Theoretical extension of elastic-perfectly plastic deformation length in roll forming of a channel section

In this paper, the Young’s modulus and the yield strength of the strip are considered in order to modify the deformation length analysis proposed by Bhattacharyya et al. New analytical equations are developed assuming an elastic-perfectly plastic material behaviour and the deformation length analysed for the simple case of roll forming a U-channel; the analytical results are verified by comparison with experimental data found in the literature. The proposed elastic-plastic deformation length is shorter than Bhattacharyya’s which is rigid-perfectly plastic. It is observed that the influence of elastic properties on the deformation length is not as significant as the plastic properties; however, the authors believe that the elastic effects become more important under conditions where a major area of the strip is under elastic deformation such as when the flange length is long

Flange Wrinkling in Flexible Roll Forming Process

AbstractFlexible roll forming is an advanced sheet metal forming process for producing variable cross section profiles. Flange wrinkling at the transition zone where the cross section changes is a major defect in the flexible roll forming process. In this paper, the flange wrinkling at the transition zone is studied using finite element analysis. The results showed that the strip deformation at the transition zone can be considered as a combination of two strip deformations observed in the conventional roll forming process and the flanging process. According to finite element analysis results, when the flange wrinkling occurs, compressive longitudinal strain is smaller than the necessary compressive longitudinal strain calculated by mathematical modeling to obtain the intended profile geometry in the compression zone. Therefore, comparison of compressive longitudinal strain obtained from the finite element analysis and the necessary compressive longitudinal strain is a good criterion to predict the flange wrinkling occurrence. A flexible roll forming setup was developed. Longitudinal strain history is obtained from the finite element simulation and is compared with the experimental data from the flexible roll forming setup. Results show a good agreement and confirm the finite element analysis

Analytical Investigating of the Pattern of Yielding Initiation for a Rotating Hallow FGM Cylinder

In this paper, the effect of radii ratio and material exponent parameters on the pattern of yielding initiation for a rotating hollow FGM cylinder is analytically investigated. The analysis is based on small deformation theory in plane-strain state and Tresca criterion has been used for yielding investigating. Assuming power-law functions for Young's modulus, density and yield stress, equilibrium equation has been analytically solved. Comparing with homogeneous cylinder and also the special case of zero exponents of density and yield stress, the presented analysis has been validated. Then the effect of radii ratio and exponent parameters on the order of stress components and yielding initiation is investigated. The results show that density and yield stress variation may have considerable effect on yielding of rotating FGM cylinder. To best knowledge of authors, the effect of density and yield stress variation and radii ratio on the yielding initiation pattern of rotating hollow FGM cylinder was not studied in the previously published researches