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2012 Vol. 33, No. 3
Published:
论文
233
Analysis of cyclic plasticity using a polycrystalline model taking account of size effect
DOI:
Using polycrystalline plasticity analytical method and considering that there were a great deal of anisotropy crystal grains in material point and that influence is coming from scale effect, stress and strain in material point were calculated adopting Taylor’s hypotheses in the paper. Hardening function of crystal slip taking scale effect into account and back stress that reflecting crystal’s directional hardening was introduced into the model, which can describe the mechanical behavior of a material, including scale effect of crystal grain under cyclic loads. The first author of the paper compiled a user material subroutine (VUMAT) in explicit arithmetic suitable for the interface of ABAQUS; it can be adopted to describe the cyclic plasticity behavior and size effect of polycrystalline metallic material under repetitive loading. The simulation of a material’s representative volume element which consists of a number of crystal grains was carried out, the results were confirmed reasonable in size effect for a polycrystal under cycle load.
2012 Vol. 33 (3): 233-241 [
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242
Effect of rock damage on phenomenon of zonal disintegration around deep circle tunnels
DOI:
The deep Rock masses is discontinuous medium containing cracks and joints. The phenomenon of zonal disintegration in deep rock masses is sensitive to the necleation,growth and coalescence of cracks. Transform from Euclidean geometry space to Non-euclidean geometry space in deep rock masses is induced by the necleation,growth and coalescence of cracks. Damage variable is applied to the damage of deep rock masses in this paper. The stress field of the surrounding rock masses around the deep circle tunnels under hydrostatic and non-hydrostatic pressure condition is obtained using the non-euclidean model,effect of damage variable on the stress field of the surrounding rock masses and the phenomenon of zonal disintegration around the deep tunnels are discussed. The distribution of fractured zones and non-fractured zones around the deep circle tunnels under hydrostatic and non-hydrostatic pressure condition is determined using Hoek-Brown criterion. The present study is helpful to understand the phenomenon of zonal disintegration in deep rock masses.
2012 Vol. 33 (3): 242-250 [
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274
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251
A STEREOLOGICAL FRACTAL COHESIVE LAW OF CONCRETE UNDER TENSITON LOADING
DOI:
A stereological type of fractal cohesive law is presented in this paper in order to describe more reasonably the soften behaviors of concrete under quasi-static uniaxial tensile loadings, in which the damage evaluation process of the fracture cross-sections and their distribution along the specimens’ axis are both considered. The derived numerical results are found to be in good agreement with the experimental data published in previous open literature. Additionally, the effects of aggregate grading type on the soften characteristic of concrete are analyzed by using the new cohesive model, which shows, under tensile loadings, that the more homogeneous the size distribution of the aggregates is, the stronger soften of concrete will be.
2012 Vol. 33 (3): 251-257 [
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268
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258
Phase Stability of Single Domain Epitaxial Ferroelectric films
DOI:
The phase stability of single domain ferroelectric PbTiO3 (PTO) epitaxial thin film as a function of the misfit strain and film thickness is studied and discussed systematically using the dynamic Ginzburg-Landau (DGL) equation by taking surface eigenstrain relaxation and depolarization field. Misfit strain-film thickness phase diagrams for various temperatures and misfit strain-temperature phase diagrams for various film thicknesses are obtained, respectively. The numerical results show that the phase diagrams in high strain zone are markedly different from previous thermodynamic predictions due to misfit dislocations. Especially, we present that there are c-phase and rotational r-phase in a broader misfit tensile strain zone. The results also express that effects of surface and depolarization field obviously shift the paraelectric phase to lower temperature and shrink the ferroelectric phase with decreasing thickness of the films
2012 Vol. 33 (3): 258-264 [
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265
Plastic flow characteristics and constitutive relation for ultra high strength and toughness steel AF1410
DOI:
In this paper, to understand the plastic flow characteristics of ultra high strength and toughness steel AF1410, and build the constitutive relations of this steel, using a CSS4410 qusia-static test machine and enhanced Hopkinson pressure and tension bar technique, uniaxial compression and tension tests are both performed. True strains exceeding 20% are achieved in these tests, over the range of strain rates from 0.001/s to about 2000/s, and at initial temperatures from 100K to 600 K. The results demonstrate that: the yield stress in tension loading is lower than it in compress loading, and the difference between the compress and tension yield stresses become larger, with increasing strain rate; the plastic flow of AF1410 steel is not very sensitive to the changes of strain rate, but is relatively sensitive to temperature; the failure strain decreases with the increasing strain rate, but is not evidently affected by temperature. Finally, based on the mechanism of dislocation motion, paralleled with a systematic experimental investigation, a physical conception constitutive model is obtained for the deformation of AF1410 steel, and is evaluated by the classical J-C model. It shows that the plastic flow of AF1410 steel, in a large range of strain rates and temperatures, could be predicted by physical conception constitutive model.
