Surface modification for improving the formability of SPA laminated composite

Abstract

The effect of surface modification on the formability of Steel–Polymer–Aluminium (SPA) laminated composites was investigated. Different types of adhesives were used as polymer layer. The layer thickness varied from 0.1 to 0.4 mm. Various surface modification models were designed. The combinations of surface models, adhesive types and layer thickness effects were investigated by both the experimental and numerical methods. The experimental results showed that the formability of SPA laminated composite is improved by surface modification. In addition to this, the effects of layer thickness and adhesive types were also observed. Experimental results were used to construct a numerical model to study the effect of these variables.

Introduction

Adhesive bonding as a method of fabrication has attracted special interest recently, as it offers potential advantage of saving the material costs and simplified manufacturing processes. In enlarging the application of adhesive joints to the mechanical elements, however, there is not enough of the necessary basic data on mechanical properties of adhesive joints [1].

In recent years, automobile manufacturers have seriously considered using Steel–Polymer–Steel (SPS) laminates for automobile parts such as fenders, doors, interior panels and others, because of their superior properties in vibration damping and weight reduction [2], [3]. Although these laminates are produced for both the application fields and are commercially available in the market, they are not used widely because of their uncontrollable geometric distortions during the processes of formation. Therefore, their applications are restricted to structural parts [4].

In order to increase the formability of the laminated Steel–Polymer–Aluminium (SPA) composite, failure mode must be studied well. In the deep drawing of a homogenous sheet, failure of the metal normally follows localised thinning caused by tension in the plane of the sheet surface. In contrast, failure of laminated sheet usually occurs in the relatively weak adhesive or in the metal/adhesive interface, leading to separation or delamination of the laminate long before thinning of the metal sheets [5], [6].

It has already been published [7] that durable and strong adhesion between incompatible can only be achieved by ion beam techniques. Unfortunately, ion beam techniques are unsuitable for metal–polymer–metal applications as its application is impossible to produce laminated composites. Therefore, new approaches are necessary to increase the bonding strength between polymer and metal components [8].

The approach used in this study for increasing mechanical bonding between these incompatible materials is the modification of surfaces of metal layers [9] by means of laser surface processing technique.

The effect of surface modifications on the mechanical properties of SPA was determined by tensile, OSU formability and mixed mode bending (MMB) tests. After finding the mechanical properties, an optimum surface model was decided, and the effect of thickness was then investigated by finite element method (FEM). The modified surface was modelled elasto plastically in l-Deas Software and OSU formability testing simulated. The model was transferred to Ansys program and then run. The results were transferred to l-Deas 2.01 Master Series program for the purpose of postprocessing.