Tool For Material Design Research Articles

Design of radiation resistant metallic multilayers for advanced nuclear systems

Helium implantation from transmutation reactions is a major cause of embrittlement and dimensional instability of structural components in nuclear energy systems. Development of novel materials with improved radiation resistance, which is of the utmost importance for progress in nuclear energy, requires guidelines to arrive at favorable parameters more efficiently. Here, we present a methodology that can be used for the design of radiation tolerant materials. We used synchrotron X-ray reflectivity to nondestructively study radiation effects at buried interfaces and measure swelling induced by He implantation in Cu/Nb multilayers. The results, supported by transmission electron microscopy, show a direct correlation between reduced swelling in nanoscale multilayers and increased interface area per unit volume, consistent with helium storage in Cu/Nb interfaces in forms that minimize dimensional changes. In addition, for Cu/Nb layers, a linear relationship is demonstrated between the measured depth-dependent swelling and implanted He density from simulations, making the reflectivity technique a powerful tool for heuristic material design.

Thermo-elastic optimization of material distribution of functionally graded structures by an isogeometrical approach

A new isogeometrical procedure for optimization of material composition of functionally graded structures in thermo-mechanical processes is introduced. The proposed method employs a generalized form of the standard isogeometric analysis method, allowing for gradation of material properties through patches. The variations of material properties are captured in a fully isogeometric formulation using the same NURBS basis functions employed for construction of the geometry and approximation of the solution. Subsequently, the applicates of control points that define the surfaces of volume fractions of the constituents are considered as the design variables and obtained by solving the optimization problem using a mathematical programming algorithm. Some numerical examples under thermal and mechanical loadings are considered to demonstrate the performance and applicability of the proposed method. Comparison of the obtained results with those of the other existing approaches such as finite elements and meshfree methods verifies the presented results. It will be seen that the proposed procedure considerably removes the difficulties of the existing methods and provides a promising tool for material design of functionally graded structures.

Development of a computational tool for materials design

An integrated modeling tool coupling thermodynamic calculation and kinetic simulation of multicomponent alloys is developed under the framework of integrated computational materials engineering. On the basis of Pandat™ software for multicomponent phase diagram calculation, the new tool is designed in an integrated workspace and is targeted to understand the composition–processing–structure–property relationships of multicomponent systems. In particular, the phase diagram calculation module is used to understand the phase stability under the given conditions. The calculated phase equilibrium information, such as phase composition and chemical driving force, provides input for the kinetic simulation. In this paper, the design of the modeling tool will be presented and the calculation examples from the different modules will also be demonstrated.

A canonical stability–elasticity relationship verified for one million face-centred-cubic structures

Any thermodynamically stable or metastable phase corresponds to a local minimum of a potentially very complicated energy landscape. But however complex the crystal might be, this energy landscape is of parabolic shape near its minima. Roughly speaking, the depth of this energy well with respect to some reference level determines the thermodynamic stability of the system, and the steepness of the parabola near its minimum determines the system's elastic properties. Although changing alloying elements and their concentrations in a given material to enhance certain properties dates back to the Bronze Age, the systematic search for desirable properties in metastable atomic configurations at a fixed stoichiometry is a very recent tool in materials design. Here we demonstrate, using first-principles studies of four binary alloy systems, that the elastic properties of face-centred-cubic intermetallic compounds obey certain rules. We reach two conclusions based on calculations on a huge subset of the face-centred-cubic configuration space. First, the stiffness and the heat of formation are negatively correlated with a nearly constant Spearman correlation for all concentrations. Second, the averaged stiffness of metastable configurations at a fixed concentration decays linearly with their distance to the ground-state line (the phase diagram of an alloy at zero Kelvin). We hope that our methods will help to simplify the quest for new materials with optimal properties from the vast configuration space available.

