COUPLED EFFECT OF TEMPERATURE AND DEGAS AND/OR MOISTURE DESORPTION ON STRENGTH OF ORGANIC COMPOSITES FOR SPACE STRUCTURAL COMPONENTS, AND DEVELOPPED RESIDUAL STRESSES

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In order to evaluate the strength and dimensional stability of fiber reinforced organic composites, especially carbon fiber reinforced plastics (CFRP), in the space environment, it is important to clarify the effects of temperature and vacuum condition on the mechanical behavior of CFRP and the microfractures.In this report, the tensile strength and Young's modulus of CFRP cross-ply laminates and short carbon fiber reinforced polyamide (SCFR-PI) composites are considered in the high vacuum condition 10^-4 Pa and the atmospheric condition at various temperatures. From the experimental results, the CFRP at low temperature 93K and 200K has smaller tensile strength than that at 298K in high vacuum condition. The strength of interfacial bonding between carbon fibers and the epoxy resin matrix becomes better in low temperature and high vacuum conditions. It is found that there exist the coupled effect of temperature and vacuum conditions on the tensile strength of CFRP cross-ply laminates and the microfractures.Even though tested at the same temperature 298 K, the SCFR-PI kept in high vacuum condition has higher tensile strength and equivalent Young's modulus than that in the atmospheric condition. The rule of mixture and the shear lag treatment can not be used to evaluate the strength and Young's modulus of SCFR-PI composites in high vacuum condition. The strengthening is attributed to the nonexistence of air around the specimens. In high vacuum condition, the matrix resin is shrank owing to the degas and/or moisture desorption from the matrix and from the interface between the matrix and fibers, and thus yield the residual stresses in the organic composites. The interfacial bonding strength between carbon fibers and the resin matrix becomes much better in high vacuum condition. The methods of characterizing them must be described for evaluation of SCFR-PI composites in space environment.