Temperature-dependent tensile and shear response of graphite/aluminum

The thermo-mechanical response of unidirectional P100 graphite fiber/6061 aluminum matrix composites (v_f = 0.47) was investigated at four temperatures: -150°F, +75°F, +250°F and +500°F, using test methods developed at Virginia Tech. Two types of tests, off-axis tension and Iosipescu shear, were used to obtain the desired properties. Good experimental-theoretical correlation was obtained for E_xx, v_xy and G₁₂. It is shown that E₁₁ is temperature independent, but E₂₂, v₁₂ and G₁₂ generally decrease with increasing temperature. Compared with rather high longitudinal strength, very low transverse strength was obtained for the graphite/aluminum. The poor transverse strength is believed to be due to the low interfacial bond strength in this material. The strength decreases significantly with increasing temperature. The tensile response at various temperatures is greatly affected by the residual stresses caused by the mismatch in the coefficients of thermal expansion of fibers and matrix. The degradation of the aluminum matrix properties at higher temperatures has a deleterious effect on composite properties. The composite has a very low coefficient of thermal expansion in the fiber direction.