of the 0 fibers provides reasonable correlation for life prediction and damage accumulation for an in-phase environment. The load range and modulus provide reasonable correlation for the life prediction and damage for out-of-phase test specimen.