Influence of void content on the flexural fracture behaviour of carbon fiber reinforced polypropylene

In order to investigate the influence of void content on the fracture behaviour of carbon fiber reinforced polypropylene (CF/PP), we investigated the relationship between the mechanical properties of carbon fiber reinforced thermoplastics and their void content using CF/PP prepreg sheet and partially impregnated sheet. Two types of flexural properties of cross-ply (CP) plates and chopped carbon fiber tape reinforced thermoplastic (CTT) plates with different void contents were measured by three-point bending tests. The flexural strength of CP specimens decreased drastically when their void content became higher than 1%, whereas the flexural strength of the CTT specimens decreased gradually with an increase in void content. Un-impregnated regions in the composites resulted in small dotted defects under loading conditions, although they were only found on the tape along the longitudinal direction in the case of CTT. In addition, a larger number of defects was observed on CP and CTT specimens with lower strengths. Therefore, cyclic loading tests were conducted to observe flexural fracture behaviour in more detail to elucidate the reason behind voids causing a decrease in strength. During these tests, the dotted defects in the CP specimens were shown to be connected along the in-plane transverse direction, while those in the CTT specimen propagated along the second layered tape.