The effects of deforming knitted glass fabrics on the basic composite mechanical properties

The effects of deforming knitted fabrics on the tensile and compressive properties of their composites have been investigated for the weft-knit Milano rib fibre architecture. The properties have been studied for both the course and wale directions for composites with fabrics deformed in either of the two directions. It was found that any change in the mechanical properties of the deformed composites with respect to their undeformed counterpart is strongly related to the changes in the knit structure brought about by the induced deformation to the knitted fabric. Deformation in the knitted fabric also affects the tensile fracture mode whereby increased deformation, be it wale- or course-wise, transforms transverse fracture to shear fracture in either loading axis. On the contrary, the compressive fracture mode is insensitive to fabric deformation. Fractographic studies using stereo-optical and scanning electron microscopy have further revealed that tensile failure is caused by fibre breakages occurring at two locations of the knitted loops-one, at the leg components and, two, at fibre crossover points, whilst compression failure is controlled by Euler buckling of the looped fibres of the knitted composite. All these characteristics were revealed to be related to the microstructure of the knitted composite laminates. (C) 1999 Kluwer Academic Publishers.