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microstructure model and crack initiation for a SiC-reinforced Si₃N₄ ceramic with differently sized SiC particles

COMPUTATIONAL MATERIALS SCIENCE 2017年 131卷 202-208页

作者： Yuan Shuowei Yang Zichun Naval Univ Engn Inst High Temp Struct Composite Mat Naval Ship 717 Jiefang St Wuhan 430033 Hubei Province Peoples R China

In this study, a microstructure model was established combining the Voronoi tessellation method with Eshelby's equivalent inclusion theory to study the failure mechanism of a Si3N4-bonded SiC refractory ceramic with differently sized SiC particles occurring under a great temperature gradient. The crack initiation and propagation under large thermal stress were calculated by employing the extended finite element method on the proposed microstructure model. The micro-cracks were found to originate in the matrix zone around the vertices of the big SiC inclusions and propagate through the matrix until encountering an adjacent SiC inclusion. The temporarily stopped micro-cracks will resume to propagate until eventually macroscopic failure occurs due to the repeated thermal shock. The thermal stress in the composite can be reduced by lowering the mismatch between the thermal expansion coefficients of the different phases in the composite, which results in a longer service life of the refractory ceramics. (C) 2017 Elsevier B.V. All rights reserved.

关键词： Refractory ceramics Failure mechanism microstructure model Voronoi tessellation Extended finite element method

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Finite element simulation of Vickers micro-indentation test of micro-nano-composite ceramic tool materials based on microstructure model

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INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS 2016年 58卷 34-41页

作者： Wang, Dong Zhao, Jun Xue, Chao Cao, Yan Xian Technol Univ Sch Mech Engn Xian 710021 Peoples R China Shandong Univ Sch Mech Engn Key Lab High Efficiency & Clean Mech Mfg MOE Jinan 250061 Peoples R China

In order to investigate the influence of microstructure on hardness, a finite element method is applied to simulate the Vickers micro-indentation process in micro-nano-composite ceramic tool materials on the basis of a microstructure level model. The microstructure model is constructed based on Voronoi Tessellation hybrid random algorithms. The secondary phase volume fraction, the nano-scale particle volume fraction, the grain centroid distribution, and the grain diameter distribution of the materials are simulated in this model. The hardness of ceramic materials is calculated by the numerical simulation results. The effects of average grain diameter, secondary phase volume fraction and nano-scale particle on the hardness of ceramic materials are investigated. The results of numerical simulation agree with the results of experiment excellently. The quantitative relationship between hardness and microstructure can be used to design the new tool material with improved properties. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： Voronoi microstructure model Hardness Finite element simulation Micro-nano-composite ceramic

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The Cs_xH_3-xPW₁₂O₄₀ catalysts microstructure model

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APPLIED CATALYSIS A-GENERAL 2013年 451卷 50-57页

作者： Sasca, V. Z. Verdes, O. Avram, L. Popa, A. Erdohelyi, A. Oszko, A. Timisoara Romanian Acad Inst Chem Timisoara 300223 Romania Univ Szeged Inst Phys Chem & Mat Sci H-6720 Szeged Hungary

The salts of the H3PW12O40 (H3PW) with Cs counter cation were prepared and characterized by thermal analysis, IR, XRD, BET, XPS LEIS and SEM methods. The samples are denoted as CsxH3-xPW12O40 (x=1, 2, 2.25, 2.5 and 3). The catalytic activity of the compounds prepared with various cesium/Keggin unit ratios was tested in ethanol conversion by pulse reaction technique. The change of catalytic activity vs. pulse number was explained by formation of strong adsorbed species on catalysts. A microstructure model of the CsxH3-xPW12O40 containing spherical aggregates, which consist of Cs3PW12O40 crystallites core coated with H3PW12O40 layers, was proposed on the basis of the structural-textural properties and their catalytic performances in ethanol conversion. The model explains the abrupt increase of the specific surface area for x>2 and also the highest selectivity for C-4 hydrocarbons on Cs2.5H0.5PW12O40 due to its special microstructure: a H3PW monolayer embedding a core of Cs3PW. The Cs concentrations on the CsxH3-xPW12O40 surface were determined by XPS and were found less than expected based on their chemical composition, but which correspond to the proposed model of microstructure. (C) 2012 Elsevier B.V. All rights reserved.

