Spectral representation of higher-order localization relationships for elastic behavior of polycrystalline cubic materials

A computationally efficient higher-order spectral framework has been formulated for the calculation of the elastic localization tensors for polycrystalline material systems using the generalized spherical harmonics as the Fourier basis. This new approach offers tremendous potential for rapid analysis of the elastic performance of a very large set of microstructures in any selected polycrystalline material system. The spectral framework transforms the complex integral relations for local stress and strain fields (derived from established generalized composite theories) into relatively simple algebraic expressions involving polynomials of structure parameters and morphology-independent influence coefficients. These coefficients need to be established only once for a given material system. In this paper, we formulate and demonstrate a viable approach to establishing the values of the second-order influence coefficients for cubic polycrystals by calibration to the results of micromechanical finite element models.     

Microstructure informatics using higher-order statistics and efficient data-mining protocols

Microstructure informatics is a critical building block of the integrated computational materials engineering infrastructure. Accelerated design and development of new advanced materials and their successful insertion in engineering practice are largely hindered by the lack of a rigorous mathematical framework for the robust generation of microstructure informatics relevant to the specific application. This paper describes a set of computational protocols that are capable of accelerating significantly the process of building the needed microstructure informatics for a targeted application. These novel protocols have several advantages over the current practice in the field: they allow archival, real-time searches, and quantitative comparisons of different instantiations within large microstructure datasets; they allow for automatic identification and extraction of microstructure features or metrics of interest from very large datasets; they allow for establishment of reliable microstructure-property correlations using objective measures of microstructure; and they provide precise quantitative insights on how the local neighborhood influences the localization of macroscale loading and/or the local evolution of microstructure leading to development of robust, scale-bridging, microstructure-property-processing linkages.     

Inverse analysis for transient moisture diffusion through fiber-reinforced composites

A new approach has been developed, based on an inverse analysis technique, to determine critical moisture diffusion parameters for a fiber-reinforced composite. This technique incorporates two distinct features: direct experimental observations of the weight gained by a composite material exposed to a humid environment, and highly detailed computational analyses that capture the actual heterogeneous microstructure of the composite. The latter feature was carried out by modeling more than 1000 individual carbon fibers that are randomly distributed within an epoxy matrix. The verification and efficacy of this technique was established by conducting an experiment on a high-grade IM7/997 carbon fiber-reinforced epoxy to determine the maximum moisture content at saturation and the diffusivity of epoxy. With the inverse analysis, the time duration required to estimate these moisture diffusion parameters could be drastically reduced as compared to conventional procedures. Subsequently, the established models were employed to characterize transient moisture absorption process within the composite. Here, it was demonstrated that modeling the heterogeneous microstructure of the composite is critical for obtaining accurate diffusion parameters, and an analytical model with effective properties does not produce correct transient moisture absorption behavior. Furthermore, the evolution of stress fields due to moisture induced volumetric expansion was quantified. It was observed that high stress concentrations develop in regions of fiber concentration. These regions then act as potential failure initiation sites that can lead to lower damage tolerance.     

Utility of microstructure modeling for simulation of micro-mechanical response of composites containing non-uniformly distributed fibers

Composite microstructures often contain non-uniformly distributed fibers having different sizes. Therefore, in finite-element (FE)-based simulations of the mechanical response of composites, the non-uniform spatial arrangement of fiber centers and distribution of fiber sizes need to be incorporated. In this contribution, a unique combination of digital image processing, microstructure modeling, and FE-based simulations is used to develop a methodology for modeling the micro-mechanical response of composites having non-uniform spatial arrangement of fibers. The methodology is developed via modeling of the micro-mechanical response of a ceramic matrix composite (CMC) containing unidirectional aligned Nicalon (SiC) fibers that are non-uniformly distributed in a glass ceramic matrix. For comparison, the micro-mechanical response of typical digital images of the composite microstructure and a simple microstructure model having periodic arrangement of fibers are also simulated. It is shown that the computer simulated microstructure model that accounts for non-uniform spatial arrangement of fibers having a range of sizes can be used for realistic parametric studies on the micro-mechanical response of the composite.     

