PRESSURE SENSITIVITY AND STRENGTH-DIFFERENTIAL EFFECT OF FIBER-REINFORCED POLYMER MATRIX COMPOSITES

Based on an energy approach, a simple nonlinear theory for the fiber-r einforced polymer matrix composite is developed. The yield stress and elastic moduli of the polymer matrix are taken to be pressure-dependen t, and the ensuring pressure sensitivity and the strength-differential effect of the overall nonlinear response are then investigated. The s tress-strain curves of the transversely isotropic composite are calcul ated at several levels of superimposed hydrostatic pressure, and it is found that the flow stress, except for a pure tension or compression along the fiber direction, can increase markedly under a high pressure . The strength-differential effect, which characterizes the different responses of the material between tension and compression, also exhibi ts a strong dependence on the loading mode and the applied pressure. T he simple theory is shown to be accurate enough to compare favorably w ith an exact solution; it also yields results which are in close agree ment with the experimental data of a graphite/epoxy system at several selected pressures.