Investigation of Residual Stresses in Cold-Formed Steel Sections with Nonlinear Strain-Hardened Material Model

In this article, forming residual stresses in cold-formed small-radius corner sections are analytically predicted with the consideration of the shift in the neutral axis and the nonlinear strain-hardened material model. The predicted forming stress results in the transverse direction show a trend of increased compressive residual stress in the outer surface and reduced tensile residual stress in the inner surface, as the corner radius-to-thickness ratio increases in small-radius bends. In the longitudinal direction, there is no significant change in the residual stress values observed in the inner and outer surfaces with respect to an increase in corner radius-to-thickness ratios. But a considerable decrease in compressive residual stress and an increase in tensile stress values are observed in the midsection areas, with an increase in the corner radius-to-thickness ratio. It is observed that the analytical peak compressive residual stress values are always higher than the experimental results. Also, the through-thickness residual stress from the numerical model is in close agreement with the analytical results. The magnitude of the maximum compressive stress in the inner half thickness is observed to be more than the magnitude of the maximum tensile stress in the outer half thickness of the corner section. The shift in the neutral axis towards the inner corner surface is much severe for lower corner radius-to-thickness ratio sections. The new approach provides a more accurate definition of initial conditions for further nonlinear structural behavior analysis of cold-formed structures.