Papers by Keyword: Fracture Criterion

Abstract: Strength and ductility data for Q235A steel from 20 oC to 950 oC was obtained from a series of experimental tests. The stress rate sensitivity was studied by conducting Split-Hopkinson Tension Bar (SHTB) test and uniaxial tension test on smooth cylindrical specimens while the influence of stress triaxiality on ductility was revealed by conducting upsetting tests, tension tests on pre-notched cylinder specimens and torsion tests on SASs. Slightly modified versions of the two Johnson–Cook (J–C) models describing flow stress and fracture strain are presented to characterize the properties of Q235A steel as function of strain rate, temperature and stress triaxiality. Corresponding model parameters were calibrated based on the test data and with the help of finite element calculation. It was found that the modified Johnson–Cook (MJC) models give more close predictive results compared with the original J–C models.

Abstract: In order to study the concrete compound crack and fracture extension problem such as brittle material, based on the analysis of the fracture criterion theory ,on the analysis of some measured data, and the near crack tip portion of the shape change energy, the strain energy criterion of Iso- line for Ⅰ-Ⅱ mixed mode crack was proposed, a crack initiation angle formula and the fracture criterion were established, and the variation law among ， with Poisson ratio was discussed . Using the criterion, the concrete compound crack was analyzed. Results show that the theoretical values are consistent with the measured values. So the criterion can be applied to analyze the mixed mode crack fracture of brittle material such as concrete.

Abstract: A method to simulate the crack growth, according to the strain energy release rate criterion, with the virtual crack close technique, is studied. The virtual crack close technique is used to calculate the strain energy release rate. To achieve the virtual crack close technique, in the FEA software of ANSYS, COMBIN14 spring elements are adopted to set up the finite element model. Then this method to simulate the crack growth is validated by three crack growth problems. This method is a useful and accurate numerical simulation method.

Abstract: In practice, the crack in some engineering materials is often compound crack. Therefore, it is important engineering significance to study on fracture problem. Based on the shape change energy near crack tip portion, the area fracture criterion of Iso-εθ line for compound crack was proposed. A crack initiation angle formula and the fracture criterion were established. The results showed that the theoretical predicted values and the measured values are consistent. The compound crack fracture line area of fracture criterion was established.Tthe formulas are easy to be derived and convenient to apply.

Abstract: With the development of economical society and the stone industry, the product of granite thin slab becomes a trend, and gets the welcome of people. The grinding technology influences the quality of granite thin slab. This paper first introduced the situation of the grinding technology of granite thin slab, analyzed the mechanism of the grinding process of granite thin slab and fractured problem by observing the fractured granite thin slab. Then, based on the Hoek-Brown criterion, we researched the fracture criterion and the critical thickness of granite thin slab when grinding. Finally, we set up the fracture criterion of the granite thin slab and built the mathematical model between the thickness of the granite thin slab and grinding process parameters. According to the thickness of the granite thin slab, grinding process parameters can be formulated, in order to ensure the granite thin slab no fractured.

Abstract: Fracture of coating materials often occurs at or near the interface, while the mechanism and criterion of interface fracture are not clear yet. A molecular dynamics simulation method was introduced to simulate the interface crack initiation, and the relationship between the interface stress and the interface fracture was found. Although a simplified model was applied, the results still showed some intrinsic features that are useful to study the process of interface fracture. At last, an interface fracture criterion was proposed.

Abstract: The finite element modeling and simulation of extremely high speed machining of Ti6Al4V alloy are presented in the paper. The Johnson-Cook’s constitutive model is used to describe the material behavior. The Johnson-Cook damage initiation criterion is used to predict the onset of damage due to void nucleation in ductile fracture. A damage evaluation law based on plastic strain energy and a fracture criterion combining the effect of different fracture mechanisms are proposed to model the progressive damage and fracture, respectively. Simulation results show that the predicted chip morphology agrees well with the experimental one. The distribution of temperature and specific cutting force are discussed later.

Abstract: The inclined surface cracks are under the mixed mode I，II，III loading conditions. In order to study the surface crack growth the stress intensity factors of the front of half-circular surface crack are calculated according to fracture analysis code-3D(FRANC3D). And the influences of inclination angle of the surface crack and the orientation angle on I，II，III mode stress intensity factors were analyzed. I mode stress intensity factor increases along the crack front with increasing inclination angle. And I mode stress intensity factor of the same inclination angle is symmetrical with respect to the orientation angle of 90 degree. II，III mode stress intensity factors are the maximum when the inclination angle is equal to 45 degree. And the behavior of II，III mode stress intensity factors along crack front for the inclination angle of 15 and 30 degree is identical with that of inclination angle of 75 and 60 degree, respectively.

Abstract: Due to the limitation of 2D simulation in fine blanking, finite element software DEFORM-3D was used to simulate the 3D model of Back Plate. In this article the Normalized Cockroft&Latham fracture criterion was chosen to simulate the blanking process. The distribution and developing trend of the hydrostatic stress, equivalent stress in the fine blanking process are predicted. When the die radii are between 0.4mm and 0.6mm, burnished surface improves. It shows that the ideal blanking clearance value is 0.6% of the material thickness. The results indicate that FE numerical simulation could effectively optimize fine blanking process and offer basis for quality improvement.

Abstract: Based on the isothermal compression experiment under constant strain rate, the deformation behavior and flow stress of as-extruded 7075 aluminum alloy at high temperature was studied. Then the fracture behavior and mechanism of 7075 aluminum alloy were investigated, the results showed that longitudinal cracking was easy to occur at a high temperature due to additional tensile stress and low melting point alloy in grain boundaries melting. Through analysis and comparing of C&L and Oyane fracture criteria, it was proved that C&L fracture criterion was more reasonable to predict fracture in 7075 aluminum alloy hot deforming, and the critical damage factor in a forming temperature range(300~450°C) for 7075 aluminum alloy was obtained.