Takushi Miyake

Microscopic observation of voids and transverse crack initiation in CFRP laminates

In situ three-point bending tests under observation using scanning electron microscopy were performed for specimens including voids to investigate the effect of voids on transverse crack initiation in carbon fiber-reinforced plastic (CFRP) laminates. First, initial failure load (i.e. applied load at the first transverse crack initiation) was investigated. Microscopic strain distributions were then measured by digital image correlation analysis using SEM pictures taken before and during loading in the in situ tests. In addition, specimens including voids and transverse cracks after the in situ tests were observed using X-ray computed tomography to clarify transverse crack onset locations with respect to void shapes and distributions. These experiment results suggested that voids actually caused strain concentration and corresponding local plastic deformation, and finally resulted in reduction of macroscopic initial failure strains in CFRP laminates.

A dry aligning method of discontinuous carbon fibers and improvement of mechanical properties of discontinuous fiber composites

Abstract A novel method for dry alignment of discontinuous carbon fibers, such as recycled carbon fibers was developed by the modification of the yarn manufacturing process. In order to achieve high production rate and application for long fibers, fluffy synthetic fibers were used as the suspending and carrying media for discontinuous carbon fibers instead of a fluid medium generally used. Using the mechanical interaction in the dry alignment method, a mixture of 200 mm long discontinuous carbon fibers and fluffy polypropylene fibers was fabricated into an aligned and homogeneously comingled sliver by drafting. Then, the sliver was spun into yarn and an aligned yarn preform was obtained. Composites, with approximately 70% of the fibers aligned within an angle of ±14° with respect to the drafting direction, were successfully produced from the preform of the aligned spun yarn. The tensile modulus of the composite specimen along the aligned direction was about 10 times larger than that along the transverse direction, and about 3.5 times larger than that for the specimens obtained from the same yarn with random orientation.