Polymer foams have shown promise as a core material for sandwich structures due to their high energy absorption capabilities, especially in the case of impact loading. Sandwich structures are widely used in marine structures and are subjected to impact loading such as those experienced under hull slamming conditions. There are few studies on the effect of defects on the tensile strength and fracture toughness of foams in the case of defects greater than the size of the cell. In the present work, an experimental study was performed to investigate the fracture behavior of foam core with sharp cracks under quasi-static and dynamic loading. The core materials used in the present study were Corecell A series styrene foams. Three-point bend experiments (ASTM standard E399) were performed using a screw-driven machine under displacement control for quasi-static loading. A split Hopkinson bar was used to conduct dynamic fracture experiments on the foams using a specially designed three point bend fixture and polycarbonate bars were used to measure the load. The critical stress intensity factor (fracture toughness) KIc was calculated from the critical load and the shape function using the principles of linear elastic fracture mechanics. The local strain fields near the crack-tip were determined using the digital image correlation (DIC) technique. The dependence of the fracture toughness of the foams as a function of density and loading rate has been determined over a wide range of loading rates. The local strain field measurements and the microstructure provided insights concerning the fracture toughness of the sandwich core foams.
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