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The high modulus and negative thermal expansion coefficient of graphite filaments provide the potential for fabrication of laminated composites exhibiting negligible thermal sensitivity. Advanced satellite and space antenna applications requiring structurally efficient materials that are distortion free over a wide range of thermal gradients and local thermal conditions are now practical. The paper describes an investigation to determine the thermal expansion characteristics of graphite composites. Thermal strain measurements over a wide temperature range, -320 to 550 F(-196 to 288 C), were made by General Dynamics using a modified Leitz dilatometer. The feasibility of measuring thermal strains with strain gages is discussed.
Measurements of the longitudinal and transverse dilatation of five composite systems containing high modulus and high tensile strength graphite fibers in three different resin binders are reported. Moisture content was found to have a significant effect on thermal strain versus temperature hysteresis characteristics of both neat resins and composites. Moisture removal at high temperature was manifested as a shrinkage in the material length, and the thermal expansion coefficient remained constant over a given temperature range after sufficient drying. With the exception of unidirectional composites, the thermal coefficient increased nonlinearly with temperature. The practical aspects of stress relaxation effects and hysteresis characteristics on unidirectional laminates are discussed. Data obtained on quasi-isotropic laminates, 0/± 60 and 0/±45/90, indicate that low expansion coefficients are obtainable.
graphite composites, fiber composites, laminates, laminated plastics, reinforcement (structures), epoxy resins, polyamide resins, spacecraft environments, thermal expansion, thermal stresses, orthotropism, anisotropy, dilatancy, strain gages, moisture content, stress relaxation, hysteresis
Hercules Incorporated, Cumberland, Md.
Materials Research, General Dynamics Convair Aerospace, San Diego, Calif.