Modeling serrated flow of SS 316L under dynamic strain aging effect
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Sådhanå (2020)45:217 https://doi.org/10.1007/s12046-020-01456-5
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Modeling serrated flow of SS 316L under dynamic strain aging effect SIDDHARTHA PATRA* , SANKAR DHAR and SANJIB KUMAR ACHARYYA Department of Mechanical Engineering, Jadavpur University, Kolkata 700032, India e-mail: [email protected] MS received 13 April 2018; revised 21 April 2019; accepted 10 January 2020 Abstract. The serrated behavior of the stress-strain curves also known as PLC effect due to dynamic strain aging of SS 316L is investigated here from room temperature to 550 C. Tensile tests were conducted for strain rates 105 102 /s. Serrations of type D, type A and type A?B were observed at different loading conditions. A material model was fitted to the experimental data to simulate the serrated flow in the stress strain diagrams. For this an approach similar to a previous study done with an Al-Mg alloy was followed. However, few changes in the analysis steps were performed to accommodate temperature dependency, a feature not addressed in the earlier work. In addition, the fitment technique was improvised so that the material model could be fit through a substantially smaller set of experimental data, thus improving the speed of the fitting process. Finally, comparisons were done between the experimental data and the results from the simulations. Critical strains from the simulations were found to be of the same order of magnitude of the experimental critical strains and the serrations could also be found in the simulated stress-strain diagrams similar in some aspects to the experimental serrations. Keywords.
Dynamic strain aging; critical strain; DSA band; PLC effect.
1. Introduction Dynamic strain aging or DSA effect in metallic materials such as ferrous and aluminum alloys results from the interaction of the mobile dislocations with the surrounding solute atoms (Beukel [1]). This results into certain average waiting time tw for the mobile dislocation before it moves to the next pinning location. As a result, serrations are observed in the stress-strain curve. This is commonly known as Portevin-Le Chatelier (PLC) effect. DSA is characterized by a negative strain rate sensitivity, strain rate sensitivity (SRS) being measured at a given temperature and strain as or S := ð1Þ o ln e_T;e In combination with viscoplasticity, this causes strain rate instability [2] as opposed to plastic strain instability which is observed at the ultimate stress value in a tensile test. The plastic strain instability condition is given by the following criterion. This paper is a revised and expanded version of an article presented in ‘‘First International Conference on Mechanical Engineering’’ held at ‘Jadavpur University’, Kolkata, India during January 4–6, 2018 (INCOM-2018).
*For correspondence
H r0 ð2Þ where, H := or oe e_. The strain rate instability is manifested as the serrations in the stress-strain diagram. However, such serrated behavior of the stress-strain plot is only obse
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