Impact strength of fiber pre-stressed composites

By applying the appropriate tension to the fibers during the curing process, the impact strength of glass-epoxy composites is improved up to 33%. Charpy tests show that the increase of the fiber prestressing increases the impact strength up to a particular level. Beyond this level, however, the increase of prestressing reduces the impact strength. The fiber prestressed samples indicate splitting breakage within the polymer that creates more new surfaces as compared with unprestressed composites. This results in the sample absorbing more energy during the impact. The splitting breakage is explained by the formation of the residual stresses in the polymeric matrix. Those stresses are controlled and promoted by fiber prestressing during the curing process.