VIBRATION ANALYSIS AND FINITE-ELEMENT MODELING FOR DETERMINING SHEAR MODULUS OF PULTRUDED HYBRID COMPOSITES

An impulse-frequency response vibration technique was employed for det ermining the shear modulus of glass/epoxy, graphite/epoxy and hybrid ( glass-graphite/epoxy) pultruded cylindrical composite rods in torsion. The distribution of the fibers and matrix in the shell-core regions w ere examined microscopically and the volume fractions of the various c onstituents determined using the stereology point counting technique. Based on the examined cross-section finite element meshes were generat ed and analyzed for predicting the shear modulus of such composite rod s. It was observed that there was close agreement between the finite e lement predictions and the experimentally obtained data for only some of the hybrid configurations. The nature of the pultrusion manufacturi ng process which causes variations in the fiber packing geometry in th e shell and core regions of hybrids has been found to significantly in fluence the accurate prediction of shear modulus, using either analyti cal or finite element methods.