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A new viscoelastic model based on generalized method of cells for fiber-reinforced composites

INTERNATIONAL JOURNAL OF PLASTICITY 2015年 65卷 22-32页

作者： Li, Huimin Zhang, Boming Beihang Univ Mat Sci & Engn Sch Beijing 100191 Peoples R China

A semi-analytical model is constructed to investigate the relaxation properties of polymer composites consisting of linearly viscoelastic matrices and transversely isotropic elastic fibers. A representative unit cell is subjected to some prescribed loadings to value the time-dependent properties of composite materials. The model is derived to describe the anisotropic viscoelastic properties of composite materials as functions of matrix and fiber properties. The present numerical algorithm is used to predict the viscoelastic properties of a graphite/epoxy composite and the results are compared with the finite element analysis of the micromechanical model. Very good agreement between numerical algorithm and finite element analysis results is illustrated for the viscoelastic properties of anisotropic composite materials. (C) 2014 Elsevier Ltd. All rights reserved.

关键词： Stress relaxation Fiber-reinforced composite material Viscoelastic material Characteristics numerical algorithms

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Stress field tomography based on 3D photoelasticity

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JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 2008年第3期56卷 1065-1085页

作者： Wijerathne, M. L. L. Oguni, Kenji Hori, Muneo Univ Tokyo Earthquake Res Inst Bunkyo Ku Tokyo 11130032 Japan Japan Agcy Marine Earth Sci & Technol Inst Res Earth Evolut Kanazawa Ku Yokohama Kanagawa 2360001 Japan

tomographic method for identification of stress fields based on 3D photoelasticity has been developed. A second order tensor field tomographic method based on the general inverse problem of 3D photoelasticity, previously developed by the authors, is found to be highly sensitive to errors in photoelastic observations. In this study a new tomographic method for stress field with fairly high robustness to errors in photoelastic observations has been developed by introducing both equilibrium condition and linear elasticity to the previously developed general tensor field tomographic method. This new stress field tomographic method expands unknown 3D stress distributions as a linear combination of independent set of basis functions and a new inverse problem is posed: identify the amplitudes of basis functions based on photoelastic observations. Just as the inverse problem of 3D photoelasticity, this newly posed inverse problem is also nonlinear and ill posed. Unlike conventional approaches to 3D photoelasticity, both these nonlinearity and ill-posedness are properly treated using a load incremental approach. Load incremental approach chops the nonlinear solution space into segments with unique Solutions by conducting photoelastic observations at sufficiently small increments in external load. Validating both numerically and experimentally, it is shown that this new stress field tomographic method has sufficient robustness against errors in photoelastic observations and is applicable to experimental stress measurements. (C) 2007 Elsevier Ltd. All rights reserved.

关键词： 3D stress field tomography nondestructive evaluation mechanical testing numerical algorithms optical interferometry

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Low order-value approach for solving VaR-constrained optimization problems

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JOURNAL OF GLOBAL OPTIMIZATION 2011年第4期51卷 715-742页

作者： Birgin, E. G. Bueno, L. F. Krejic, N. Martinez, J. M. Univ Sao Paulo Dept Comp Sci IME USP BR-05508090 Sao Paulo Brazil Univ Estadual Campinas Inst Math Stat & Sci Comp IMECC Dept Appl Math BR-13083859 Campinas SP Brazil Univ Novi Sad Dept Math & Informat Novi Sad 21000 Serbia

In Low Order-Value Optimization (LOVO) problems the sum of the r smallest values of a finite sequence of q functions is involved as the objective to be minimized or as a constraint. The latter case is considered in the present paper. Portfolio optimization problems with a constraint on the admissible Value at Risk (VaR) can be modeled in terms of a LOVO problem with constraints given by Low order-value functions. Different algorithms for practical solution of this problem will be presented. Using these techniques, portfolio optimization problems with transaction costs will be solved.

关键词： Optimization Augmented Lagrangian Order-value optimization Low order-value optimization Value at risk numerical algorithms

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Converting to and from dilated integers

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IEEE TRANSACTIONS ON COMPUTERS 2008年第4期57卷 567-573页

作者： Raman, Rajeev Wise, David S. Dept Comp Sci Leicester LEQ 7RH Leics England Indiana Univ Dept Comp Sci Bloomington IN 47405 USA

Dilated integers form an ordered group of the Cartesian indices into a d-dimensional array represented in the Morton order. Efficient implementations of its operations can be found elsewhere. This paper offers efficient casting (type)conversions to and from an ordinary integer representation. As the Morton order representation for 2D and 3D arrays attracts more users because of its excellent block locality, the efficiency of these conversions becomes important. They are essential for programmers who would use Cartesian indexing there. Two algorithms for each casting conversion are presented here, including to-and-from dilated integers for both d = 2 and d = 3. They fall into two families. One family uses newly compact table lookup, so the cache capacity is better preserved, The other generalizes better to all d, using processor-local arithmetic that is newly presented as abstract d-ary and (d-1)-ary recurrences. Test results for two and three dimensions generally favor the former.

