Investigations on Delamination Behavior of Sandwich Sheets

Steel/polymer/steel (sandwich) sheets show several advantages in comparison to monolithic materials when strength, stiffness and damping characteristics are set to an optimum. Although the mechanical properties of sandwich sheets were improved over the last years, the application of such hybrid materials in the automotive industry is not very well-established due to insufficient knowledge about forming characteristics. However, it is difficult to detect the delamination during the forming process between the interlayer and the cover sheet. Delamination is defined as a separation between the polymer interlayer and the metal sheet while both of the layers remain in physical contact. After occurrence of failure, the two interlayers are still bonded and stick together because of weak Van-der-Waals forces (kissing bonds), which makes it difficult to detect any separation or delamination. In this paper, fundamental multi-axial testing methods for the detection of delamination in sheet metal forming are introduced and discussed.