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Mathematical modeling of the mean flow stress, fractional softening and grain size during the hot strip rolling of C-Mn steels

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ISIJ INTERNATIONAL 1996年第12期36卷 1500-1506页

作者： Siciliano, F Minami, K Maccagno, TM Jonas, JJ 1) Depertment of Metallurgical Engineering McGill University 2) On leave from Kashima Steel Works Sumitomo Metal Industries Ltd.

The logs for plain C-Mn grades from tour different hot strip mills were analyzed in order to calculate the mean flow stress developed at each stand. The calculation, based on Sims's equations, takes work roll flattening, redundant strain, and the forward slip ratio into account. The stresses are compared with the predictions of a model based on an improved Misaka mean flow stress equation in which strain accumulation as well as the kinetics of static and dynamic recrystallization are fully accounted for, A good fit is observed between the model predictions and the mill data, with agreement generally falling within the interval +/-15%.

关键词： hot strip rolling static recrystallization dynamic recrystallization metadynamic recrystallization kinetics microstructure modeling computer spreadsheet

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A strain energy model for the prediction of the effective coefficient of thermal expansion of composite materials

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COMPUTATIONAL MATERIALS SCIENCE 2012年第1期53卷 241-250页

作者： Xu, Yingjie Zhang, Weihong NW Polytech Univ Lab Engn Simulat & Aerosp Comp Xian 710072 Shaanxi Peoples R China NW Polytech Univ Key Lab Contemporary Design & Integrated Mfg Tech Xian 710072 Shaanxi Peoples R China

In this paper, a strain energy model is developed for the prediction of the effective coefficient of thermal expansion (CTE) of composite materials. This model is based on the relationship established between the strain energy of the microstructure and that of the homogenized equivalent model under specific thermo-elastic boundary conditions. Expressions in closed-form are derived for the effective CTE in terms of the strain energy and effective elastic tensor. Different kinds of composites are tested to validate the model. Representative unit cells with specific boundary conditions are used to evaluate effective CTEs that are compared with available results obtained numerically and experimentally. (C) 2011 Elsevier B.V. All rights reserved.

关键词： Coefficient of thermal expansion Strain energy microstructure modeling Numerical prediction Composite material

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Predicting grain structure in high pressure die casting of aluminum alloys: A coupled cellular automaton and process model

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COMPUTATIONAL MATERIALS SCIENCE 2019年 161卷 64-75页

作者： Gu, Cheng Lu, Yan Cinkilic, Emre Miao, Jiashi Klarner, Andrew Yan, Xinyan Luo, Alan A. Ohio State Univ Dept Mat Sci & Engn Columbus OH 43210 USA Alcoa Tech Ctr New Kensington PA 15068 USA Ohio State Univ Dept Integrated Syst Engn Columbus OH 43210 USA

Grain structure is one of the most important factors that affect the mechanical properties of metallic alloys. Accurate prediction of as-cast grain structure is critical in the design and manufacturing of metal castings using an integrated computational materials engineering (ICME) approach. In this paper, a three-dimensional (3-D) model based on cellular automaton (CA) and process simulation was developed for predicting grain size of components produced by high pressure die casting (HPDC) of aluminum alloys. The concurrent nucleation and growth of grains were considered in the model. A test specimen casting, consisting of different wall thicknesses, was simulated using a finite element based casting process simulation software ProCAST (R). The thermal history of the simulated casting was extracted and used in subsequent mesoscale CA modeling. Different thermal conditions were used to simulate grain nucleation and growth during HPDC. The grain morphology, grain density and grain size were obtained by CA modeling. Electron backscatter diffraction (EBSD) analysis was performed on aluminum castings of different wall thicknesses under various cooling rates to validate the simulation results. The 3-D grain structure model is in excellent agreement with the experimental results, and can be used in ICME design and development of aluminum castings.

关键词： Solidification grain structure High pressure die casting microstructure modeling Casting simulation Cellular automaton

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Numerical modeling of Fluid Flow and Solidification Characteristics of Ultrasonically Processed A356 Alloys

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ISIJ INTERNATIONAL 2014年第8期54卷 1830-1835页

作者： Nastac, Laurentiu Univ Alabama Dept Met & Mat Engn Tuscaloosa AL 35487 USA

The main objectives of this study is to determine the fluid flow characteristics and cavitation phenomena during molten A356 alloys processed via high power ultrasonic treatment (UST) as well as the resulting solidification microstructure of the ultrasonically processed A356 alloys. A previously developed UST modeling approach is applied to obtain the simulation results in this study. The modeling approach consists of two main models: (1) A CFD UST cavitation model is applied to simulate acoustic streaming, cavitation and bubble dynamics during molten alloy processing and (2) A stochastic mesoscopic modeling to predict microstructure evolution during alloy solidification. The first model can predict the amount of the cavitated phase that is used to determine the number of potential nuclei formed due to the UST processing. The second model uses the predicted number of nuclei from the first model as an input to predict the microstructure evolution during the solidification of cast alloys. In addition, the UST model predicts the fluid flow characteristics that include flow profile, velocity vectors and magnitude, pressure contours, and streamlines under two different gravity conditions. The fluid flow characteristics are analyzed to ensure that proper ultrasonic stirring and cavitation of the melt are achieved.

