The Response of Sandwich Panels with Rigid Polyurethane Foam Cores under Flexural Loading.

An experimental study is undertaken to investigate and optimize the processing conditions in the fabrication of the sandwich structures designed for flexural load bearing applications. Sandwich beams with two glass/epoxy faces and a rigid polyurethane foam core were constructed under four different processing conditions. Wet and dry faces were applied at two temperatures to attain these four conditions. It has been shown that in comparison with the first processing condition (wet at 25°C) the specific flexural strength of the second one (dry at 25°C), third one (dry at 70°C) and fourth one (dry at 70°C with a thin layer of an adhesive) are increased 38%, 209% and 267%, respectively. The reason behind this significant enhancement is demonstrated to be related to the debond strength of the core-face interface. It has been demonstrated that the debond strength of the core-face and core plays an important role in enhancing the flexural rigidity and controlling of the failure mechanisms. If the core material be polymeric foam, the core and debonding strengths at the core-face interface will almost entirely dictate the structural sandwich composite performance especially under flexture. Results showed that the core strength decreases, but the debonding strength of the core-face interface increases with the increment of the processing temperature during the preparation of the rigid polyurethane foam core. We also observed that with increasing the debonding strength of the core-face interface, the failure mode changes from debonding of the core-face interface to the failure of the face. Finally, the sandwich structures were obtained with the excellent performance under flexural loading.