2012 Vol. 33 (3): 265-272 [
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317
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273
Study on Mechanism of Laminated Crack Defect in the Upsetting Process of Heavy Disk-Shaped Forgings
DOI:
Aiming to laminated crack defect occurring in the upsetting of heavy disk-shaped forgings, finite element analysis technique was using to establish coupling thermo-mechanical simulation model for upsetting process. By aid of the model, the distributions of equivalent strain, equivalent strain rate and its’ gradients. After analyzing the change law of the different fields, a model of laminated crack defect was setted up based on strain and strain rate gradient, and obtain the morphology distribution of laminated crack at the center of forgings. The numerical simulation result coincides well with the experimental data.
2012 Vol. 33 (3): 273-278 [
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279
A Modified Couple Stress Linear Elasticity and Finite Element Method for Generalized Elastic Bodies
DOI:
Upon on the theory of elasticity with couple-stress, a modified constitutive equation between couple stress and curvature tensor is developed in this paper, taking account of the deformation as a result of translation and rotation in generalized elasticity bodies under infinitesimal deformation. The penalty function method is used to construct the constrained variational form for generalized elasticity, with the rotational angle as independent degree of freedom to relax the C1 continuity in finite element. The finite element equation of motion is given for the generalized elastic body, discretized by elements with 8-nodes and 48 degree of freedom. Static and dynamical analysis of a cantilever beam are presented showing the advantage in structural analysis fields for the generalized elasticity with couple stress effects, comparing to the classic elasticity and structural mechanics. In contrast to the classical elasticity and structural mechanics, the generalized elasticity for deformation body can capture the size dependent effects in material, which have a great influence on the dynamical characteristic of micro-structure.
2012 Vol. 33 (3): 279-287 [
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358
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288
The Interaction between a Screw Dipole in Inhomogeneity/Reinforced Phase and a Confocal Blunt Crack in Elliptical Inhomogeneity
DOI:
By using the complex variable method of Elasticity, the interaction between a screw dipole inside the Inhomogeneity/Reinforced Phase and a confocal blunt crack in elastic elliptical inhomogeneity is investigated and the closed solutions are obtained for this problem. The stress field of inhomogeneity, the image force and image torque acting on the center of screw dipole, the stress intensity factor of the blunt crack tip are obtained in the series form. Simultaneously, the influence law of the dip angle of screw dipole , the size of blunt crack and the material parameters on them are analyzed. The numerical results show that the image force, image torque and stress intensity changes periodically with the dip angle of screw dipole; the blunt crack in inhomogeneity can evidently strengthen the repulsion of hard matrix to dislocation and weaken the attraction of soft matrix to dislocation; there is an unstable equilibrium position for screw dipole when the inhomogeneity is hard and the equilibrium position will approach to the interface as the curvature of blunt crack increasing; the variation of will appear a critical value that can change the direction of stress intensity factor.
2012 Vol. 33 (3): 288-295 [
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296
Properties of the derivatives of Lode angle with respect to stress
DOI:
The Lode angle is often introduced into yield function or plastic potential function for accounting the complex mechanical behaviors, such as influences of intermediate principle stress and stress path on failure and deformation, of granular soil. Therefore, the derivative of Lode angle with respect to stress (denoted as ) must be involved for the calculation of plastic strain. Yet, the singularity of occurs at the stress states which correspond to the repeated principle stress, so it is difficulty to obtain the principle value of . A new method for calculation of principle value of are presented in the study，and some basic properties of are discussed in detail.
