Improving the formability of sandwich sheets by the hydrostatic effect of encapsulated media

Various sandwich structures have been developed as lightweight structures. They have excellent specific stiffness owing to their low density. However, owing to the existence of various failure modes, which are classified into core shear failure, tensile fracture of the face sheet, buckling of the face sheet, and delamination, it is difficult to deform sandwich sheets without any failure. A new forming strategy was proposed in this study. Buckling of the face sheet during drawing was suppressed by filling the encapsulated media in a 3D core between the face sheets to exploit its hydrostatic effect. This process is similar to the freeze-bend method, in which the pipe is filled with ice during bending to suppress wrinkles and flattening. Ice, wax, and low-melting alloys were used as the encapsulated media, and their formability and ease of removal were investigated. Further, a shear strength test was performed on the specimens that were cut out from the drawn products to evaluate failure during forming. Based on these experimental results, the characteristics required for the encapsulated media were summarized.