Abstract
Many fatigue damage detection system for CFRP composite structures has been developed recently, but they were not successful. In this paper a new fatigue damage detection method by measuring Poisson's ratio change is described. The phenomena that Poisson's ratio change is more sensitive than stiffness change was discovered by a simple FEM analysis. Then more precise FEM analysis has been carried out and confirmed the phenomena. And, Poisson's ratio change on 0/90 and quasi-isotropic CFRP laminates were calculated. From the static strength test results, damages such as transverse cracks could not be detected by Poisson's ratio change, because of the non-linearity of the longitudinal stiffness of CFRP laminates. However, in case of fatigue tests, it was observed that a liner relation exists between the transverse crack density and Poisson's ratio change, for example, 0.5 crack/mm transverse crack density led to 3-5% Poisson's ratio change. This system would be useful not only for damage detection of coupon tests, but also for a health monitoring system of actual aircraft structures in the future.
