连铸机外论文中英文对照资料外文翻译文献.docx

1、连铸机外论文中英文对照资料外文翻译文献中英文对照资料外文翻译文献Effect of Porosity on Deformation, Damage,and Fracture of Cast SteelR.A. HARDIN and C. BECKERMANNA combined experimental and computational study is performed to investigate the eect ofcenterline shrinkage porosity on deformation, damage, and fracture of cast steel und

2、er tensiletesting. Steel plates containing shrinkage porosity are cast in sand molds, machined into testcoupons, and tensile tested to fracture. The average volumetric porosity in the gage section ofthe specimens with porosity ranges from 0.10 to 0.27 pct. Ductility in the test castings withporosity

3、 is markedly reduced with the percent elongation data ranging from 12.8 to 19.6 pct; vs22 pct elongation for the sound material. Radiographic imaging is used to measure andreconstruct the porosity eld in the test specimens. The reconstructed porosity eld is then usedin a nite-element stress analysis

4、 simulating the tensile testing. Local elastic properties arereduced according to the porosity fraction present. Porous metal plasticity theory is used tomodel the damage due to porosity and the fracture. Good agreement is obtained between themeasured and predicted stressstrain curves and fracture b

5、ehaviors. The reduction in ductility ispredicted well by comparing the measured and the simulated elongations. The computationalmodeling approach used in this study allows for a detailed evaluation of the eect of porosity,including its size, shape, and location, on the fracture behavior of steel cas

6、tings.DOI: 10.1007/s11661-013-1669-zThe Minerals, Metals & Materials Society and ASM International 2013I.INTRODUCTIONSTEEL castings are under-utilized because of uncertainties in their performance and lack of expertise in casting design. Discontinuities in castings, like porosity,play an important r

7、ole in casting underutilization.Porosity creates uncertainty in a designs robustness,since there are no methodologies for including its presence in the design. As a result, designers employ overly large safety factors to ensure reliability leading to heavier components than necessary. Contributing t

8、o the issue, the processes of designing and producing castings are usually uncoupled except for the specication of nondestructive evaluation (NDE) requirements. Unless mdesign engineers have test data or experience for a part,they call for NDE requirements without knowing how this relates to part pe

9、rformance. By predicting porosity accurately from casting simulation and realistically modeling its eects on the part performance, engineers can develop robust designs that are tolerant of the porosity and reliable. In the current study, engineering approaches have been applied to simulate the eect

10、of porosity on deformation, damage, and fracture for a cast steel during tensile testing, and the simulationresults are compared with measurements.The material used in this study is ASTM A216 Grade WCB steel. It is a cast carbon steel having a combination of good ductility and strength. It has the f

11、ollowing chemical composition (maximum wt pct): C 0.3; Mn 1.0;P 0.035; S 0.035; Si 0.6; Cu 0.3; Ni 0.5; Cr 0.5; Mo 0.2;and V 0.03; and the total of Cu, Ni, Cr, Mo, and V cannot exceed 1.0 wt pct. At room temperature, Grade WCB steel has a yield strength and a tensile strength of 248 and 485 MPa, res

12、pectively, and 22 pct elongation as minimum tensile requirements in ASTM A216. Failure of such ductile metals occurs on the microscopic scale by mechanisms of void nucleation, growth, and coalescence.1Voids can pre-exist as microporosity and can also nucleate from imperfections like second-phase par

13、ticles. After nucleation, voids grow with increasing hydrostatic stress and local plastic straining. As voids nucleate and grow, the void (or porosity) volume fraction increases. The voids begin to interact, and the porosity fraction at which interactions between voids begins is the critical porosit

14、y volume fraction fc. As plastic strain continues to increase, local necking and coalescence occur in the material between voids until a connected chain of voids forms and failure occurs. The porosity fraction at which fracture occurs is the failure porosity volume fraction fF. The eects of porosity

15、 on the structural performance of carbon and low alloy steel castings on the macroscopic scale are not as clearly dened as they are on the microscopic scale. In previous studies, the eects of large amounts of porosity on stiness and fatigue life were investigated.2,3 Porosity less than a few percent

16、 does not result in a measurable loss of stiness, or large stress concentrations, or stress redistribution, but itgreatly aects fatigue resistance.4,5Also, the presence of low-level porosity will reduce the ductility of metals since microvoids pre-exist before any stress is applied and the nucleatio

