Delamination Crack Growth of Unidirectional CF/PEEK Composite in Creep at Elevated Temperatures

The behavior of delamination crack growth in creep was investigated using DCB specimens of unidirectional CFRP, APC-2 (carbon fiber : AS4 and matrix : poly-ether-ether-ketone (PEEK)) at the test temperatures from 443 K (170°C) to 483 K (210°C). The creep crack grew steadily along the boundaries between the matrix and the fiber. The crack opening displacement (COD) rate measured during the crack growth test coincided with the elastic COD rate calculated from the change in elastic compliance due to the crack growth. It implied that the creep took place only in the vicinity of the crack tip and the creep zone was surrounded by te elastic stress field. Such a small scale creep (SSC)condition might be caused by the constraint of matrix deformation by the fibers, which was partly proven by the experimental observation of the crack-tip white-colored zone at the specimen side, caused by a large creep deformation. Thus, the crack growth rate was insensitive to the test temperature and correlated well with the elastic energy release rate.