关键词： analysis programming techniques numerical algorithms design performance memory hierarchy caches paging compilers classes quadtrees octrees dilation contraction.

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IMPLEMENTING CONTINUOUS-SCALE MORPHOLOGY VIA CURVE EVOLUTION

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PATTERN RECOGNITION 1993年第9期26卷 1363-1372页

作者： SAPIRO, G KIMMEL, R SHAKED, D KIMIA, BB BRUCKSTEIN, AM BROWN UNIV ENGN MAN MACHINE SYST LABPROVIDENCERI 02912 TECHNION ISRAEL INST TECHNOL DEPT COMP SCIIL-32000 HAIFAISRAEL

A new approach to digital implementation of continuous-scale mathematical morphology is presented. The approach is based on discretization of evolution equations associated with continuous multiscale morphological operations. Those equations, and their corresponding numerical implementation, can be derived either directly from mathematical morphology definitions or from curve evolution theory. The advantages of the proposed approach over the classical discrete morphology are demonstrated.

关键词： MATHEMATICAL MORPHOLOGY SCALE-SPACE CURVE EVOLUTION PARTIAL DIFFERENTIAL EQUATIONS DIGITAL IMPLEMENTATION numerical algorithms

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Dynamic ruptures in recent models of earthquake faults

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JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 2001年第9期49卷 2209-2244页

作者： Ben-Zion, Y Univ So Calif Dept Earth Sci Los Angeles CA 90089 USA

We discuss several problems of dynamic rupture relevant to mechanics of earthquake faults, material sciences, and physics of spatially extended dissipative systems. The problems include dynamic rupture along an interface separating different elastic solids., dynamic rupture on a planar surface governed by strongly velocity-weakening friction, and elastodynamic calculations of long deformation history on a smooth fault in an elastic continuum. These separate problems share a number of methodological and conceptual issues that form recurring themes in the paper. An important methodological issue for computational schemes is dependency of numerical results on the used grid size. This arises inevitably in computer simulations when the assumed constitutive laws do not include a length scale (e.g., of shear or extensional displacement) over which material properties evolve. Such simulations do not have a stable underlying solution, to which they may converge with sufficient grid refinement. However, they may provide rough approximations-lacking at present a rigorous foundation-to the behavior of systems containing elements of discreteness (associated with abrupt fluctuations) at scales relevant to observations of interest. Related important conceptual issues are connections between. or when appropriate separation of, small scale phenomena (e.g., nucleation of rupture, processes at rupture front) and large scale features of the response (e.g., overall space-time dimensions of rupture, statistics of many events). Additional recurring conceptual topics are crack vs. pulse modes of dynamic rupture, the stress under which earthquake faults slip, and the origin of spatio-temporal complexities of earthquakes. These seemingly different issues probably have one or more common origins. Dynamic rupture on an interface between different solids. strongly velocity-weakening friction on a homogeneous fault, and strong fault zone heterogeneities can all produce narrow self-healing slip p

关键词： crack propagation and arrest dynamics friction layered material numerical algorithms

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Designs of learning controllers based on autoregressive representation of a linear system

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 1996年第2期19卷 355-362页

作者： Phan, MQ Juang, JN NASA LANGLEY RES CTR STRUCT DYNAM BRANCH HAMPTON VA 23681 USA

Learning controllers that improve tracking performance through repeated trials are derived. The design is based on an autoregressive representation of a linear system. This input-output model can be interpreted in terms of an observer in state-space form. The control input is modified at every repetition as the system learns to produce a desired response, even in the presence of unknown repetitive disturbances. The coefficients of a nominal autoregressive model are first identified from input-output data. Using the identified coefficients, simple linear feedback learning controllers are designed that can correct for the errors that remain. An optimal learning gain matrix is also derived given the identified model. numerical examples are provided to illustrate the proposed learning approach.

