冲压工艺中几何及内圆角对模具应力产生的影响毕业论文外文翻译.docx

1、冲压工艺中几何及内圆角对模具应力产生的影响毕业论文外文翻译附录A 外文文献Effects of geometry and fillet radius on die stresses in stamping processesAbstract: This paper describes the use of the finite element method to analyze the failure of dies in stamping processes. For the die analyzed in the present problem, the cracks at differe

2、nt locations can be attributed to a couple of mechanisms. One of them is due to large principal stresses and the other one is due to large shear stresses. A three-dimensional model is used to simulate these problems first. The model is then simplified to an axisymmetric problem for analyzing the eff

3、ects of geometry and fillet radius on die stresses. 2000 Elsevier Science S.A. All rights reserved.Keywords: Stamping; Metal forming; Finite element method; Die failure1. IntroductionIn metal forming processes, die failure analysis is one of the most important problems. Before the beginning of this

4、decade, most research focused on the development of the- oretical and numerical methods. Upper bound techniques 1,2, contact-impact procedures 3 and the finite element method (FEM) 4,5 are the main techniques for analyzing stamping problems. With the development of computer technology, the FEM becom

5、es the dominant technique 6-12.Altan and co-workers 13,14 discussed the causes of failure in forging tooling and presented a fatigue analysis concept that can be applied during process and tool design to analyze the stresses in tools. In these two papers, they used the punching load as the boundary

6、force to analyze the stress states that exist in the inserts during the forming process and determined the causes of the failures. Based on these concepts, they also gave some suggestions to improve die design.In this paper, linear stress analysis of a three-dimensional (3D) die model is presented.

7、The stress patterns are then analyzed to explain the causes of the crack initiation. Some suggestions about optimization of the die to reduce the stress concentration are presented. In order to optimize the design of the die, the effects of geometry and fillet radius are discussed based on a simplif

8、ied axisymmetric model.2. Problem definitionThis study focuses on the linear elastic stress analysis of the die in a typical metal forming situation (Fig. 1). The die (Fig. 2) with a half-moon shaped ingot on the top surface is punched down towards the workpiece which is held inside the collar, and

9、the pattern is made onto the workpiece. Cracks were found in the die after repeated operation: (i) when the die punched the workpiece, there is crack initiation between the tip of the moon shaped pattern and one of the edges (Crack I); and (ii) after repeated punching, there is also a crack at the f

10、illet of the die (Crack II).The present work was carried out with the following objectives: (i) to establish the causes of the crack initiation; and (ii) to study the effects of geometry and fillet radius.3. Simulation and analysis3.1. 3D simulationThe simulation is performed with the FEM code Abaqu

11、s 15. Twomeshes are created for the die shown in Fig. 3a and b. The 3D solid elements for the workpiece are C3D8 (8- node linear brick) elements. There are about 4000 nodes and 3343 elements in the coarse mesh model, and 7586 nodes and 6487 elements in the fine mesh model. The boundary condition inv

12、olves fixing the bottomof the die, i.e., U2=0 for all the nodes on the die bottom. A pressure of 200 MPa is applied on the top surface of the half-moon pattern. Youngs modulus is 200 GPa and Poissons ratio is 0.3.In order to analyze the principal stress concentration area in the region of Crack I, d

13、ifferent cases are studied. Let the models shown in Fig. 3a and b be Case 1. A new 3D model (Case 2) is used as shown in Fig. 3c. The die is separated into three parts. The Abaqus command *CONTACT PAIR, TIED is used to tie separate surfaces together for joining dissimilar meshes. The advantage of th

14、is model is its convenience in changing the mesh of the half-moon pattern and its position. First, the half-moon pattern is moved 6 mm towards the center (Case 3) as shown in Fig. 3d. Second, the fillet radius of the half-moon pattern is changed from 0 to 0.5 mm (Case4) as shown in Fig. 3e.3.2. Resu

15、lts and discussionFor the two meshes used in Case 1. The maximum principal shear stress (S12) distribution at the region of fillet are shown in Fig. 4a and b. The results show that the stress distribution patterns are the same for the two different meshes, and therefore, the convergence of the solut

16、ions is established.Altan and co-workers 14 have presented the stress analysis of an axisymmetric upper die. In their work, when the material of the workpiece flows to fill the volume between the dies and collar, the contact surface of the die is stretched. At the area of the transition radius, the

17、principal stresses change direction and reach high tensile values.According to their analysis, the fatigue failure is due to two factors: (i) when the stress exceeds the yield strength of the die material, a localized plastic zone generally forms during the first load cycle and undergoes plastic cyc

