Shock loading of three-dimensional woven composite materials

The effect of shock loading on three-dimensional (3-D) woven composite materials has been experimentally studied. The preform materials used in this work, known under trademark 3Weave™, were manufactured by 3TEX using S-2 glass fiber roving. Four different preforms, having areal weights 93, 98, 100, and 190 oz/yd2, were used in fabrication of single-layer and two-layer composites. The respective composites were made using VARTM process with Dow Derakane epoxy/vinyl ester resin. A shock tube was used to create the shock loading for the study and was chosen for its ability to provide highly consistent and repeatable levels of shock loading. The material’s resistance to shock loading was evaluated using such parameters as surface and internal visual damage, the magnitude of permanent (i.e., after-shock, residual) deflection, and post-mortem compressive strength. The observed visual damage consisted of surface discolorations at low shock load levels and progressed to surface fiber breakage accompanied by internal delaminations and breakage of the through thickness (Z-directional) fibers at higher shock load levels. The onset of permanent deflection in the form of bulging was observed in the panels tested at pressures of 5.65 MPa and higher with maximum values of 8–9 mm found in the 93 and 100 oz/yd2 preform composites tested at a pressure of 8.1 MPa. The compressive strength of the materials was also found to decrease in both the warp and weft fiber directions with increasing test pressures. Over the range of shock pressures applied in this series of tests, the 98 oz/yd2 preform composite was found to perform best in terms of a smaller amount of visual damage, lower permanent deflection, and higher post-mortem compressive strength.