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作者： Quirien Eibhilin KROL ECOLE POLYTECHNIQUE FEDERALE DE LAUSANNE

学位级别：博士

Snow microstructure and its evolution play an important role for various applications of snow physics in cryospheric sciences. The main modes of microstructure evolution in snow are referred to as isothermal and temperature gradient metamorphism. The former describes the coarsening driven by interfacial energy while the latter is dominated by recrystallization processes induced by temperature gradients. An accurate description of these processes in snowpack models is of key importance. However, common snowpack models are still based on traditional grain metrics, originally tailored to field observations, and empirical evolution laws. This treatment of snow microstructure is essentially unrelated to recent advances of snow observations by micro- computed tomography ( μ CT). The present thesis contributes to the solution of this problem by i) identifying suitable microstructure parameters ii) deriving evolution equations for these from first principles and iii) developing methods that allow to utilize 4D μ CT measurements of snow as a link between local ice crystal growth and upscaled microstructure as relevant on the scales of interest for common snowpack models. To this end, three studies have been conducted. The first study focuses on estimating local ice-crystal growth rates from interface tracking by analyzing 4D μ CT data of in-situ snow metamorphism experiments under isothermal and temperature gradient conditions. For temperature gradient metamorphism, diffusion-limited growth is considered, while for isothermal metamorphism the data is compared to kinetics and diffusion limited growth. Despite considerable scatter, in both cases the significance of underlying growth laws could be statistically confirmed. The second study uses μ CT images from a variety of snow samples to investigate the role of grain shape in the context of microwave and optical properties of snow. Grain shape can be objectively defined via size-dispersity of structure from the second moment o

关键词： snow crystal growth metamorphism microstructure modeling grain shape exponential correlation length mean curvature Gaussian curvature micro-computed tomography

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Semisolid casting of automotive component: Water pump lid

Semisolid casting of automotive component: Water pump lid

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9th International Conference on Semi-Solid Processing of Alloys and Composites

作者： Wang, H. Xu, J. Univ So Queensland Fac Engn & Surveying Toowoomba Qld 4350 Australia Gen Res Inst NonFerrous Met Beijing 100088 Peoples R China

ISBN: (纸本)3908451264;9783908451266

Water pump lid is selected as the automotive component to be cast using semisolid casting technology. Semisolid feedstock of alloy A357 was produced by a vertical continuous DC casting with electromagnetic stirring. Non-dendritic structure was obtained in the feedstock billets. A 6-station induction beating system was developed for feedstock billet reheating. Multi-stage reheating and well controlled reheating process resulted in a uniform temperature profile in the billet. Semisolid casting was carried out in a conventional high pressure die casting machine. Die design and casting parameters were adjusted to be suitable for semisolid casting. Compared with the conventional liquid melt casting, semisolid casting resulted in a much higher microstructural integrity with reduced shrinkage porosity.

关键词： semisolid metal processing microstructure modeling Al-Si alloy

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Application of a Material Model to Predict Rolling Forces and microstructure during a Hot Ring Rolling Process

Application of a Material Model to Predict Rolling Forces an...

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7th International Conference on Physical and Numerical Simulation of Materials Processing (ICPNS 2013)

作者： Henke, T. Hirt, G. Bambach, M. Rhein Westfal TH Aachen Inst Met Forming IBF Intzestr 10 D-52056 Aachen Germany

ISBN: (纸本)9783037857281

Ring rolling is an incremental bulk forming process. Hence, the process consists of a large number of alternating deformations and dwell steps. For accurate calculations of material flow and thus ring geometry and rolling forces in hot ring rolling processes, it seems necessary to consider material softening due to static and post dynamic recrystallization which could occur between two deformation steps. In addition, due to the large number of cycles, the modeling results, especially the prediction of grain size, can easily be affected by uncertainties in the input data. However, for small rings and ring material with slow recrystallization kinetics, the interpass times can be short compared to the softening kinetics and the effect of softening can be so small, that microstructure evolution and the description of the materials' flow behavior can be de-coupled. In this paper, a semi-empirical JMAK-based model for a stainless steel (1.4301/ X5CrNi18-9/ AISI304) is presented and evaluated by the use of experiments and other investigations published in [1],[2]. Finite Element (FE) simulations of a ring rolling process with a high number of ring revolutions and thus multiple, incremental forming steps were conducted based on ring rolling experiments. The FE simulation results were validated with the experimentally derived rolling force and evolution of ring diameter. The microstructure evolution was calculated in a post processing step considering the investigated evolution of strain and temperature. In this calculation the interrelations between the fraction of dynamically recrystallized microstructure, the evolution of post-dynamically recrystallized microstructure and the final grain size have been considered. Both, the calculated final microstructure and the evolution of rolling force and ring geometry calculated stand in good agreement with the experimental investigations.

关键词： Ring rolling microstructure modeling JMAK

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Building microstructures from the atoms up: Microstructural science supporting ICMSE

Building microstructures from the atoms up: Microstructural ...