Two-step homogenization simulation for multidomain and multigrain structures in piezoelectric materials

In this paper, a two-step scale-up procedure based on asymptotic homogenization theory is proposed for hierarchical structures consisting of multigrains and multidomains in piezoelectric materials. Intragranular domains are modeled as a microstructure during the first-step homogenization. Then, in the second-step homogenization, an aggregate of randomly oriented grains is modeled by applying the first-step homogenized material properties of multidomains to every grain. A dual-domain structure consisting of positive and negative directional domains with a 180° orientation gap is computed for case study analysis. The three-dimensional electron backscatter diffraction-measured microstructure is employed for the multigrain structure. The effect of the domain configuration on the macroscopic homogenized material properties of polycrystalline piezoelectric materials is investigated through the two-step homogenization process. In particular, the material property changes caused by the piezoelectric effect, which cannot be estimated by the mixture law, are discussed for multigrain and multidomain structures.     

多晶材料细观力学建模与模拟软件的开发与应用

Thermal Prophet-RVE是最近自主开发的一款基于实际微观组织数据的多晶材料细观力学模拟软件.本文着重对其软件架构、基本功能及技术特点进行介绍,并模拟了铁素体/马氏体双相钢生产过程马氏体相变引起的变形和双相组织在拉伸载荷作用下的细观力学行为.结果表明,基于材料实际微观组织数据构建的微结构模型能够高度还原组织...     

Spectral methods for microstructure design

Microstructure design is a vital enabling technology for modern industry that promises to short circuit the traditional empirical-based methods for design of new materials. However, inverse design methods that underlie microstructure design are generally computationally intensive, thus limiting their widespread adoption. This paper presents an inverse design approach that is based upon spectral methods in order to achieve a highly efficient framework for rapid design of materials. Some initial applications of the approach are briefly outlined.     

Simulation-assisted materials design for the concurrent design of materials and products

Engineering design has historically been taught using the paradigm of selecting materials on the basis of tabulated databases of properties (mechanical, physical, chemical, etc.). Recent trends have moved toward concurrent design of material composition and microstructure together with the component/system level. The goal is to tailor materials to meet specifi ed ranges of performance requirements of the overall system. Often these multiple performance requirements are in confl ict in terms of their demands on composition and microstructure. This paper explores the elements of a decision-based robust design framework for concurrent design of materials and products, focusing on enhancing the fraction of decisions supported by modeling and simulation.     

Microstructure evolution during homogenization of Al–Mn–Fe–Si alloys: Modeling and experimental results

Microstructure evolution during the homogenization heat treatment of Al–Mn–Fe–Si, or AA3xxx, alloys has been investigated using a combination of modeling and experimental studies. The model is fully coupled to CALculation PHAse Diagram (CALPHAD) software and has explicitly taken into account the two different length scales for diffusion encountered in modeling the homogenization process. The model is able to predict the evolution of all the important microstructural features during homogenization, including the inhomogeneous spatial distribution of dispersoids and alloying elements in solution, the dispersoid number density and the size distribution, and the type and fraction of intergranular constituent particles. Experiments were conducted using four direct chill (DC) cast AA3xxx alloys subjected to various homogenization treatments. The resulting microstructures were then characterized using a range of characterization techniques, including optical and electron microscopy, electron micro probe analysis, field emission gun scanning electron microscopy, and electrical resistivity measurements. The model predictions have been compared with the experimental measurements to validate the model. Further, it has been demonstrated that the validated model is able to predict the effects of alloying elements (e.g. Si and Mn) on microstructure evolution. It is concluded that the model provides a time and cost effective tool in optimizing and designing industrial AA3xxx alloy chemistries and homogenization heat treatments.     

