A New Method for Correcting the Stress-Strain Curves after Bulging in Metals

Document Type: Original Article

Authors

1 Mechanical Engineering Department, Hamedan Branch, Islamic Azad University, Hamedan, Iran.

2 Department of Computer Science, South Tehran Branch, Islamic Azad University, Tehran, Iran.

Abstract

True stress-strain curve has a basic role in the analysis of deformation in theoretical plasticity and numerical simulations. Because of the triaxial state of stresses in the necking or bulging zones, in tension and the compression tests respectively, the true stress-strain curves obtained from relationsare no longer valid and must be corrected. Various correction techniques have been proposed and can be found in literatures. In this study, a new semi-analytical approach 
for correction of the stress-strain curve in compression test for circular cross-section specimens was introduced and a relation for the correction factor was derived based on the theory of plasticity. This relation requires only a few experimental surface strain measurements which can easily be done using an image processing technique. The correction factor formula was obtained in terms of the initial radius of specimen, the bulge radius, and the surface strain on the bulge surface. The proposed approach in this study was compared with the results of the numerical simulations. Simulation was used to correct the stress-strain curve based on the optimization method with comparing the bulging profile of tested samples and ones simulated by using genetic algorithm. 

Keywords


[1] G.H. Majzoobi, F. Fariba, M.K. Pipelzadeh, S. Hardy, A new approach for the correction of the stress-strain curves after necking in metals, J. Strain. Analysis., 13 (2014) 253-266.
[2] F. Barati, S. Kazemi, Modeling flow stress compressive curves of AZ71 Magnesium alloy at high temperature and various strain rates, J. Science and Today World., 3 (2014) 72-74.
[3] P.W. Bridgeman, The stress distribution at the neck of a tension specimen, Trans. Amer. Soc. Metal, 32 (1944) 553-574.
[4] E. Siebel, A. Pomp, Determination of flow stress and friction with the upsetting test. Mitt. KWI, 9 (1927) 157-171.
[5] Kocaker, B, Production properties prediction after forming process sequence, MSc Thesis. Turkey: Middle East Technical University; 2003.
[6] Y. Sato, Y. Takeyama, An extrapolation method for obtaining stress-strain curves at high rates of strain in uniaxial compression, Tech. Rep. Tohoku. Univ., 44 (1980), 287-302.
[7] E. Parteder, R. B¨unten, Determintion of flow curve by means of a compression test under sticking friction condition using an iterative finite- element procedure, J. Mater. Process. Tech., 74 (1998) 227-223.
[8] G.H. Majzoobi, F. Fres, Determination of material parameter under dynamic loading part I: Experiments and simulation, J. Comp. Mater., 49 (2010) 192-200.
[9] G.H. Majzoobi, R. Bagheri, J. Payandeh-Peyman, Determination of material parameter under dynamic loading part II, Optimization, J. Comp. Mater. Sci., 49 (2010) 201-208.
[10] O. Etttouny, D. Ehardt, A method for in-process failure prediction in cold upset firging, J of engineering and industrial, 105 (1983) 161-167.
[11] ASTM, E8. Standard methods of tension testing of metallic materials, Annual book of ASTM standard. American society for testing and materials. 3.01.