The preparation and performance of short carbon fiber reinforced adhesive for bonding carbon/carbon composites
Introduction
Because of their excellent performance in mechanical properties at high temperatures even exceeding 2000 °C, carbon/carbon (C/C) composites are well attractive for aeronautic and astronautic structure materials [1], [2], [3], [4]. But those composites are very difficult to use directly with a large size and complex shape due to their brittle character [5]. In addition, their high preparation cost restricts their further development [6], [7]. Thereby, the joining process for C/C composites discreteness and worn C/C composites is quite essential. However, some main traditional processes, such as riveting, bolting and threading, are not suitable applications in joining C/C composites for the inevitable problem of stress concentration [8]. Comparing the above processes, the adhesive is the most promising processes for joining C/C composites. Moreover, the bonding process shows an irreplaceable value in high temperature usage condition for the composites.
The design for bonding C/C composites needs a fast, safe, easy and low cost bonding method. Two kinds of adhesives have been developed, one of which is the organic adhesive, such as phenolic resin and tetraethylorthosilicate adhesives [9], [10]. Wherein, the phenolic resin adhesive heat-treated at 1800 °C could form a carbon bonding layer, and the tetraethylorthosilicate adhesive could form a silica layer. This kind of bonding layer represented high bonding strength below 1800 °C, while it had certain limitations such as low fracture toughness and bad thermal shock resistance for its single phase structure. The other kind of adhesive is inorganic adhesive, such as barium–aluminum–borosilicate (SABB) [11], Si and metals [12]. The SABB adhesive showed low bonding strength for that the adhesive and C/C substrate were bonded only by their physical interactions. Si and metals could react with C/C substrate to form carbide bonding layers, but their low oxidation resistance and thermal mismatch with C/C substrate limited their application. In some previous studies [13], [14], [15], short carbon fiber (SCF) was used as a reinforcement phase for some composites, which presented high tensile strength, good thermal shock resistance and low thermal expansion coefficient (TEC).
In the present paper, a kind of SCF reinforced adhesive was developed for bonding C/C composites. The adhesive consisted of organic and inorganic materials and integrated both of their advantages. This adhesive represented satisfactory bonding strength with the heat treatment temperatures below 1700 °C, and it showed good thermal shock resistance below 1500 °C.
Section snippets
Materials
The two-dimensional C/C materials for preparing C/C specimens produced by the rapid direction diffused chemical vapor infiltration (CVI), and their performs were fabricated by spreading layers of PAN based plain carbon cloth made in Jilin Carbon Plant, which has been described elsewhere [1]. The configuration of specimens is shown in Fig. 1. The joint face paralleled to the direction of carbon fiber in C/C composites. The bonding surfaces of specimens were treated by following procedures:
Failure model for bonded specimens
The bonded specimens had various failure models, which could be categorized in terms of definition given in Fig. 4, wherein three kinds of failure models corresponded to following failure mechanisms:
- (1)
Bonding layer failure mechanism, specimens ruptured in the bonding layer according to Model I. The bonding strength of the bonding layer was lower than that of interface layer and the interlaminar shear strength of C/C substrate, and then the strength of specimens (τ) could be expressed as
where τ
Conclusions
Bonding strength was enhanced by minimizing bonding thickness, and 80 μm was the optimized thickness. Bonding strength increased with increasing heat-treatment temperature from 300 °C to 800 °C. While from 800 °C to 1200 °C, SiO2, Al2SiO5 and Al2O3 signified to advance the strength of SCF and the bonding strength of adhesive, and then the bonding strength was larger than the interlaminar shear strength of C/C composites. At relative high heat-treatment temperature, 1200–1700 °C, the bonding strength
Acknowledgments
This investigation was supported by the Program for New Century Excellent Talents in University (NCET 05–0195) and Beijing Municipal Science and Technology program (Y0406001040211).
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