DESIGNING A FUNCTIONALLY GRADED S-2 GLASS/EPOXY COMPOSITES FOR IMPROVED ENERGY ABSORPTION

Abstract

SC-15 epoxy while the low yield strength epoxy was a TGDDM based modified system with monoamine functionalized partially reacted structure (mPRS), synthesized by collaborators at Drexel University. Compared to the baseline VARTM panel made from plain weave S-2 glass fabric with a 463 sizing and SC-15 epoxy, the penetration resistance was improved by ~25% by using a low yield strength with a high interface strength combination of 8-harness satin with mPRS. The thin laminate samples (6 mm) showed a 14% improvement in V50 when normalized by areal weight compared to a plain weave/SC-15 baseline by using plain weave/TGDDM with 20%mPRS. These two systems were combined to make an FGM panel (1.8 cm thick, 1.2 cm DoP system on strike face and 0.6 cm thin laminate on the back surface) which allowed for a 18% % increase in energy absorption capability compared to the baseline VARTM plain weave/SC-15 system on an equivalent areal density basis. This study demonstrates that the ballistic performance of GFRP can be improved through a material by design approach where constituents are varied through the thickness for maximum energy absorption.Glass fiber reinforced polymers (GFRPs) are often used in protective-structural applications due to their high specific stiffness, strength, and energy absorption. During an impact event, GFRP laminates absorb energy at multiple length scales through fiber/matrix interphase debonding, resin plasticity, fiber failure, fabric ply delamination, and overall laminate deformation. Meanwhile, the through-thickness role and energy absorption mechanism of the GFRP going through a penetration event changes from a confined punch shear/crush under hydrostatic compression on the front face to delamination and in-plane tension failure in the layers near the back face. Traditional composite panels use a single fabric/sizing and resin which are not optimized for the different energy absorption mechanisms at the different phases of impact and penetration. This indicates a potential opportunity to improve the impact performance of GFRPs by functionally grading the constituents through-thickness of the laminate to optimize the specific properties of the constituents during to improve penetration resistance. In this study, a 1.8 cm thick functionally graded (FGM) composite was designed using the depth of penetration tests to select the strike face material system and a thin laminate ballistic perforation test for the back side material selection. Two commercially available S-2 glass fabrics, an 814 g/m2 plain weave with a 463 sizing and a 302 g/m2 8-harness satin fabric with 933 sizing, were tested with low and medium yield strength epoxy resins. The medium yield strength is the baseline