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NUMERIcaL DESIGN OF DIE LAND FOR SHAPE EXTRUSION

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Chinese Journal of mechanical engineering 2001年第1期14卷 91-93页

作者： Hao Nanhai department of mechanical engineering,Taiyuan Heavy Machinery Institutex Li Kezhi Northwestern Polytechnical university 太原重型机械学院山西太原西北工业大学陕西

In the extrusion of shapes with flat faced die,the proper design of die land is of critical importance in avoiding the generations of geometry defects.A methodology for the design of die land,which consists of a simulation adjustment iteration,is *** metal flow in extrusion is simulated by the three dimensional finite element method and the die land is adjusted according to the simulation *** the formulae for adjustment of the die land and the criterion for the judgment of proper die land are *** extrusion of an L section shape is chosen as the computational example and the result is compared with the industrial design.

关键词： Extrusion Die design Finite element method

Complex Velocity Potential for an Ellipse and a Circle in Translation and Rotation

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Communications in Nonlinear Science and Numerical Simulation 1997年第4期2卷 252-257页

作者： R.SUN &A.T.CHWANG (department of mechanical engineering,The university of Hong Kong,H.K.) department of mechanical engineering The University of Hong Kong Hong Kong China

This paper investigates the analytical solutions of two- dimensional Neumann- type external boundary- value problem for an ellipse and a circle in complex analysis *** transformation of harmonics between two planes is expanded in Laurent *** circle theorem is extended so as to suitto the system of the ellipse and the circle. By means of Basset’s process,the harmonic expressions of the system are found in the form of recurrence formulae which are suitable for numerical *** complex velocity potential of the system in translation and rotation is represented by the summation of the harmonic expressions.

关键词： velocity potential two bodies

Rolling Element Bearing Diagnostics by Combination of Envelope Analysis and Wavelet Transform

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Journal of university of Science and Technology Beijing 2001年第1期8卷 69-74页

作者： Ying Tang, Qiao Sun mechanical engineering School, university of Science and Technology Beijing, Beijing 100083, China department of mechanical engineering, university of calgary calgary Alberta T2N 1N4, canada mechanical engineering School Univ. of Sci. and Technology Beijing Beijing 100083 China

Rolling element-bearing diagnostics has been studied over the last thirty years, and envelope analysis is widely recognized as being the best approach for detection and diagnosis of rolling element bearing incipient failure. But one of the on-going difficulties with envelope technique is to determine the best frequency band to envelop. Here, wavelet transform technique is introduced into envelope analysis to solve the problem by capturing bearing defects-sensory scales (i.e. frequency bands). A modulated Gaussian function is chosen to be the analytical wavelet because it coincides well with bearing defect-induced vibration signal patterns. Vibration signals measured from railway bearing tests were studied by the proposed method. cases of bearings with single and multiple defects on inner and outer race under different testing conditions are presented. Experimental results showed that the proposed method allowed a more accurate local description and separation of transient signal part, which were caused by impacts between defects and the mating surfaces in the bearing. The combination method provides an effective signal detection technique for rolling element-bearing diagnostics.

关键词： continuous wavelet transform envelope analysis rolling element bearing diagnostics

Numerical Simulation of Shrinkage cavity Formation in Spheroidal Graphite Iron castings Based on Micro Modeling

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International Journal of Minerals,Metallurgy and Materials 1998年第1期12卷 9-12页

作者： Wenzhen Li Baicheng Liu Shantong Jin (Metallurgy engineering School, university of Science and Technology Beijing, Beijing 100083, China)(department of mechanical engineering, Tsinghua university, Beijing 100084, China) Metallurgy engineering School University of Science and Technology Beijing Beijing 100083 China department of mechanical engineering Tsinghua University Beijing 100084 China

A micro-modeling method (MM) for the quantitative prediction of the shrinkage cavity formation in SGiron castings is proposed. The mathematical models describing the volume changes during the solidification ofspheroidal graphite cast iron are established based on the models of solidification kinetics. The shrinkage cavityformation of T-shaped SG iron castings is calculated with MM method. The calculated results are compared with theexperimental results. It is shown that the predicted size, shape and distribution of shrinkage cavity by MM methodare in good agreement with the measured results.

