外文原文2：Numerical Simulation of Residual Stress during Stamping-Forging Forming of 2024 Aluminum Alloy Sheet Metal.pdf

1、Numerical Simulation of Residual Stress during Stamping-forging Forming of 2024 Aluminum Alloy Sheet Metal Da Li, Lei Deng, Xinyun Wang*, Junsong Jin and Juchen Xia State Key Lab of Material Processing and Die (b) elastic unloading stress; (c) residual stress r The residual stress can be determined

2、from Eq. (2) 10： 22 3 (3) 1() 2 rs hZ Z h = i 22 3 (3)2 () 2 s rs hZ ZZ h = i i i i. (2) where s is the yield strength and Z is the distance between the neutral layer and the calculated position. As shown in Fig. 1, the distribution of residual stress in the plate after unloading is more complex. In

3、 the bending process, the bending stress is simple tension and compressive stress, while the residual stress is showing alternative distribution of tension and compressive stress after unloading to maintain balance in the plate. The inner layer of round corner remains residual tension stress and the

4、 outer layer remains residual compressive stress. This state is caused by different deformation mode in the inner and outer layers during bending process. The stamping-forging forming process proposed in this paper can adjust the residual stress field by changing the deformation mode of bending roun

5、d corner. Its schematic is shown in Fig. 2. 1904Progress in Materials and Processes Fig.2 Schematic of the stamping-forging forming process In Fig. 2, r is the inner radius of the bending round corner; t is the thickness of sheet; is the bending angle; and s is the distance between punch and sheet.

6、The relative bending radius is calculated by r/t. The thickening degree of upsetting can be determined by the ratio of s and t. First, the punch is pushed down until the distance between the die and the punch reaches t. In this process, the bending deformation of sheet is occurred. Then the punch is

7、 fixed after it is shifted up to a distance of s. Both pressing blocks on each side are pushed along the inclined wall of the die. The thickening of sheet is occurred with upsetting force, and the sheet finally fit with the punch. In the upsetting process, the round corner and straight side of the s

8、heet both occurs the plastic deformation. Finite element simulation of stamping-forging process Simulation scheme. Two bending angles (=90, 120) and two relative bending radii (r/t=2.5, 3) were selected in the numerical analysis of bending and stamping-forging process of 2024 aluminum alloy V-shaped

9、 piece. And the thickening degree was 10%. Material properties test. The material used in this study was cold-rolled 2024 aluminum alloy plate of length 60 mm and thickness 2 mm. Its heat treatment condition was T4. In order to obtain material properties needed in the finite element simulation, the

10、uniaxial tensile test of aluminum plate at room temperature was conducted. Tensile specimens were prepared by wire electrical discharge machining along the rolling direction. The tensile tests were conducted in a universal testing machine (Zwick/Roell Z020) and the tensile speed was 1 mm/min. The pl

11、astic section of true stress-strain curve is shown in Fig. 3. It can be seen from the change in the trend of the curve that the fracture mode of alloy is brittle fracture at room temperature. The maximum true plastic strain is 0.171 and the fracture stress is 679 MPa. The yield strength and elastic

12、modulus measured in the test are 395 MPa and 70 GPa, respectively. Fig.3 The plastic section of true stress-strain curve Establishment of finite element model. The 2-D finite element models of the bending and stamping-forging process were established by Abaqus/Explicit, as shown in Fig.4. Due to the

13、 ratio of width to thickness is larger than 8, the deformation process can be regarded as a plane strain process. A two-dimensional and four-node plane strain element with reduced integration and Advanced Materials Research Vols. 602-6041905 hourglass control 11, CPE4R element, was used to mesh the

14、aluminum plate. Contact condition adopted the penalty contact condition with a tangential friction coefficient of 0.1. The Youngs Modulus of 70 Gpa, Poissons ratio of 0.31, and constitutive relationship were derived from tensile test data. After the simulation of the forming process, the residual st

15、ress field after springback was calculated by Abaqus/Standard. (a) (b) Fig.4 Finite element models: (a) bending model (=90); (b) stamping-forging model (=90) Results and discussion Stress and strain distribution after bending and stamping-forging. In order to clearly observe and coMPare internal res

16、idual stress in different forming processes, the stress and strain distribution in V-shaped piece when bending angle is 90and relative bending radius is 2.5 are shown in Fig. 5. (a) (b) (c) (d) (e) (f) Fig.5 Stress and strain distribution before and after stamping-forging (=90, r/t=2.5): (a)Equivale

17、nt plastic strain after bending; (b) Equivalent plastic strain after stamping-forging; (c) X-axis plastic strain after bending; (d) X-axis plastic strain after stamping-forging; (e) X-axis residual stress after bending; (f) X-axis residual stress after stamping-forging 1906Progress in Materials and

18、Processes We can see from Fig. 5(a) that the equivalent plastic strain of non-deformation zone in the straight side is zero, and the deformation is mainly occurred at the round corner. The equivalent strain gradually decreases from the inner and outer edges to the neutral layer in where strain is ze

19、ro. In Fig. 5(b), the equivalent strain is greater than that of piece without upsetting shown in Fig. 5(a), and tends to be uniform at the round corner. This indicates that the plastic deformation has occurred in the whole plate under the upsetting force. Fig. 5(c) shows that x-axis plastic strain v

20、alue of inner layer is negative, while the outer value is positive, which indicates the fibers of inner layer are compressed and the outer ones are stretched. The maximum compressive strain in the inner side of round corner is 0.142, and the maximum tension strain in the outer side of round corner i

21、s 0.154. After upsetting, the maximum compressive strain is 0.152, and the maximum tension strain is 0.147, as shown in Fig. 5(d). It illustrates the increased compressive strain in the plate after upsetting can compensate part of the tension strain, which can make stretched fibers to be recovered.

