Compressive and Bending Resistance of the Thin-Walled Hat Section Beam with Strengthened Ridgelines

To overcome some drawbacks of using UHSS (Ultra High Strength Steel) in vehicle weight reduction, like spot weld HAZ (Heat Affected Zone) softening, hard machining and brittleness, a new solution of ultra-high stress strengthening was proposed and applied to the ridgelines of thin-walled structures in this paper. Firstly, stress distribution characteristics, the laws of stress variation and the compressed plate buckling process of the rectangular thin-walled beam under compressive and bending load were analyzed in elastic plastic stage by theory and Finite Element (FE) simulation. Secondly, based on elastic plastic buckling theory of the compressed plate and stress distribution similarity of the buckling process of the thin-walled box structure, three factors influencing the ultimate resistance enhancement of thin-walled hat section beam were found, and the rationality and accuracy of cross section ultimate resistance prediction formulas were also verified by FE simulation. Finally, compared with the bending and compressive resistance of the original thin-walled hat section beam, it shows that the bending and compressive resistance of the same thin-walled hat section beam was improved significantly by two ultra-high stress strengthened ridgelines. This strengthening method not only improves the bending and compressive resistance of the hat section beam by over 70%, but also enhances its bending fracture resistance durability by nearly two times. Obviously, it provides an excellent technology choice for designing thin-walled parts subjected to compressive and bending loads in vehicle body structure.