铸造金属耐磨材料研究的进展

详细介绍了耐磨材料奥氏体锰钢、低合金钢和白口铸铁的成分、组织、性能及其应用进展,还对耐磨钢结材料和耐磨铸造复合材料以及新开发的高硼铸造耐磨合金进行了评述,期待为科学选择耐磨材料提供参考。     

Generalized practical models of cylindrical plunge grinding processes

This paper presents generalized grinding process models developed for cylindrical grinding processes based on the systematic analysis and experiments. The generalized model forms are established to maintain the same model structures with a minimal number of parameters so that the model coefficients can be determined through a small number of experiments when applied to different grinding workpiece materials and wheels. The relationships for power, surface roughness, G-ratio and surface burning are established for various steel alloys and alumina grinding wheels. It is shown that the established models provide good predictive capabilities while maintaining simple structures.     

Elastic–plastic property closures for hexagonal close-packed polycrystalline metals using first-order bounding theories

Property closures delineate the complete set of theoretically feasible combinations of macroscale (homogenized) properties in a given material system. A novel spectral framework called microstructure sensitive design (MSD) was recently formulated and demonstrated to be capable of delineating elastic–plastic property closures in a number of composite material systems. In particular, it was successfully applied to cubic polycrystals, where it was assumed that the crystallographic texture had a dominant influence on the macroscale properties of interest. Application of these procedures to hexagonal polycrystals posed significant computational difficulties, because of the need to represent the texture in the hcp polycrystals in a much larger number of dimensions in the Fourier space compared with what was needed for the cubic polycrystals. This paper reports new computational schemes for delineating elastic–plastic closures for hcp polycrystals using the spectral framework of MSD. The primary focus of this paper continues to be on the influence of the crystallographic texture (in the hcp polycrystal) on the components of the macroscale anisotropic elastic stiffness, macroscale anisotropic tensile yield strength, and the macroscale R ratios (ratio of the transverse strains in tensile deformation mode) exhibited by the material.     

Application of cold drawn lamellar microstructure for developing ultra-high strength wires

Composite materials having lamellar structure are known to have a good combination of high strength and ductility. They are widely used in the fields of automobiles, civil engineering and construction, machines and many other industries. An application of lamellar microstructure for developing ultra-high strength steel wires was studied and discussed. Based on the experimental results, the relationships between the strength increase and microstructure development during the cold wire drawing were studied to reveal the strengthening mechanism. As cold drawing proceeds, the wire strength extremely increases, the microstructure changes from large single crystal lamellar structure to very fine polycrystalline lamellar one which has nano-sized grains, high dislocation density and amorphous regions. From the results obtained, it is concluded that heavy cold drawing technique is an effective method for lamellar composite to get high strength wires. Furthermore, formation process of the best microstructure for producing the ultra-high strength wires was also discussed.     

Advances in multi-scale modeling of solidification and casting processes

The development of the aviation, energy and automobile industries requires an advanced integrated product/process R&D systems which could optimize the product and the process design as well. Integrated computational materials engineering (ICME) is a promising approach to fulfill this requirement and make the product and process development efficient, economic, and environmentally friendly. Advances in multi-scale modeling of solidification and casting processes, including mathematical models as well as engineering applications are presented in the paper. Dendrite morphology of magnesium and aluminum alloy of solidification process by using phase field and cellular automaton methods, mathematical models of segregation of large steel ingot, and microstructure models of unidirectionally solidified turbine blade casting are studied and discussed. In addition, some engineering case studies, including microstructure simulation of aluminum casting for automobile industry, segregation of large steel ingot for energy industry, and microstructure simulation of unidirectionally solidified turbine blade castings for aviation industry are discussed.     

Microstructural modeling of the homogenization heat treatment for AA3XXX alloys

The microstructure evolution during homogenization of AA3XXX alloys involves i) the reduction in the microsegregation formed during solidification, ii) the nucleation, growth and coarsening of intra-granular dispersoids, and iii) the growth/dissolution of inter-granular constituent particles. A model that is able to simulate these phenomena and their interaction has been developed recently. It features fully coupling with CALPHAD software. In this paper, the homogenization model is introduced and its predictive power is demonstrated by successfully reproducing experimentally measured microstructure features for an industrial extrusion alloy (AA3003). As such, the model represents a valuable tool for optimizing the design of industrial AA3XXX alloy homogenization heat treatment parameters.     

