Experiment Research on Tensile and Compression Cyclic Loading of Sheet Metal

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Procedia Engineering 207 (2017) 1916–1921

International Conference on the Technology of Plasticity, ICTP 2017, 17-22 September 2017, Cambridge, United Kingdom

Experiment Research on Tensile and Compression Cyclic Loading of Sheet Metal Qun Li, Miao Jin, Zongyuan Zou*, Shiyan Zhao,Qingling Zhang, Peng Li Yanshan Yanshan University,Qinhuangdao,066004,China University,Qinhuangdao,066004,China

Abstract Abstract In the the process process of of cyclic cyclic loading, loading, the the sheet sheet metal metal appears appears Bauschinger Bauschinger Effect Effect and and the the mechanical mechanical properties properties changes. changes. The The sheet sheet is is In prone to to be be unstable unstable in in the the compression compression process. process. If If jigs jigs are are installed installed on on the the sheet, sheet, the the strain strain is is difficult difficult to to be be measured measured exactly. exactly. prone And the the frictional frictional force force between between sheet sheet and and jigs jigs has has an And an influence influence on on the the experimental experimental results. results. In In order order to to solve solve these these problems, problems, aa testing testing system system is is developed developed for for large large strain strain cyclic cyclic loading loading of of sheet sheet metal. metal. The The testing testing system system includes includes the the prevent prevent instability instability jigs, jigs, clamping clamping force force testing testing system, system, fatigue fatigue testing testing machine, machine, and and non-contact non-contact strain strain measuring measuring instrument. instrument. The The system system was was used used to to carry out out the the cyclic cyclic tensile-compression tensile-compression experiment carry experiment with with different different strain strain control control for for B170 B170 and and DP590 DP590 plates, plates, and and the the stress-strain stress-strain curve curve is is obtained. obtained. In In addition, addition, the the change change in in clamping clamping force force was was tested tested and and the the effect effect of of friction friction was was eliminated, eliminated, so so the the accurate accurate tensile-compressive stress-strain stress-strain curve curve was was obtained. obtained. tensile-compressive © 2017 2017 The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. © © 2017 The Authors. Published by Ltd. Peer-review under responsibility responsibility ofElsevier Peer-review under of the scientific committee the International Conference on theofTechnology Peer-review under responsibility of the scientific committee of theof International Conference on the Technology Plasticity. of Plasticity.. Keywords: Keywords: cyclic cyclic loading, loading, large large strain, strain, prevent prevent instability instability jigs, jigs, frictional frictional force, force, sheet sheet

1. Introduction 1. Introduction Tensile-compression cyclic cyclic loading loading is is complex complex deformation deformation behavior behavior under under cyclic cyclic loading. loading. In Tensile-compression In the the process process of of tensile-compression cyclic The stress-strain stress-strain curve tensile-compression cyclic loading, loading, most most metal metal will will appear appear Bauschinger Bauschinger Effect(Hu,1994). Effect(Hu,1994). The curve under cyclic cyclic loading loading can under can be be obtained obtained directly directly by by tensile-compression tensile-compression cyclic cyclic loading loading test test (Chen (Chen Zhongchun Zhongchun 2009 2009 & & Zang Shunlai 2007).

* * Corresponding Corresponding author. author. Tel.: Tel.: 15369701769; 15369701769; fax: fax: 0335-8074783. 0335-8074783. E-mail E-mail address: address: [email protected] [email protected] 1877-7058 1877-7058 © © 2017 2017 The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. Peer-review under under responsibility responsibility of of the scientific committee Peer-review Plasticity..

of the International Conference on the Technology of

1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the International Conference on the Technology of Plasticity. 10.1016/j.proeng.2017.10.961

