Analysis of Modulus and Strength of Dry and Wet Thermoset and Thermoplastic Composites Loaded in Transverse Tension

Micromechanical finite element analysis of modulus and strength of transverse tension loaded continuous fiber composites is presented and related to experimental data for dry and wet glass/epoxy, carbon/epoxy, glass/polyphenylsulfide (PPS) and carbon/bismaleimide (BMI)-epoxy composites. Transverse tensile strength predictions employed the combined mechanical and residual stress states at the fiber/matrix interface and in the matrix in conjunction with debonding and matrix failure criteria. Due to lack of experimental data on fiber/matrix interfacial strengths, an ideal bond was assumed by assuming that the interfacial tensile and shear strengths were the same as those for the matrix. The Cooper-Kelly transverse strength model was also examined. Predictions of the transverse Young's modulus using finite elements were overall in good agreement with experimental values at dry and wet conditions. The transverse stress levels corresponding to debond initiation and matrix failure generally decreased with increased amounts of absorbed moisture which is consistent with experimental observations, but due to the ideal fiber/matrix bond assumption, the strength predictions tended to be unconservative. The Cooper-Kelly Model with a weak fiber/matrix interface yielded highly conservative strength predictions.