Forming potential of low-density laminates

Abstract

Metal/polymer/metal sandwich laminates show a rising rate in a variety of applications, for instance in automotive and aircraft industry. Due to the dissimilarity between the metal skin sheets and the polymer core, characterizing the forming potential of such laminates is a necessity. In this study, steel skin sheets and polypropylene-polyethylene copolymer as core sheet – called sandwich laminates - were used. They were produced in a roll bonding process using an adhesive agent. One major research point in IMET is investigating the effect of core and skin thicknesses on the forming behavior and mechanical properties of the sandwich laminates. Forming behavior is evaluated using deep drawing in addition to determining the forming limit curves (FLC). Bonding strength is evaluated by lap shear tests. More-over, the durability of the steel/polymer joints are evaluated under hydrothermal ageing conditions following heating/cooling regime cycles. Basically, the mechanical properties were determined using tensile testing. The adhesion test results show good adhesion strength and a cohesive failure mode. The lap shear strength after ageing shows no remarkable deterioration. The deep drawability of the sandwich laminates depends on the thicknesses of the layers and their volume fraction. With increasing the core thickness, the limiting drawing ratio (LDR) decreases and the probability of wrinkling in the flange area and cracking is higher as well. In case of different skin thicknesses in one sandwich, the best setting condition is to position the thinner skin in contact with the forming tool (punch) if acceptable by design.