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The cyclic loading research of metal bar is relatively easy, and there are corresponding standards which can be used for reference. However, the cyclic loading research of metal sheet is much more difficult. Because sheet is prone to be unstable in compression. The prevent instability jigs are needed to be installed on both sides of sheet. But with above prevent instability jigs, friction will appear between sheet and installation. Thus it is difficult to obtain accurate cyclic stress-strain relationship. So avoiding sheet instability under compression and eliminating the influence of friction on the experimental results, then to obtain accurate cyclic stress-strain relationship is crucial. The research of jigs preventing instability and cyclic loading has been done by many scholars. Boger(2005) added the entity flat on both sides of the specimen to apply a lateral force to restrain compression buckling. The tension and compression expeimental curve to compression strain of 8% was measured. The Bauschinger Effect of Al6022 and Mg AZ31B were studied. Kuwabara(2009) put two crossing comb teeth to limit compression buckling. The tension and compression experimental curve to compression strain of 6% was measured. The Bauschinger Effect of 0.25mm thick phosphor bronze sheet and 1.2mm thick of alloy sheet (AA6016-T4) were studied. Yoshida(2002) put multiple specimens bonding together to overcome the limitation of instability of single specimen. He measured the cyclic tension and compression experimental curve to compression strain of 8%. The Bauschinger Effect of mild steel sheet (SPCC) and high strength steel sheet (SPFC) were studied. Jian Cao(2009) designed a set of new jig for ordinary tensile experimental machine, using two mutual sliding wedge block to clamp the palte specimen to restrain compression buckling, measuring the cyclic tension and compression experimental curve to compression strain of 12%. The Bauschinger Effect of 0.8mm thick BH180 steel and 1.6mm thick DP600 steel were studied. Dihui Liu(2013) and other scholars improved the experiment apparatus of Jian Cao, and the versatility and reliability of the device are enhanced. The Bauschinger Effect of super deep steel DC06 was studied. The above research work builds a good foundation for plane cyclic tension and compression experimental research methods. To solve the problems that the clamping force cannot be measured accurately in the process of the compression and real-time strain is measured inaccurate, a set of sheet metal tensile and compression cyclic loading testing system for large deformation is developed in this paper. This system can undertake large compressive strain under cyclic tension and compression test, obtain accurate strain values, get clamping force between the fixture and specimen, eliminate the friction force. 2. Testing system In order to study the characteristics of sheet metal under large strain cyclic loading, a set of sheet metal tensile compression testing system is developed in this paper. This system includes specimens, the prevent instability jigs and clamping force testing system, fatigue testing machine and non-contact strain measuring instrument, the testing system is shown in Fig 1.

fatigue testing machine specimen and the prevent instability device

non-contact strain measuring instrument

clamping force testing system

Fig 1 The testing system

2.1 Prevent instability jigs and clamping force testing system The single piece of specimen is used in test. As shown in Fig 2, in order to prevent instability of the sheet

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specimen in the process of compression, the prevent instability jigs was installed on the both sides of the specimen. a

b

(a) the prevent instability jigs

(b) specimen

Fig 2 Prevent buckling device

The prevent instability jigs is suitable for ordinary experiment machine, mainly includes three parts, which are fixed plates, clamping plates and a buffer. There are four fixed plates which are divided into two pairs. The four fixed plates are installed on the clamping position on both ends of the specimen through pins. There are four clamping plates located in the center of the specimen, coated the parallel section and the circular arc transition section. Each side of parallel section of the specimen had a clamping plate, and each side of the buffer has a clamping plate. The four clamping plates are connected by eight bolts. The comb teeth structure was designed to be installed between the clamping plates and fixed plates, then the comb teeth can slide freely. In the process of tensile, the distance between the tip and root of the comb increased, but there is still a part of the overlap. In the process of compression, the distance between the tip and root is reduced, but without hitting. Thus in the process of cyclic loading, the prevent instability jigs can cover the specimen, and the specimen is always protected by the device. In order to do accurate analysis of the test result after adding the prevent instability jigs, the clamping force testing system is designed. The clamping force testing system is composed of force sensor and IMC data acquisition system. The change of the clamping force can be measured by the force sensor installed between the specimen and buffer; the signal is collected and processed by IMC data acquisition system; the real-time change of the clamping force is processed and displayed by the test software. 2.2 Non-contact strain measurement Due to the prevent instability jigs covers the specimen, the contact extensometer cannot be installed on the specimen. So the Instron AVE2 optical non-contact extensometer is used to measure the axial deformation in this test. Two slotted hole opened on the clamping plate 1 is the tag on the surface of specimen. The processing software can accurately calculate the strain in the process of test by comparing the change of mark point locations. 3. Cyclic tensile-compression test process The experimental materials are B170P1 and DP590 high strength steel plate, and the thickness is 0.7mm. The material parameters are summarized in Table1. Table.1 The material parameters Brand

σs (MPa)

σb (MPa)

δ (%)

