Stretch bending - the plane within the sheet where strains reach the forming limit curve

IDDRG2016 conference on "Challenges in Forming High-Strength Sheets".

Neuhauser, F.M.^1,2 ; Terrazas, O.R.^1 ; Manopulo, N.^2 ; Hora, P.^2 ; Van Tyne, C.J.^1

Advanced Steel Processing and Products Research Center, Colorado School of Mines, 920 15th St, Golden

CO

80401, United States^1

Institut für Virtuelle Produktion, Department of Mechanical and Process Engineering, Swiss Federal Institute of Technology, ETH Zurich, Tannenstrasse 3, Zurich

8092, Switzerland^2

关键词: Analytical analysis;    Angular stretch bend tests;    Concave surface;    Dual-phase steel;    Experimental test;    Forming limit curve;    Primary objective;    Stretch-bending;   

Others  :  https://iopscience.iop.org/article/10.1088/1757-899X/159/1/012011/pdf
DOI  :  10.1088/1757-899X/159/1/012011

来源: IOP

【 摘 要 】

Finite element analysis (FEA) was used to model the angular stretch bend test, where a strip of sheet metal is locked at both ends and a tool with a radius stretches and bends the center of the strip until failure. The FEA program used in the study was Abaqus. The FEA model was verified by experimental work using a dual phase steel (DP600) and with a simplified analytical analysis. The FEA model was used to simulate the experimental test for various frictional conditions and various radii of an upward moving tool. The primary objective of the study was to evaluate the concave-side rule, which states that during stretch bending the forming limit occurs when the strains on the concave surface plane of the bent sheet (i.e. bottom plane) reach the forming limit curve (FLC). The verification with experimental data indicates that the FEA model represents the process very well. Only conditions where failure occurred on or near the tooling are included in the results. The FEA simulations showed that the actual forming limit of the sheet occurs when the strains on the bottom plane of the sheet (i.e. concave side of the bend) reach the forming limit curve for high friction and small tool radii. For lower friction and for larger tool radii the actual forming limit occurs when strains on other planes in the sheet (i.e. mid planes or top surface plane) reach the forming limit curve. The implications of these results suggest that care must be taken in assessing forming operations when both stretch and bending occur. Although it is known that the FLC cannot predict the forming limit for small bend radii, the common assumption that the forming limit occurs when the strains for the middle thickness plane of the sheet reach the forming limit curve or that the concave side rule is often made. Understanding the limits of this assumption needs to be carefully and critically evaluated.