Fold-resistant characteristics of the laminate composites for flexible structure

There is considerable interest in the use of flexible laminate composite materials to improve the deployable structures for space applications. Critical to acceptance of these materials is the ability to achieve high packaging strains without damage. However, there does exist more or less damage during the process of folding and unfolding for the laminate composites. Better understanding of folding damage, therefore, is needed for the design of laminate composites and folding pattern. In this work we present a study on the fold-resistant characteristics of two different laminate composites, which were fabricated by covering the aramid fiber/epoxy and carbon fiber/epoxy prepregs respectively with polyimide film on both sides. The results of tensile tests on 3-layer structure laminate composites show that the fold-resistant properties of aramid fiber/epoxy composites could be improved with increasing of the resin content and decreasing of the fiber bundle diameter. For carbon fiber/epoxy composites, the effects of resin content and fiber bundle diameter on reduction rate of fracture strength were more complex. There existed a best range of resin content and fiber bundle diameter. The microscopic observations show that folding resulted in piling up of resin and damage of reinforcing fiber, which would decrease the mechanical properties.