Numerical and Experimental Investigation of Residual Stresses in Cold Formed Truck Frame Rail Sections

Cold formed carbon steel C sections are often employed as load carrying structural members in heavy commercial trucks. The cold forming operations employed during the making of these members generate certain amount of residual stresses throughout the sections. As the residual stresses play a significant role in determining the structural behavior of truck frame rail members, a careful assessment of residual stresses resulting from cold forming operation is needed. In the present investigation, residual stresses in frame rail corner sections were numerically predicted with the help of non-linear Finite Element (FE) analysis in ABAQUS and compared with the experimentally measured residual stress values using X-ray diffraction technique. It has been observed that the numerically predicted residual stresses are in agreement with the experimentally measured residual stresses in forming direction. In the direction perpendicular to forming, while the trends of numerical and experimental residual stresses were observed to follow the same pattern, some deviation in stress values were observed in the inner half of the corner sections. The deviation in residual stress values are mainly due to the effect of steel sheets undergoing coiling-uncoiling processes prior to forming operation, which is not considered as part of numerical analysis; whereas the coiling-uncoiling residual stresses are inherited in experimentally measured residual stresses. The measured residual stresses along with corresponding equivalent plastic strains and virgin material properties in terms of stress-strain relationships can be considered as initial conditions in numerical models for further fatigue life analysis of truck frame rail structures.