关键词： solidification shrinkage numerical simulation micro modeling spheroidal graphite cast iron

Evaluation of Surface Cracks Using Magnetic Flux LeakageTesting

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Journal of Materials Science & Technology 2002年第4期18卷 319-321页

作者： Luming LI, Songling HUANG, Peng ZHENG and Keren SHINUT Center, mechanical engineering department, Tsinghua university, Beijing 100084, China NDT Cent. Mech. Eng. Dept. Tsinghua Univ. Beijing 100084 China

The magnetic field distribution characteristics of surface cracks with various widths are discussed based on finite element (FEM) results. The crack depth was 0.20 mm, the width range was from 0.02 to 1.00 mm. The results showed that crack width and lift-off (the distance between surface and sensor) will influence signals. Discussed in this paper is the influence of various lift-off parameters on the peak to peak values of the normal component in magnetic flux leakage testing. The effects can be applied to evaluate surface breaking cracks of different widths and depths. An idea is presented to smooth narrow, sharp crack tips using alternating current (AC) field magnetization.

关键词： Magnetic flux leakage testing (MFL) Slot width Finite element method (FKM)

EFFECTS OF STATIC ELECTRIC FIELD ON THE FRACTURE BEHAVIOR OF PIEZOELECTRIC CERAMICS

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Acta Mechanica Sinica 2002年第5期18卷 537-550页

作者： Tong-Yi Zhang (department of mechanical engineering,Hong Kong university of Science and Technology,Clear Water Bay,Kowloon,Hong Kong,China) department of mechanical engineering Hong Kong University of Science and Technology Kowloon Hong Kong China

The paper gives an overview on experimental observations of the failure behavior of electrically insulating and conducting cracks in piezoelectric ce- *** experiments include the indentation fracture test,the bending test on smooth samples,and the fracture test on pre-notched(or pre-cracked)compact ten- sion *** electrically insulating cracks,the experimental results show a com- plicated fracture behavior under electrical and mechanical *** data are much scattered when a static electric field is applied.A statistically based frac- ture criterion is *** electrically conducting cracks,the experimental results demonstrate that static electric fields can fracture poled and depoled lead zirconate titanate ceramics and that the concepts of fracture mechanics can be used to mea- sure the electrical fracture ***,the electrical fracture toughness is much higher than the mechanical fracture *** highly electrical fracture toughness arises from the greater energy dissipation around the conductive crack tip under purely electric loading,which is impossible under mechanical loading in the brittle ceramics.

关键词： fracture piezoelectric and dielectric ceramics insulating and conducting cracks bending tests indentation fracture tests

TWO METHODS OF SOLVING DYNAMIC RESPONSE BY DISCRETIZATION OF GURTIN VARIATIONAL PRINCIPLE

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Acta Mechanica Sinica 1985年第2期1卷 171-183页

作者： Zhang Ruqing Dong Ming department of mechanical engineering, Chongqing university department of mechanical engineering Chongqing University Chongqing China

Based on the Gurtin variational principle and the finite element method two recurrenceformulae of solving dynamic response are derived in this paper. The first recurrence formula which isconditionally stable is obtained by adopting "dual temporal finite element" to discretize the Gurtinvariational principle and then making use of convolution, while the second, an unconditionally stableone derived by discritizing the variational principle in each time step and taking appropriateintegration parameter θ.

关键词： variational principle structural dynamics computer mechanics finite element analysis.

NOVEL METHOD SOLVING NUMERIcaL INSTABILITIES IN TOPOLOGY OPTIMIZATION

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Chinese Journal of mechanical engineering 2002年第1期15卷 22-26页

作者： Guo Dongming Wang Xiaoming Liu Zhenyu department of mechanical engineering，Dalian university of Technology， Dalian 116023，China department of mechanical engineering Dalian University of Technology Dalian 116023 China

Numerical instabilities are often encountered in FE solution of continuumtopology optimization. The essence of the numerical instabilities is given from the inverse partialdifferential equation (PDE) point of view. On the basis of the strict mathematical theory, a novelmethod, named as window filter and multi-grid method, which solves the numerical instabilities, isproposed. Convergent analyses and a numerical example are presented.

关键词： Topology optimization Gaussian windows Checkerboard pattern

Study on Bonding of Steel-mushy Al-7graphite

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Journal of university of Science and Technology Beijing 2001年第4期8卷 283-285页

作者： Peng Zhang, Yunhui Du, Daben Zeng department of mechanical engineering Tsinghua university. Beijing 100084, China department of mechanical engineering Tsinghua University Beijing 100084 China

The bonding of steel-mushy Al-7graphite was studied. The relationship between interfacial shear strength of bonding plate and solid fraction of Al-7graphite mushy was obtained, and the interfacial structure of bonding plate was determined. The results showed that: under the condition of 500 degreesC for preheat temperature of steel plate and 10 mm/s for rolling speed, the largest interfacial shear strength of bonding plate was 70.1 MPa when solid fraction of Al-7graphite mushy was 34.6%.

关键词： interfacial shear strength solid fraction interfacial structure