Materials Science Forum Vols. 575-578

Abstract: Soil is a complex material whose properties are elastic, plastic and viscious. The selection of a proper constitutive relation is important in the study of stratum movement induced by underground excavation in modern cities. First, based on the Fast Lagrangian Analysis of Continua (FLAC) method, the elastic response stress (p, q) distribution induced by a circular tunnel is analyzed, and the surrounding soil is divided into four categories: p increase q increase, p increase q decrease, p decrease q increase, p decrease q decrease according to p-q stress path. The character of p-q distribution and the plastic zone induced by tunneling in clay are compared when the Mohr-Coulomb model (M-C), the Drucker-Prager model (D-P) and the Modified Cam-Clay model (C-C) are adopted; the C-C model is considered to be suitable for simulating underground excavation problems. Second, factors such as stratum character, stress path and relative position between soil and excavation are thought to be important in the selection of a proper constitutive relation, accounting for the geological condition of Beijing and measuring techniques being used in geotechnical engineering. Fine grained soils such as clay and silt can be modeled by the C-C model. Coarse grained soil, for containing and not containing excavation, may be represented using the M-C model considering strain softening and the normal M-C model. Finally, with the aid of FLAC method and its internal language FISH, a scheme of estimating and controlling parameter input is suggested.

Abstract: Hydrogen induced cracking (HIC) is one of main type of damage to metallic materials in H2S solution. 08Cr2AlMo steel is a type of material developed especially for heat exchanger pipe bundle used under H2S condition in recent years. Calculation models of the construction units in 08Cr2AlMo steel with or without hydrogen were established based on the empirical electronic theory in solid (EET) and valence electron structure of the construction units in this steel was calculated. The results show that hydrogen bond is formed between the hydrogen solved in the steel and other atoms in the steel. The cleavage energy of crystal plane with hydrogen bond is increased and that without hydrogen bond is decreased. Hydrogen results in the remarkable difference of the cleavage energy of different crystal planes and changes the bond distribution in the structure units. The mechanical property of the units has directional properties. In these units, the microcracks propagate along the cleavage plane with small binding energy and so the brittle fracture of the crystal occurs. The elements of Cr, Al, Mo are able to strengthen the basal body without carbon, and have little effect on the plastic nature. In the structure unit with carbon, carbon increases the anisotropy of mechanical property and alloying agents decrease the plastics of the steel further. The alloying agents of Cr and Mo decrease plastic nature loss of the steel due to decrement of the anisotropy of mechanical property in the unit with hydrogen. The alloying agent of Al has little effect on the loss of plastic nature.

Abstract: The nickel-based superalloy GH80A is a typical difficult-to-cut material. It has been used in a good many kinds of aeronautical key structures because of its high yield stress and anti-fatigue performance at high temperature. But selection of cutting parameters in actual machining process mainly depends on experience and lacks of scientific utterance. In this paper, finite element method (FEM) was introduced to study the chip formation process when machining nickel-based superalloy GH80A. By the way of lagrangian finite element approach and material failure, adiabatic shear band (ASB) and periodic fracture were simulated with the help of former researchers’ studies on the material constitutive relation. Both the mechanism of adiabatic shearing phenomenon at primary shear zone and periodic crack in the free surface were analyzed, chip formations under different cutting parameters were got and compared carefully. The root cause of saw-tooth chip formation under different cutting speeds was discussed.

Abstract: A new-type of solid rotor asynchronous magnetic coupling which works on the principle of electromagnetic induction is researched by ourselves. This kind of asynchronous magnetic coupling can solve the problem effectively that the permanent magnets on its inner rotor is demagnetized if its temperature is too high, because its inner rotor need not the permanent magnets. in order to study the transmission capability of the new-type magnetic coupling, its magnetic field should be analyzed. Because of its magnetic field variety, it is extremely complicated and a precision result is difficult to be got by the analytic method of the magnetic field calculation. Here the software ANSYS FEM is used to analyze its magnetic field. And some formulas were deduced and used to calculate its torque. The experimental and calculational results indicate that this design is practicable.

