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Theoretical determination of thermal diffusivity of composite material

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Journal of University of Science and Technology Beijing 2004年第1期11卷 44-47页

作者： ThomasKabayabaya FanYu XinxinZhang DepartmentofEnergyEngineering MechanicalEngineeringSchoolUniversityofScienceandTechnologyBeijingBeijing100083China

A very simple model based on the Quadrupole method was used in thetheoretical analysis of thermal diffusivity of composite materials of Cu-PVC, PVC-Cu-PVC, andCu-PVC-Cu. The use of MATLAB software with a return to real space using the Stehfest algorithm makesthe time of calculation very short. The thermal responses on the rear face of each consideredsample, which determine the thermal diffusivity were represented. A mathematical demonstration whichconfirmed the results was given. Thermal diffusivity determined from the rear face thermalresponses were compared with the results of the thermal diffusivity calculated by considering thecomposite materials to be homogeneous, and a discussion on the two kinds of results was provided.

关键词： thermal diffusivity composite material thermal conductivity heatconduction quadrupole method

Over-relaxation effect of deformed austenite on ageing behavior of an Nb-bearing microalloyed steel

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Journal of University of Science and Technology Beijing 2005年第3期12卷 248-251页

作者： ShaoqiangYuan ShanwuYang XueminWang XinlaiHe DepartmentofMaterialsPhysics UniversityofScienceandTechnologyBeijingBeijing100083China TangshanCollege Tangshan063000China／／DepartmentofMaterialsPhysicsUniversityofScienceandTechnologyBeijingBeijing100083China

The ageing behavior of an Nb-bearing microalloyed steel at 525℃ was investigated by thermo-simulation test, hardness measurements and transmission electron microscopy (TEM). Prior to ageing, the steel was deformed in austenite zone followed by a long relaxation. Experimental results indicate that the hardness decreases gradually in the initial stage until ageing for 120 min, and then increases continuously until 1200 min. The coarsened precipitates (>10 nm) formed in deformed austenite remain nearly unchanged in size, even after ageing for long time, while the further precipitates, which nucleate in a phase, contribute to the increasing of hardness. By comparison, the undeformed samples in austenite subjected to the same ageing process display a very similar hardness change trend to that of over-relaxation ones and have higher hardness values at each corresponding period.

关键词： over-relaxation ageing hardness precipitates

Dynamic response to road roughness on a tractor-semitrailer system with driver body model

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Journal of University of Science and Technology Beijing 2002年第4期9卷 305-310页

作者： ShengLing YunqiuHan JiangLiu CivilandEnvironmentalEngineeringSchool UniversityofScienceandTechnologyBeijingBeijing100083.China MechanicalEngineeringSchool UniversityofScienceandTechnologyBeijing.Beijing100083.China

A linear mass-spring system model of a tractor-semitrailer together withdriver body parts and sprung seat is presented. Natural frequencies of the system are calculated andresponse of components in the system to road roughness is completed by means of computer simulationand power spectral density (PSD) approach in all of road conditions and loading cases. The resultsshow that the severest situation of response of the system occurs when the road in rough conditionand vehicle unladen. The most sensitive frequency to human body parts is around 0.9 Hz, and modeltypes of a human body seem to be not significant to the response of a heavy tractor-semitrailersystem, including to the response of the driver himself.

关键词： tractor-semitrailer dynamic response road roughness computersimulation power spectral density

Spark plasma sintering on mechanically activated W-Cu powders

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Rare Metals 2004年第3期23卷 269-273页

作者： JIAChengchang LIZhigang HEYuntao QUXuanhui SchoolofMaterialsScienceandEngineering UniversityofScienceandTechnologyBeijingBeijing100083China

Mechanically activated W-Cu powders were sintered by a spark plasma sinteringsystem (SPS) in order to develop a new process and improve the properties of the alloy. Propertiessuch as density and hardness were measured. The microstructures of the sintered W-Cu alloy sampleswere observed by SEM (scanning electron microscope). The results show that spark plasma sinteringcan obviously lower the sintering temperature and increase the density of the alloy. This processcan also improve the hardness of the alloy. SPS is an effective method to obtain W-Cu powders withhigh density and superior physical properties.

关键词： powder metallurgy W-Cu alloy spark plasma sintering mechanical activation

Study on the electronic structures of REBaCuO superconductors and their relation to superconductivity

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Rare Metals 2002年第4期21卷 313-318页

作者： ZHANGBaodong CHENNing 等 DeparntmentofPhysicalChemistry UniversityofScienceandTechnologyBeijingBeijing100083China MaterialsEngineeringSchool UniversityofScienceandTechnologyBeijingBeijing100083China

Electronic structures of REBaCuO (RE=La, Pr, Nd, Sm, Gd, Dy, Ho and Er)systems were calculated by means of SCF-Xα -SW methods. Results show that there is an inner-orbitcoupling for these oxide superconductor systems. The inner-orbit coupling was resulted from theinteraction of two electronic orbits of RE 5p and O 2s, since they have similar energy state levelsand relatively larger orbital electronic clouds. Compared with experimental facts, it is also foundthat the overlap in space between the two orbits has a similar tendency to T_c and the number ofenrolling electrons has a close relation to J_c, therefore, the influence of inner-orbit coupling onsuperconductivity could not be overlooked.

