Performance of tailored joints in discontinuous ceramic cored sandwich structures

Stephens, Jonathan
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University of Delaware
Composite sandwich structures with discontinuous ceramic tile cores offer a unique combination of structural and penetration resistance at minimum weight. Panels of these materials are often bolted to vehicles to provide soldier protection. Design guidelines and durability of bolted attachments in static and fatigue loadings are not well understood. In this study, Discontinuous Ceramic Cored Sandwich Structures, comprised of S2-Glass/epoxy composite face sheets bonded to a ceramic tile core are fabricated and tested to understand the complexities of stress distribution and load transfer between materials and the stress concentrations and failure modes in the bolted connections. Static testing of the composite structure with and without bolted joints provides insight into failure modes and joint capacity. Fatigue testing provides insight into long term durability as measured by stiffness loss, residual strength and change in failure modes. Previous testing has been performed to study the in-plane stresses and failure modes due to tensile loading with pinned joints. This study examines the effect of bolt torque through static loading and quantifying the changes in failure progression and load capacity. Data provided from these tests allow for fatigue parameters to be established in order to examine stiffness loss and joint sensitivity to fatigue loading. Stress relaxation testing is performed on each of the DCCS constituents to estimate the magnitude of clamp load loss due to mechanical features in the joint and viscoelastic properties of the DCCS Structure. The information gathered from these experiments is used as an integral part of the design process to create a more structurally efficient, durable bolted joint for this composite structure.