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Sequential simulation and neural network in the stress-strain curve identification over the large strains using tensile test

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ARCHIVE OF APPLIED MECHANICS 2017年第6期87卷 1077-1093页

作者： Jenik, Ivan Kubik, Petr Sebek, Frantisek Hulka, Jiri Petruska, Jindrich Honeywell Technol Solut Turanka 100-1387 Brno 62700 Czech Republic Brno Univ Technol Inst Solid Mech Mechatron & Biomec Fac Mech Engn Tech 2896 2 Brno 61669 Czech Republic Inst Appl Mech Resslova 972-3 Brno 60200 Czech Republic

Two alternative methods for the stress-strain curve determination in the large strains region are proposed. Only standard force-elongation response is needed as an input into the identification procedure. Both methods are applied to eight various materials, covering a broad spectre of possible ductile behaviour. The first method is based on the iterative procedure of sequential simulation of piecewise stress-strain curve using the parallel finite element modelling. Error between the computed and experimental force-elongation response is low, while the convergence rate is high. The second method uses the neural network for the stress-strain curve identification. Large database of force-elongation responses is computed by the finite element method. Then, the database is processed and reduced in order to get the input for neural network training procedure. Training process and response of network is fast compared to sequential simulation. When the desired accuracy is not reached, results can be used as a starting point for the following optimization task.

关键词： Ductility Constitutive behaviour Metallic materials numerical algorithms Optimization Elastic-plastic deformation

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A unified constitutive model for asymmetric tension and compression creep-ageing behaviour of naturally aged Al-Cu-Li alloy

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INTERNATIONAL JOURNAL OF PLASTICITY 2017年 89卷 130-149页

作者： Li, Yong Shi, Zhusheng Lin, Jianguo Yang, Yo-Lun Rong, Qi Huang, Bo-Ming Chung, Tsai-Fu Tsao, Cheng-Si Yang, Jer-Ren Balint, Daniel S. Imperial Coll London Dept Mech Engn London SW7 2AZ England Natl Taiwan Univ Dept Mat Sci & Engn Taipei Taiwan

A set of unified constitutive equations is presented that predict the asymmetric tension and compression creep behaviour and recently observed double primary creep of pre-stretched/naturally aged aluminium-cooper-lithium alloy AA2050-T34. The evolution of the primary micro- and macro-variables related to the precipitation hardening and creep deformation of the alloy during creep age forming (CAF) are analysed and modelled. Equations for the yield strength evolution of the alloy, including an initial reversion and subsequent strengthening, are proposed based on a theory of concurrent dissolution, re nucleation and growth of precipitates during artificial ageing. We present new observations of so-called double primary creep during the CAF process. This phenomenon is then predicted by introducing effects of interacting microstructures, including evolving precipitates, diffusing solutes and dislocations, into the sinh-law creep model. In addition, concepts of threshold creep stress o-th and a microstructure-dependant creep variable H, which behave differently under different external stress directions, are proposed and incorporated into the creep model. This enables prediction of the asymmetric tension and compression creep-ageing behaviour of the alloy. Quantitative transmission electron microscopy (TEM) and related small-angle X-ray scattering (SAXS) analysis have been carried out for selected creep-aged samples to assist the development and calibration of the constitutive model. A good agreement has been achieved between the experimental results and the model. The model has the potential to be applied to creep age forming of other heat-treatable aluminium alloys. (C) 2016 The Authors. Published by Elsevier Ltd.

关键词： Creep age forming Ageing Microstructures Constitutive behaviour numerical algorithms

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Disorder is good for you: the influence of local disorder on strain localization and ductility of strain softening materials

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INTERNATIONAL JOURNAL OF FRACTURE 2017年第2期205卷 139-150页

作者： Tuzes, Daniel Ispanovity, Peter Dusan Zaiser, Michael Eotvos Lorand Univ Dept Mat Phys Pazmany Peter Setany 1-A H-1117 Budapest Hungary Friedrich Alexander Univ Inst Mat Simulat WW8 Dr Mack Str 77 D-90762 Furth Germany

We formulate a generic concept model for the deformation of a locally disordered, macroscopically homogeneous material which undergoes irreversible strain softening during plastic deformation. We investigate the influence of the degree of microstructural heterogeneity and disorder on strain localization (formation of a macroscopic shear band) in such materials. It is shown that increased microstructural heterogeneity delays strain localization and leads to an increase of the plastic regime in the macroscopic stress-strain curves. The evolving strain localization patterns are characterized.

