Nonlinear Mechanical Properties of a Thermoset Matrix Composite at Elevated Temperatures

Abstract

Models are presented for describing the stress-strain relationships and the strengths of a thermoset matrix composite exposed to elevated temperature. The models take into account the nonlinear elastic characteristics of the material. For Fiberite 976 resin and for unidirectional Fiberite T300/976 composite the constants required in the models were determined by measuring the tensile, compressive, and shear properties, and Poisson ratios at 75, 250, 300, and 350°F. The strengths, initial (stress → 0) moduli, and initial Poisson's ratios of the unidirectional composite were calculated from the known resin and fiber properties using micromechanics equations. A procedure is also described which, together with the stress-strain-strength models developed in this study, can be used to calculate the deformations and strengths of loaded multidirectional laminates at high temperatures. To evaluate the accuracies of the models and the calculation procedure deformations and strengths of multidirectional Fiberite T300/976 laminates were calculated. These results were compared to data obtained at temperatures ranging from 75 to 350°F. The calculated results agreed well with the data.