The effect of pre-strain on the material behaviour and the Bauschinger effect in the bending of hot rolled and aged steel

Compression and bend tests were performed on an annealed and aged carbon steel that had been pre-strained by different amounts. A bending model was developed to analyse the bending response of the material. While the bending test results agreed well with some of the material trends found in previous studies focusing on the Bauschinger effect, an overly high reduction of the bending yield with pre-strain was observed. Calculation of the moment curvature diagram for the pre-strained material based on the tensile and compression test data using the analytical model did not fit the experimental curve. In the control of yield phenomena by the industrial processes of temper rolling, skin passing, tension levelling and roller levelling, the effectiveness of the treatment is usually judged from tensile testing after treatment. However, the present work shows that where the yield phenomena have been removed by pre-processing, that the tensile test will not predict the subsequent bending behaviour and that the bending test may provide greater insight. This may have important consequences in the study of cold roll forming where shape defects in the product are believed to originate from small strain forward and reverse bending deformations that will be strongly affected by the Bauschinger and yield effects.