变压器中性点过电压保护综述

综述了变压器中性点保护理论，根据国内变压器中性点绝缘的实际情况，依据电力部下达的“过电压与接地技术方事故技术措施”对变压器中性点保护参数做出了参考设置。     

Analytical Model for the Piecewise Linearly Graded Doping Drift Region in LDMOS

提出了体硅LDMOS漂移区杂质浓度分布的一种二维理论模型,根据该模型,如果要使带有场极板的LDMOS得到最佳的性能,那么LDMOS漂移区的杂质浓度必须呈分段线性分布.用半导体专业软件Tsuprem-4和Medici模拟证明了该模型十分有效,根据该模型优化得到的新型LDMOS的击穿电压和导通电阻分别比常规LDMOS增加58.8%和降低87.4%.     

Simulation of Artificial Grain Feeding in Order to Reach Dynamical Bed Stabilisation Along the River Rhine

The Wesel-Xanten stretch of the fiver Rhine between km-812.5 and km-821.5 is one of the reaches where strong erosion leads to high maintenance efforts conceming navigability.In order to improve the naviga- tion conditions without aggravating the flood protection,but also ensuring that the ecological system of the river is not damaged,investigations of the morphodynamical processes in connection with artificial grain feeding ac- tivities have to be carried out by Federal Waterways Engineering and Research Institute.The performance of artificial grain feeding along a stretch of the lower Rhine near Wesel to prevent bed erosion by balancing sedi- ment transport was simulated in a scientific way by sensitivity studies in a 2D depth-average numerical model with graded sediment transport approach.The target of the investigations is to study the interaction of bed load supply and hydro-/morphodynamical features,and then especially to analyse and control the grain feeding measures in this section of the Rhine river.First the administrative background and target of artificial grain feeding along the waterways and then the special features regarding flow and transport characteristics of the stretch are described.After introducing shortly the mathematical basis for modelling graded sediment transport and some special treatments for the case of artificial grain feeding activities,some validation results for graded sediment are discussed.A series of numerical simulations with the objective of testing the model sensitivity to different model parameters has been carried out.Further,results of numerical simulations for the case of grain feeding are presented.     

Bonding strength of graded anti-corrosive coatings of fluoroethylenepropylene （FEP）/polyphenylene sulfide （PPS）

Fluororesin-based anti-corrosive coatings including graded FEP/PPS were prepared on carbon steel by melt powder coating, the bonding strength of all coating systems was determined by the pull-off test. It is found that the poor adhesion of fluororesin coatings to metallic substrates is improved obviously by the graded coating structure of FEP/PPS, and the bonding strength reaches up to 11.8 MPa for the five-layer system. Examination by electron probe microanalysis （EPMA） verifies that the distribution of main components is graded in the five-layer system, which is responsible for the enhancement of the interfacial bonding.     

Thermoelectric properties of p-type （Bi0.15Sb0.85）2Tes-PbTe graded thermoelectric materials with different barriers

The p-type （Bi0.15Sb0.85）2Te3 and PbTe are typical thermoelectric materials used for low and middle temperature range and functional graded materials （FGM） is an inevitable way to widen the working temperature range. Here two segments graded thermoelectric materials （GTM） consisting of （Bi0.15Sb0.85）2Te3, PbTe and different barriers were fabricated by the common hot pressure method. Metals Fe, Mg and Ni were used as barriers between the two segments. The diffusion of different barriers between the barriers and bases were analyzed by electron microprobe analysis （EMA）. The phase and crystal structures were determined by X-ray diffraction analysis （XRD）. The thermoelectric properties were measured at 303 K along the direction parallel to the pressing direction. The results show that the compositional diffusion occurs when there is no barrier at the interface of the two segments, and the diffusion of Pb is most obvious; as the barrier material, the diffusion of metals Fe, Mg and Ni between different bases is not very obvious, and the thermoelectric properties of GTM is much better than that of the original segment.     

