3D Reinforced Composite Face Sheets and Functionally Graded Polymeric Foam Cores for Blast and Impact Hazard Mitigation

Lightweight sandwich structures are being used in aeronautics, marine, automotive, and offshore structural applications considering their high specific strength and stiffness along with energy absorption features. Sandwich structures comprise of face sheets typically made of aluminum or fiber-reinforced composites bonded to core materials like metallic foams, honeycomb, polymeric foams or balsa wood having a cellular structure. One main limitation of composite material face sheet is the absence of fibers in thickness direction, which greatly reduces damage tolerance and impact resistance. Current research is focused on investigating the dynamic behavior of sandwich structures having composite laminates with 3D reinforcement as face sheets, and various configurations of functionally graded polymeric foam as the core material. Woven carbon/epoxy composite laminate with dense reinforcement of milled fibers in the Z-direction is the chosen candidate face sheet material. A comparison study was performed to assess the dynamic behavior of SupercompositeTM laminates with dense reinforcement in the Z-direction. ROHACELL® HERO (from Evonik) foam with three different density variations were used to assemble various configurations of functionally graded cores for optimizing the energy absorption in sandwich structures. Response of the functionally graded core material under dynamic compression was evaluated at various strain-rates with forward impact tests performed on a modified Split Hopkinson Pressure Bar (SHPB) from REL. Dynamic behavior of face sheet materials under transverse compression and blast loads was evaluated with SHPB and a shock tube. Low velocity impact tests were performed on the functionally graded core and face sheets using CEAST 9450 drop weight impact test system. High-speed video imaging and Digital Image Correlation (DIC) techniques were utilized for tracking the side view deformation of sandwich beam specimens and rear surface out-of-plane deflections of laminates. Experimental results of the functionally graded ROHACELL® foam configurations with aluminum face sheets subjected to air blast load were compared with the shock response obtained using computational modeling of sandwich beam specimens in ABAQUS/ EXPLICIT. This research helped in gaining further understanding of the utilization of 3D reinforced composite face sheets and functionally graded polymeric core materials to enhance energy absorption of sandwich structures for blast and impact hazard mitigation