B170P1

205

361

42

DP590

365

661

27

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Test scheme is as follows: uniaxial tensile test for B170P1 and DP590, with the strain rate of 1.5%/min; tensilecompression cyclic loading test for B170P1 and DP590, with the strain value of 4%, 5%, 6%, the strain rate of 1.5%/min. The purpose of uniaxial tensile test is to provide reference standard to the tensile-compression cyclic loading test The specimen and the prevent instability jigs are installed in the fatigue experiment machine, clamped on the both side of fixed plate by the hydraulic horizontal pushing clamp. The test adopted strain control mode, and the strain rate is 1.5%/min. The specimen was subjected to tension before compression, and two tensile-compression cycle was conducted under symmetry strain control mode. In order to avoid the error caused by the instrument, the environment and human factors, the test in each group are of three specimens and then the results are taken the average value. The strain amplitude for cyclic tensile compression curves of B170P1 and DP590 in the test was 4%, 5%, 6% (as shown in Fig 3). The specimens after test are shown in Fig 4. It can be seen from Fig 4 that the instability of the specimen in the compression process can be restrained by the prevent instability jigs, then large strain cyclic tensile compression test can be conducted by using the device. b

400

4%

0

5%

-200

6%

true stress/MPa

200

-400 -600

-0.06

-0.03

0.00

true strain

0.03

0.06

true stress/MPa

a

800 600 400 200 0 -200 -400 -600 -800

4% 5% 6%

-0.06

-0.03

0.00

true strain

0.03

0.06

Fig 3 Cyclic tensile compression curve (a) B170P1 (b) DP590

Fig 4 The specimens after test

4. Result analysis In order to reduce the friction between the specimen and the clamping plate in the test, a 0.02mm thick layer of teflon film was sprayed on the surface of the parallel part, the transition part of the sheet specimen and the clamping plate for the specimen. In the test, the prevent instability jigs produces frictional resistance, and the direction of friction is in the opposite direction of the load imposed by machine. Thus the load measured was bigger than the real one, so the value of friction load needs to be eliminated. Due to the deformation of the specimen gage section is uniform, the value of friction can be calculated by Coulomb friction condiction. As the real-time value of specimen clamping force was measured by force sensor, the real-time friction was calculated using the Coulomb friction law of F=μN. Thus the exact cyclic tensile compression stress-strain curve was obtained by eliminating the influence of friction

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The frictional force can be calculated using the clamping force and the sliding friction coefficient between the specimen and clamping plate. Then the frictional force of cyclic loading curve can be eliminated. Through the above method, the curve of DP590 with strain amplitude of 6% strain was processed, the real stress-strain curve was obtained. The true stress-strain curve and original data curve are both shown in Fig 5. The proportion of the frictional force is about 1% to 2%. Putting the stress-strain curve being processed and the uniaxial tensile stressstrain curve together, the coincidence of the two curves is very well. This suggests that the way to eliminate friction is reasonable. The frictional force can be quantitative and the influence of frictional force between the jigs and specimen can be eliminated. uniaxial tensile ——original curve a b 800 600 400 200 0 -200 -400 -600 -800

true stress/MPa

true stress/MPa

- - - -processing curve

-0.06

-0.03 0.00 0.03 true strain

0.06

700 600 500 400 300 200 100 0 -100

processing curve

0.00

0.02

0.04

true strain

0.06

0.08

Fig 5 The contrast between original curve and processing curve

The cyclic tensile-compression stress-strain curves of B170P1 and DP590 with symmetry strain amplitude value of 4%, 5%, 6% and uniaxial tensile curves are shown in Fig. 6. The coincidence of the initial section of cyclic curves and uniaxial tensile curve is very well. It shows that the experimental data is reliable and the frictional force is eliminated effectively.

uniaxial tensile

true stress/MPa

400 200

4%

0

5%

-200

6%

-400

-0.06 -0.03 0.00 0.03 0.06 0.09

true strain

b

true stress/MPa

a

uniaxial tensile

800 600 400 200 0 -200 -400 -600 -800

4% 5% 6%

-0.06 -0.03 0.00

0.03

true strain

0.06

0.09

Fig 6 The cyclic loading curve after removing frictional force (a)B170P1 (b)DP590

5. Conclusions (1) The sheet metal tensile and compression testing system is developed, and the two cyclic tension and compression stress-strain curves with compressive strain of 8%-12% were obtained. (2) The clamping force curve between the prevent instability jigs and specimen can be measured using this test system. Meanwhile, the influence of the friction force can be eliminated and the accurate stress-strain curve can be obtained.

