力学学报

PROPAGATION OF PLANE WAVES IN TRANSVERSELY ISOTROPIC FLUID-SATURATED POROUS MEDIA

Based on the Biot's theory for fluid-saturated porous media, the propagation of plane waves in transversely isotropic porous materials is studied. The characteristic equations for wave propagation are derived and solved analytically. The results show that four waves, the first and second quasi-longitudinal waves(QP1 and QP2), the quasi-transverse wave(QSV) and the anti-plane transverse wave (SH), propagate with different speeds. The analytical expressions for wave speeds andattenuations are presented. The c...

1997, 29(3): 257-268. doi: 10.6052/0459-1879-1997-3-1995-225

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DIFFRACTION OF FLEXURAL WAVES AND DYNAMIC STRESS CONCENTRATIONS IN ORTHOTROPIC PLATES WITH AN ARBITRARY CUTOUT

In this paper, based on the governing equation for flexural waves of orthotropic plates, diffraction of elastic waves by cutouts and dynamic stress concentrations in the thin plate has been studied. An analytic method to solve dynamic stress concentrations in the plate with an arbitrary cutout is established. An asymptotic expansion solution that satisfies the boundary conditions on the edge of cutouts is obtained. Therefore the solution of the problem can be normalized by means of this method. Numerical re...

1997, 29(3): 269-277. doi: 10.6052/0459-1879-1997-3-1995-226

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DISCRETE SLIP MODEL OF CRYSTALS AND FINITE ELEMENT ANALYSIS

Based on the experiment results of single crystals, a discrete slip model is established to describe the crystal plastic deformation. The main characteristics of the model is that the slip deformation of the crystal is macro innhomogeneous and the distribution of slip bands is discrete. Crystal plastic theory and finite element method are used to analyse the finite deformation of the model. Digital results display the discrete characteristics of the crystal slip deformation. The calculated stress strain r...

1997, 29(3): 278-286. doi: 10.6052/0459-1879-1997-3-1995-227

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INTERACTION MBETWEEN INTERFACE MACROCRACK AND MICROCRACKS

With the use of the dislocation method of complex potential function, this paper studies the interaction between the interface macrocrack and the interface or beneath-interface microcracks by the construction and numerical solution of singular integral equations. The results show that the remote field phase angle ψ and Dunder′s parameter α have great influnce on the interaction between interface macrocrack and microcracks, while the effect of ψ on the shielding zone is far less than that of α.

1997, 29(3): 287-295. doi: 10.6052/0459-1879-1997-3-1995-228

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NUMERICAL MODELING OF FATIGUE CRACK GROWTH WITH CYCLIC HARDENING OF MATERIAIS

A method of finite element modeling of fatigue crack growth and closu re behavior is presented. The cyclic plastic hardening behavior of materials is taken into account. The chosen cyclic plasticity constitutive model has been exa min ed. After a discussion about the influence of finite element mesh on the numerical results, a mesh optimization criterion is suggested. Employing the suggested mumerical method and considering the crack closure effect, we investigate the evolution of the profile of crac...

1997, 29(3): 296-305. doi: 10.6052/0459-1879-1997-3-1995-229

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HOMOGENIZATION METHOD OF STRESS ANALYSIS OF COMPOSITE STRUCTURES

A homogenization method has been presented for deter min ing the stress distributions of composite structures. In this method, the composite structures are depicted by a homogeneous macrostructure and a heterogeneous microstructure. All quantities are expressed as functions of microscopic coordinates and macroscopic coordinates, and expanded into asymptotic series. Based on the perturbation method, the stress analysis problem leads to a microscopic homogenization problem and a macroscopic homogenizati...

1997, 29(3): 306-313. doi: 10.6052/0459-1879-1997-3-1995-230

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THE CALCULATION OF PIEZOELECTRIC MATERIALS WITH A MIXED MODE CRACK

A stiffness derivative technique to deter min e the strain energy release rate has been generalized to the plane strain fracture problem of piezoelectric materials. By using the numerical solution to piezoelectric materials obtained by finite element method as the actual fields and Sosa's asymptotic expressions for the electricmechanical fields in the vicinity of the crack as the auxillary fields, the generalized reciprocal M integeral method is used to solve the stress intensity factors K I ,K ...

1997, 29(3): 314-322. doi: 10.6052/0459-1879-1997-3-1995-231

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BLOCK SEAMS MODEL FOR DISCONTINUUM MECHANICS ANALYSIS

Based on the characteristics of rock structures, the block seams model, which can be used in the numerical simulation of the continuum and discontinuum mechanics, is established by constraint variational principles. In this model, the continuous condition is introduced into the energy functional by the Lagrange method and penalty method so that either the continuum or discontinuum problems can be simulated by the model. The formulations of the rigid finite element and traditional constant stress element...

1997, 29(3): 323-331. doi: 10.6052/0459-1879-1997-3-1995-232

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THE STUDY OF NANOMETER--DEFORMATION WITH THE SCANNING TUNNELING MICROSCOPE

By using the scanning tunneling microscope, a new method was put forw ard for measuring the nanometer-deformation with the atom structure. This measuring principle was used to measure the residual deformations of the irradiated single crystal graphite (HOPG) and the Si(111)7×7 surface after atom manipulation. The experimental results verify the present nanometer grid method for measuring nonometer-deformation.

