Impact analysis of casting parts considering shrinkage cavity defect

Shrinkage cavity may be detrimental to mechanical performances of casting parts.As a consequence,design engineers often use overly large safety factors in many designs due to insufficient understanding of quantitative effects of shrinkage cavity defects.In this paper,process of Al alloy wheel impact test was computationally analyzed for both the wheel models with and without shrinkage cavity defects.Based on shrinkage cavity data obtained from industrial CT (Computerized Tomography),the shrinkage cavity defects were modeled with SSM (Shape Simplification Method),which reconstructs shrinkage cavity defects to hollow spheroid primitives.After the impact simulation was conducted,the results show that under impact test condition,the wheel considering shrinkage cavity defects may fracture while the sound-assumed wheel may not.

Finite element simulation of real cavity closure in cast Ti6Al4V alloy during hot isostatic pressing

The healing behavior of shrinkage cavity inside the cast Ti6Al4V alloy during hot isostatic pressing(HIP)was investigated experimentally by interrupted hot isostatic pressing tests.The X-ray micro computed tomography was used to record the morphology changes before and after hot isostatic pressing.The two-dimensional geometry obtained by the microCT scan was used in simulation to study the evolution of the real shrinkage cavity during hot isostatic pressing.Shrinkage cavities,shrinkage porosity and small gas pores can be effectively eliminated under proper HIP conditions.The two-dimensional morphology in the simulation results agrees well with the experimental results.This study reveals that plastic deformation,creep and diffusion are the main mechanisms of cavity closure during hot isostatic pressing.In addition,the simplified elliptical pores with aspect ratios at different positions were used to replace the real pores to further study the factors affecting the position of dimples after HIP by simulation.It is found that the position of the dimples mainly depends on the aspect ratio of the elliptical pore and the distance between the pore surface and the external surface of the geometric model.

Effect of forced lamina flow on microsegregation simulated by phase field method quantitatively

The influence of supercooled melt forced lamina flow on microsegregation was investigated. The concentration distribution at solid-liquid boundary of binary alloy Ni-Cu was simulated using phase field model coupled with flow field. The microsegregation, concentration maximum value, boundary thickness of concentration near upstream dendrite and normal to flow dendrite, and downstream dendrite were studied quantitatively in the case of forced lamia flow. The simulation results show that solute field and flow field interact complexly. Compared with melt without flow, in front of upstream dendrite tip, the concentration boundary thickness is the lowest and the concentration maximum value is the smallest for melt with flow. However, in front of downstream dendrite tip, the results are just the opposite. The zone of poor Cu in upstream dendrite where is the most severely microsegregation and shrinkage cavity is wider and the concentration is lower for melt with flow than that without flow.

Research of Final EMS for Bloom in Ansteel

In this paper,the best final EMS frequency for bloom continuous casting is proposed.For 280×380 bloom,the best frequency is in the range of 4;Hz.Simulation results also show that,with this frequency,the electromagnetic force in the molten steel in the bloom reaches stronger and the electromechanical transformation rate of the stirring equipment is higher.The flow fields in the bloom with the various stirring parameters are simulated also.The final EMS parameters for bloom are optimized base on the simulation results.The experimental results show that,for high carbon steel,the best stirring frequency is 7 Hz and the current is 500A.In order to alleviate negative segregation of the low and medium carbon steel,the stirring frequency and the current should be 4Hz and 430A,respectively.

Preliminary Investigation on the Role of Vitrification in Pre-Implantation Genetic Diagnosis

Objective To investigate the feasibility of vitrification of blastocysts following blastomere biopsy. Methods Among patients undergoing pre-implantation genetic diagnosis （PGD）, artificial shrinkage of the blastocoelic cavity and subsequent vitrification of applicable surplus blastocysts after day-3 blastomere biopsy were performed. According to patient requirements, thawed blastocysts were transferred into patients due to pregnancy failure after fresh embryo transfer, ectopic pregnancy, ovarian hyperstimulation. Results Twenty-four PGD cycles were carried out. According to genetic diagnosis and the development of blastocysts, transfer was cancelled in 7 cycles due to absence of applicable embryos or ovarian hyperstimulation. In the remaining 17 cycles, 26 blastocysts were thawed and transferred, which resulted in 13 implanted （50.0%）. Clinical pregnancies were observed in 11 patients （64.71%）. Following transfer, 30 applicable blastocysts in 10 cycles were cryopreserved. Six patients received transfer of thawed blastocysts. All 8 thawed embryos survived and were transferred, and singleton pregnancies occurred in 5 patients. Two women delivered healthy infants and 3 pregnancies are ongoing. Conclusion Vitrification with artificial shrinkage is effective for preserving blastocysts following blastomere biopsy.