A new method for fracture based on surface roughness in foil micro-deep drawing.doc
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1、精品论文A new method for fracture based on surface roughness in foil micro-deep drawing5YU Hailiang1,2(1. School of Mechanical, Materials, Mechtronic Engieering, University of Wollongong;2. School of Mechniacl Engineering, Shenyang University)Abstract: With the development of the micro-electro-mechanica
2、l systems (MEMS) technology and miniaturization of products, more attentions have been paid to the micro forming technology. The10paper proposed a new model which couples the Gurson-Tvergaard-Needleman damage model andrandom foil surface roughness distribution to investigate the fracture behavior of
3、 foils during micro-deep drawing. Results show that local non-uniform strain distribution due to the foil roughnessresults in crack occurrence. The calculated shape of fractured blank is in good agreement with experimental result. This study provides a new method to study the damage behavior in micr
4、oforming15process, and the findings are of guiding significance for understanding the damage behavior in the microforming process.Key words: Micro-deep drawing; ductile fracture; finite element method; stainless steel foil; surface roughness200IntroductionWith the development of the micro-electro-me
5、chanical systems (MEMS) technology and miniaturization of products 1, more attentions have been paid to the micro forming technology to improve through put for product development and creation along with the expansion of the market 2.25Surface roughness is an important factors that influence the qua
6、lity of a component, which has an impact on their functional performance 3, 4. In the micro-deep drawing process with decreasing the blank thickness, the surface roughness becomes the most important for the feasibility of micro forming processes, due to the increase of the surface to volume ratio wh
7、en scaling down process dimensions 5. Chang et al 6 found that smaller workpiece surface30roughness resulted in a low and constant friction in the early stage of the micro extrusion.An experimental program has been carried out for hydroforming of stainless steel micro-tubes by Zhuang et al 7. It was
8、 found that failure took place randomly, which was significantly different from observations of failure in hydroforming of macro-tubes by traditional macro Finite Element Method (FEM), where failure loads and locations were predictable. This35occurs because wall thinning of micro-tubes in forming pr
9、ocesses is non-uniform, i.e. localized necking takes place randomly. Damage mechanisms have to be understood for large plastic strain and complex multiaxial loadings 8. Wielage et al 9 found the fracture occurred at punch force levels well below those predicted by common equations. They pointed out
10、these phenomena couldbe accounted for by non-uniformity in the flow behavior of the material.40The FEM has been used in the simulation of the deep drawing process 10-15. Hu 10 used the size dependent FEM with friction functions to determine an optimum blank shape for a flange free rectangular micro
11、workpiece which was validated in experimental investigation. Manabi 11 et al used the two-dimensional finite element method to predict the roughness of workpiece during micro-deep drawing, but they did not consider the fracture behavior of materials. Ling et al 13, 1445used the Gurson-Tvergaard- Nee
12、dleman (GTN) ductile amage model to analyze the fractureFoundations: The financial support from the Vice-Chancellors Fellowship Grant at the University of Wollongong; the National Natural Science Foundation of China (51105071); Doctorate Foundation of the Ministry of Education of China (200900421200
13、05).Brief author introduction:University of Wollongong; Shenyang University. E-mail: - 6 -behavior of stainless steel sheet deep drawing, however, the surface roughness was not considered in models. In this paper, we firstly presented a three-dimensional finite element model considering both the dam
14、age and surface roughness of blank to study the fracture behavior during micro-deep drawing. The simulated shape of fractured blank is in good agreement with the experimental50result.1ModelFig. 1 shows the illustration of deep drawing process. The main geometrical dimension sizes are listed in Table
15、 1 11. The blank material is stainless steel (SUS 304) ultrathin foil of 23 m thickness.55Fig. 1 Illustration of deep drawing and dimension sizeTable 1. Geometrical parameters in deep drawing in Fig. 1 11ParametersValueDiameter of blank (DB), mm1.1Thickness of blank (TB), m23Diameter of drawing die
16、(DD), mm0.69Radius at corner of die (RD), mm0.1Diameter of punch (DP), mm0.654Radius at corner of punch (RP), mm0.1In the simulation, the punch, die and blank hold are considered as rigid. The GTN model is employed to simulate the fracture behavior of blank. GTN model, as shown in Eq. (1) 12, has60b
17、een proved successful to predict mechanical degradation and failure in tensile-dominantprocesses,(f )s eq f = () 2 + 2q fcosh 3 q 2s H ) - (1 + q 21 v3 Vs 02 s 0(1)where, f , fv is the void volume fraction. The parameters q1, q2, q3 are materials coefficients. For the SUS 304 stainless steel, the Yo
18、ungs modulus is 199 MPa, Poissons ratio 0.285, yield65stress 286 MPa, ultimate stress 668 MPa , and the true stress versus true plastic strain is listed inTable 2, other parameters in GTN model are listed in Table 3 13, 14.Table 2. Parameters of true stress versus true plastic strain adopted in FE m
19、odel 14True strain0.000.040.100.170.200.270.400.53True stress, MPa218385491604655761954112570Table 3. Main parameters in GTN model 13Parametersf0fcfFfN NSNq1q2q3Value0.0010.02230.1520.0040.30.11.51.02.25In the models, we assumed the maximum surface roughness peak is 500 nm. In the FE model, every el
20、ement was given a random roughness value from 0 to 500 nm.The three-dimensional geometrical model of the stainless steel foil micro deep drawing was established with the parameters above and meshed with quadrilateral elements by shell-type75elements. The roughness of the blank was considered in the
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