关键词： Fracture Microstructures Inhomogeneous material numerical algorithms Probability and statistics

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Efficient Scalable Parallel Higher Order Direct MoM-SIE Method With Hierarchically Semiseparable Structures for 3-D Scattering

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IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION 2017年第5期65卷 2467-2478页

作者： Manic, Ana B. Smull, Aaron P. Rouet, Francois-Henry Li, Xiaoye Sherry Notaros, Branislav M. Colorado State Univ Dept Elect & Comp Engn Ft Collins CO 80523 USA Lawrence Berkeley Natl Lab Computat Res Div Berkeley CA 94720 USA

A novel fast scalable parallel algorithm is proposed for the solution of large 3-D scattering problems based on: 1) the double (geometrical and current-approximation) higher order (DHO) method of moments (MoM) in the surface integral equation (SIE) formulation and 2) a direct solver for dense linear systems utilizing hierarchically semiseparable (HSS) structures. Namely, an HSS matrix representation is used for compression, factorization, and solution of the system matrix. In addition, a rank-revealing QR decomposition for memory compression is used, with a stopping criterion in terms of the relative rank tolerance value. A method for geometrical preprocessing of the scatterers based on the cobblestone distance sorting technique is employed in order to enhance the HSS algorithm accuracy and parallelization. numerical examples show how the accuracy of the DHO HSS-MoM-SIE method is easily controllable by using the relative tolerance for the matrix compression. Moreover, the examples demonstrate low memory consumption, as well as much faster simulation time, when compared to the direct LU decomposition. The method enables dramatically faster monostatic scattering computations than iterative solvers and reduced number of unknowns when compared to low-order discretizations. Finally, great scalability of the algorithm is demonstrated on more than one thousand processes.

关键词： Curved parametric elements direct solvers fast solvers hierarchically semiseparable (HSS) structures higher order (HO) modeling low-rank matrix approximation method of moments (MoM) multilevel matrix compression numerical algorithms parallelization polynomial basis functions scalability scattering surface integral equation (SIE)

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A differential-exponential hardening law for non-Schmid crystal plasticity finite element modeling of ferrite single crystals

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INTERNATIONAL JOURNAL OF PLASTICITY 2017年 91卷 268-299页

作者： Mapar, A. Ghassemi-Armaki, H. Pourboghrat, F. Kumar, K. S. Michigan State Univ Dept Mech Engn E Lansing MI 48824 USA Michigan State Univ Dept Chem Engn & Mat Sci E Lansing MI 48824 USA Brown Univ Sch Engn Providence RI 02912 USA Ohio State Univ Dept Integrated Syst Engn Dept Mech & Aerosp Engn Columbus OH 43210 USA ArcelorMittal Global R&D E Chicago IN 46312 USA

Crystal plasticity finite element (CPFE) modeling of multi-phase, third generation advanced high strength steel (3GAHSS) requires finding the hardening parameters of slip systems operating in different phases (e.g. FCC, BCC, BCT). It is common to see the Schmid law used to model the deformation of BCC crystals. However, researches by Bassani and others have shown that BCC crystals could obey the non-Schmid law. In this paper we examined the differences between using a CPFE model based on the Schmid versus a non Schmid law to model the uniaxial compression of single crystal ferrite micropillars with distinct orientations carved out of dual phase DP980 and three-phase QP980 steel sheets. To accurately model the changing hardening rate of the single crystal, a new exponential hardening model was developed that would differentially harden slip systems. Criteria for transitioning from stage Ito stage II hardening of single crystals were also developed and verified. Finally, it was shown that it is not sufficient to use only one single crystal micropillar compression force-displacement curve for the calibration of the non-Schmid CPFE model. The predictions of the resulting model would be unreliable, and its accuracy highly dependent on the orientation of the micropillar chosen for calibration. However, when two mircopillar compression force-displacement curves were used for calibration, the model's predictions were consistently accurate. Using more than two curves for calibration did not result in significant improvements. (C) 2016 Published by Elsevier Ltd.