1997, 29(3): 332-335. doi: 10.6052/0459-1879-1997-3-1995-233

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DATA ACQUISITION AND PROCESSING SYSTEM USED FOR FLOW FIELD DISTORTION OF AIRCRAFT INLET

This article describes a high speed data acquisition and real time storing, real time processing system for flow field distortion measurement and analysis of aircrafts' inlet/engine, focuses on system's research background, domestic and foreign information, main technical difficulties,the constitution, functions and technical properties of this completed system, finally, lists several important and key technologies solved in the period of research and manufacturing

1997, 29(3): 336-342. doi: 10.6052/0459-1879-1997-3-1995-234

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SIMULATION ON SLOPE RUNOFF AND SOIL EROSION IN A RAINING EVENT

The paper deals with the model of runoff and erosion in slope land. The solution to the one dimensional hyperbolic runoff equations and sediment equation are obtained respectively by using the characteristics method and finite difference method. The simulation calculations were conducted for real rain processes and compared with experimental data of field test. The results show that the model and the program are reasonable and practical, and they are useful in the study of the soil erosion.

1997, 29(3): 343-348. doi: 10.6052/0459-1879-1997-3-1995-235

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BROWNIAN DYNAMICS SIMULATION OF FENE DUMBBELL MODELS WITH CONFIGURATION DEPENDENT FRICTION COEFFICIENTS

Results of nonequilibrium Brownian dynamics simulations of the steady state and transient rheological behavior of nonlinear elastic dumbbell models in elongational flow is reported. The simulations include exa min ation of the effects of configuration dependent friction coefficients and spring parameter. The nonlinear random dynamical theory is used to analyze phase diagrams and an interpretation of no S shaped curves for the elongational viscosity or for the mean square end to end distance is gi...

1997, 29(3): 349-354. doi: 10.6052/0459-1879-1997-3-1995-236

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PATH SELECTION AND NUMERICAL SIMULATION OF INTERFACIAL FRACTURE

The concepts of interfacial fracture energy and mode mixity are used to investigate the growth paths of interfacial cracks. Numerical approach based on the finite element method is applied to calculate the energy release rate and to simulate the growth process of a crack. Various configurations of interfacial fracture of bimaterials can be simulated. It is shown that the process of interfacial fracture is controlled by the interfacial toughness and phase angle of mode mixity. The predicted crack paths agre...

1997, 29(3): 355-358. doi: 10.6052/0459-1879-1997-3-1995-237

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THE PROJECTED CONSERVATION THEORY OF THE J k VECTOR FOR MICROCRACK INTERFACE CRACK SHIELDING

It is proved from analytical treatments and computer experiments that the projected conservation relation of the J k vector, found for microcrack shielding problems in brittle homogeneous cases, is also valid for the shielding problems in bimaterial solids, although the characteristic oscillating stress singularity exists near the tip for an interface crack and the tension and shear modes are inherently coupled near the tip. As the relation is shown to be universal, it could be called as the projected c...

1997, 29(3): 359-364. doi: 10.6052/0459-1879-1997-3-1995-238

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RANDOM RESPONSE OF BEAM UNDER MOVING RANDOM LOAD IN THE LINE SOURCE FORM

By using generalized Duhamel's integral and integral transform, this paper investigates random response of an infinite beam on the Kelvin viscoelastic foundation subjected to a moving load. It's found that displacement response of the beam is a non stationary random process even if the moving load is a stationary process. The follow up coordinate system is established to make the displacement became a stationary random process.

1997, 29(3): 365-368. doi: 10.6052/0459-1879-1997-3-1995-239

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PARALLEL COMPUTATIONAL SCHEME FOR THE MANIPULATOR FORWARD DYNAMICS BASED ON THE NON-RECURSIVE FORMULATION

An augmented computational model for the forward dynamics is developed by using the Jourdain principle and the vector of Lagrange multipliers. Because some redundant computations are introduced, the data dependency in the model is reduced and hence the parallelism of this model is increased. A parallel computational scheme with O(n) processors for the manipulator forward dynamics is presented based on this model.

1997, 29(3): 369-372. doi: 10.6052/0459-1879-1997-3-1995-240

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TWO POINT BOUNDARY VALUE INVERSE DYNAMIC METHODS OF FLEXIBLE MANIPULATORS ——THEORETICAL ANALYSIS AND EXPERIMENTAL RESULTS

Two point boundary value inverse dynamic methods of flexible manipulators based on optimal control theory are proposed in the present paper. The open loop inputs obtained by the proposed method can make the flexible manipulator accomplish the point to point motion or trajectory tracking while greatly reduce or eli min ate the influence of the flexibility on the accurate positioning. Numerical imitation and experimental results coincide with the theoretical analyses.

1997, 29(3): 373-379. doi: 10.6052/0459-1879-1997-3-1995-241

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DIGITAL MOIRE SYSTEM WITH PHASE SHIFTING METHOD

A new deformation measurement technique with digital moire methods is presented. The image of a grating bonded onto a body under exa min ation is acquired with a CCD camera. The sample frequency is chosen as the times of grating density. Then, a special phase shifting method is realized by using digital signal processing technique. The influence of phase shift error and high harmonics in grating signal is automatically corrected.

1997, 29(3): 380-384. doi: 10.6052/0459-1879-1997-3-1995-242

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1997 Vol. 29, No. 3

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