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International Conference on Solid-Solid Phase Transformations in Inorganic Materials 2015, PTM 2015

作者： Holm, Elizabeth A. De Cost, Brian Goins, Philip Humberson, Jonathan Ma, Taichong Department of Materials Science and Engineering Carnegie Mellon University PittsburghPA United States

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Understanding mechanical size effects in metallic mi- crowires: synergy between experiment and simulation

Understanding mechanical size effects in metallic mi- crowir...

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作者： Ravi Raj Purohit Purushottam Raj Purohit UNIVERSITE DE POITIERS

学位级别：博士

Polycrystalline metallic microwires produced by cold-drawing exhibit significant mechanical strength that make them ideal candidates for reinforcement of composites. Previous studies on polycrystalline pure nickel wires have indicated a significant size dependence of their yield and tensile strength as well as their ductility. The aim of this study is to understand these size effects by in-situ X-ray diffraction (XRD) analysis and crystal plasticity finite element (CPFE) simulations. In-situ monotonous and cyclic tensile tests under synchrotron radiation were carried on microwires with diameters ranging from 100 to 40µm. The commercially obtained 100µm as-drawn wires exhibit a core-shell architecture with <111> fiber texture dominant in core and heterogeneous dual fiber texture <111> and <100> in the shell. Reduction of specimen size by electropolishing leads to wires having a homogeneous microstructure, whereas reduction of specimen size by further cold drawing leads to wires with a sharper texture while retaining the core-shell architecture. The yield and tensile strength of the electropolished wires increase with decreasing diameter, whereas the ductility decrease with decreasing diameter. In the case of cold-drawn wires, the yield and tensile strength, and also the ductility was observed to increase with decreasing diameter. The XRD analysis indicates successive yielding of grain families under iso-strain condition. The gradient in the texture of the microwire was seen to activate deformation mechanisms which are not seen for microwires with homogeneous texture. To understand the influence of different microstructural parameters, and notably the influence of crystallographic texture, 3D representative microstructure was generated and CPFE simulations were carried out. The simulated average behavior of different grain families (<111>, <100>) agrees well with the experimental results. The CPFE simulations indicate heterogeneity in the stress field across the micro

关键词： size effects polycrystalline nickel microwires cold-drawing electropolishing high energy XRD micro-texture microstructure modeling CPFE simulations

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Voronoi Diagram Approximated Austenite Grain Mapping and Voronoi Algorithm-Based microstructure Prediction of Quenched C35 Steel 1st

Voronoi Diagram Approximated Austenite Grain Mapping and Vor...

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1st International Conference on Energy, Material Sciences and Mechanical Engineering, EMSME 2020

作者： Sanchu, S. Biju, N. Namboothiri, V.N.N. Division of Mechanical Engineering School of Engineering Cochin University of Science and Technology Kochi India

ISBN: (纸本)9789811627934

Ability of Voronoi diagram in predicting the microstructure evolution during martensite transformation in C35 steel quenched from complete austenite range is analyzed in this work. The input needed for constructing Voronoi diagram is the position of individual seeds. Since diffusionless transformation is considered in this work, knowledge about the grain boundary is essential. Using image processing software ImageJ, from the micrograph obtained experimentally, austenite grain map is identified. This grain map is converted into equivalent Voronoi diagram. The micrograph of quenched steel is analyzed to determine number of martensite blocks in the final structure. Using these two inputs, Voronoi diagram is constructed. The result represents the microstructure in quenched condition. On comparison between simulated microstructure and micrograph, it is evident that Voronoi diagram-based simulation technique can effectively be used for modeling microstructure evolution during quenching of C35 steel. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

关键词： Grain map Martensite formation Micrograph microstructure modeling Voronoi diagram

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Numerical simulation of rock pore-throat structure effects on NMR T_2 distribution

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Applied Geophysics 2008年第2期5卷 86-91页

作者：王克文李宁中国石油勘探开发研究院北京100083

We built a three-dimensional irregular network model which can adequately describe reservoir rock pore-throat structures. We carried out numerical simulations to study the NMR T2 distribution of water-saturated rocks. The results indicate that there is a good correlation between T2 distribution and the pore radius frequency histogram. The total T2 distribution can be partitioned into pore body and pore throat parts. The effect of parameters including throat radius, pore-throat ratio, and coordination number of the micro- pore structure on the T2 distribution can be evaluated individually. The result indicates that： 1 ） with the increase of the pore throat radius, the T2 distribution moves toward longer relaxation times and its peak intensity increases; 2） with the increase of the pore-throat ratio, the T2 distribution moves towards longer T2 with the peak intensity increasing and the overlap between pore body T2 and pore throat T2 decreasing; 3） With the increase of connectivity, the short T2 component increases and peak signal intensity decreases slightly.

