抄録
The authors have developed a built-in ultrasonic propagation system consisting of macro fiber composite (MFC) actuators and fiber Bragg grating (FBG) sensors. The MFCs and FBGs can be integrated into composite laminates because of their small size and high fracture strain. This system can propagate multiple modes of broadband Lamb waves in CFRP laminates and can identify all the modes by synchronized actuation of two MFCs and measurement with two FBGs on both surfaces of the laminate. Hence, a new delamination detection method has been established on the basis of the change in the frequency dispersion caused by the mode conversions at the delamination edges. However, the frequency dispersion is also affected by the temperature change. From a practical point of view, it is important to compensate the temperature effect on this detection method. Hence, in this research, we conducted experiments for CFRP quasi-isotropic laminates with an artificial delamination at various temperatures in a thermostatic chamber, in order to evaluate the effect of environmental temperature on the frequency dispersion of anti-symmetric (A) modes. As a result, with an increase in the temperature, the time of flight (ToF) of A_0 mode increased and that of A_1 mode decreased. However, ToF of A0 was independent of delamination length L and the dispersion slope of A1 changed depending on the L because of the mode conversions. Hence the environmental temperature can be estimated from the ToF of A_0, and the estimated temperature can be used to compensate the temperature effect on the change in the dispersion slope of A_1. Therefore, we will be able to evaluate the delamination length in CFRP laminates with compensation of temperature change.
