Temperature Effect on Delamination Detection Method in CFRP Laminates Using Mode Conversions of Lamb Waves

Abstract

The authors have developped a built-in ultrasonic propagation system consisting of macro fiber composite (MFC) actuators and fiber Bragg grating (FBG) sensors. When two MFCs on both surfaces of the laminate are actuated in sychronization and two FBGs receive the propagated waves simultaneously, multiple modes of broadband Lamb waves can be propagated in the laminate and types of all the modes can be identified. Therefore, a new detection method of delamination in laminates could be established based on the dispersion change caused by the mode conversions at the delamination edges. However, since the dispersion is also affected by the temperature change, it is important to compensate the temperature effect on this detection method. Hence, we conducted experiments for CFRP quasi-isotropic laminates with an artificial delamination at various temperatures in a thermostatic chamber, in order to evaluate the temperature effect on the dispersion of anti-symmetric (A) modes. The obtained results indicated that the environmental temperature can be estimated from the change in the time of flight of A0 mode, and it can be used to compensate the temperature effect on the change in the dipersion slope of A1 mode. Therefore, we will be able to evaluate the delamination length in CFRP laminates with temperature compensation. Furtheremore, we evaluated the main reason of the temperature effect with FEM analysis through changes in properties of laminates, adhesive layer, and MFC actuators.