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

Kenichi Shimizu,Keisuke Tanaka,Yuya Hasegawa,G Hénaff

doi:10.1051/matecconf/201816507002

Kenichi Shimizu, Keisuke Tanaka + Show 2 more

Open Access

https://doi.org/10.1051/matecconf/201816507002

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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/dNincreases with increase in thickness for MD specimen. Conversely,da/dNdecreases 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 betweenda/dNandΔρfor all specimens tend to merge into a unique relationship.

Highlights

Short-fiber reinforced plastics (SFRP) are expected to be used more widely in order to reduce the weight of vehicles such as automobiles
The molded short carbon-fiber reinforced plastics (SCFRP) plates have three-layer structure where the fiber orientation in the shell layer is parallel to molding flow direction (MFD) and that of the core layer is nearly perpendicular to MFD
The thickness of the shell layer does not increase even if the plate thickness increases, i. e. the fraction of the core layer increases with increase in the plate thickness

Summary

Introduction

Short-fiber reinforced plastics (SFRP) are expected to be used more widely in order to reduce the weight of vehicles such as automobiles. The injection molding process makes the production of SFRP components more economical and at higher rates. The mechanical properties of SFRP components are very much anisotropic, depending on the fiber orientation produced by injection molding. Since the applications of SFRP in fatigue-sensitive components are steadily increasing in automobile industries, the anisotropic fatigue properties should be assessed in relation to the fiber orientation. The molded SCFRP plates have three-layer structure where the fiber orientation in the shell layer is parallel to molding flow direction (MFD) and that of the core layer is nearly perpendicular to MFD. The fiber orientation produced by injection molding has a big influence on the propagation rate and path of fatigue cracks [1-8]. Because the crack propagation rate perpendicular to aligned fibers is much slower than that parallel to fibers, the crack propagation rate is different between in the shell layer and in the core layer

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