Abstract: Flow stress in cold bulk metal forming has been getting more and more important because of the advances in finite element simulation techniques. It is not simple, compared to hot bulk metal forming, because of the problem at the large strain of over 2.0. It is coupled with strain rate and temperature as well as strain, even though their effects are neglected in most cases for practical application to common cases. However, the problem gets serious when we are interested in the engineering for cold working of difficult-to-form or high strength materials. In this paper, we emphasize the importance of accurate description of flow behaviors at the room temperature in terms of strain, damage, strain rate and temperature for preventing the failure cases occurring especially in cold forging [1]. Then, we conduct literature survey covering the experimental and numerical ways [2, 3, 5] of describing the flow stress and coupling it with strain rate and temperature. An advancement direction is proposed to enhance the practicability.

References:
1. J. G. Eom, Y. H. Son, S. W. Jeong, S. T. Ahn, S. M. Jang, D. J. Yoon, M. S. Joun, 2014, Effect of strain hardening capability on plastic deformation behaviors of material during metal forming, Mater. Design., V. 54, 1010-1018.
2. Joun MS, Eom JG, Lee MC. 2008, A new method of acquiring true stress-strain curves over a large range of strains using a tensile test and finite element method. Mech Mater. V. 40, pp. 586-593.
3. Eom JG, Chung WJ, Joun MS. 2014, Comparison of rigid-plastic and elastoplastic finite element predictions of a tensile test of cylindrical specimens. Key Eng Mater, V. 622-623, pp. 611–616.
4. M. S. Kim, B. J. Gu, S. M Hong, Determination of post-necking stress-strain relationship for zirconium low-oxidation based on actual cross-section measurements by DIC, J. Mech. Sci. Tech., V. 34, pp. 4211-4217.

Biography: Dr. ManSoo Joun is a Professor of Gyeongsang National University (GNU) in South Korea. He graduated from Seoul National University for his bachelor degree, from Korea Advanced Institute of Science and Technology (KAIST) for his master degree, and from Pohang University of Science and Technology (POSTECH) for his Ph.D. degree. His Ph.D. thesis topic was the optimal die shape design in extrusion or drawing, which is the first application example of finite-element based optimal design of die-shape or process conditions in bulk metal forming. After his Ph.D., he has developed and commercialized a general-purpose metal forming simulator called AFDEX, which is competitive in terms of solution accuracy and user-friendliness as an Altair APA software. He has constructed international cooperative network based on the AFDEX, involving ALTAIR (USA/Global), JSOL(Japan), BRIMET(China), ARAI/DHIO(India), MARii/UiTM(Malaysia), UNAM(Mexico), etc. and has organized MFCAE (Metal Forming CAE) for 23 years and GISPAM (GNU International Summer Program of AFDEX for the State of Mexico) for 6 years. He had been in charge of Technology Innovation Center (TIC) of GNU for 18 years, which is the only TIC specialized at metal forming and powder forging in South Korea.