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Ngoc-Trung Nguyen

Bio: Ngoc-Trung Nguyen is an academic researcher from Pohang University of Science and Technology. The author has contributed to research in topics: Formability & Hardening (metallurgy). The author has an hindex of 8, co-authored 13 publications receiving 177 citations. Previous affiliations of Ngoc-Trung Nguyen include Indian Institute of Technology Delhi & Purdue University.

Papers
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Journal ArticleDOI
TL;DR: Large-strain monotonic and cyclic loading tests of AZ31B magnesium alloy sheets were performed with a newly developed testing system, at different temperatures, ranging from room temperature to 250 °C, and a critical temperature was identified to account for the transition between the twinning-Dominant and slip-dominant deformation mechanisms.
Abstract: Large-strain monotonic and cyclic loading tests of AZ31B magnesium alloy sheets were performed with a newly developed testing system, at different temperatures, ranging from room temperature to 250 °C. Behaviors showing significant twinning during initial in-plane compression and untwinning in subsequent tension at and slightly above room temperature were recorded. Strong yielding asymmetry and nonlinear hardening behavior were also revealed. Considerable Bauschinger effects, transient behavior, and variable permanent softening responses were observed near room temperature, but these were reduced and almost disappeared as the temperature increased. Different stress–strain responses were inherent to the activation of twinning at lower temperatures and non-basal slip systems at elevated temperatures. A critical temperature was identified to account for the transition between the twinning-dominant and slip-dominant deformation mechanisms. Accordingly, below the transition point, stress–strain curves of cyclic loading tests exhibited concave-up shapes for compression or compression following tension, and an unusual S-shape for tension following compression. This unusual shape disappeared when the temperature was above the transition point. Shrinkage of the elastic range and variation in Young’s modulus due to plastic strain deformation during stress reversals were also observed. The texture-induced anisotropy of both the elastic and plastic behaviors was characterized experimentally.

67 citations

Journal ArticleDOI
TL;DR: In this paper, a constitutive model is proposed to predict the mechanical behavior of Mg alloy sheets, which can accurately predict the yielding asymmetry behavior and the stress-strain curve featured by the unusual sigmoidal shape.

44 citations

Journal ArticleDOI
TL;DR: In this article, the mechanical behavior of AZ31B Mg alloy sheets under in-plane tension-compression (or compression-tension) cyclic loading was experimentally measured for various pre-strains and temperatures.

24 citations

Journal ArticleDOI
TL;DR: In this paper, the design of drawbead is optimized by treating it as a multi-objective problem with maximum dome height and minimum weldline movement as objectives, which were constructed as metamodels through a genetic algorithms based approach.
Abstract: Formability of a tailor welded blank (TWB) is affected by the strength ratio of the base metals joined. In this paper, formability of TWB with very high strength ratio made by joining twinning-induced plasticity (TWIP) and low carbon steels is numerically studied using a limiting dome height test. The drawbead geometry at the weaker side is modified to increase the dome height. The design of drawbead is optimized by treating it as a multi-objective problem with maximum dome height and minimum weldline movement as objectives, which were constructed as metamodels through a genetic algorithms based approach. The necessary data for the metamodeling are generated by finite element (FE) simulation using the commercial solver, LS-DYNA®. The multi-objective optimization is carried out using a predator–prey genetic algorithm. The Pareto front estimated using this evolutionary approach is validated using FE simulations and a good correlation is obtained.

20 citations

Journal ArticleDOI
TL;DR: In this article, a robust multiobjective optimization based on evolutionary algorithm is proposed to minimize the error in yield stress and plastic strain ratio simultaneously and thereby overcomes the limitations in the approaches used before.
Abstract: The texture induced anisotropy of yield strength in cold rolled sheet metals is modeled using anisotropic yield criteria. The classical and other optimization methods used so far to determine the yield coefficients are limited by fixed set of experimental data, initial guess values, and pre-determined weight factors. A robust multiobjective optimization based on evolutionary algorithm proposed in this paper minimizes the error in yield stress and plastic strain ratio simultaneously and thereby overcomes the limitations in the approaches used before. The new approach is tested using Hill48 and Barlat89 yield criteria for five different materials from literature. The new approach is observed to improve the prediction capability of yield coefficients when compared to earlier approaches. The Pareto frontier obtained in the new approach can serve as a comparative tool to evaluate the accuracy of different yield criteria.