关键词： Yield condition Crystal plasticity Finite elements numerical algorithms Non-Schmid law

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The exploration of nonlinear elasticity and its efficient parameterization for crystalline materials

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JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 2017年 107卷 76-95页

作者： Thomas, John C. Van der Ven, Anton Univ Calif Santa Barbara Dept Mat Santa Barbara CA 93106 USA

Conventional approaches to analyzing the very large coherency strains that can occur during solid-state phase transformations are founded in linear elasticity and rely on infinitesimal strain metrics. Despite this, there are many technologically important examples where misfit strains of multi-phase mixtures are very large during their synthesis and/or application. In this paper, we present a framework for constructing strain-energy expressions and stress-strain relationships beyond the linear-elastic limit for crystalline solids. This approach utilizes group theoretical concepts to minimize both the number of free parameters in the strain-energy expression and amount of first-principles training data required to parameterize strain-energy models that are invariant to all crystal symmetries. Within this framework, the strain-energy and elastic stiffness can be described to high accuracy in terms of a set of conventional symmetry-adapted finite strain metrics that we define independent of crystal symmetry. As an illustration, we use first-principles electronic structure data to parameterize strain energy polynomials and employ them to explore the strain energy surfaces of HCP Zr and Mg, as well as several important Zr-H and Mg-Nd phases that are known to precipitate coherently within the HCP matrices of Zr and Mg. (C) 2017 Elsevier Ltd. All rights reserved.

关键词： Finite strain Elastic material Anisotropic material Constitutive behavior numerical algorithms

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Glide mobility of the 1/2[1101(001) edge dislocation in UO₂ from molecular dynamics simulation

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INTERNATIONAL JOURNAL OF PLASTICITY 2017年 89卷 85-95页

作者： Lunev, A. V. Kuksin, A. Yu. Starikov, S. V. Russian Acad Sci Joint Inst High Temp 13 Bld 2Izhorskaya St Moscow 125412 Russia Moscow Inst Phys & Technol Moscow 141700 Russia

Both the mechanical properties of oxide nuclear fuel and the high burn-up grain restructuring are known to be related to dislocation motion. Previous studies show that at temperatures above 1000 K slip on 001) crystallographic planes in UO2 is dominant, and 1/2(110)(001} dislocations should have the highest mobility. However, no information is available on the temperature and stress dependence of dislocation velocities in UO2. This information is required as input in higher scale simulation techniques, such as dislocation dynamics, to gain an insight into the unusual plastic behaviour of this oxide. In this study we employed molecular dynamics to gather a representative set of data on the 1/2(110) (001) dislocation motion in UO2 at temperatures from 1000 to 2000 K and shear stress from 25 to 1000 MPa. We found that dislocation motion was thermally activated, with two distinct modes of motion. Based on this knowledge, we selected an analytic expression for dislocation velocity and performed fitting to MD data. This expression described the simulation data well, and was also used to make a physically justified prediction for dislocation velocities at typical operating conditions of the oxide nuclear fuel. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： Dislocations Ceramic material numerical algorithms Atomistic simulation

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Anisotropic Locally Conformal Perfectly Matched Layer for Higher Order Curvilinear Finite-Element Modeling

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IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION 2017年第12期65卷 7157-7165页

作者： Smull, Aaron P. Manic, Ana B. Manic, Sanja B. Notaros, Branislav M. Colorado State Univ Dept Elect & Comp Engn Ft Collins CO 80523 USA Univ Calif Berkeley Dept Phys Berkeley CA 94720 USA

A perfectly matched layer (PML) method is proposed for electrically large curvilinear meshes based on a higher order finite-element modeling paradigm and the concept of transformation electromagnetics. The method maps the non-Maxwellian formulation of the locally conformal PML to a purely Maxwellian implementation using continuously varying anisotropic and inhomogeneous material parameters. An approach to the implementation of a conformal PML for higher order meshes is also presented, based on a method of normal projection for PML mesh generation around an already existing convex volume mesh of a dielectric scatterer, with automatically generated constitutive material parameters. Once the initial mesh is generated, a PML optimization method based on gradient descent is implemented to most accurately match the PML material parameters to the geometrical interface. The numerical results show that the implementation of a conformal PML in the higher order finite-element modeling paradigm dramatically reduces the reflection error when compared to traditional PMLs with piecewise constant material parameters. The ability of the new PML to accurately and efficiently model scatterers with a large variation in geometrical shape and those with complex material compositions is demonstrated in examples of a dielectric almond and a continuously inhomogeneous and anisotropic transformation-optics cloaking structure, respectively.

