Identification of the Plastic Deformation Characteristics of AL5052-O Sheet Based on the Non-Associated Flow Rule

Quoc Tuan Pham,김영숙 대한금속·재료학회 2017 METALS AND MATERIALS International Vol.23 No.2

This study aims to determine the plastic deformation characteristics of aluminum 5052-O based on non-associatedflow rule. To achieve this goal, a new strain hardening model named as Kim-Tuan hardening modelis proposed to perfectly describe the stress-strain relation of the studied material in terms of the uniaxial tensiletest and to predict the material’s post-necking behavior. Additionally, the plastic behaviors of AL5052-O sheetare described by two approaches: the associated flow rule with YLD2000-2d yield function and the nonassociatedflow rule with Hill's quadratic function (NAFR-Hill48). The parameters of these functions werederived from the material properties that were obtained from uniaxial tensile tests and bulge test. The flow curvebased on Kim-Tuan model and plastic behaviors obtained from two above-mentioned approaches were importedinto a finite element analysis code to simulate the hydraulic bulge test for this material to confirm the precisionof material characteristics achieved before. The simulation results based on the NAFR-Hill48 match wellwith the experiment results of bulge test while the YLD2000-2d provides highly accurate predictions foranisotropy of this material.

Evaluation of Press Formability of Pure Titanium Sheets

Pham, Quoc Tuan,Kim, Young Suk Trans Tech Publications, Ltd. 2016 Key Engineering Materials Vol.716 No.-

<P>Commercially pure titanium (CP Ti) has been actively used in plate heat exchangers due to its light weight, high specific strength, and excellent corrosion resistance. However compared with automotive steels and aluminum alloys, only limited research has been conducted on the plastic deformation characteristics and press formability of CP Ti sheets. In this study, the mechanical properties, including the anisotropic property and the stress-strain relation, of the CP Ti sheet are clarified in relation to press formability. A new proposed strain hardening model, Kim-Tuan equation, is successful in perfectly describing the stress evaluation for strain increment of this material during strain path. The forming limit curve (FLC) of the CP Ti sheet as a criterion for press formability was experimentally evaluated by punch stretching testing and analytically predicted via Hora’s modified maximum force criterion. The predicted FLC based on the Kim-Tuan strain hardening equation and the appropriate yield function correlates well with the experimental results of the punch stretching test.</P>

A study on distortion of stainless steel AISI 304 sheets during butt-welding process

Quoc-Tuan Pham(팜쿽투완),Duc-Toan Nguyen(규엔득투완),Jong-Kyu Park(박종규),Young-Suk Kim(김영석) 대한용접·접합학회 2015 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2015 No.11

APPLICATION OF A GRAPHICAL METHOD ON ESTIMATING FORMING LIMIT CURVE OF AUTOMOTIVE SHEET METALS

Quoc Tuan Pham,Jinjae Kim,The-Thanh Luyen,Duc-Toan Nguyen,김영석 한국자동차공학회 2019 International journal of automotive technology Vol.20 No.Supp

In the automotive engineering community, the modified maximum force criterion proposed by Hora and coworkers is considered acceptable for theoretically estimating the forming limit curve (FLC) of sheet metals. Based on this criterion, a graphical method is proposed to simplify evaluation of the FLC. This paper investigates the proposed graphical method in a special case by using a power-hardening law and the Mises yield function, which leads to an explicit expression of the critical strains according the strain paths. The FLC of a DP590 sheet estimated using the proposed method is compared with that estimated using existing analytical methods. The proposed method provides the best prediction of the FLC of the tested material. For verification, the calculated FLC is then adopted into the finite-element method to predict the punch stroke at fracture of several notched specimens subjected to Nakazima tests. The good agreement between the predicted and experimentally determined values of the punch strokes verifies the ability and potential of the proposed method in industrial engineering.

