ABSTRACT:

Fatigue strength of carbon fiber reinforced plastic, CFRP, in which pitch type carbon fiber was combined in an epoxide resin matrix with a fiber content of 33% by weight, was studied by means of an AE method and fractography. For CFRP, the ratio of fatigue strength to ultimate tensile strength is, greater than that of epoxide resin. Such a, result suggests that the pitch type carbon fiber contributes to an increase in fatigue strength under cyclic stress. Also, the fatigue strength for CFRP decreases with increasing mean stress.

1. INTRODUCTION

Pitch type carbon fiber has recently been developed and has many superior properties. It is necessary to estimate the fatigue properties for CFRP so as to be widely used as the components of structures. It is well known that for CFRP, an effect of cyclic stress appears as a fatigue damage(Fujii and Zako, 1985). Many studies have been investigated for the fatigue properties of PAN type CFRP. Maiser et al(1986) have found that the fatigue damage can be divided into three stages. Poursartip et al(1986) have shown that the fatigue damage is the decohesion with the cracking of resin matrix. An acoustic emission method may analyze the fatigue damage in CFRP(Suzuki et aI, 1987, Shiwa et aI, 1986). In this study, an acoustlC emission method used to analyze fatigue damage in pitch type CFRP. Because fatigue damages of resin matrix, carbon fiber and their interface were related with microscopic fracture morphology, the fatigue properties for CFRP tried to be clear using an acoustic emission method and fractography.

2. MATERIALS AND EXPERIMENTAL PROCEDURE

The material used is carbon fiber reinforced plastic in which coaltar pitch type carbon fiber were randomly combined in epoxide resin with a fiber content of about 33%.

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