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Acknowledgements The authors gratefully acknowledge financial supports provided by Nature Science Foundation of China (No.51475408), and Nature Science Foundation of Hebei Porvience (No. E2013203271). References [1]Han K,van Tyne C J, Levy B S.Effect of Strain Rate on the Bauschinger Effect Response of Three Different Steel[J].Metallurgical and Materials Transactions A,2005,36:2379-2384. [2]Miyauchi K. Stress-Strain Relationships in Simple Shear of In-Plane Deformation for Various Steel Sheet Efficiency in Sheet Metal Forming[J]. Proc of IDDRG, (1984), 360-371. [3]Merklein M,Biasutti M.Forward and Reverse Simple ShearTest Experiments for Material Modeling in Forming Simu-lations[J]. Steel Research Internation,2011,702-707. [4]Boger, R. K,Wagoner, R H, Barlat F, Lee M, Chung K. Continuous,Large Strain,Tension-compression Test of SheetMaterial[J]. International Journal of Plasticity 2005,(21): 2319-2343. [5]Kuwabara T,Kumano Y, Ziegelheim J, et al.Tension-compr-ession Asymmetry of Phosphor Bronze for Electronic Partsand its Effect on Bending Behavior[J].International Journal of Plasticity 2009,(25):1759-1776. [6]Yoshida F, Uemori T, Fujiwara K. Elastic-plastic Behavior of Steel Sheet under In-plane Cyclic Tension-Compression at Large Strain[J]. International Journal of Plasticity, 2002, (18): 633-659 [7]Cao J,Lee W, Cheng HS, et al. Experimental and Numeirical Investigation of Combined Isotropic-kinematic Harding Behavior of Sheet Metals[J]. International Journal of Plasticity 2009, (25): 1759-1776. [8]Chen Zhongchun,Mackawa S,Takeda T. Bauschinger Effectand Multiaxial Yield Behavior of Stress—rversed Mild St-eel[J].Metallurgical and Materials Transactions A,1990,30:3069-3076. [9]Hu Z. Work—hardening Behavior of Mild Steel under St-ress Reversal at Finite Strains[J]. Acta Metallurgica et Ma-terialia,1994,42:34813491. [10]Han, K., C. J. Van Tyne, et al. (2005). "Effect of strain and strain rate on the bauschinger effect response of three different steels." Metallurgical and Materials Transactions A 36(9): 2379-2384. [11]Stout, M. G. and A. D. Rollett (1990). "Large-strain Bauschinger effects in fcc metals and alloys." Metallurgical Transactions A 21(12): 3201. [12]Lee Myoung-Gyu, R.H.Wagoner, J.K.Lee, K.Chung, H.Y.Kim. Constitutive modeling for anisotropic/asymmetric hardening behavior of magnesium alloy sheets[J]. International Journal of Plasticity, 2008, 24:545-582. [13]J.Bauschinger. Changes of the elastic limit and the modulus of elasticity on various metals[J]. Civilingenieur.1881, 27:289-348. [14]N.Chawla, B.Jester, D.T.Vonk. Bauschinger effect in porous sintered steels[J]. Materials Science and Engineering A .2003, 346:266272. [15]G.D.Moan, J.D.Embury. A study of the bauschinger effect in Al-Cu alloys[J]. Acta Metallurgica.1979, 27(5):903. [16]C.H.Caceres, J.R.Griffiths, P.Reiner. The influence of microstructure on the Bauschinger effect in an Al-Si-Mg casting alloy[J]. Acta Mater.1996,44(1):15-23. [17]ZANG Shunlai, GUO Cheng, ZHANG Ke. Investigation on the material constitutive model in sheet metal forming[J]. Journal of Plasticity Engineering, 2007, 14(2):97-102. [18]LI Qun. Research on cyclic deformation behaviors of sheet flowing through drawbead and its subsequent forming performance[D]. Qinhuangdao : Yanshan University, 2011. [19]LI Guangyao, WANG Hu, YANG Xujing, et al. Some new topics on process design and mould manufacture for sheet metal forming[J]. Journal of Mechanical Engineering, 2010, 46(10):31-39. [20]NIU Tao, KANG Yonglin, GU Hongwei, et al. Bauschinger effect of high grade X80/X100 pipeline steels[J]. Journal of University of Science and Technology Beijing, 2010, 32(9):1144-1149. [21]ERALP D, DIERK R. Mechanical and microstructural single-crystal Bauschinger effects : Observation of reversible plasticity in copper during bending[J]. Acta Materialia, 2010, 58(18):6055-6063. [22]JORDON J B, HORSTEMEYER M F, SOLANKI K. Damage and stress state influence on the Bauschinger effect in aluminum alloys[J]. Mechanics of Materials, 2007, 39(10):920-931. [23]M Samuel. Influence of drawbead geometry on sheetmetal forming[ J]. Journal of Materials ProcessingTechnology,2002.122:94-103 [24]HAN X, WANG G, LIU G P. A modified tikhonov regularization method for parameter estimations of a drawbead model[J]. Inverse Problems in Science and Engineering, 2009, 17(4):437-449.