Scholarly article on topic 'Strain path diagram simulation of AA 5182 Aluminum alloy'

Strain path diagram simulation of AA 5182 Aluminum alloy Academic research paper on "Materials engineering"

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Procedia Engineering
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{"Sheet metal forming" / "AA 5182" / "Strain path diagram" / FEM}

Abstract of research paper on Materials engineering, author of scientific article — Marrapu Bhargava, Asim Tewari, Sushil Mishra

Abstract Aluminum alloys are most promising material in automotive applications due to its light weight and high strength to weight ratio. However, its formability is low when compared to automotive steels. The present paper deals with formability analysis of AA 5182 using different simulation parameters. The simulated strain path diagram (SPD) of AA 5182 was plotted using different element (mesh) sizes and hardening laws. It has been found that effect of mesh size is prominent in SPD simulation. Also a strong trend was found when hardening law was changed. The variation of strains with dome height is also studied.

Academic research paper on topic "Strain path diagram simulation of AA 5182 Aluminum alloy"

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Procedía Engineering

ELSEVIER

Procedía Engineering 64 (2013) 1252 - 1258

www.elsevier.com/locate/procedia

International Conference On DESIGN AND MANUFACTURING, IConDM 2013

Strain path diagram simulation of AA 5182 Aluminum alloy

Marrapu Bhargava*, Asim Tewari, Sushil Mishra

Department of Mechanical Engineering, IIT Bombay, Mumbai, India

Abstract

Aluminum alloys are most promising material in automotive applications due to its light weight and high strength to weight ratio. However, its formability is low when compared to automotive steels. The present paper deals with formability analysis of AA 5182 using different simulation parameters. The simulated strain path diagram (SPD) of AA 5182 was plotted using different element (mesh) sizes and hardening laws. It has been found that effect of mesh size is prominent in SPD simulation. Also a strong trend was found when hardening law was changed. The variation of strains with dome height is also studied.

© 2013 The Authors. Published by Elsevier Ltd.

Selection and peer-review under responsibility of the organizing and review committee of IConDM 2013 Keywords: Sheet metal forming, AA 5182, strain path diagram, FEM

1. Introduction

The demand for light weight and high strength sheet metals has increased rapidly in automotive applications. In recent years Aluminum is playing a vital role in automotive industry for weight reduction, increased fuel economy and stringent pollution standard. However the disadvantage of using these alloys is its low formability, anisotropy nature during deformation and high cost. The applications of aluminum sheets in automotive industries are body closures such as door inner and outer panels lift gates, floor pans, hood etc. Al 5xxx series is extensively used for inner panels where complex shape is desired. Jingjing li et al. (2013) [1] studied forming limit analysis for two-stage forming of 5182-O aluminum sheet with intermediate annealing to increase its formability. They studied

* Corresponding author. Tel.: +91-9004669353; fax: +0-000-000-0000 . E-mail address: mbhargava@iitb.ac.in

1877-7058 © 2013 The Authors. Published by Elsevier Ltd.

Selection and peer-review under responsibility of the organizing and review committee of IConDM 2013 doi: 10. 1016/j .proeng .2013.09.205

strain and stress based FLD for pre annealing and post annealing AA 5182. They found that intermediate annealing increases the formability of AA 5182. However complete strain path diagram and failure prediction has not been studied for this material. Strain and stress based forming limit diagrams, uniaxial and biaxial warm behavior, texture, microstructure, formability on TWB are extensively studied [1-7] but the strain path diagram (SPD) of AA 5182 and the strain development with deformation is not fully understood. This is the motivation of the present study. The present paper deals with the effect of mesh size on the formability of AA 5182. The strain path diagrams of AA 5182 were simulated using PAMSTAMP 2G Finite Element software. Hardening behavior of this material was represented by using Hollomon equation and direct experimental data through tensile test. The variation of strains with the dome height is shown in this paper.

