Effect of Thickness on Fatigue Crack Propagation in Injection Molded Short Carbon Fiber Reinforced Plastics

¹ Department of Mechanical Engineering, Meijo University, Nagoya, Japan
² Graduate School, Department of Mechanical Engineering, Meijo University, Nagoya, Japan
³ Department of Research, Nagoya Industrial Science Research Institute, Nagoya, Japan

^* Corresponding author: kshimizu@meijo-u.ac.jp

Abstract

The influence of plate thickness on the fatigue crack propagation behavior was studied by using center-notched specimens which were cut from injection-molded plates of short carbon-fiber reinforced polyphenylene sulfide (PPS) at two fiber angles relative to the molding flow direction (MFD), i. e. θ=0 deg. (MD), 90 deg. (TD). The short carbon-fiber reinforced plastics (SCFRP) plates have three-layer structure where the fiber orientation is parallel to MFD in the shell layer and is nearly perpendicular in the core layer. The fraction of the core layer increases with increase in the plate thickness. In the relation between the crack propagation rate, da/dN, and stress intensity factor, ΔK, da/dN increases with increase in thickness for MD specimen. Conversely, da/dN decreases for TD specimen. The crack opening displacement along the crack was measured by using the digital image correlation (DIC) method. The measured crack opening displacement become larger with increase in the plate thickness for MD specimens. Contrary, measured values become smaller with increase in the plate thickness for TD specimen. The crack-tip-opening radius, Δρ, was estimated from the parabolic approximation of the crack opening displacement distribution near the crack tip. The relationships between da/dN and Δρ for all specimens tend to merge into a unique relationship.