17、n stage is bypassed. Porosity larger than a few percent in metals causes gross section loss,and locally reduces their eective stiness.68This higher-level porosity is not uniformly distributed throughout the entire cast part, and the material properties in the casting are heterogeneous. As a result,s

18、tress redistribution occurs in parts because of macropores, and stress concentrations occur near them, which lead to localized plastic deformation and the development of microcracks causing failure. Generally speaking, the performance of a casting with macroporosity depends on the amount, size, and

19、location of porosity relative to the cast components geometry and loading. All these factors must be considered together. Determining the eects of large levels of porosity on part ,performance is typically more case-by-case dependent than for lower levels It has been proposed that the stiness and st

20、rength behaviors of porous materials can be categorized into three groups based on porosity amounts9: less than 10,10 through 70 pct, and materials with greater than 70pct. This division is promoted because the materials at the extremes (70 pct) behave quite dierently.The highest porosity group is n

21、ot applicable to cast steels; these are foams and cellular structures. The elasticplastic behavior of porous materials in the 10,through 70 pct porosity range exhibit a nonlinear dependence on the amount of porosity2,69The behavior of materials in the lowest range demonstrate a more linear dependenc

22、e on porosity amount, assuming that voids do not interact 10and by considering isolatedpores,11or a uniform distribution of pores.12Applying the ductile failure micromechanical mechanisms described previously, one such micromechanics-based model is the porous metal plasticity model. It is available

23、in the nite element analysis (FEA) softwareABAQUS.1115In the model, the volume fraction of porosity is a primary state variable, and the inelastic ow of the material is modeled as voids grow and coalesce at higher strains until failure occurs. Porous metal plasticity was developed assuming voids are

24、 spherical and grow as spheres. It also assumes the materials plastic behavior is dependent on hydrostatic pressure because of the porosity, and therefore neglects eects of shear stresses on porous material behavior. Considering this and the limitations of porous metal plasticity, there have been nu

25、merous developments in modeling of ductile fracture16 addressing other void geometries and stress states. While not state-of-the-art, porous metal plasticity is a constitutive model readily available to designers of cast components, and can be a useful tool to investigate the eect of porosity on a c

26、astings fracture behavior. It is a common constitutive model found in many commercial nite element packages. This article uses the porous metal plasticity model in FEA to predict the ductile fracture of cast steel with centerline porosity. The primary goal of the current study tests whether or not t

27、his commonly available model can predict the fracture of steel with relativelylarge amounts of porosity detectable through typical industrial radiography. Here, castings with porosity were produced, made into plate specimens, and radiographed. The porosity was quantitatively determined from the radi

28、ographs. The castings underwent tensile testing. Using porosity data from the radiographs, nite element stress models of the test specimens with porosity were created, and the tensile testing simulated using an elasticplastic material model. Results of the simulated fracture are compared here with t

29、he measured fracture to test the models capabilities in predicting the fracture behavior of steelwith centerline shrinkage porosityII. MATERIAL PREPARATION,MEASUREMENT, AND ANALYSISA.Cast Specimens and Mechanical TestingFor the tensile fracture study presented in this article,WCB steel specimens wer

30、e produced from 2.5 cm thick 9 12.7 cm wide vertically cast plates of two lengths (38.1 cm and 45.7 cm) as shown in Figure 1(a). The plates were designed through casting simulation with MAGMAsoft17to contain centerline shrinkage as shown in Figures 1(b) and (c). Five cast plates were produced and te

31、sted from the longer length castings, and four were produced and tested for the shorter-length castings. The letters D and E were used to identify the shorter and longer plates, respectively; followed by numbers 1 through 5. The cast plates were normalized and tempered, and machined into 19-mm-thick

32、 tensile test coupons with a gage section width of 86 mm as shown in the front and side views for the specimen in Figure 2(a). The tensile specimen dimensions for the plates with centerline porosity were determined from the ASTM E8 tensile test standard.18 The positioning of the extensometer on the narrow/thickness face of the specimen is indicated in Figure 2(a). In Figure 2(b), a smaller tensile test specimen is shown, which was machined from the porosity-free (orsound) section of a cast plate. The specimen shown in Figure 2(b) was tested to characte