关键词： Network model NMR T2 distribution Pore structure microstructure modeling

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Microstructural modeling on electrical conductivities of 3-D carbon/epoxy woven composites along different directions

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COMPOSITE STRUCTURES 2024年 329卷

作者： Liu, Zhuodong Xue, Yousong Sun, Baozhong Gu, Bohong Hu, Meiqi Donghua Univ Coll Text Shanghai Frontier Sci Res Ctr Modem Text Shanghai 201620 Peoples R China Jiangsu Hengli Chem Fibre Co LTD Suzhou 215000 Jiangsu Peoples R China

Carbon fiber composites have widely been used in aircrafts and high speed vehicles. Electrical conductivity of the carbon fiber composites is critical to electrical safety for the aircrafts and vehicles under high voltage applications. Here we report microstructural modeling on electrical conductivities of three-dimensional (3-D) carbon/ epoxy angle-interlock woven composites along on-axis and off-axis directions. A 3-D resistor network model and finite element analysis (FEA) model based on fabric microstructure have been developed to reveal the electric conductivities along different directions. We have found that the conductivity of the woven structure exhibits full anisotropy. The difference of electrical conductivity between in-plane and through-thickness direction decreased due to the existence of through-the-thickness carbon fibers. The electrical conductivity through-thickness direction increases with warp directional length. With increasing off-axis directional length, the conductivity perpendicular to the off-axis direction increases, while the conductivity parallel to the off-axis direction remains basically unchanged. Electric potential distribution and electrical current density are highly related with fabric structure and current directions. Owing to the dependence of mechanical properties are also related with fabric structure and directions, it is expected that both the electrical and mechanical properties of the 3-D woven carbon/epoxy composites could be optimized simultaneously from the composite microstructure designs.

关键词： Carbon fiber composites 3-D woven architecture microstructure modeling Electrical conductivity Electric current density distribution

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Simulation of Dynamic and Meta-Dynamic Recrystallization Behavior of Forged Alloy 718 Parts Using a Multi-Class Grain Size Model

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MATERIALS 2021年第1期14卷 111页

作者： Gruber, Christian Raninger, Peter Stanojevic, Aleksandar Godor, Flora Rath, Markus Kozeschnik, Ernst Stockinger, Martin Mat Ctr Leoben Forsch GmbH A-8700 Leoben Austria Voestalpine BOHLER Aerosp GmbH & Co KG A-8605 Kapfenberg Austria TU Wien Inst Mat Sci & Technol A-1060 Vienna Austria Univ Leoben Dept Prod Engn A-8700 Leoben Austria

Dynamic and meta-dynamic recrystallization occur during forging of alloy 718 aircraft parts and thus change the microstructure during a multistep production route. Since the prediction of the resulting grain structure in a single grain fraction is not able to describe microstructures with bimodal or even multimodal distributions, a multi-class grain size model has been deployed to describe the recrystallization mechanisms during thermomechanical treatments and predict the resulting grain size distributions more accurately. As forging parameters, such as temperature, strain rate and maximum strain influence the flow curve and consequently the recrystallization behavior, a series of double cone compression experiments has been carried out and used to verify and adapt the material parameters for the multi-class grain size model. The recrystallized fractions of the numerical and experimental results are compared and differentiated in view of the recrystallization mechanism, i.e., dynamic and meta-dynamic recrystallization. The strong dependence of the recrystallization kinetics on the initial grain size is highlighted, as well as the influence of different strain rates, which shall represent typical forging equipment.

关键词： alloy 718 microstructure modeling multi-class grain size dynamic recrystallization meta-dynamic recrystallization screw press hammer forging

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Automatic processing of an orientation map into a finite element mesh that conforms to grain boundaries

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MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING 2016年第5期24卷 055014-055014页

作者： Dancette, S. Browet, A. Martin, G. Willemet, M. Delannay, L. Univ Lyon INSA Lyon Lab MATEIS CNRS UMR5510 F-69621 Villeurbanne France Catholic Univ Louvain ICTEAM B-1348 Louvain La Neuve Belgium Univ Grenoble Alpes SIMAP F-38000 Grenoble France CNRS SIMAP F-38000 Grenoble France Catholic Univ Louvain iMMC B-1348 Louvain La Neuve Belgium

A new procedure for microstructure-based finite element modeling of polycrystalline aggregates is presented. The proposed method relies (i) on an efficient graph-based community detection algorithm for crystallographic data segmentation and feature contour extraction and (ii) on the generation of selectively refined meshes conforming to grain boundaries. It constitutes a versatile and close to automatic environment for meshing complex microstructures. The procedure is illustrated with polycrystal microstructures characterized by orientation imaging microscopy. Hot deformation of a Duplex stainless steel is investigated based on ex-situ EBSD measurements performed on the same region of interest before and after deformation. A finite element mesh representing the initial microstructure is generated and then used in a crystal plasticity simulation of the plane strain compression. Simulation results and experiments are in relatively good agreement, confirming a large potential for such directly coupled experimental and modeling analyses, which is facilitated by the present image-based meshing procedure.

关键词： image-based mesh microstructure modeling graph segmentation crystal plasticity EBSD

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