Smart structure for suppression of mode I and II crack propagation in CFRP laminates by shape memory alloy TiNi actuator

A shape memory alloy TiNi actuator was used to suppress mode I and II propagation of interlaminar cracks in carbon fiber reinforced plastics, CFRP. Pre-strained TiNi sheets were attached on the surface of CFRP with the direction of the actuation strain parallel to the crack propagation direction. They were heated to introduce the recovery strain for the suppression of interlaminar crack propagation under static loading of mode I or II and cyclic loading of mode I. The change in fracture toughness and crack propagation rate with the application of the recovery strain was investigated. The results show that the fracture toughness increased due to the actuation strain and stiffness increase by the attachment of the actuator in both mode I and II. The average fracture toughness after the introduction of the actuation strain was 2.8 times larger than the initial value without the effect of stiffness increase in mode I. The improvement was more evident in mode I than in mode II, where the friction between fracture surfaces was more effective. The fatigue crack propagation rate was remarkably decreased by the introduction of the actuation strain. The difference in the crack propagation rate between specimens with and without actuators was more than an order of magnitude after the activation of the actuator. The introduction of the actuation strain by TiNi sheets attached parallel to the fiber direction of CFRP was found to be effective for the suppression of fatigue crack propagation.