Investigation of Manufacturing Residual Stresses in Cold Formed Truck Frame Rail Sections

摘要

Series of manufacturing processes such as coiling-uncoiling, cold forming and hole cutting processes involved in the making of truck frame rail sections leave certain amount of manufacturing imperfections into the frame rail. As the manufacturing imperfections in the form of residual stresses play a significant role in determining the dynamic structural behavior of truck frame rail members, a careful assessment of residual stresses resulting from coiling-uncoiling and cold forming processes is needed. In the present investigation, non-linear Finite Element (FE) simulation of coiling-uncoiling and cold forming processes were carried out and the resulting residual stresses in frame rail corner, flat web and flange sections were compared with the experimentally measured residual stress values using X-ray diffraction technique. It is observed that in corner sections, the numerically predicted residual stresses are in close agreement with the experimentally measured residual stresses in forming (transverse) direction. In the direction perpendicular to forming (longitudinal direction), while the trends of numerical and experimental residual stresses are observed to follow the same pattern, some deviation in stress values are observed in the inner half of the corner sections. As the coiling-uncoiling process is the main cause for the residual stress presence in flat web and flange sections, the computed coiling-uncoiling residual stresses in longitudinal directions are compared with experimentally measured residual stresses in frame web sections and the trends are observed to be in good agreement. Whereas the magnitudes of coiling-uncoiling residual stresses in transverse direction are found to be very low and considered to be insignificant for the comparative analysis. These residual stresses along with corresponding equivalent plastic strains and virgin material properties in terms of stress-strain relationships can be considered as initial conditions for the accurate prediction of truck frame rail fatigue behavior.