Forming limit diagram (FLD) is an important tool to ascertain if a given sheet metal can be formed into a particular geometry. Formability of sheet metals can be influenced by material variables (microstructure, thickness, etc.) and process variables (strain rate, temperature, etc.). This capability enables measuring sheet formability at different strain rates and temperatures. In addition, modeling approaches have been developed to predict the formability’s strain-rate dependence.
Quasi-static formability is determined using an Interlaken SP150 limiting dome height (LDH) setup with 4-in. diameter hemispherical punch or Marciniak fixture. Test temperatures up to ~350°C are possible. High-rate formability is determined using electrohydraulic forming (EHF) at room temperature, in free-forming mode (i.e., without a die) or inside a conical die. Both quasi-static and high-rate tests are integrated with non-contact strain and strain-rate measurement using digital image correlation (DIC) capable of microsecond time resolution. Materials tested include aluminum (Al) alloys, magnesium (Mg) alloys, and steels. Other materials also can be tested, depending on the application.
Pacific Northwest National Laboratory’s subject matter expertise, together with integrated experiments and modeling, is employed to predict and validate FLD dependence on strain rates, which is unique among U.S. Department of Energy laboratories. Stereo imaging for all tests allows quantitative determination of deformation history in three dimensions, at microsecond time resolution, and for verifying assumptions underlying the FLD. Both individual sheets and tailor-welded blanks have been extensively characterized and studied.
Use typically is coordinated with the capability expert and via collaborative funding proposals or contracts.
Name: Aashish Rohatgi
- Rohatgi, A., Soulami, A., Stephens, E.V., Davies, R.W., Smith, M.T., 2014. An investigation of enhanced formability in AA5182-O Al during high-rate free-forming at room-temperature: Quantification of deformation history. Journal of Materials Processing Technology, 214, pp. 722-732.
- Rohatgi, A., Stephens, E.V., Soulami, A., Davies, R.W., Smith, M.T., 2011. Experimental characterization of sheet metal deformation during electro-hydraulic forming”. Journal of Materials Processing Technology, 211, pp. 1824-1833.
- R.W. Davies, G.J. Grant, H.E. Oliver, M.A. Khaleel, and M.T. Smith, "Forming-limit Diagrams of Aluminum Tailor-welded Blank Weld Material,” Metallurgical and Materials Transactions A, Vol. 32A, Feb. 2001, 275-283.