Damage detection of structures is considered to be very important for securing safety, determining economical replacement time, and improvement of manufacturing and operating conditions by analyzing the cause of damage. The structural health monitoring (SHM) concept has many advantages compared with classical Non-destructive test/evaluation (NDT/NDE) methods, primarily because the classical techniques of NDT/NDE are not suitable for /n situ implementation. In this paper, new real-time, in-situation damage detection methods for composite laminates through the use of embedded FBG sensors is presented. The first method traces the ply stress states of a laminate and compares them with failure criteria. Experimental results show that laminates experience fracture when the ply stress states are beyond the boundaries of failure criteria. Fatigue load made a strain increase caused from accumulated damage. In this method, critical damage can be detected by the ply stress state proximity to the boundary of the failure criteria. The second method is to monitor the curvature and deformation of a beam. Curvature is a representation of a beam deformation. And the value is varied not only by load change but also by material degradation that was caused by damage. If we can set some critical curvature value which indicates definite damage occurrence and growth, we can use it as a safety reference value by comparing it with curvature distribution of the beam element in service. However, experimental results show that we cannot detect abnormal peak of curvature distribution of a beam under displacement control and low cycle of loading.
본논문은 복합 적층판 내부에 FBG 센서 삽입을 통한 구조물의 건전성 감시 기법 제시를 목표로 하였다. 제시한 첫번째 기법은 3개의 서로 다른 각도를 가진 플라이에 FBG 센서를 삽입하여 적층판 전체의 플라이 응력을 추적하는 기법이다. 두번째 기법은 굽힘하중을 받는 적층판 보의 응력 분포를 감시하는 기법으로 이역시 FBG 센서를 내부 삽입하여 여러 점에서 다점측정한 변형률 신호를 이용하여 구현하였다. 제시한 기법의 검증과 실제 실험 결과를 제시하였다.