熔铸-扩散法制备黄铜/钨铜功能梯度材料的研究

对用熔铸-扩散法制备的黄铜，钨铜功能梯度材料进行了研究，对界面区域的元素成分分布和微观组织结构进行了分析，对界面区域的电导率、结合强度及抗脉冲大电流损伤性能进行了测试。结果表明：用该法制备的黄铜，钨铜功能梯度材料，界面区域由成分和组织渐变的三层结构组成；电导率在界面区域呈渐变分布趋势，没有出现电导率突变现象；这种结构缓解了因热性能不匹配而造成的热应力，提高了黄铜与钨铜合金的结合强度；界面的抗脉冲大电流损伤性能良好。     

An advanced numerical method for computing elastodynamic fracture parameters in functionally graded materials

A new meshless method for computing the dynamic stress intensity factors (SIFs) in continuously non-homogeneous solids under a transient dynamic load is presented. The method is based on the local boundary integral equation (LBIE) formulation and the moving least squares (MLS) approximation. The analyzed domain is divided into small subdomains, in which a weak solution is assumed to exist. Nodal points are randomly spread in the analyzed domain and each one is surrounded by a circle centered at the collocation point. The boundary-domain integral formulation with elastostatic fundamental solutions for homogeneous solids in Laplace-transformed domain is used to obtain the weak solution for subdomains. On the boundary of the subdomains, both the displacement and the traction vectors are unknown generally. If modified elastostatic fundamental solutions vanishing on the boundary of the subdomain are employed, the traction vector is eliminated from the local boundary integral equations for all interior nodal points. The spatial variation of the displacements is approximated by the MLS scheme.     

Evaluation of R-curve behavior of ceramic-metal functionally graded materials by stable crack growth

This paper deals with the fracture toughness and R-curve behavior of ceramic-metal functionally graded materials (FGMs). A possibility of stable crack growth in a three-point-bending specimen is examined based on the driving force and resistance for crack growth in FGMs, and the distribution of fracture toughness or R-curve behavior is evaluated on FGMs fabricated by powder metallurgy using partially stabilized zirconia (PSZ) and stainless steel (SUS 304). The materials have a functionally graded surface layer (FGM layer) with a thickness of 1 mm or 2 mm on a SUS 304 substrate. Three-point-bending tests are carried out on a rectangular specimen with a very short crack in the ceramics surface. On the three-point-bending test, a crack is initiated from a short pre-crack in unstable manner, and then it propagates in stable manner through the FGM layer with an increase in the applied load. From the relationship between applied load and crack length during the stable crack growth in the FGM layer, the fracture toughness is evaluated. The fracture toughness increases with an increase in a volume fraction of SUS 304 phase.     

Finite element simulations of crack propagation in functionally graded materials under flexural loading

Cracks in stepped and continuously graded material specimens under flexural loading were investigated via finite element analysis. Calculation of mechanical energy release rates and propagation angles with crack-opening displacement correlation and the local symmetry (K_II = 0) criterion, respectively, provided results most efficiently and accurately, as compared with compliance and J-integral approaches and other deflection criteria. A routine was developed for automatic crack extension and remeshing, enabling simulation of incremental crack propagation. Effects of gradient profile and crack geometry on crack-tip stresses and crack propagation path are examined, and implications of these for optimal design of graded components against failure by fast fracture are discussed.     

Computer Simulation of Distribution of Reinforced Particles in Functionally Graded Materials Fabricated by Centrifugal Casting

A mathematic model is developed with viscosity of molten matrix,centrifugalforce,casting temperature,mold temperature and other parameters taken intoconsideration for preditction of the distribution of reinforced particles during centrifugalcasting of FGM,and the simulation of distribution of reinforced particles and thesolidification process during centrifugal casting is performed with the aid of computergraphics.SiC_p/A356 FGM is fabricated by centrifugal casting.The results of computersimulation of distribution of reinforced particles are in good agreement with experimentalobservations.