An efficient method to estimate the post-necking behavior of sheet metals

Pham, Quoc-Tuan,Oh, Seok-Hwan,Kim, Young-Suk Springer-Verlag 2018 INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TE Vol.98 No.9

Usefulness of three parameters models in engineering plasticity and sheet metal forming research

Quoc-Tuan Pham(팜쿽투완),Seok-Chul Shin(신석철),Young-Suk Kim(김영석) 한국소성가공학회 2015 금형가공 심포지엄 Vol.2015 No.8

From an overview of mechanical engineering, it is accepted that the plasticity of metals is a strongly nonlinear problem in which many nonlinear curves are required to describe important characteristics of plasticity such as flow curve, yield locus and ductile fracture. Much effort has been made to capture these characteristics by introducing many parameters to precisely express the experimental results. For example, to describe the stress-strain relation of materials, Swift and Voce models are widely used, and Hill non-quadratic and Hosford yield functions are usually applied in modeling the yield locus, because of their simple expression with only two parameters. Similarly, the most ductile failure models with a few parameters are Clift and Oyane models. However, the above-mentioned models have at most two parameters in their equations and intrinsically have limited accuracy. Of course, introduction of more parameters in plasticity models may yield more accurate solutions, such as the Barlat (2003) yield function which has eight parameters. Nevertheless, these proposed models significantly increase the computational cost and may introduce inevitable errors in estimating their parameters. To overcome this disadvantage, this study proposes three-parameter models to describe the governing equation of the above mentioned topics. These models achieve a balance between accuracy and computational cost in engineering.

Characterization of the isotropic-distortional hardening model and its application to commercially pure titanium sheets

Pham, Quoc Tuan,Lee, Myoung Gyu,Kim, Young Suk Pergamon Press 2019 International journal of mechanical sciences Vol.160 No.-

<P><B>Abstract</B></P> <P>Commercially pure titanium sheets have been widely used in various industrial applications owing to their lightweight nature, superior formability, and excellent corrosion resistance. Previous studies showed that accurate modelling of material characteristics, such as anisotropic yield function and hardening, is essential for the simulation of sheet metal forming with titanium sheets. For example, the non-quadratic anisotropic yield function Yld2000-2d and the modified Kim–Tuan hardening model were used to model initial anisotropy and reproduce flow stress curves at large strains. However, even with these advanced constitutive models for describing the anisotropic behavior of sheet metals, further improvement is necessary to simulate anisotropy evolution, or distortional hardening, in pure titanium sheets. In this study, distortional hardening was experimentally measured under both uniaxial and balanced biaxial loading conditions. Moreover, the evolution of the Yld2000-2d function was modelled as a function of equivalent plastic work. For validation, the developed material models were applied in finite element simulations to analyse deformation behavior in uniaxial tension, hydraulic bulge, and punch-stretching tests. It was confirmed that this approach accurately described material response during these three tests.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Experimental observation of distortional hardening behaviour and three-stage deformation behavior for a pure titanium sheet. </LI> <LI> A procedure to reproduce these material behaviours for the tested material by using an evolutionary yld2000-2d yield function and modified Kim–Tuan hardening law. </LI> <LI> Simulation results of uniaxial tensile tests, hydraulic bulge test, and punch-stretching tests match well with experimental data. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Influence of the post-necking prediction of hardening law on the theoretical forming limit curve of aluminium sheets

Pham, Quoc-Tuan,Lee, Bong-Hyun,Park, Kee-Cheol,Kim, Young-Suk Elsevier 2018 International journal of mechanical sciences Vol.140 No.-

<P><B>Abstract</B></P> <P>This study clarified the influence of the post-necking prediction of the hardening law on the theoretical forming limit curve (FLC) of aluminium sheets subjected to punch-stretching tests. A procedure was developed to identify the parameters of a recently developed hardening model (Kim–Tuan hardening model) based on the curve fitting method. Subsequently, this model was used to capture the post-necking behaviours of two aluminium alloy sheets (AL5052-O and AL6016-T4), which were compared with those of various other hardening models, including the Swift model, Voce model, Hockett–Sherby model, Ghosh model, and a linear combination of the Swift and Voce models. These hardening models, with their extrapolations for post-necking prediction, were employed to analytically calculate the FLCs of the tested materials based on the modified maximum force criterion (MMFC). Furthermore, a simple and effective method was found to estimate the level of limited strain in the plane strain mode, namely FLC<SUB>0</SUB>. The proposed method was used to clarify the influence of the hardening law and yield function on the level of the computed FLC. The results indicated that the flow curves predicted by the Kim–Tuan hardening model effectively matched the experimental data obtained from uniaxial tensile tests, while their extrapolations provided intermediate predictions of the post-necking behaviour between the flow curves of the Swift and Voce models. In addition, the proposed hardening model improved the accuracy of the computed FLC for the studied materials.</P> <P><B>Highlights</B></P> <P> <UL> <LI> New formulation for strain hardening function is presented. </LI> <LI> A procedure for identifying parameters of proposed hardening model is developed based on curve fitting method. In this procedure, stress and strain data obtained from standard uniaxial tensile test were utilized. </LI> <LI> New method is presented for estimating the level of limited strain in the plane strain mode, FLC<SUB>0</SUB>. Based on this method, influence of post-necking prediction of hardening law on forming limit curve of aluminium sheet is discussed. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

