Studies on Behavior of Carbon and Fiberglass Epoxy Composite Laminates under Low Velocity Impact Loading using LS-DYNA

The desired characteristics of materials in modern aircraft applications require high specific modulus and high specific strength for low specific weight. Composite structures, fabricated using carbon and glass fabrics in conjunction with epoxy resin manufactured via the heated vacuum assisted resin transfer molding (H-VARTM) process are now being considered as a low cost alternative to conventional materials without compromising the mechanical properties. It is important to study the response of composite structures under out-of-plane impact loading which may cause considerable damage to the different layers even at low impact energy levels. In the present study, response of composite laminates under low velocity impact loading was investigated using LS-DYNA. The composite laminates were manufactured by the H-VARTM process using basket weave E-Glass fabrics and plain weave AS4 carbon fabrics with the Epon 862 resin system and Epicure-W as a hardening agent. A composite laminate, with 10 layers of carbon and fiberglass fabrics, was modeled using 3D solid elements in a mosaic fashion to represent plain and basket weave patterns. Mechanical properties were calculated by classical micro-mechanical theory and assigned to the elements as orthotropic elastic material properties. The LS-DYNA results were compared with experimental drop test results using the Dynatup Low Velocity Impact Test Machine. The main considerations for comparison were maximum impact load and the energy absorption by the laminates. Progressive damage for fiberglass laminates was reported for six impact energy levels from 128 ft-lbf (incipient damage) to 768 ft-lbf (upper bound) with the increasing increments of 128 ft-lbf. For carbon laminates impact energy levels are half as that of fiberglass.