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Numerical study on residual stresses in press-braked advanced high-strength cold-formed steel angles by finite element simulation
Abstract
Cold-formed steel is widely used in structural framing for its beneficial high strength-to-weight ratio, recyclability, and for convenient transportation and construction. 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 un- precedented 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. The cold-forming process, such as press-braking, induces residual stresses which affect the strength and stability behavior of the structural members. Existing numerical studies quan- tified the residual stress of conventional cold-formed steel, but studies of residual stresses in high-strength cold-formed steel are limited. This paper develops computational models to simulate the press-brake process of cold-formed AHSS sections and investigates their residual stress distribution through the simulation. The results are validated with recently conducted experimental studies. Numerical modeling of the press-braking process on AHSS angles by the finite element method was conducted. The model incorporated the residual stresses induced by coiling and uncoiling before the press-braking opera- tion was performed. Lipped angles were studied where the angles were press-braked 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. Two different inner corner radii, 1.98-mm and 3.57-mm (5/64-inch and 9/64-inch), were investigated. Stresses at the cross-section corners, legs, and lips on both inner and outer surfaces along the sheet coiling direction were extracted from the analysis results. The stress data from the simulation was validated with its counterparts from a series of experimental measurements using the sectioning method, which are presented in a companion paper.