关键词： oxide superconductors SCF-Xα-SW methods electronic structures

Microstructure evolution of an Ni-Cr-Co base superalloy heat-treated at 704 and 760℃

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Rare Metals 2003年第3期22卷 169-174页

作者： ZHAOShuangqun XIEXishan HighTemperatureMaterialsResearchlaboratories UniversityofScienceandTechnologyBeijingBeijing100083China；DepartmentofPhysicsNingxiaUniversityYinchuan750021China HighTemperatureMaterialsResearchLaboratories UniversityofScienceandTechnologyBeijingBeiiing100083China

Thermodynamic calculation, SEM (scanning electron microscopy), TEM(transmission electron microscopy), XRD (X-ray diffraction), phase extraction, and chemical analysiswere employed to study the phase stability and phase precipitation in a new Ni-Cr-Co basesuperalloy heat-treated at 704 and 760 ℃ for a long tune. The results show that the precipitates ofthis new alloy heat-treated at standard annealing condition and heat-treated at 704 and 760℃ for atime up to 2000 h are γ′, MC, M_(23)C_6, and M_6C, and η phase forms at grain boundaries and inmatrix of samples heat-treated at 760 ℃ as well. The mass fractions of γ′ (+η), MC, M_(23)C_6,and M_6C in all samples have no large changes with an increase in aging time, but γ′ precipitatesgrow obviously. The γ′-to-η transformation in the samples heat-treated at 760℃ took place withincreasing aging time. The η precipitates form a Widmanstaetten pattern and the γ′ phases haveremelted partly in the samples heat-treated at 760 ℃. The alloy maintains a better microstructuralstability during prolonged aging at 704 ℃, but a worse microstructural stability during prolongedaging at 760 ℃.

关键词： Ni-Cr-Co base superalloy thermodynamic calculation microstructuralstability precipitate phase analysis

Microstructural morphology of the semi-solid high carbon steel T12 before and after rheo-rolling

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Journal of University of Science and Technology Beijing 2005年第2期12卷 139-142页

作者： JiguangLi YonglinKang AiminZhao YiSun ManCheng MaterialsScienceandEngineeringSchool UniversityofScienceandTechnologyBeijingBeijing100083China

The semi-solid high carbon steel T12 was rolled in a closed box groove under a certain condition by the rheo-rolling equipment, and the microstructural morphology of the semi-solid T12 before and after deformation was investigated by optical mi- croscope to analyze and summarize the microstructure evolution law of T12 deformed in semi-solid state. The experiment results show that the grain shape before deformation of the semi-solid T12 steel displays globule or ellipse by the electromagnetic stirring, the distribution of solid and liquid phases is homogeneous. But the microstructure of semi-solid product after rheo-rolling exhibits macrosegregation that the distribution of liquid and solid phases changes, the liquid phases divorce from the solid phases. In the transverse section, most of the solid phases get together in the center of the specimen, the liquid phases flow to the surface or the edge of the specimen, and the grains occur plastic deformation while reduction increased. In longitudinal section, the middle micro- structure of the specimen is more homogeneous than that at the head or tail, the head microstructure is similar to the tail and the size of the grains is not homogeneous.

关键词： semi-solid high carbon steel T12 rheo-rolling microstructural morphology

Isothermal grain growth of reactive spray formed 7075 alloys in semi-solid state

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Journal of University of Science and Technology Beijing 2004年第5期11卷 411-414页

作者： HuiminLiu HuaCuit BinYang JishanZhang StateKeyLaboratoryforAdvancedMetalsandMaterials UniversityofScienceandTechnologyBeijingBeijing100083China

The grain growth behavior in reactive spray formed 7075+2.91 vol percent TiCAl alloy was studied and compared with that of spray formed 7075 Al alloy at semi-solid state. Theeffects of in-situ TiC particles on the microstructure of spray formed 7075 Al alloy were alsoinvestigated. The specimens were heat-treated isothermally at various temperatures between thesolidus and liquidus of 7075 Al alloy for times in the range of 10-60 min, then quenched in *** microstructure of reheated specimens was characterized using scanning electron microscopy andoptical microscopy. The grain size was measured using a mean linear intercept method. Results showthat the in-situ TiC particles can effectively retard grain growth and refine the grain at a limitedsize. The grain growth exponent in Arrhenius equation increases from 2 to 3, which indicates thatthe in-situ TiC particles have the significant pinning effect on grain coarsening in the semi-solidstate.

关键词： reactive spray forming semi-solid state grain growth in-situ TiC particles

Experiment research on grain drying process in the heat pump assisted fluidized beds

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Journal of University of Science and Technology Beijing 2004年第4期11卷 373-377页

作者： JingYang LiWang FiXiang LigeTong HuaSu MechanicalEngineeringSchool UniversityofScienceandTechnologyBeijingBeijing100083China

A heat pump assisted fluidized bed grain drying experimental system wasdeveloped. Based on this system, a serial of experiments was performed under four kinds of air cycleconditions. According to the experimental analysis, an appropriate drying medium-air cycle for theheat pump assisted fluidized bed drying equipment was decided, which is different from the commonlyused heat pump assisted drying system. The experimental results concerning the drying operationperformance of the new system show that the averaged coefficient of performance (COP) can reach morethan 2.5. The economical evaluation was performed and the power consumption for removing a kilogramwater from grains was about 0.485 kW-h/kg (H_2O), which shows its reasonable commercial efficiencyand great application potentiality in future market.

关键词： heat pump fluidized bed grain drying air recycle