A new approach for the correction of stress-strain curves after necking in metals

作者：Majzoobi Gholam Hossain; Fariba Farzad; Pipelzadeh Mohammad K^*; Hardy Stephen J

来源：The Journal of Strain Analysis for Engineering Design, 2015, 50(2): 125-137.

DOI：10.1177/0309324714555384

• Stress-strain curve
• correction factor
• material model
• image processing
• numerical simulation

The true stress-strain curve has a significant role in the analysis of deformation in theoretical plasticity and numerical simulations. Because of the triaxial state of stress in the neck zone, the relationship that is normally obtained from the engineering stress-strain curve is no longer valid and must be corrected. Various correction techniques have been proposed and can be found in the literature. In this study, a new semi analytical approach for the correction of the stress-strain curve for circular cross-section specimens (axisymmetric) is introduced and a relation for a correction factor is derived based on the theory of plasticity. The relation requires only a few experimental surface strain measurements which can easily be made using an image processing technique. In the new method, the neck zone is divided into a number of thin walled toroidal elements. The algorithm for the correction factor is obtained in terms of the initial specimen radius, the neck radius and the z-strain on the neck surface. In this work, the true stress-strain curve, that is obtained using the image processing, follows a power law trend before the onset of necking and a linear trend after necking. However, the method is not limited by the trend of the stress-strain curve and can accommodate any trend describing the stress-strain relationship. The proposed approach is compared with methods proposed by Bridgman-Leroy, Bridgman, Davidenkov and Spiridonova, Siebel and Schwaigere and also numerical simulations. The number of simplifying assumptions in the present work is less than that of the Bridgman approach and some of the other methods.

• 出版日期2015-2