Nomenclature

E Youngs modulus (GPa)

UTS Maximum load (MPa)

Re Yield strength (MPa)

K Strength coefficient (MPa)

n Work hardening exponent

r Anisotropy

P Density (kg/ m3)

9 Poisons ratio

2. Experimental procedure

The chemical composition of AA 5182 used for this study is given in table 1.The tensile test is done according to ASTM E8 standards. The tensile test is carried out at different strains and strain rates at room temperature using INSTRON 5182 universal testing machine for 0o, 45o, 90o from rolling direction of the sheets. The planar anisotropy 'r' values were measured for 0o, 45o, 90o according to ASTM E517. The mechanical properties measured using tensile test and 'r' test are tabulated in table 2.

Table 1: Chemical composition used for this study in (%):

Material Al Mg Mn Fe Si

AA5182 95.12 4.3 0.34 0.21 0.03

3. Simulation procedure

The FEM simulation is done using PAMSTAMP 2G software. The standard LDH tool geometry was used for sheet deformation (hemispherical punch (Diameter: 101.6mm) inside a die opening (Diameter: 105.7mm)) [8]. The tools that are required like punch, die, blank holder, blank and draw bead are generated in a commercial CAD package solid works. The dimensions of the blanks are 25x200, 50x200, 75x200, 100x200, 125x200, 150x200, 175x200, 200x200 mm2 to generate different strain paths from uniaxial to biaxial stretching. The CAD geometry is simulated using the parameters listed in the table 2. Hill 48 yield law is used for the simulation. Hollomon law and direct experimental tensile test data (from yield stress to ultimate tensile stress) was used for the hardening behavior of the material. Element sizes considered for FEM analysis are 2, 1, 0.5 mm. Blank holding force of 240 KN and mesh refinement level of 1 is used for the simulation. The simulations are carried out till a dome height of 50 mm is reached. A point is created on the center of the sample at 50 mm dome height to find the strain path diagram. A graph is plotted with major strain on ordinate and minor strain on abscissa to find the strain path diagram. Hollomon law and experimental tensile test data results are compared in strain path diagram. The data for

localized necking and diffused necking is taken from Jingjing Li [9] and plotted in strain path diagram to compare with experimental results.

Table 2: Properties used for the simulation

Youngs modulus, E (GPa) 69

Maximum load, UTS (MPa) 282

Yield strength, Re (MPa) 12

Strength coefficient, K (MPa) 582

Work hardening exponent, n 0.33

ro , r45, r90 0.75, 0.85, 0.85

Density, p (kg/ m3) 2.7

Poissons ratio, 9 0.31

4. Results and discussion

4.1. Strain path diagram of AA 5182 using Hollomon law

Fig. 1 shows the simulated strain path diagram of AA 5182 by using Hollomon law as the hardening behavior of the materials. SPD was plotted taking element near the localized region. No two strain paths intersect for an element size, suggesting that the major and minor strains are sufficient to fully describe the state of deformation in these sheets. Element sizes of 2, 1, 0.5 are considered and compared. Element size of 2 and 1 almost follow the same strain path but for element size of 0.5 the strains are less in plane strain region. In uniaxial and biaxial regions the strain path is almost similar for all the element sizes. Experimental forming limit curve (FLC) for diffused and localized necking is plotted in SPD. The dotted lines show the localized necking and dashed lines show diffuse necking. It can be observed that element size of 0.5 are very close to diffused necking FLC.

-— \ 1 \ 3

0.3 ■ / ...............'/jf

......... \V \ N y \ ..........j ¡I jf

0.2 - Mesh Size 2 ___________''fjp

Mesh Size 1 Mesh Size 0.5

......localized necking [9] v.\ A kr

— diffuse necking [9] 'Ar

0 i i i i

Minor Strain

Fig. 1 SPD of AA 5182 by using Hollomon law in hardening curve

Figures 2, 3, 4 show the major and minor strains with dome height during LDH testing. The variation of strains till dome height of 50 mm is shown. The black colour line in fig. 2 shows that localization is taking place from that dome height. After reaching a dome height of 22, 28, 42 mm localization is taking place in all the mesh sizes in uniaxial, plane and biaxial region respectively. Element size of 2, 1 follow the same strain path but element size of 0.5 shows different strain paths. It is observed that strains getting saturated after certain dome height because of localization of strains.

