Abstract
The authors of this paper obtained residual strength and damage accumulation data on an unaged composite material system consisting of a graphite reinforced polymer [[0/90]2w]s five harness satin weave. Tests were conducted under ambient conditions as well as typical aircraft temperature (120°C). The data was intended to be used to develop models of damage and failure modes to predict remaining strength and life of the material as a function of material properties and environmental factors. The models are based on damage tolerance concepts where remaining strength is used as a measure of damage accumulated in the composite and failure is assumed to occur when the remaining strength equals the applied strength.
Initial mechanical properties appeared unchanged from room temperature to elevated temperature (120°C). Matrix cracking, however, was markedly lower at elevated temperature. The major fatigue damage modes observed were matrix cracking and delamination. Residual strength for specimens fatigued at room temperature was only minimally affected while a stiffness reduction of approximately 7% was seen for specimens tested at 85 and 74 percent UTS and 50 and 75% life. At room temperature, the saturation crack density as a result of fatigue was the same as the crack saturation density found from tensile failure. At elevated temperature, the strength was again unaffected but the stiffness reduction was greater at about 12%. In addition, the crack saturation density for specimens fatigued at elevated temperature was the same as the saturation crack density for specimens fatigued at room temperature.
Because no changes in remaining strength were found, the model originally considered in this study for life prediction could not be used. Further consideration will be given to using or developing a more suitable model after more data at elevated temperature and with moisture are obtained.
