Abstract
A micromechanical finite element model (FEM) has been developed using ANSYS to investigate the effects of temperature and cross-ply stacking on failure of graphite fiber-reinforced epoxy matrix (P75 graphite/934 epoxy) composites. Thermal residual stresses develop as a result of the difference in the coefficients of thermal expansion of the fiber and the matrix, and the operating and stress-free or cure temperature. It has been shown that these thermal stresses can be large enough to cause matrix cracking and possibly even laminate failure. Results from the 3-D micromechanical FEM are compared to those of the 2-D work, using laminated plate theory, done by Bowles and Griffin. A new curve of ultimate radial stress as a function of temperature was also developed. Using this curve, it is shown that the [0]s laminate model does not cross the failure criterion line when subjected to a delta temperature of −500°F. The [0/0/90/90]s model, however, reaches the ultimate radial stress at a temperature of about −15°F, assuming a stress-free temperature of 350°F. Bowles and Griffin’s ultimate radial stress curve, based on a single radial peaking factor, predicted the matrix failure at about 32°F. Further investigation of the model examines the effect of thermal loading on the matrix cracking.
