Formability Prediction and Springback Evaluation of Adhesive-Bonded Steel Sheets

Abstract

The mechanical properties of adhesive were evaluated by two different approaches to predict the formability of adhesive-bonded steel sheets by finite element (FE) simulations. The epoxy adhesive properties were varied by changing the hardener/resin (H/R) ratios. The true stress-strain behaviour of adhesive was evaluated from (i) direct tensile testing of adhesive samples (Approach-1) and (ii) rule of mixtures' concept applicable to adhesive-bonded sheets (Approach-2). The evaluated mechanical properties of adhesive through both the approaches were incorporated during simulation of tensile test and in-plane plane-strain formability test. The forming limit strains of adhesive-bonded sheets were evaluated during predictions by necking criteria, namely thickness gradient necking criterion (TGNC) and effective strain rate ratio based criterion (ESRC), and validated with the experimental limit strains. It is found that the limit strains predicted by both the approaches are moderately accurate with respect to experimental data. There is not much difference in limit strains of adhesive-bonded sheets obtained from Approach-1 and Approach-2. The TGNC shows better prediction as compared to ESRC. Further, the present study investigates the springback of adhesive-bonded sheets during V-bending with the influence of H/R ratio of adhesive, shims, and wire reinforcement. The results show that there is a considerable influence of H/R ratio on springback and about 8-20°reduction depending on the presence or absence of shim. But the wire reinforcement shows insignificant effect on V-bending of adhesive-bonded sheets.

Influence of Adhesion Properties on the Crash Behavior of Steel/Polymer/Steel Sandwich Crashboxes: An Experimental Study

“…This can be attributed to the absence of the steel/polymer interlayer shear strength, which is responsible for achieving and improving stiffness and strength as well as stability (in terms of the springback). This result is in good correlation with those of the literature [9,10]. As a result of the adhesion quality, further phenomena appeared on the structural level, e.g., global buckling instead of the desired progressive folding, as discussed later in Section 3.…”

“…Additionally, the adhesion strength significantly influenced the tensile properties; with good bonding, the rule of mixtures could be applied to estimate those tensile properties [8]. Moreover, the springback angle was reduced under bending by improving the adhesion strength and becomes similar to a monolithic sheet [9]. With improved adhesion properties, the deep-drawability could be enhanced as well [10][11][12].…”