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Experimental study on residual stresses in press-braked advanced high-strength cold-formed steel lipped angles by sectioning method
Abstract
The rapid advancement of metallurgy during the past two decades has resulted in a new family of steel known as advanced high-strength steel (AHSS) that has a unique microstructure which enables unprecedented combinations of strength and ductility. The material properties and behavior of the AHSS structural members must be quantified to bring AHSS to the construction industry. This includes the residual stresses induced in the structural member due to the cold-forming process. The quantification of residual stresses, including the magnitude and distribution, is necessary to determine the impact of residual stress on the strength and stability of AHSS structural members. One method to measure residual stresses is the sectioning method, which is a destructive method where the cross-section is cut into strips and the measured change in strain after sectioning is converted to residual stress. Existing experimental studies quantified the residual stress of conventional cold-formed steel, but studies of residual stresses in high-strength cold-formed steel are limited. In this study, a series of residual stress experimental measurements of press-braked AHSS lipped angles using the sectioning method was conducted. The angles were formed from a 1.8-mm thick dual-phase steel sheet with a nominal yield strength of 580 MPa and a nominal ultimate strength of 980 MPa. The outer-to-outer lengths are 63.5-mm (2.5-inch) for the legs and 25.4-mm (1.0-inch) for the lips. Strains at the cross-section corners, legs, and lips on both inner and outer surfaces along the sheet coiling direction were measured by electrical strain gages and were used to calculate the residual stresses. The effect of the corner radius on the residual stresses was investigated, which included two inner corner radii (1.98-mm and 3.57-mm, or 5/64-inch and 9/64-inch). The results were compared to previous measurements of non-lipped press-braked AHSS angles.