Study on evolution of internal damage in CFRP in fatigue process
Tanaka Kohhei; Kanagawa Yasushi; Murakami Sumio
Abstract:Development of internal damage evolution in plates and thin tubular specimens of CFRP laminates under static and dynamic loadings are discussed by means of Acoustic Emission measurements and micrographical observations. The mechanical behavior of three kinds of specimens, i.e. undamaged laminate plates [+45 degree4/-45 degree4]s, damaged plates [+45 degree4/-45 degree4]s subjected to drop weight impact and undamaged tubular specimens [+-45 degree]4, under quasi static and fatigue loadings is observed first. Then the mechanism of the resulting inelastic behavior and the change in the mechanical properties are discussed in relation to the evolution of internal damage. Finally the distribution and the evolution of matrix cracks and delamination in the sliced section of the specimens are measured quantitatively in several stages of fatigue process. The dependence of damage distribution on the loading condition is elucidated. Namely, in the case of the stress ratio R = -0.25, the growth of damage zone involving the main crack is localized, and the main crack forms large delamination. On the other hand, for the stress ratio R = 0, small cracks are distributed sparsely, but the main crack is not observed until the final stage of the fatigue process. Key Words:CFRP, damage, impact damage, loading condition, main crack, delamination, damage process, acoustic emission, fatigue, stiffness reduction