关键词： Computational electromagnetics (CEMs) curved parametric elements finite-element method (FEM) hexahedral elements higher order modeling numerical algorithms numerical optimization perfectly matched layer (PML) polynomial basis functions scattering transformation electromagnetics

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Toward an Algorithmic Control Theory

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2017年第2期40卷 194-196页

作者： Tsiotras, Panagiotis Mesbahi, Mehran Georgia Inst Technol Daniel Guggenheim Sch Aerosp Engn Atlanta GA 30332 USA Univ Washington William M Boeing Dept Aeronaut & Astronaut Seattle WA 98195 USA

The February 2017 Special Issue of Journal of Guidance, Control and Dynamics discusses papers that reflect some of the current trends in control community that best represent novel intersections of aerospace guidance and control and computation. the paper by AcAÇikmesAÇe and colleagues and the paper by Scharf and colleagues aim to explore the adoption of convex optimization and custom solvers based on interior point algorithms for powered descent guidance. In the same vein, the paper by Nicotra and colleagues examines the adoption of convex optimization for fast reference governors. Real-time nonlinear optimal control provides the backbone of the contributions by Lu and colleagues, Adurthi and colleagues, Sagliano and colleagues, Ferranti and Keviczky, De La Torre and colleagues, Zidek and Kolmanovsky, and finally by Liu and colleagues. All these papers examine topics ranging from entry guidance, onboard trajectory generation, predictive flight control, trajectory optimization for autonomous suspended load operations, computational optimal control with disturbance, and guidance for constrained impact. Approximate dynamic programming in the context of nonlinear adaptive control is discussed in the paper by Zhou and colleagues, whereas MPC-based approaches with embedded convex optimization solvers are the subject of the contributions by Lee and Mesbahi, Lee and colleagues, and Petersen and colleagues, with applications in constrained landing, underactuated spacecraft, and constrained attitude control with reaction wheels, respectively. The extension of MPC in the context of model predictive path integral control is explored in the paper byWilliams and colleagues, which also examines parallel implementations. Finally, a semi-analytic approach is examined in the paper by Gerlach and Doman for ballistic airdrops.

关键词： Nonlinear Adaptive Control Feedback Control Convex Optimization Powered Descent Guidance Computer Algorithm Trajectory Optimization Information Processing Computational Fluid Dynamics Unmanned Aerial Vehicle numerical algorithms

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A modelling approach for city locating logistic platforms based on combined forward and reverse flows

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IFAC-PapersOnLine 2017年第1期50卷 11701-11706页

作者： Ndhaief, Nadia Bistorin, Olivier Rezg, Nidhal LGIPM Université de Lorraine Ile de Saulcy Metz57000 France LGIPM ICN Business School 13 Rue Michel Ney 54000 France

Logistics platforms and reverse logistics are the most used solutions addressing daily problems in urban areas such as noise, pollution and cost. Their main goal is to ensure sustainable development in modern cities. The paper proposes an approach based on forward and reverse flows in urban logistic. To that end, we present a location-allocation of logistics platforms in a reverse logistics system. We, then, locate allocation and evaluate their effect on logistic platforms. In doing so, we present a mathematical model of the city logistics platform to specify location-allocation problem. Our model considers both flows: urban freight and reverse logistics. Subsequently, we improve city logistics platform's financial situation by reducing operating costs. Finally, we use a numerical algorithm for optimization and illustration purposes. © 2017

关键词： Logistics Location Operating costs Optimization Planning Sustainable development City logistics Location allocation Location allocation problem Logistics platforms numerical algorithms Reverse flow Reverse logistics Urban logistics

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