关键词： Autoregressive Model State Space Representation Satellites Three Degrees of Freedom Control Moment Gyros numerical algorithms Feature Learning Nonlinear Systems Computing Robots

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A visco-damage model for brittle materials under monotonic and sustained stresses

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INTERNATIONAL JOURNAL FOR numerical AND ANALYTICAL METHODS IN GEOMECHANICS 2005年第3期29卷 287-310页

作者： Papa, E Taliercio, A Politecn Milan Dept Struct Engn I-20133 Milan Italy

A theoretical model is proposed to describe the evolution of damage in brittle materials, such as concrete and masonry, subjected to increasing or sustained stresses of relatively high intensity. The model is based on the introduction of suitable damage variables in a rheological model. In this way, it is possible to describe the material behaviour under stresses either increasing or constant in time. The capabilities of the model in describing the mechanical response of material elements subjected to different stress histories are illustrated. Some correlations with experimental data from tests performed on masonry and concrete specimens are presented, to assess the reliability of the theoretical predictions. The results of some numerical applications to non-proportional stress paths are also illustrated. Finally, the limitations of the proposal are discussed and possible further improvements are envisaged. Copyright (C) 2005 John Wiley Sons, Ltd.

关键词： creep damage concrete anisotropy numerical algorithms

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Thermally-activated non-Schmid glide of screw dislocations in W using atomistically-informed kinetic Monte Carlo simulations

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INTERNATIONAL JOURNAL OF PLASTICITY 2015年 65卷 108-130页

作者： Stukowski, Alexander Cereceda, David Swinburne, Thomas D. Marian, Jaime Tech Univ Darmstadt Inst Mat Sci D-64287 Darmstadt Germany Lawrence Livermore Natl Lab Phys & Life Sci Directorate Livermore CA USA Univ Politecn Madrid Inst Fus Nucl E-28006 Madrid Spain Univ London Imperial Coll Sci Technol & Med Dept Phys London SW7 2AZ England Culham Sci Ctr CCFE Abingdon OX14 3DB Oxon England

Thermally-activated 1/2 screw dislocation motion is the controlling plastic mechanism at low temperatures in body-centered cubic (bcc) crystals. Dislocation motion proceeds by nucleation and propagation of atomic-siz... 详细信息

Thermally-activated 1/2 < 111 > screw dislocation motion is the controlling plastic mechanism at low temperatures in body-centered cubic (bcc) crystals. Dislocation motion proceeds by nucleation and propagation of atomic-sized kink pairs in close-packed planes. The atomistic character of kink pairs can be studied using techniques such as molecular dynamics (MD). However, MD's natural inability to properly sample thermally-activated processes as well as to capture {110} screw dislocation glide calls for the development of other methods capable of overcoming these limitations. Here we develop a kinetic Monte Carlo (kMC) approach to study single screw dislocation dynamics from room temperature to 0.5T(m), and at stresses 0 < sigma < 0.9 sigma(P), where T-m and sigma(P) are the melting point and the Peierls stress. The method is entirely parameterized with atomistic simulations using an embedded atom potential for tungsten. To increase the physical fidelity of our simulations, we calculate the deviations from Schmid's law prescribed by the interatomic potential used and we study single dislocation kinetics using both projections. We calculate dislocation velocities as a function of stress, temperature, and dislocation line length. We find that considering non-Schmid effects has a strong influence on both the magnitude of the velocities and the trajectories followed by the dislocation. We finish by condensing all the calculated data into effective stress and temperature dependent mobilities to be used in more homogenized numerical methods. (C) 2014 Elsevier Ltd. All rights reserved.

关键词： Dislocations Metallic material numerical algorithms Ductility

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DUCTILE FAILURE SIMULATION IN SPHERODIZED STEEL USING A CONTINUUM DAMAGE MECHANICS COUPLED FINITE ELEMENT FORMULATION

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INTERNATIONAL JOURNAL OF COMPUTATIONAL METHODS 2010年第2期7卷 319-348页

作者： Gautam, Sachin S. Dixit, P. M. Indian Inst Technol Kanpur Dept Mech Engn Kanpur 208016 Uttar Pradesh India

Ductile fracture occurs due to microvoid nucleation, growth and, finally, coalescence into microcracks. These microcracks grow in the presence of stresses leading to fracture. In this work, a criterion based on this phenomenon is used to simulate ductile fracture in a class of steel specimens. A critical value of the damage variable, estimated from experimental results, is used as an indicator of fracture initiation. A continuum damage mechanics model is employed to incorporate the damage in the constitutive relation of the material. A damage growth law based on experimental results is used. It is observed that the damage reaches the critical value first at the center in both the cylindrical and prenotched specimens. Thus, the failure begins at the center and then grows radially outward toward the free surface. The analysis is carried out till the damage reaches the critical value across the whole cross-section, at which point the specimen is considered to have failed.

关键词： Fracture continuum damage mechanics finite elements numerical algorithms

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