In many sheet metal forming processes the sheet material undergoes a series of bending-unbending cycles as it flows over tool radii. In order to numerically predict the outcome of such forming processes and in particular the shape of the part after springback, it is necessary to use a constitutive model that is able to accurately reproduce the cyclic behaviour of the sheet metal. Indeed, the loading history has a significant effect on the springback response of the formed part and the prediction of springback after a stamping operation will only be accurate if the cyclic work hardening behaviour of the sheet material is correctly described by the constitutive model. Therefore it is necessary to experimentally characterize the cyclic behaviour of sheet materials up to large strain amplitudes. A new testing fixture was designed to cyclically load sheet specimens in simple shear. The design of the corresponding sheet specimen was optimized using finite element simulations of the shear test. Both the fixture and test specimens were then fabricated, and a series of tests was conducted. The strain distribution and the strain history in the gauge region of the test specimens were measured with an ARAMIS optical strain measurement system, and cyclic stress-strain data were successfully obtained for four grades of automotive sheet steel (HSLA, DP600, DP980 and TRIP780).
|Keywords:||Sheet Metal Forming Processes, Advanced High Strength Steels, Springback, Cyclic Shear Tests, Digital Image Correlation System, Shear Strain, Cyclic Stress-Strain Curves|
M.A.Sc. Candidate, Department of Mechanical, Automotive and Materials Engineering, University of Windsor, Windsor, Canada
Professor, Department of Mechanical, Automotive and Materials Engineering, University of Windsor, Windsor, Canada
Experiential Learning Specialist, Department of Mechanical, Automotive and Materials Engineering, University of Windsor, Windsor, Canada