关键词： A356 alloy ultrasonic processing fluid flow characteristics solidification microstructure multiscale modeling of ultrasonic stirring and cavitation microstructure modeling

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Lattice Boltzmann modeling of dendritic growth in forced and natural convection

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COMPUTERS & MATHEMATICS WITH APPLICATIONS 2011年第12期61卷 3585-3592页

作者： Sun, D. K. Zhu, M. F. Pan, S. Y. Yang, C. R. Raabe, D. Southeast Univ Jiangsu Key Lab Adv Metall Mat Nanjing 211189 Peoples R China Max Planck Inst Eisenforsch GmbH Dept Microstruct Phys & Met Forming D-40237 Dusseldorf Germany

A two-dimensional (2D) coupled model is developed for the simulation of dendritic growth during alloy solidification in the presence of forced and natural convection. Instead of conventional continuum-based Navier-Stokes (NS) solvers, the present model adopts a kinetic-based lattice Boltzmann method (LBM), which describes flow dynamics by the evolution of distribution functions of moving pseudo-particles, for the numerical computations of flow dynamics as well as thermal and solutal transport. The dendritic growth is modeled using a solutal equilibrium approach previously proposed by Zhu and Stefanescu (ZS), in which the evolution of the solid/liquid interface is driven by the difference between the local equilibrium composition and the local actual liquid composition. The local equilibrium composition is calculated from the local temperature and curvature. The local temperature and actual liquid composition, controlled by both diffusion and convection, are obtained by solving the LB equations using the lattice Bhatnagar-Gross-Krook (LBGK) scheme. Detailed model validation is performed by comparing the simulations with analytical predictions, which demonstrates the quantitative capability of the proposed model. Furthermore, the convective dendritic growth features predicted by the present model are compared with those obtained from the Zhu-Stefanescu and Navier-Stokes (ZS-NS) model, in which the fluid flow is calculated using an NS solver. It is found that the evolution of the solid fraction of dendritic growth calculated by both models coincides well. However, the present model has the significant advantages of numerical stability and computational efficiency for the simulation of dendritic growth with melt convection. (C) 2010 Elsevier Ltd. All rights reserved.

关键词： Lattice Boltzmann method microstructure modeling Dendritic growth Melt convection

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Biaxial mechanics of thermally denaturing skin- Part 2: modeling

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ACTA BIOMATERIALIA 2022年第0期140卷 421-433页

作者： Rausch, Manuel Meador, William D. D. Toaquiza-Tubon, John Moreno-Flores, Omar Tepole, Adrian Buganza Univ Texas Austin Dept Biomed Engn Austin TX 78712 USA Univ Texas Austin Dept Aerosp Engn & Engn Mech Austin TX 78712 USA Univ Texas Austin Oden Inst Computat Engn & Sci Austin TX 78712 USA Purdue Univ Sch Mech Engn W Lafayette IN 47907 USA Purdue Univ Weldon Sch Biomed Engn W Lafayette IN 47907 USA

Understanding the response of skin to superphysiological temperatures is critical to the diagnosis and prognosis of thermal injuries, and to the development of temperature-based medical therapeutics. Unfortunately, this understanding has been hindered by our incomplete knowledge about the nonlinear coupling between skin temperature and its mechanics. In Part I of this study we experimentally demonstrated a complex interdependence of time, temperature, direction, and load in skin's response to superphysiological temperatures. In Part II of our study, we test two different models of skin's thermomechanics to explain our observations. In both models we assume that skin's response to superphysiological temperatures is governed by the denaturation of its highly collageneous microstructure. Thus, we capture skin's native mechanics via a microstructurally-motivated strain energy function which includes probability distributions for collagen fiber orientation and waviness. In the first model, we capture skin's response to superphysiological temperatures as a transition between two states that link the kinetics of collagen fiber denaturation to fiber coiling and to the transformation of each fiber's constitutive behavior from purely elastic to viscoelastic. In the second model, we capture skin's response to superphysiological temperatures instead via three states in which a sequence of two reactions link the kinetics of collagen fiber denaturation to fiber coiling, followed by a state of fiber damage. Given the success of both models in qualitatively and quantitatively capturing our observations, we expect that our work will provide guidance for future experiments that could probe each model's assumptions toward a better understanding of skin's coupled thermo-mechanics and that our work will be used to guide the engineering design of heat treatment therapies. Statement of significance Quantifying and modeling skin thermo-mechanics is critical to our understanding of skin phy

关键词： Constitutive modeling Nonlinear mechanics Viscoelasticity Damage mechanics Soft tissue microstructure modeling Anisotropy Arrhenius kinetics

