Experimental and Numerical Investigations of the Bending Characteristics of Laminated Steel

Laminated steel, as studied in this work, is a sheet metal product that consists of two steel sheets with a relatively thin polymer layer between them. It has been developed for applications requiring sound and vibration damping. The objective of the study concerns bending operations, in particular how tooling and sheet geometry, material properties, and process parameters affect the shape and integrity of formed parts. Two cases are being considered: wipe bending and draw bending. Investigation of each case has experimental and numerical components, the latter using the finite element method.Because of the particular construction of laminated steel, bending can involve some issues that are not of concern when bending solid steel sheet. In wipe bending an undesirable, permanent curl is present upon completion of the operation, while in draw bending the shape of the part and the state of the polymer layer are of concern. Therefore, it was important to establish how the geometry and material state after bending depend on the process parameters. Experimentally, it was necessary to design and build a set-up for each type of bending that had the required flexibility to change tooling parameters. Numerically, the problem is highly nonlinear because it involves large deformations in the steel sheets and the polymer layer as well as nonlinear material models for both. In addition, for draw bending the loading is complicated by factors such as localized deformations under the draw beads and the sliding motion of the sheet with respect to the tooling, which introduce loading/unloading cycles. Modeling of the mechanical response of the polymer layer was particularly challenging, but appropriate models have been implemented that give reasonable comparisons between experimental measurements and numerical results. In addition, parametric studies have shown how the curl and state of the polymer layer depend on various parameters that are not easily varied in the experiments.This work presents and explains the mechanics of bending laminated steel. It is anticipated that the results can be used to improve processing of this material during bending operations.