18、ling during subsequent unloading and reloading, thus microscopic cracks initiate; and (ii) tensile principal stresses cause the microscopic cracks to grow and lead to the subsequent propagation of the cracks.The Von Mises stress distribution is shown in Fig. 5a. Very high stress occur in the half-mo

19、on and fillet regions. If the contact pressure keeps increasing, plastic zones will form first in these two regions.Fig. 5b shows the maximum principal stress (SP3) distribution pattern. In order to show the area of Crack I initiation, Fig. 5c provides a zoomed view of the area. It is clear that a t

20、ensile principal stress (SP3) concentration of 25.5 MPa exists between the half-moon pattern and the free edge and is the cause of crack initiation.Since Crack I propagates nearly normal to the 1-2 plane, the direction of the stresses which cause the crack initiation must be parallel to that plane.

21、Fig. 5d shows the direction of the maximum principal tensile stress at node 145 and confirms Crack I is normal to the 1-2 plane.After repeated punching, Crack II initiates in the fillet region, and gives rise to fatigue failure. The geometry in the local area is very similar to the case which Altan

22、and co-workers 14 have analyzed. However, there are no contacts tresses in that area for the present case, and Fig. 5b shows that the maximum principal stresses are all compressive at the fillet. Fig. 5e shows that there is high shear stress (S12) concentration at the fillet which is about 30 MPa. T

23、he shear stresses seem to be the stresses which lead to the initiation and propagation of cracks.The results of the four cases (Cases 1-4) for the largest maximum principal stresses are listed in Table 1.When the number of elements for the half-moon pattern is increased from 10 to 70, the largest pr

24、incipal stress at the position of Crack I initiation is increased by (30.5-25.5)/ 30.5=16%(Case 2). The principal stresses are very sensitive to the half-moon pattern.Cases 2-4 show the effect of location of the half-moon and its fillet radius. If the half-moon pattern is moved 6 mm towards the cent

25、er, the largest principal stress at the position of Crack I is reduced by (25.3-30.5)/30.5=-17% (Case 3). If the fillet radius of the half-moon pattern is changed to 0.5 mm, the principal stress is reduced (28.5-30.5)/ 30.5=-7% (Case 4). Therefore both these methods can reduce the stress concentrati

26、on, the first being more effective.4. Effects of geometry and fillet radius on die stress distribution4.1. 2D modelingIn order to optimize the die, the effects of geometry and fillet radius on die stress distribution are discussed further. An axisymmetric model is used (Fig. 6) for the analysis.Init

27、ially, the radius r1 of the inner cylinder is set to 10 mm, the height h of the inner cylinder is set to 5 mm, and the height H of the outer cylinder is set to 25 mm. Also, r2 is the radius of the outer cylinder, and the ratio r2/r1 is changed from 1.2 to 1.5, 2.0, 3.0 and 4.0. The radius R of the f

28、illet ischanged from 2.0 to 0.5 mm, and h is changed from 5 to 2 and 0 mm. The pressure is given as 200 MPa at the top surface. The nodes at the bottom edge are fixed, and all others are free to translate (except those on the axis in the radial direction).4.2. Results and discussionA total of 30 cas

29、es were studied. Parameters that are varied include r2/r1 ratio, h, and fillet radius R. These 30 cases are shown in Table 2. For all cases, r1 is fixed at 10 mm and H is fixed at 25 mm.4.2.1. Effect of r2/r1The effect of varying the r2/r1 ratio is examined for cases with the value of h fixed at 5 m

30、m. Fig. 7a-c with the value of h fixed at 5 mm and varying ratio of r2/r1 shows that the maximum value of the principalstress (SP3) reduces with increasing r2/r1, and changes in position from a point on the surface to below the surface. This trend is reflected in Fig. 8a.On the other hand, Fig. 8b i

31、ndicates that the maximum shear stress (S12) becomes larger with increasing ratio of r2/r1. The rate of this increase drops with increasing r2/r1. The shear stress patterns for some cases are shown in Fig. 7f-h.4.2.2. Effect of height hThe effect of height h of the inner portion is examined for thre

32、e cases with h=0, 2 and 5 mm with R fixed at 2 mm. From Fig. 8a, it can be seen that the maximum principal stress (SP3) increases marginally with increasing h up to r2/r1 of 2, after which the trend is reversed. However, for large h, the effect becomes less important. On the other hand, the maximum shear stress is higher with increasing h for the same r2/r1 ratio. Stress patterns are shown in Fig. 7a, d-f, i and j.4.2.3. Effect of fillet radius RThe effect of fillet radius R is examined for two cases with R=0.5 and 2 mm. The results are shown in Fig. 8c and