19 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, an anisotropic continuum-based plasticity model is proposed to capture the large strain cyclic hardening behavior of magnesium alloys for both monotonic and reverse loading paths.

87 citations

Journal ArticleDOI
TL;DR: In this paper, the influence of different shearing patterns on mechanical and forming behavior at room temperature of equal channel angular pressing (ECAP) processed AZ31 sheets was investigated. And the improved formability of the ECAP processed sheets was attributed mainly to low r -value and high n -value.
Abstract: The present work investigates the influence of different shearing patterns on mechanical and forming behavior at room temperature of equal channel angular pressing (ECAP) processed AZ31 sheets. Hot-rolled AZ31 (Mg-3Al-1Zn, wt%) sheets, with dimensions of 200×200×1.8 mm 3 , were processed at 225 °C with channel angle of 110° regarding processing routes A, C and D. Shear deformation induced by ECAP weakens the texture and promotes a broad angular distribution of basal planes in the pressing direction on routes A and C. Especially, processing on route D makes basal planes tilted towards the rolling direction and transverse direction by 90° rotation in the sheet plane. Due to the increased activity of basal slip, ECAP processed sheets exhibit the decrease in yield strength and r -value and increase in uniform strain and n -value in the pressi n g direction. As a result, route C has the largest uniform elongation in the rolling direction and route D provides a quasi-isotropic hardening behavior at room temperature. The improved formability of the ECAP processed sheets is attributed mainly to low r -value and high n -value. At Nakajima tests, route D provides higher forming limits than the as-rolled sample. The microstructure on route D exhibits a drastic reduction in the fraction of {10−12}-{10−11} double twins. This twinning mode leads to premature failure of the as-rolled sample under biaxial stretching. Consequently, microstructure-texture control induced by ECAP can enhance the cold formability of AZ31 sheets.

78 citations

Journal ArticleDOI
TL;DR: In this article, the authors distinguish fracture porosity and matrix porosity in coalbed methane reservoirs through a novel approach which is the joint usage of NMR transverse relaxation (T2) measurements and rock physics modeling based on Levenberg-Marquardt (LM) algorithm.

75 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigate systematically twinning and detwinning behaviors of {10 1 ¯ 2} twins in pre-compressed pure Mg and AZ31 and AZ91 alloys.

71 citations

Journal ArticleDOI
TL;DR: Large-strain monotonic and cyclic loading tests of AZ31B magnesium alloy sheets were performed with a newly developed testing system, at different temperatures, ranging from room temperature to 250 °C, and a critical temperature was identified to account for the transition between the twinning-Dominant and slip-dominant deformation mechanisms.
Abstract: Large-strain monotonic and cyclic loading tests of AZ31B magnesium alloy sheets were performed with a newly developed testing system, at different temperatures, ranging from room temperature to 250 °C. Behaviors showing significant twinning during initial in-plane compression and untwinning in subsequent tension at and slightly above room temperature were recorded. Strong yielding asymmetry and nonlinear hardening behavior were also revealed. Considerable Bauschinger effects, transient behavior, and variable permanent softening responses were observed near room temperature, but these were reduced and almost disappeared as the temperature increased. Different stress–strain responses were inherent to the activation of twinning at lower temperatures and non-basal slip systems at elevated temperatures. A critical temperature was identified to account for the transition between the twinning-dominant and slip-dominant deformation mechanisms. Accordingly, below the transition point, stress–strain curves of cyclic loading tests exhibited concave-up shapes for compression or compression following tension, and an unusual S-shape for tension following compression. This unusual shape disappeared when the temperature was above the transition point. Shrinkage of the elastic range and variation in Young’s modulus due to plastic strain deformation during stress reversals were also observed. The texture-induced anisotropy of both the elastic and plastic behaviors was characterized experimentally.

67 citations