Materials Science Forum Vols. 575-578

Abstract: The transformation production and recrystallization for Mo Micro-alloy Steel had been carried out on the Gleeble-3800 thermo-mechanical simulator. Based on the schedule, TMCP was applied to two stages multi-pass hot rolling experiments and the influences of the technological parameters on microstructure and mechanical property were analyzed. The results showed that the microstructure, precipitation and mechanical property of Mo Micro-alloy steel were strongly affected by the start-rolling temperature, the end-rolling temperature, the cooling rate and the relaxation time. The appropriate parameters were used and the ideal volume fraction of the acicular ferrite was observed by using metallographic microscope and transmission electron microscope(TEM).

Abstract: Incremental in-plane bending is a flexible and laborsaving manufacturing technology for short production runs in a variety of sizes and shapes. But the technology parameters are interactive intimately and it is hard to forecast and control the bending radius accurately. Based on the features of incremental in-plane bending and the advantage of expert system dealing with problems, an expert system of incremental in-plane bending by designing knowledge base of representation of creation regulation, reasoning system based on rules and search mechanism and explaining system based on prefabricating text has been researched and developed in this paper. The system, making use of ADO technology, Access database and Visual Basic, develops knowledge base, database and reasoning system. Based on client / server model, the system realizes a seamless link between Visual Basic and Matlab by using ActiveX. The system can perform functions of bending radius forecasting and forming program evaluating and optimizing. It has a friendly interface and it is easy to operate and convenient for maintenance.

Abstract: In accordance with hydraulic bulging strengthening technology for large generator retaining rings (Mn18Cr18N), the bulging deformation process of retaining rings is simulated by MARC software. The key factors such as the punch taper angle and contact pressure are analyzed which influence on the deformation. It has been proofed for carbon steels with small ratio mould .It is observed that adjusting the punch taper angle and controlling the contact pressure theoretically can make the rings deforming uniformly during the hydraulic bulging strengthening processes, and these results provided the credible theoretical bases of technology application.

Abstract: The properties of different Cu surface were studied by the pseudo-potentials method based on density function theory. The lattice constant obtained with GGA(Generalized Gradient Approximation) is close to the experimental values than that with LDA(Local Density Approximation), so we adopt the GGA to simulate the cohesive energies and the surface energies of the Cu(100), Cu(110) and Cu(111) surface. The simulated results are shown to be in agreement with the macroscopic validity of the experimental measurements.

Abstract: Evolutions of profiles for a cylindrical specimen during hot compression were calculated with finite element methods. The calculations have been carried out with different characteristics of flow behaviors for the alloy 16CrMo4. Variations in the maximal radius of the specimen are determined predominately on geometric factors of the compression, while indifferent to magnitudes as well as strain hardening rates of flow stresses. This result was verified by hot compression testes of two different alloys employing Gleeble experiments. The increment of the maximal radius within a definite strain range is enhanced by introducing significant temperature gradients.

Abstract: The development of internal stress in injection molded parts is analyzed. Different from other researches, this study uses a new modified Maxwell model to calculate the internal stress. On the basis of the creep experiments of injection molded parts, a non-linear constitutive equation is proposed. Non-linear finite element equation to calculate the internal stress is derived. By means of this model, the internal stress of an injection molded polystyrene plate is simulated. The effects of mold wall temperature, cooling time and packing pressure on the development of internal stress are investigated. The predicting results are in good agreement with experimental data.

Abstract: A method of Monte Carlo combined with welding experiments was adopted to study the grain size and microstructure in welding heat affected zone of the ferrite stainless steel. Firstly, the kinetic equation of grain growth was established with the experimental data . Then , a simulation procedure based on the kinetic equation was worked out. Agreement between Monte Carlo simulation result and the real experiment results was obtained.

Abstract: The objective of this research was to develop methods for improved the uniformity of temperature distribution within plasma surface alloying furnace by simulating the heat transfer process and numerical calculation. Results show that the structure of charging basket, hanging auxiliary cathode plates in both sides of charging basket and blackness of material influence strongly temperature distribution within the plasma surface alloying furnace. Discharge intensity of the center zone can be weakened through increasing the distance between backs both column blades in center of the furnace, which decreased the consumption of discharge power in center, depressed temperature of the center zone of the furnace. Intensity of discharge in fringe of the charging basket can be reinforced and that of discharge in center can be weakened when auxiliary cathode plates were hanged to outer flank of the charging basket, which increased boundary temperature of the system, at the same time the auxiliary cathode plate plays a heat preservation role. Decreasing the blackness of outside material of charging basket may decrease heat dissipating capacity of outside, decrease temperature difference of outside and center of the furnace and improve the uniform of temperature distribution in the furnace.

Abstract: In this paper, the reliability of welded pressure pipe with circumferential surface crack was calculated by using three dimensional stochastic finite element method. This method has overcome the shortcomings of conservative results in safety assessment with deterministic fracture mechanics method. The calculation of reliability was based on three dimensional elastic-plastic stochastic finite element program which was developed by ourselves. The effects of variables such as fracture toughness, bending moment and the depth of the circumferential surface crack on the structure reliability were also discussed. The calculation results indicate that the crack depth has great effect on the reliability of the welded pipe. When the mean value of the crack depth is changed from 3mm to 7mm, the failure probability of the welded pipe will change from 10-8 to 10-2. The bending moment also has great effect on the reliability of the welded pipe. When the mean value of moment is changed from10000 N.m to 15000 N.m, the failure probability of the welded pipe increases dramatically for the same circumferential crack depth. Irrespective of the changing of moment, the pipe has higher reliability if the crack depth is less than 5mm(a/t<0.5, t is the thickness of the pipe). The method has put forward a new way for safety assessment of welded pipe with circumferential surface crack.

Abstract: Fatigue strength of welded structures can be estimated by obtaining local notch stress concentration under the service loading. On the bases of considering influence of weld geometry details and micro-support notch effect at weld toe, the local notch stress fields of welded structure of large-scale electromotor rotor were simulated by global-local analysis in finite element method (FEM) to evaluate the fatigue strength. The fatigue notch factors of different weld shapes were also determined. For longitudinal fillet weld of shaft-ribs welded structure under moment of torsion, as well as sealing weld in axis head faces of ribs under gravity, the simulation results show that at weld toe the fatigue notch factor of concave fillet weld is the lowest, the one of flat fillet weld is second lowest, and the one of convex fillet weld is the highest.