Prediction of residual stresses in cold formed corners

Abstract

This paper presents the investigation of residual stresses on the corners of cold formed high strength structural steel members. In order to achieve magnitude of residual stresses at inside corner of cold bent section, two-dimensional nonlinear finite element analyses (FEA) have been performed by simulating the press-braking process in Ansys software. These simulations were performed by defining material properties of two types of structural steels i.e. S355 and S650 while plate thickness of 5 mm and 10 mm has been used. During the analyses, ro/t ratio of 4, 5, 6 and 7 for 5 mm plate thickness and ro/t ratio of 6, 7 and 8 for 10 mm plate thickness with bent angle of 1100, 1000, 900, 800 and 700 have been maintained. As a result of theses analyses, the tension residual stresses obtained on the middle of the inside surface of the bend range from 60% to 92% of the yield strength of the material. These FE-simulations do not only provide the magnitude of residual stresses but also give a zig-zag type residual stress distribution pattern through the plate thickness. These results were then compared to the values predicted by equations proposed by Dat in 1980 which were found in good agreement.