Fig. 2 Variation of strains with dome height in uniaxial region

Dome Height

Fig. 4 Variation of strains with dome height in biaxial region

4.2. Strain path diagram of AA 5182 by experimental tensile data as hardening curve

Fig. 5 shows the simulated strain path diagram of AA 5182 by using experimental tensile test data as the hardening law. The dotted lines show the localized necking and dashed lines show diffuse necking. The experimental tensile test data strains are matching with experimental diffused necking FLC in all the element sizes except in biaxial region. The strains are less in experimental tensile test data when compared to Hollomon law. The reason for having less strain is the data considered for the analysis is from yield stress to ultimate tensile stress. This data belongs to uniaxial region and plane strain region but not the biaxial region.

Fig. 5 SPD of AA 5182 by using experimental tensile data in hardening law

Figures 6, 7, 8 show the major and minor strains with dome height during LDH testing. The black colour line in fig. 6 shows that localization is taking place from that dome height.The same observations which are made in Hollomon law is observed in experimental tensile test data except that strain localization is taking place earlier compared to Hollomon law. After reaching a dome height of 22, 25, 35 mm strain localization is taking place in all the element sizes in uniaxial, plane and biaxial region respectively.

Fig. 6 Variation of strains with dome height in uniaxial region

Biaxial minor element size 2

Dome Height

Fig. 8 Variation of strains with dome height in biaxial region

5. Conclusions

The formability is lower in plane strain region than uniaxial and biaxial region. In the strain path diagram no two strain paths intersect each other stating that major and minor strains are sufficient to describe the state of deformation in these sheets. It is observed that strain localization is taking place after reaching a certain dome height. Effect of element size is clearly visible in strain path diagrams. Experimental tensile test data in hardening law is matching with experimental diffused necking FLC. An appropriate failure criterion has to be chosen for simulating forming limit diagram.

[1] Jingjing, L., John, E C., Thomas, B S., Louis, G Hector J., S, Jack H., 2013. Forming limit analysis for two-stage forming of 5182-O aluminum sheet with intermediate annealing, International Journal of Plasticity 45, p. 21.

[2] Daoming, L., Amit, G., 2003. Tensile deformation behavior of aluminum alloys at warm forming temperatures, Materials Science and Engineering A 352, p. 279.

[3] Daoming, L., Amit, K G., 2004. Biaxial warm forming behavior of aluminum sheet alloys, Journal of Materials Processing Technology 145, p. 281.

[4] Xiang-Ming, C., James, G M., 2002. Texture, microstructure and formability of SC and DC cast Al-Mg alloys, Materials Science and Engineering A 323, p. 32.

[5] Amit, V B., Ghassan, T K., 2004. Formability Improvement in aluminum tailor welded blanks via material combinations, Journal of Manufacturing Process 6(2), p. 134.

[6] Wonoh, l., Kyung-Hwan, C., Daeyong, K., Junehyung, K., Chongmin, K., Kazutaka, O., Wagoner, R H., Kwansoo, C., 2009. Experimental and numerical study on formability of friction stir welded TWB sheets based on hemispherical dome stretch tests, International Journal of Plasticity 25, p. 1626.

[7] Amir, A Z., Jos, S., Rinze, B., 2009. Formability prediction of high strength aluminum sheets, International Journal of Plasticity 25, p. 2269.

[8] Hecker, S., 1974. A cup test for assessing stretchability, Mech Eng Quart 14, p. 30.

[9] Jingjing, L., 2011. Characterization of post- annealing mechanical behavior of preformed aluminum alloy 5182-O, PhD thesis, p. 83.

References