关键词： Heteropoly compounds Cesium tungstophosphates Keggin structure Ethanol conversion microstructure model XPS measurements

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Generation of Three-Dimensional microstructure model for Discontinuously Reinforced Composite by Modified Random Sequential Absorption Method

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JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY-TRANSACTIONS OF THE ASME 2016年第2期138卷 021001页

作者： Zhou, Jiming Qi, Lehua Gokhale, Arun M. Northwestern Polytech Univ Sch Mech Engn Xian 710072 Peoples R China Georgia Inst Technol Sch Mat Sci & Engn Atlanta GA 30332 USA

Computer simulation of mechanical behavior of discontinuously reinforced composites containing randomly oriented short-fibers/whiskers presents an attractive opportunity for reduction of the number of experiments and resources required for microstructure design of such advanced materials. It is desirable to perform such simulations using microstructure model that accounts for randomness in angular orientations and locations of the short fibers/whiskers. In this contribution, a methodology is presented for efficient simulation of the required microstructural model through modification of well-known random sequential adsorption (RSA) algorithm for microstructure simulation through its application to the microstructure of Mg-alloy matrix composite containing randomly oriented short carbon fibers. The modified RSA algorithm enhances accuracy and efficiency of the complex geometric details of the randomly oriented short-fiber reinforced composite microstructure. Simulated microstructural model of composite is implemented in ABAQUS to simulate the mechanical response of the Mg-matrix composite containing randomly oriented short carbon fibers. The generated complex microstructure model in ABAQUS code is sliced into thin slices for reducing computing resources. The simulated results from multiple sliced models were averaged to approximate the result for the full volume element. The simulated mechanical response by use of multiple sliced models is validated via comparison with the experimental data.

关键词： microstructure model discontinuously reinforced composites modified random sequential absorption ( RSA) property prediction sliced thin micromodel

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Prediction of macroscopic effective elastic modulus of micro-nano-composite ceramic tool materials based on microstructure model

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CERAMICS INTERNATIONAL 2022年第13期48卷 18558-18566页

作者： Wang, Dong Zhang, Zhenzhen Li, ZhiBao Wang, Qinghua Qiu, Bo Han, Quanli You, Wenyao Xian Technol Univ Sch Mech Engn Xian 710021 Peoples R China Aecc Xian Aeroengine Ltd Xian 710021 Peoples R China

In order to investigate the effect of microstructure parameters on the elastic modulus, based on the microstructure model represented by Voronoi tessellation, the reasonable macro-micro connection and boundary conditions were proved through the Hill's lemma, and the uniaxial tensile process of composite ceramic tool materials was simulated. The influences of grain size, second phase volume fraction and nanoparticle volume fraction on elastic properties were studied through numerical simulation, and the elastic modulus of composite ceramic tool materials was predicted. The results showed the elastic modulus of Al2O3-based ceramic tool materials could be increased effectively with the contents of the second phase TiB2 and nano-particle TiC being 20% and 10%, respectively. The numerical simulation results were in good agreement with the experimental results.

关键词： Micro-nano-composite ceramic microstructure model Elastic properties Prediction

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A simple microstructure model based on the Cox-BESQ process with application to optimal execution policy

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JOURNAL OF ECONOMIC DYNAMICS & CONTROL 2021年 128卷

作者： Da Fonseca, Jose Malevergne, Yannick Auckland Univ Technol Business Sch Dept Finance Private Bag 92006 Auckland 1142 New Zealand Univ Paris 1 Pantheon Sorbonne PRISM Sorbonne EA 4101 17 Rue Sorbonne F-75005 Paris France Univ Paris 1 Pantheon Sorbonne Labex ReFi 17 Rue Sorbonne F-75005 Paris France

We develop a microstructure model whose order flow is driven by a Cox-BESQ process. We derive important analytical properties of the Cox-BESQ process in order to explicit the stock price dynamics at different time scales, provide different parameter estimators and solve the optimal execution problem. We implement the model using a large data set of stock index and bond futures. Our results show that the Cox-BESQ process provides an alternative framework to the Hawkes process to build a microstructure model that is very flexible and has an explicit solution. (C) 2021 Elsevier B.V. All rights reserved.

关键词： microstructure model Stochastic intensity model Cox-BESQ process Optimal execution

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Estimating the price impact of trades in a high-frequency microstructure model with jumps

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JOURNAL OF BANKING & FINANCE 2015年 61卷 S205-S224页

作者： Jondeau, Eric Lahaye, Jerome Rockinger, Michael Swiss Finance Inst Zurich Switzerland Univ Lausanne CH-1015 Lausanne Switzerland Fordham Univ New York NY 10023 USA

We estimate a general microstructure model of the transitory and permanent impact of order flow on stock prices. Jumps are detected in both the transaction price (observation equation) and fundamental value (state equation). The model's parameters and variances are updated in real time. Prices can be altered by both the size and direction of trades, and the effects of buy-initiated and sell-initiated trades are different. We estimate this model using tick-by-tick data for 12 large-capitalization stocks traded on the Euronext-Paris Bourse. We find that, at tick frequency, the overnight return, the intraday jumps, and the continuous innovations represent approximately 7%, 8.5%, and 36.7% of the total variation of stock returns. The microstructure model explains on average 47.7% of the total variation. Once jumps are filtered and parameters are estimated in real time, we also find that the price impact of trades is symmetric on average. However, the price of highly liquid stocks with a large proportion of sell-initiated orders tends to be more sensitive to buy trades, whereas the price of less liquid stocks with a large proportion of buy-initiated orders tends to be more sensitive to sell trades. (C) 2015 Elsevier B.V. All rights reserved.

