EFFECT OF RESIN CROSS-LINK DENSITY ON THE IMPACT DAMAGE RESISTANCE OFLAMINATED COMPOSITES

It is generally recognized that fiber-reinforced laminated composites are susceptible to damage resulting from low-velocity impacts, Over re cent years, many strategies have been devised to increase tile fractur e toughness of resin matrix materials with the aim of improving the co mposite's overall resistance to impact damage. One popular strategy fo r enhancing the fracture toughness of thermosets involves increasing t he molecular weight between crosslinks, which, in turn, enhances the r esins ductility. in this paper, we investigate the efficiency of this toughening approach with regard to resisting damage in composite lamin ates subjected to low-velocity impacts. A mechanistic study shows that at least two distinct processes occur during an impact event. First, the laminate experiences a local failure, which resembles a Hertzian f racture process followed by subsequent delamination between the plies, Hertzian fracture occurs once ata critical threshold level initiates laminate damage through the development of a spatially configured arra y of matrix microcracks, which resemble that of a Hertzian cone togeth er with radial cracks. Further damage accumulates in the laminate by i nter-ply delamination with the size of delaminated area increasing coi ncident with the impact load. Systematic changes in resin. crosslink d ensity show that both damage initiation and accumulation are affected. However, the maximum resistance far damage initiation occurs al a muc h higher crosslink density than that measured for damage accumulation.