No abstract

The dynamic out-of-plane compressive response of E-glass composite corrugated sandwich cores have been measured for impact velocities ranging from quasistatic to 175 ms −1 . Laboratory scale sandwich cores of relative densityρ ≈ 33% were manufactured from 3D woven E-glass and stitched to S2-glass face-sheets via a double line of Kevlar yarn. Two variants of the sandwich cores were investigated: sandwich cores with the empty spaces between the corrugations filled with a PVC foam, and unfilled corrugations. The stresses on the rear faces of the dynamically compressed sandwich cores were measured using a direct impact Kolsky bar. The compression tests on both the corrugated cores and the parent strut wall material confirmed that these relatively high relative density corrugated cores failed by microbuckling of the strut wall material under quasistatic loading. Moreover, the foam filling did not have any significant effect on the measured responses. The peak stresses of both the strut wall material and corrugated cores increased approximately linearly with strain rate for applied strain rates less than about 4000 s −1 . This increase was attributed to the strain rate sensitivity of the composite matrix material that stabilised the microbuckling failure mode of the E-glass composite. At higher applied strain rates the response was reasonably rate insensitive with compressive crushing of the glass fibres being the dominant failure mode. A simple model utilising the measured dynamic properties of the strut wall material accurately predicts the measured peak strengths of the filled and unfilled corrugated cores.

Three-dimensionally woven E- and S2-glass fiber textiles have been used in the past to create delamination-resistant corrugated core sandwich panels. During subsequent out-of-plane loading, the E-glass composite core struts and S2-glass composite faces are subjected to either compressive or tension loads. This study has investigated the relationships between the three-dimensional fiber architecture, fiber properties and the mechanical response of representative samples of the core and faces. Using X-ray computed tomography and optical microscopy to characterize the three-dimensional fiber architectures, it is found that the in-plane warp and weft fibers suffer significant off-axis displacement (waviness) due to their interaction with through thickness z-fiber tows. The consequence of this fiber waviness on the relationships of the in-plane tensile and compressive mechanical properties, along with fiber type, fiber volume fraction, and strut aspect ratio are experimentally investigated. The large initial misalignment angle of the warp and weft fiber tows results in a strut compressive strength that is substantially lower than its tensile strength due to compressive failure by either elastic or localized fiber microbuckling. Simple micromechanical models are used to relate the compressive strength of the three-dimensional woven composite struts to strut aspect ratio, fiber volume fractions in the three directions and the three-dimensional fiber architecture.

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 ...