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The constitution of martensite volume fraction in Fe-31wt%Ni-0.02wt%C

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JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T 2019年第1期8卷 140-146页

作者： Costa Guimaraes, Jose Roberto Rios, Paulo Rangel Univ Fed Fluminense Escola Engn Ind Met Volta Redonda Volta Redonda RJ Brazil Univ Fed Fluminense Mal Moura 338H-22C BR-05641000 Sao Paulo SP Brazil

This paper analyzes the constitution of martensite volume fraction, that is, the size-distribution of martensite units in quenched-transformed austenite in the microstructure. We correlate this distribution to the martensite shape-strain relaxation. The modes of relaxation athermal/auto-accommodation or thermal-activated dislocation mobility and the sequential formation of the martensite units control the variation of the mean martensite unit volume as well as the uniformity of the transformation. (C) 2017 Brazilian Metallurgical, Materials and Mining Association. Published by Elsevier Editora Ltda.

关键词： Martensitic transformations microstructure modeling Phase transformations Steels Fe-Ni alloys

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Effect of clinker phase distribution within cement particles on properties of a hydrating cement paste

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CONSTRUCTION AND BUILDING MATERIALS 2013年第Jan.期38卷 941-949页

作者： Erdogan, Sinan T. Middle E Tech Univ Dept Civil Engn TR-06531 Ankara Turkey

SEM/X-ray images of cements in the Virtual Cement and Concrete Testing Laboratory were analyzed and used in simulations to investigate the effect of spatial distribution of clinker phases within particles on hydration and resulting properties. Percentages of the clinker phases actually consumed in the total hydrated clinker at any time during hydration ('active phase content's) are different than those measured on the unreacted powder ('overall phase content's), which may weaken predictions of the overall rate of hydration and property (heat and strength) development especially at early ages, and when hydration is incomplete. A demonstration in 2D of how 'active phase content's differ from the measured 'overall phase content's at different degrees of hydration, is provided as well as one in 3D, using a hydration model, for one of the cements. The influence of phase distribution on hydration and property development is discussed by comparing four different cases/microstructures hydrated under the same model conditions. For the same phase contents and fineness, differences in distribution have a significant effect on early-age properties but a lesser effect at later ages. (C) 2012 Elsevier Ltd. All rights reserved.

关键词： Cement hydration microstructure modeling SEM Clinker phases Characterization

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A model for equiaxed eutectic solidification with melt convection and solid-phase transport

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INTERNATIONAL JOURNAL OF CAST METALS RESEARCH 1999年第6期11卷 527-532页

作者： Yang, BJ Leon-Torres, J Stefanescu, DM Univ Alabama Dept Met & Mat Engn Tuscaloosa AL 35487 USA

This paper presents a method to track microstructural evolution during eutectic solidification using a coupled fluid flow - mass transport model. The continuum formulations were used to describe the macroscopic transports of mass, energy, and momentum, associated with the microstructural evolution, for two-phase systems. It was assumed that the liquid flow is driven by thermal and solutal buoyancy, as well as solidification contraction. The eutectic cell (grain) of cast iron was assumed to have a spherical morphology, The microstructural model includes the gray-to-white eutectic transition and the influence of microsegregation on the eutectic temperature. A continuous nucleation law was used in calculation. Rules for grain movement have been developed to track the nucleation, growth and movement of grains because of melt convection. Three test cases are discussed to demonstrate the influence of melt convection and solid phase transport on microstructure evolution for eutectic cast iron.

关键词： solid phase-transport microstructure modeling

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LIMIT THEOREMS FOR NEARLY UNSTABLE HAWKES PROCESSES

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ANNALS OF APPLIED PROBABILITY 2015年第2期25卷 600-631页

作者： Jaisson, Thibault Rosenbaum, Mathieu Ecole Polytech Paris CNRS Ctr Math Appl UMR 7641 F-91128 Palaiseau France Univ Paris 06 CNRS Lab Probabil & Modeles Aleatoires UMR 7599 F-75252 Paris France

Because of their tractability and their natural interpretations in term of market quantities, Hawkes processes are nowadays widely used in high-frequency finance. However, in practice, the statistical estimation results seem to show that very often, only nearly unstable Hawkes processes are able to fit the data properly. By nearly unstable, we mean that the L-1 norm of their kernel is close to unity. We study in this work such processes for which the stability condition is almost violated. Our main result states that after suitable rescaling, they asymptotically behave like integrated Cox-Ingersoll-Ross models. Thus, modeling financial order flows as nearly unstable Hawkes processes may be a good way to reproduce both their high and low frequency stylized facts. We then extend this result to the Hawkes-based price model introduced by Bacry et al. [Quant. Finance 13 (2013) 65-77]. We show that under a similar criticality condition, this process converges to a Heston model. Again, we recover well-known stylized facts of prices, both at the microstructure level and at the macroscopic scale.

关键词： Point processes Hawkes processes limit theorems microstructure modeling high-frequency data order flows Cox-Ingersoll-Ross model Heston model

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