Evaluation of interlaminar fracture toughness of directly bonded CFRTP laminate and aluminum alloy

The interlaminar fracture toughness is one of the important mechanical properties of composite materials. However, in the case of joining between dissimilar materials having different linear expansion coefficients, there are issues such as the specimen curves due to the thermal residual stress, and it is difficult to evaluate pure fracture toughness. In order to solve this problem, an end notched flexure (ENF) testing was also performed to evaluate the mode II interlaminar fracture toughness of dissimilar material specimens with thermal residual stresses. It was confirmed that the value of interlaminar fracture toughness changed depending on the orientation of the test piece, and that the interlaminar fracture toughness considerating the thermal residual stresses could be successfully evaluated by placing the carbon fiber reinforced thermoplastics (CFRTP) laminate on the upper part of the specimen. In addition, it was confirmed that when the load exceeds a certain value, plastic deformation occurs, where after the interlayer fracture toughness cannot accurately be evaluated.