Abstract: 10mm-5A06 aluminum alloy was butt-welded in a single pass by the plasma-gas metal arc (plasma-MIG) welding procedure, the joints were subjected to X-ray inspection, the microstructure and mechanical performance of weld were also studied. The results indicate that plasma-MIG welding is superior to regular conventional MIG welding on the aspects of reducing weld porosity, increasing joint quality and improving deposition efficiency. Good weld joint with less porosity and excellent mechanical properties is obtained, which can reach as 92.62% tensile strength and 85.12% elongation percentage as base metal. Dimples in which the precipitated phase is the solid solution based on Al3Mg2 are observed in fracture scanning electron micrograph and the fracture mode is ductile rupture. α-Al and Al3Mg2 ,α-Al and eutectic structure are observed respectively in fusion area and in weld zone. The wire feed rate and melting rate can come to 14.5m/min and 80g/min respectively for the 1.6mm welding wire by the plasma-MIG welding process on the premise that the tensile strength of the joints meet the requirements.

Abstract: The FDM numerical simulation software, View-Cast system, was employed to simulate the mould-filling and solidification process in low pressure die casting (LPDC) of Al-alloy motor enclosure. The distribution of liquid fraction, temperature field and the solidification pattern of casting were revealed and the formation mechanism as well as distribution rule of the potential defects, namely gas pores and shrinkage pores, were predicted. Furthermore the solutions to eliminate them were presented. By reducing the pouring rate, the turbulent flow at the corner of casting had eased, so the gas pores could be eliminated. Then the force-cooling system was installed on the top of mould, which could reduce the volume of liquid islands efficiently so that the shrinkage defects can be decreased to its limit.

Abstract: Experimental simulations of thermomechanical processing (TM) using press forging of Si-Mn TRIP (transformation induced plasticity) steel were performed. In order to rationalize the retained austenite (RA) volume fraction, six TM schedules were employed at experiment where different austenite conditioning was considered. The various multiphase structure characteristics were obtained after of TM processing, with different volume fraction of ferrite, bainite and RA. The modification of structural characteristics influenced the mechanical properties of TRIP steel. The present work also focuses on monitoring of RA transformation during mechanical incremental straining using in situ neutron diffraction technique. This method is used to characterize the kinetics of RA transformation and its stability during the straining.

Abstract: The improved geometrical accuracy and better surface finish of worms are required, especially in automobile industry. To meet this requirement, whirling process has been used in the manufacture of worm. Whirling process is a cutting process in which a series of cutting edges on the whirling ring remove material by turning over the rotating workpiece. In this study, cutting characteristics of the worm in whirling process has been analyzed. The undeformed chip models of front and side cutting edges were established. Using the undeformed chip models and DEFORM software, cutting force analyses are carried out. The calculated cutting force imposed on the tool is nearly the same as the sum of the forces calculated which are separately imposed on the front and side cutting edges.

Abstract: ANSYS implicit finite element method (FEM) was used to simulate the process of controlled cooling of 50mm heavy plate. And the corresponding cooling curve and temperature field distribution were obtained from the calculations. The results indicated the section inhomogeneity of temperature at different place from surface to center of steel plate. Different cooling conditions were compared to analyze the effect of cooling schedule on section inhomogeneity, which could provide theoretical basis for selecting appropriate cooling schedule to alleviate the section effect.

Abstract: The type, shape and distribution of carbide take directly effect on the mechanical properties of high chromium castings. Vanadium is able to stabilize the structure of carbide in high chromium cast iron, meanwhile the hardness of carbide containing vanadium can reaches about 2800HV. In some cases, vanadium can also refine the microstructure. Rare-earth is able to change the shape of carbide in cast iron, refine the grain size of ferrite and improve the mechanical properties of castings. In this experiment, intention of adding vanadium and rare-earth is modification of mechanical properties with the proper heat treatment technology. With the help of SEM, the characteristics of carbide, such as shape, distribution and quantity can be observed and mechanical properties have been improved for better wear-resistance.