22、The x-axis residual stress distribution after bending is shown in Fig. 5(e). In non-deformation zone the residual stress is nearly zero, while in deformation zone the inner layer remains residual tension stress and the outer layer remains residual compressive stress. The maximum residual tension and

23、 compressive stress are 241 MPa and 284 MPa, respectively. In Fig. 5(f), the inner and outer layers of round corner all remain residual compressive stress after upsetting, while the middle region remains residual tension stress. In the straight wall, the residual stress is within the range of 2 MPa,

24、 while at the round corner, the maximum tension and compressive stress are reduced to 95 MPa and 90 MPa, respectively. This indicates the residual stress has been significantly reduced after upsetting. Residual stress field after stamping-forging. After stamping-forging, the distribution of x-axis r

25、esidual stress x was determined along the sheet thickness. 70 integration points were selected along the path shown in Fig. 6. The residual stresses of profiles are shown in Fig. 7. Fig. 6 Measurement path of x-axis residual stress at the bending section (a) (b) Fig. 7 Residual stress profiles befor

26、e and after stamping-forging: (a) =90 ; (b) =120 Advanced Materials Research Vols. 602-6041907 In Fig. 7(a) and (b), the residual stress distribution in bended parts are basically the same under different conditions. There is residual tension stress in the inner surface, and alternative distribution

27、 of tension stress and compressive stress from inner to outer. On both sides of plates neutral layer, there exist two peak values of residual tension and compressive stress. However, the trend of residual stress distribution after upsetting has been changed. The residual tension stress in inner laye

28、r is transformed into compressive stress. And it remains residual tension stress within the range from 0.5 mm to 1.5 mm in the plate. The maximum residual tension and compressive stress after bending increases with increasing of relative bending radius and bending angle. The maximum tension stress r

29、eaches 261 MPa, and the maximum compressive stress reaches 307 MPa. After stamping-forging the residual stress reduction is all more than 60%. It can be seen that the upsetting process makes distinct improvement on the residual stress field. The plate is divided into two regions in bending process.

30、Inner layer is compressed and occur compressive strain. Outer layer is stretched and occur tension strain. During the upsetting process, part of the tension strain of outer layer is compensated and tends to be compressive strain. Therefore, bending-upsetting can significantly improve the distributio

31、n of the residual stress field, which is beneficial to improve the dimensional accuracy and performance in sheet metal forming. Forming accuracy after stamping-forging. In elastic-plastic bending deformation, the plastic strain will be retained in the plate after unloading, while the elastic deforma

32、tion recovers. So it is inevitable to lead to springback. Too large springback angle will seriously affect the dimensional accuracy and the using performance of parts. In this paper, the influence of stamping-forging process on forming accuracy is also obtained. Fig. 8 Springback angle before and af

33、ter stamping-forging The relationship between springback angle and relative bending radius under different condtions is shown in Fig. 8. The springback angles after bending are all positive, and increase with increasing of bending angle and relative bending radius. After upsetting, the springback an

34、gles are all negative, and the maximum reachs -1.9. The outer zone of round corner is elongated and inner zone is shortened during bending. After unloading, the recovery trend of both zones make the plate straight, so it appears a springback angle. However, after upsetting, because both inside and o

35、utside areas are compressed, the recovery trend can be offset by each other. Due to the negative springback angle appeared after upsetting, we can assume that there must be a moment of zero in the transition process from positive to negative. It is suggested that we can achieve zero springback by ch

36、anging the upsetting reduction, which has a positive significance on the control of dimensional accuracy in forming process of plate parts. Conclusions A new method to adjust the residual stress field based on stamping-forging process was proposed in this paper. The following conclusions can be draw

37、n from this study. (1) The residual stress field in 2024 aluminum plate after bending appeared to be an alternative distribution of tension and compression stress with large gradient. The maximum residual stress appeared at both sides of the neutral layer, and its amplitude was within the range of 3

38、00 MPa. 1908Progress in Materials and Processes After upsetting, the stress gradient became relatively small. There remained residual compression stress in the inner and outer layers of round corner, while residual tension stress in the middle zone. The amplitude was reduced to the range of 100MPa.

39、Therefore, the stamping-forging forming process is an effective method to reduce the residual stress in 2024 aluminum alloy plate. (2) Due to inner and outer areas were all subjected to large compressive deformation during stamping-forging process, the springback was commendably improved by upsettin

40、g. In addition, the negative springback was appeared after upsetting, which provides a suggestion for the study of changing the upsetting reduction to adjust the springback compensation, even to achieve the zero springback. Acknowledgements The authors wish to express sincere gratitude for the grant

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