Nondestructive Damage Characterization of Carbon Fiber Composites through Improved Thermoelastic Technique
T.Uenoya and T.Fujii
Abstract:The development and validation of thermoelastic damage analysis (TDA) is described to characterize damage in carbon fiber (CF) fabric composites. CF composites are suddenly ruptured without appearing obvious decrease in modulus with load increase, whereas often used as structural materials. We need to detect and estimate early damage, to monitor the damage progress, and to predict residual life of the materials. The TDA can greatly enhance conventional thermoelastic stress analysis (TSA) image of composites including early damage, which illustrates stress image having stress changes due to damage initiation/progression and also is very noisy due to the microscopic heterogeneity and weave construction of composite materials. The advantage of the TDA is demonstrated with evaluation of the damage in the plain-weave CF/plain epoxy composites and the toughened one with rubber-modified epoxy under fatigue loading as well as cyclic stepwise loading. The TDA images from the composites remarkably depended on the matrices in the composites. The TDA results compared well with those obtained using different NDT-techniques: scanning acoustic tomography, acoustic emission technique, and edge replica technique. The TDA offered valid damage information in features and amount of stress release and ability to determine quantitative estimation of fatiugue damage was also discussed. Key Words: Thermography, Thermoelastic analysis, Fatigue damage, Fiber reinforced plastics, Carbon fiber fabric composites, Non-destructive inspection, Damage evaluation