A Graphical Method to Estimate Forming Limit Curve of Sheet Metals

Pham, Quoc Tuan,Nguyen, Duc Toan,Kim, Jin Jae,Kim, Young Suk Trans Tech Publications, Ltd. 2019 Key Engineering Materials Vol.794 No.-

<P>Since its foundation, the concept of forming limit diagram has been widely accepted in sheet metal forming community as a powerful tool for studying formability. There are pyramid models that were developed to estimate the forming limit curve theoretically, for example, Swift's diffuse necking criterion, Hill's localized necking criterion, Marciniak and Kuczynski model, Modified Maximum Force Criterion, <I>etc</I>.. Implement of these models, however, is a laborious task. To simply the task, this study presents a graphical method to estimate forming limit curve of sheet metal. Some new insights into the Modified Maximum Force Criterion, the Hora method, are discussed. The insights pertain to the use of a graphic tool to estimate limit strains at three critical forming modes in sheet metal forming that are the uniaxial tension, plane strain, and equi-biaxial tension. Connecting three points by linear lines yields to a simple graph of forming limit curve. Method validation is supported by comparing the estimated forming limit curve with experimentally measured data for several automotive sheet metals.</P>

A numerical and experimental study on the mechanical characteristics of sheet material by the hydraulic bulge test and uniaxial tensile tests

Quoc-Tuan Pham(팜콕투완),Jin-Jae Kim(김진재),Young-Suk Kim(김영석),Seong-Jin Kwon(권성진) 한국자동차공학회 2016 한국자동차공학회 부문종합 학술대회 Vol.2016 No.5

Unixaial tensile test is the most common method used to identify the mechanical characteristics for sheet materials. However, several sheet forming processes lead to large plastic deformation in which the plastic strain is over the maximum uniform elongation of uniaxial tensile test, for instance, clinch forming, hydroforming, stamping and deep drawing. Therefore, post-necking behavior of sheet materials is a currently attractive research topic where these studies focus on the behavior of metals beyond the uniaxial tensile elongation. This study aims to determine the flow curves and yield locus of aluminum 5052 sheets by performing the hydraulic bulge test and uniaxial tensile tests. To obtain this goal, firstly, a series of uniaxial tensile tests are performed in order to evaluate the yield stress and anisotropic plasticity coefficients in three orientations 0°, 45° and 90° respect to the rolling direction. Secondly, the hydraulic bulge test is carried out to achieve biaxial stress-strain curve. From this curve, biaxial yield stress and biaxial anisotropic plasticity coefficients are derived. Moreover, a new strain hardening function is proposed to perfectly describe stress-strain relation of studied material in term of uniaxial tensile test and predict the post-necking behavior of this material. The biaxial stress-strain curve is transformed into an effective stressstrain curve, then this curve is compared with the fitting results of new strain hardening function in rolling direction to highlight the accuracy of post-necking prediction of proposed equation. Thirdly, the parameters of Yld2000 yield function are derived from above-mentioned mechanical properties to describe yield locus of aluminum 5052 sheets. Finally, the achieved effective stress-strain curve and yield locus are imported into a FE analysis code to simulate the hydraulic bulge test of this material. The simulation results match well with the experiment records and it is reasonable to conclude that the novel approach to determine the mechanical characteristics achieved from this study can be applied for other sheet materials.