The Mechanical Response of a Hybrid Foam Glass-Epoxy Composite Corrugated Cellular Structure Sandwich Panel

Abstract

The mechanical response of a novel hybrid glass-fiber composite corrugated cellular structure sandwich panel when subjected to out-of-plane compressive loading is investigated to evaluate the structure's potential adaptation into vehicle armor. Inspired by the persistent military need to develop effective, lightweight armor for vehicle protection against buried Improvised Explosive Devices (IEDs), this study provides a detailed analysis of the compressive response of the hybrid corrugated sandwich structure under quasi-static and dynamic loading.The through-thickness (out-of-plane) compressive strength, stiffness, densification strain, and energy absorption of the core is measured through quasi-static loading, along with peak failure strengths and impulse mitigation under dynamic compression and high explosive sand blast loading. The goal is to identify and characterize the quasi-static response of this novel hybrid composite corrugated sandwich panel core, core struts, and associated constitutive materials through empirical testing, develop quasi-static analytic predictions for the strength and modulus of the core and core struts, and finally, empirically investigate the dynamic strength and impulse mitigation performance along with the associated dynamic failure mechanisms. A vehicle armor must be able to provide through-structure pressure reduction and impulse mitigation.The hybrid composite corrugated sandwich panel concept is the first all-inclusive, singlestep infused composite sandwich panel ever to be manufactured. Constructed using a delamination resistant, three dimensionally (3D) woven fiber architecture, E-glass is used to construct a corrugated core with struts oriented at 60° (from the horizontal) and a stronger S2-glass is used for the facesheets. Divinycell H130 PVC foam is used to support the fiber structure in the corrugated pattern during infusion and provide a foam-strut stabilization to increase the compressive strength. A modified-Vacuum Assisted Resin Transfer Molding (VARTM) process was used in conjunction with a novel pressure differential technique created to construct core struts with fiber volume fraction ranging from 30-60% . Compressive strut failure was observed to be governed by Euler buckling at low strut slenderness ratios (t/l ≤ 0.07) and completely transitioned to plastic microbuckling at higher ratios (t/l ≥ 0.14). For low fiber volume fraction struts, υ f ≈ 35%, strengths ranged from 85-125 MPa while for high fiber fraction struts, υ f ≈ 56%, strengths ranged from 100-275 MPa. The elastic modulus relation was approximately linear to iii the fiber volume fraction ranging from 12-25 GPa. Negligible differences in the strength and modulus of the E-glass and S2-glass composite struts under compressive loading were observed, revealing a significant factor in material choice for glass based composites used in compressive design. Struts failing by plastic microbuckling were hypothesized to be largely influenced by the matrix shear strength and the initial average fiber tow ...