Multi-scale modeling of the viscoplastic response of As-fabricated microscale Pb-free Sn3.0Ag0.5Cu solder interconnects

A mechanistic multiscale modeling framework is proposed, to capture the dominant creep mechanisms and the influence of key microstructural features on the measured secondary creep response of microscale as-fabricated Sn3.0Ag0.5Cu (SAC305) solder interconnects. Mechanistic creep models of dislocation climb and detachment are used to capture the dispersion strengthening mechanisms in the Sn–Ag eutectic phase. These models are combined at the next length scale, with micromechanics-based homogenization schemes, to capture the load-sharing between Sn dendrites and intermetallic phases. The next higher length scale (Sn grains) is not addressed here since secondary creep response is empirically found to be insensitive to grain microstructure. Theoretical insights into the influence of microstructural features on the viscoplastic behavior of microscale SAC305 interconnects are provided. The model effectively captures the effect of alloy composition and aging loads on SAC solders, thereby aiding in the effective design and optimization of the viscoplastic behavior of SAC alloys.     

A framework for automated analysis and simulation of 3D polycrystalline microstructures. Part 2: Synthetic structure generation

This is the second of a two-part paper intended to develop a framework for collecting data, quantifying characteristics and subsequently representing microstructural information from polycrystalline materials. The framework is motivated by the need for incorporating accurate three-dimensional grain-level morphology and crystallography in computational analysis models that are currently gaining momentum. Following the quantification of microstructural features in the first part, this paper focuses on the development of models and codes for generating statistically equivalent synthetic microstructures. With input in the form of statistical characterization data obtained from serial-sectioning of the microstructures, this module is intended to provide computational modeling efforts with a microstructure representation that is statistically similar to the actual polycrystalline material.     

A multi-scale statistical study of twinning in magnesium

Hexagonal close packed (HCP) materials such as Mg, Zr, Ti, and Be are used in automotive, nuclear, aeronautic, and defense technologies. Understanding and controlling the formability of these materials is extremely relevant for these technologies. Such understanding requires an understanding of deformation twinning, an important deformation mechanism in HCP. Here we present a multi-scale modeling paradigm that passes information from the atomistic scale to the mesoscale represented by an individual grain in a polycrystalline metal. The single crystal model is, in turn, integrated into an Effective Medium model, which relates the behavior of all grains in the aggregate to the bulk response, such as stress-strain and texture evolution. This article focuses on application of the multi-scale model to HCP polycrystalline magnesium.     

Multi-scale analysis of engineering surfaces

Conventional surface characterization techniques involving random process analysis are limited in characterizing multi-scale surface features relevant to manufacturing processes and functions. This paper introduces a novel technique for multi-scale characterization of engineering surfaces by applying wavelet transform. The main advantages of wavelet transform over other existing signal processing techniques are its space-frequency localization and multi-scale view of the components of a signal. Utilizing these properties of wavelet transform, we can effectively apply multi-channel filter banks to the surface data and link the manufacturing and functional aspects of a surface with its multi-scale features. Surfaces produced by typical manufacturing processes are analyzed using wavelet transform, and the usefulness of wavelet transform in the multi-scale analysis of engineering surfaces is demonstrated.     

搅拌摩擦加工研究进展

搅拌摩擦加工(FSP),是一种新型的材料塑性变形加工方法,它是在搅拌摩擦焊(FSW)的基础上提出的。从发明至今,研究者已经成功将FSP用于铸造金属微观组织细化、超塑性材料的制备、材料表面改性以及各种复合材料的制备中。搅拌摩擦加工工艺与搅拌摩擦焊接工艺基本相同,工艺参数对搅拌摩擦加工材料质量有很大的影响。综述了搅拌摩擦加工近年来的研究进展,主要包括不添加增强相的FSP和添加增强相的FSP两大类。其中不添加增强相的FSP主要有铸造金属微观组织细化和超塑性材料制备,添加增强相的FSP主要有材料表面改性和复合材料制备。搅拌摩擦加工制备复合材料根据添加相是否与基体反应生成增强相,又分为非原位合成法制备复合材料与原位合成法制备复合材料。文中对以上内容分别进行了总结与评述,最后指出了FSP今后发展应用的方向。