THE EFFECT OF MICROSTRUCTURE ON THE ELASTIC-MODULUS AND STRENGTH OF PREFORMED AND COMMERCIAL GMTS

A new technique was used to fabricate preformed glass fiber/polypropylene GMTs. The method utilizes thermoplastic powder and fiber roving in a spray-up procedure in which a porous preform is fabricated, heated and molded. The objective was to compare the properties of various preformed GMT compositions with two commercial GMTs and to relate the mechanical properties to the microstructure of the materials. Preformed GMTs were fabricated with various fiber lengths and with or without a fiber/matrix adhesion promotor. Processing observations, microstructure, tensile creep modulus, and tensile strength of these preformed GMTs are reported. Fiber length and the addition of a fiber/matrix adhesion promotor had generally little effect on the modulus and strength of the preformed GMT. Comparisons with two structurally different commercial GMTs also showed negligible effects on modulus and strength. The major reason for this is suggested to be the inhomogeneity of the materials. The mechanical properties are controlled by local inhomogeneities rather than by the general microstructure of the material. These inhomogeneities arise from the fiber arrangement in the semi-finished sheet or preform. Since the microstructure of preformed GMT can be controlled, this material is well suited for future studies on the effects of better fiber dispersion.