Experimental and Numerical Investigation of Mode I and Mode II Interlaminar Behavior of Ultra-Thin Chopped Carbon Fiber Tape-Reinforced Thermoplastics

This manuscript describes an experimental and numerical study conducted to investigate two representative cases of delamination in ultra-thin chopped carbon fiber tape-reinforced thermoplastics (UT-CTT): delamination in a double cantilever beam (DCB, mode I) and delamination in an end-notched flexure (ENF, mode II). In examples of mode I delamination, unstable crack growth resulted in sawtooth-like load–displacement curves after the initial stage of increasing load, while some specimens displaying mode II delamination exhibited stable crack propagation. The crack surfaces of DCB and ENF UT-CTT specimens were observed by a three-dimensional measurement macroscope and a scanning electron microscope. The values of mode I and mode II interlaminar fracture toughness were obtained based on linear elastic fracture mechanics and beam theory in reference to JIS K 7086 standard, respectively. Furthermore, numerical analysis utilizing the surface-based cohesive zone model based on the triangular traction–separation law was used to predict the delamination behavior in UT-CTT. The minimum and maximum values of critical strain energy release rate were used to define the range of load–displacement curves corresponding to unstable crack propagation under mode I, while the parameters including interlaminar shear strength and friction were taken into account for the predictions of delamination propagation under mode II. The numerically predicted load–displacement curves showed good correlation with the theoretical and experimental results. The research provides interlaminar mechanical properties for damage modeling and numerical simulation method to express fracture behaviors of UT-CTT structures.