High fracture resistance of carbon fiber treated by electron beam irradiation
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A crack reduction by electron beam (EB) irradiation treatment for carbon fiber, used without the traditional method of accompanying heat, was developed to modify the mechanical properties at lower temperature. The EB treatment improved the resistance to fracture. Namely, the maximum ratio of fractured samples (maxRf) and the minimum bending strain on fracture (min⑀f) were defined as simple indicators of fracture resistance and became smaller by the EB treatment. Furthermore, a critical density of dangling bonds for a fracture was suggested and determined for carbon fiber treated by EB irradiation. The EB irradiation to reduce cracking and the determination of the critical density of dangling bonds are new concepts that can be broadly applied in the fields of aerospace and rapid-transit production engineering.
I. INTRODUCTION
Carbon fiber composites have found application as structural materials in the fields of aerospace and rapid transit engineering.1,2 The first step in producing carbon fiber composite materials involves bundling the fibers, which often results in fiber fracture. It is difficult to handle the fractured fibers in the bundling machine. Heat treatment is typically used to enhance the fracture stress of carbon fiber3 because at high temperatures carbon atoms diffuse and rearrange at each crystal lattice point near cracks. To modify the various properties at lower temperature, materials have been often treated with electron beam (EB) irradiation.4 – 6 In the present study, EB irradiation of high electrical potential (170 kV) was used to migrate carbon atoms of a crack and the incoherent interface in a carbon fiber. Such carbon atom migration probably dulls the edge of sharp crack tips at a temperature lower than that required in conventional heat treatment. This study showed that sharp crack reduction could be accomplished by using sheet EB irradiation without applying heat. Because the EB treatment serves to prevent carbon fiber fracture, use of the treatment should decrease the failure frequency in the production process of carbon fiber composite bundles, thereby making the handling of carbon fiber bundles easier. Therefore, the EB treatment should prove useful to produce carbon fiber composite materials for a wide variety of applications. The purpose of the present work is to enhance the high
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J. Mater. Res., Vol. 16, No. 6, Jun 2001 Downloaded: 13 Mar 2015
fracture resistance of carbon fiber treated by electron beam irradiation. The critical density of dangling bonds for fracture was defined and determined as part of this work. EB treatment is a new concept to enhance carbon fiber fracture resistance, used without accompanying heat, and has broad potential applications in the fields of aerospace and rapid-transit production engineering.
II. EXPERIMENTAL
The carbon fiber (6 × 10−6 m in diameter, Filament 12000f; Asahi-Nippon Carbon Fiber Co. Ltd., Tokyo, Japan) was cut into 10-mm-long pieces. Heat treatment temp
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