关键词： microstructure model Jumps Noise Volatility Kalman filter Particle filter

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model-Based Estimation of the Strength of Laser-Based Plastic-Metal Joints Using Finite Element microstructure models and Regression models

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MATERIALS 2021年第17期14卷 5004页

作者： Berges, Julius Moritz van der Straeten, Kira Jacobs, Georg Berroth, Joerg Gillner, Arnold Rhein Westfal TH Aachen Inst Machine Elements & Syst Engn Eilfschornsteinstr 18 D-52062 Aachen Germany Fraunhofer Inst Laser Technol ILT Steinbachstr 15 D-52074 Aachen Germany

Plastic-metal joints with a laser-structured metal surface have a high potential to reduce cost and weight compared to conventional joining technologies. However, their application is currently inhibited due to the absence of simulation methods and models for mechanical design. Thus, this paper presents a model-based approach for the strength estimation of laser-based plastic-metal joints. The approach aims to provide a methodology for the efficient creation of surrogate models, which can capture the influence of the microstructure parameters on the joint strength. A parametrization rule for the shape of the microstructure is developed using microsection analysis. Then, a parameterized finite element (FE) model of the joining zone on micro level is developed. Different statistical plans and model fits are tested, and the predicted strength of the FE model and the surrogate models are compared against experiments for different microstructure geometries. The joint strength is predicted by the FE model with a 3.7% error. Surrogate modelling using half-factorial experimental design and linear regression shows the best accuracy (6.2% error). This surrogate model can be efficiently created as only 16 samples are required. Furthermore, the surrogate model is provided as an equation, offering the designer a convenient tool to estimate parameter sensitivities.

关键词： hybrid joints simulation laser manufacturing model-based engineering microstructure model mechanical design surrogate modelling product development

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The Sorting Method of The Same Pattern Compound Material Based on Basic Element model of Surface microstructure

The Sorting Method of The Same Pattern Compound Material Bas...

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4th International Conference on Manufacturing Science and Engineering (ICMSE 2013)

作者： Xu, Shimeng Ma, Runbo Du, Jianhua Liu, Junhong Jin, Qi Acad Armored Force Engn Sect Math Beijing 100072 Peoples R China Acad Armored Force Engn Dept Equipment Maintenance & Remfg Beijing 100072 Peoples R China

ISBN: (纸本)9783037856925

Based on the elliptic element model, the new sorting method on the same pattern compound materials was given in this paper according to the pictures obtained by electronic microscopy systems on the surfaces. Here, the block design combined with variance analysis was introduced to sort the compound materials that contained that the copper-base mingled with graphite, silica and other non-pronounced components. Here, the five kinds of the same pattern compound materials were proposed for sorting, only the graphite distribution was considered and their mixture ratios of components were separately 10%, 15%, 20%, 25%, 30%. At last, through experiment data and statistical analysis, the result of sorting was basically corresponding to the above mixture ratios of components.

关键词： compound material surfaces microstructure model basic element block designs sorting method

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microstructure models for cellular materials

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COMPUTATIONAL MATERIALS SCIENCE 2009年第4期44卷 1397-1407页

作者： Redenbach, Claudia Univ Appl Sci Darmstadt & Fraunhofer Inst Ind Math ITWM D-67663 Kaiserslautern Germany

Laguerre tessellations generated by random sphere packings are promising models for the microstructure of cellular or polycrystalline materials. In this paper, the case of hard sphere packings with lognormal or gamma distributed volumes is investigated. The dependence of the geometric characteristics of the Laguerre cells on the volume fraction of the sphere packing and the coefficient of variation of the volume distribution is studied in detail. The moments of certain cell characteristics are described by polynomials, which allows to fit tessellation models to real materials without further simulations. The procedure is demonstrated by the examples of open polymer and aluminium foams. (C) 2008 Elsevier B.V. All rights reserved.

关键词： Open foam Polycrystalline material microstructure model Random Laguerre tessellation Sphere packing

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