Mechanical Deformation Mechanisms in Knitted Fabric Composites

Knitted fabric composites have certain advantages over woven composites, particularly in their ability to conform to complicated contours. As a consequence, however, they demonstrate inferior mechanical characteristics compared to woven materials as a direct result of the presence of bent fibers. Such a knitted fabric composite made from, for example, glass fibers in a polyurethane matrix, can be used as an orthopaedic splinting bandage for immobilizing fractures of the upper and lower limbs. Relatively little research has been reported on knitted fabric composites; therefore, a study on the mechanical deformation mechanisms of knitted fabric composites was initiated. It was observed that knit patterns, type of fiber, size of fibers used, size of loops, coatings and lay-up procedure were all variables that could affect the structure/property relationship of knitted fabric composites. Tensile testing with optical measurement of strain was performed on knitted substrate and coated bandages in both the course and wale directions. Results indicated that the knitted fabrics function as link mechanisms at the microscopic level, with knitted loops straightening and bending before the individual elements of the knitted yarn take up significant load and material deformation. Theoretical modeling of the glass knit structure, in both the course and wale directions, agrees well with experimental testing.