High velocity impact of Dyneema laminates of varying size
Date
2014
Authors
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Publisher
University of Delaware
Abstract
This research focuses on the high velocity impact response of Dyneema HB-26 panels consisting of a unidirectional UHMWPE fiber reinforced polyurethane matrix in a cross-ply laminate. During high velocity impact by a penetrator, significant energy absorption occurs through various deformation mechanisms related to penetration, delamination, and tensile failure of the layers that undergo large transverse deformation and often extends to the panel boundaries. The influence of panel size on ballistic resistance and associated damages studied for a range of areal densities. The test matrix consisted of impacting 1.5 and 2.5 psf laminates with panel dimensions of 24x24 inches, 14x14 inches, 8x8 inches with a hardened steel 30 caliber fragment simulation projectile. The V50 or ballistic limit was calculated for each combination of areal density and panel size. Ballistic limit was found to increase approximately 50% with areal density for all panel sizes. Ballistic limit was also found to increase approximately 6-8% as panel size decreased from 24 x 24 inches to 8 x 8 inch for both areal densities. Detailed damage analysis included measuring the panel transverse back-surface deflection during impact, C-scan analysis to determine size and shape of delamination patterns, cross sectioning of the panels to show through thickness damage mechanisms, and SEM imaging to show fiber-matrix level failure modes. Characteristic damage consisted of a center hole at the point of impact surrounded by circular pattern of delamination with four localized and orthogonal strip delamination oriented in the fiber direction extending outward. The back surface deflection formed a cone with a characteristic angle. The damage analysis of the various panel sizes showed that the strip delaminations in the primary fiber direction reached the free edges in the smallest panels. In these panels, material undergoes localized deformation through edge pull in which dissipated additional energy through frictional sliding between layers. This also resulted in larger back surface deflections during impact that slowed the projectile over a longer time and distance and prevented the projectile from fully perforating the material. This effect was most prevalent in the smallest and thickest panels (i.e. 8x8inch/ 2.5 psf panels).