This article presents a new understanding on the deformation mechanics of flexible roll forming and is focused on the occurrence of flange wrinkling. The presentation draws from the experimental and numerical simulation of flexible roll forming to the determination of the wrinkling limits by means of a new theoretical and experimental methodology based on the utilization of rectangular test specimens loaded in axial compression. This research work is performed in mild steel sheets and the results show that the combined evolution of the effective strain with stress triaxiality obtained from finite element modelling of flexible roll forming and from the rectangular test specimens loaded in axial compression can be successfully utilized to predict the occurrence of flange wrinkling in variable cross-sectional profiles produced by flexible roll forming. The proposed methodology can, therefore, be considered an alternative to existing approaches based on simplified analytical and numerical procedures.
Semi-crystalline thermoplastic-based composite laminates and fiber metal laminates have a narrow forming temperature window, which limits formability of these products. The intention of this study was investigation of nonmelting amorphous polyvinyl chloride as a proper matrix to increase the formability and forming temperature window of these products. For this, [45/−45] and [0/90] layups of polyvinyl chloride-based composite laminates and fiber metal laminates were produced using the film-stacking procedure and later press formed into channel sections at six temperatures in the range of 80 to 200°C. The effects of the layups and forming temperatures on the forming loads and spring back of the formed profiles were measured, and their effects on the fiber buckling, wrinkling, and delamination of the profiles were evaluated using optical microscope images. The effects of layups and forming temperatures on the deformation mechanisms were also analyzed using the grid strain analysis method. Of the fiber metal laminates, 160°C was found as the minimum forming temperature, and for the composite laminates, 120 and 160°C were found as the minimum proper forming temperatures of [45/−45] and [0/90] layups, respectively. Finally, the forming temperature windows and formability of polyvinyl chloride matrix composite laminates and fiber metal laminates were found higher than semi-crystalline matrices.
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