2012 Vol. 33 (3): 296-301 [
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简报
302
Wave propagation method for in-plane vibration of curved pipe conveying fluid
DOI:
The Flügge curved beam was applied to approximate the curved pipe to obtain the dynamic equations of in-plane vibration of curved pipe conveying fluid based on total inextensible assumption and the fluid acceleration was also deduced. After establishing the wave propagation and reflection matrices, the wave propagation method for calculating the natural frequency of curved pipe’s in-plane vibration was proposed. In the example, the critical velocity of a semi-circular pipe with clamped support at both ends was calculated. The result was compared with that in existing literature and great agreement was shown. Finally, the first four natural frequencies of clamped-clamped semi-circular pipe conveying fluid were obtained in six different cases of fluid velocity. The results shown that the increasing fluid velocity can make the natural frequencies of pipe decreased and when the fluid velocity increased to a certain value, the first natural frequency vanished.
2012 Vol. 33 (3): 302-308 [
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291
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309
Analysis of Static Bending Model of Microcantilever Gas Sensor Considering the Change of Neutral Layer Position
DOI:
Microcantilever is a kind of biochemical sensor with high sensitivity. In this paper, the change of neutral layer position caused by adsorption-induced stress is introduced into modeling, and the static bending model of microcantilever with monolayer molecules is established based on energy method. On this basis, the relationship between the curvature radius of microcantilever and its thickness, Young’s modulus and adsorbed molecules distance and the effect of change of neutral layer position on the performance prediction of microcantilever are investigated using the microcantilever adsorbed with water molecules. The results showed that 1)the relationship between the curvature radius and Young’s modulus, thickness and adsorbed molecules distance can be expressed using the linear, quadratic and eight approximation function; 2)the predicted error of bending curvature radius caused by the change in neutral layer position slightly increases with decreasing Young’s modulus and thickness, whereas the effect of distance between adsorbed molecules on the error is significant; 3)the change in neutral layer position can cause a significant effect on the sensitivity and surface strain of the microcantilever.
2012 Vol. 33 (3): 309-316 [
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293
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317
Free vibration of multi-layered piezoelectric spherical shells with imperfect interfaces
DOI:
Upon introducing two displacement and stress functions, two independent state equations are established from the three-dimensional piezoelectricity for free vibration of multilayered piezoelectric spherical shells with imperfect interface. The state equations with variable coefficients are then transferred to ordinary differential equations by expanding the state variables into series of spherical harmonic functions and using the approximate laminate model. Also, the behavior of the imperfect interface is described in detail, and the transfer relation of the state vectors at the interface is obtained so that the global transfer relation between state vectors at the outmost and innermost surface of the shell is derived. Two frequency equations corresponding two classes of vibration are then obtained by incorporating the free traction conditions at the surfaces. Numerical examples are performed with indication that the imperfect interface indices for elastic field have significant effects on the natural vibration frequencies of the shell, but the electrically conductivity of the interface has little effect.
2012 Vol. 33 (3): 317-324 [
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325
SAFETY EVALUATION OF NON-PROBABILISTIC RELIABILITY MODEL OF STRUCTURES
DOI:
With the consideration of interval variables in non-probabilistic reliability model, three kinds of parameters, reliability index, safety factor and set-theoretic reliability measurement, were adopted to represent the reliability and safety measurement of the structures. The physical means of the three kinds of parameters were described through geometric representation and the value range and practical region were pointed out. Furthermore, the differentiation among three kinds of parameters was investigated in design concept, measurement and representation formation, so that the function relationship among them was then built up. The researching results extend the non-probabilistic theory for structure design. The optimal scheme has demonstrated through examples and results were discussed.
2012 Vol. 33 (3): 325-330 [
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331
Study and Prediction of Compression Deformation Behavior for Pure Sintered Mo Powder
DOI:
Based on the yield criterion and plastic constitutive equation for compressible dense materials，the yield function for sintered powder materials during plastic compression deformation was derived．Cylindrical Mo specimens with different values of the initial relative density were prepared by using vacuum sintering technology．The effects of the initial relative density，deformation temperature and strain rate on the flow stress of the sintered Mo powder were studied by uniaxial compression tests proceeded at MTS810 system．The empirical regression model of the flow stress was established and the yield equation during compression deformation was determined．Based on these studies，the elasto-plastic constitutive model for the sintered Mo powder was established．These studies are significant for improving the simulation accuracy and formulating reasonable forming process for sintered Mo powder．
2012 Vol. 33 (3): 331-335 [
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312
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