Micromechanics investigation of hygro-elastic behavior of cellular materials with multi-layered cell walls

In this paper, the hygro-elastic behavior of two-dimensional periodic honeycombs composed of multi-layered cell walls is investigated using a computational micromechanics approach. Detailed numerical results for the effective hygro-expansion coefficients and the elastic moduli of honeycombs are obtained. The influence of the arrangement of the cell wall layers and the geometrical parameters of the honeycombs on the effective hygro-elastic properties is examined. Limiting cases are considered, and the validity of the model is established by comparison with the analytical solutions available in the existing literature. The obtained results suggest that the layered architecture of the cell wall enhances the anisotropy in swelling behavior of honeycombs with irregular configuration which is reflected in their transverse hygro-expansion coefficients while regular honeycombs show isotropic behavior. The proposed model explains the complex thermo-hygro-mechanical behavior of natural cellular materials and provides a predictive tool for bio-mimetic material design.

ChemInform Abstract: Molecular Simulations for Energy, Environmental and Pharmaceutical Applications of Nanoporous Materials: From Zeolites, Metal—Organic Frameworks to Protein Crystals

AbstractReview: 74 refs.

Molecular simulation of micro-structures and gas diffusion behavior of organic–inorganic hybrid amorphous silica membranes

A molecular dynamics (MD) technique using h- pcff force field was adopted to analyze the micro-structure and gas transport behavior of an organic–inorganic hybrid bis(triethoxysilyl)ethane (BTESE) silica membrane. The membrane fractional free space (FFS), cavity size distribution (CSD), and fractional accessible volume (FAV) were estimated to discuss how doped Si–C–C–Si segments affect a silica network. The radial distribution function (RDF) of atom pairs was analyzed to investigate the micro-structure of a hybrid silica network. The gas diffusion behavior, including the thermal motion and diffusivity, was calculated to understand the gas transport behavior of the BTESE silica membrane. The analyses of the FFS, CSD, and FAV of the silica membrane indicated that the silica network would expand to form a larger cavity size, indicating a high potential for increased gas permeance. The RDF diagram indicates that the hybrid silica matrix provides a looser structure with higher network fluctuation than that of the pure silica membrane. The gas diffusion behavior analysis revealed that the hybrid silica membrane contained more effective free space, which prompted H 2 diffusivity and also produced a good H 2/SF 6 diffusivity ratio. The MD technique was successfully applied to simulate the characteristics and gas diffusion behaviors of the hybrid BTESE silica membrane. Demonstration of the superior properties of hybrid BTESE silica using MD technique proves itself to be a promising tool for material development and design on a microscopic view.

Molecular simulations for energy, environmental and pharmaceutical applications of nanoporous materials: from zeolites, metal–organic frameworks to protein crystals

Nanoporous materials have widespread applications in chemical industry, but the pathway from laboratory synthesis and testing to practical utilization of nanoporous materials is substantially challenging and requires fundamental understanding from the bottom up. With ever-growing computational resources, molecular simulations have become an indispensable tool for material characterization, screening and design. This tutorial review summarizes the recent simulation studies in zeolites, metal-organic frameworks and protein crystals, and provides a molecular overview for energy, environmental and pharmaceutical applications of nanoporous materials with increasing degree of complexity in building blocks. It is demonstrated that molecular-level studies can bridge the gap between physical and engineering sciences, unravel microscopic insights that are otherwise experimentally inaccessible, and assist in the rational design of new materials. The review is concluded with major challenges in future simulation exploration of novel nanoporous materials for emerging applications.

Multi-objective ceramic matrix composite material design using the variable fidelity model management optimization framework

The increasing computational requirements of advanced numerical tools for simulating material behaviour can prohibit direct integration of these tools in a design optimization procedure where multiple iterations are required. Therefore, a design approach is needed that can incorporate multiple simulations (multi-physics with different input variables) of varying fidelity in an iterative model management framework that can significantly reduce design cycle times. In this research, a material design tool based on a variable fidelity model management framework is applied to obtain the optimal size of a second phase, consisting of silicon carbide (SiC) fibres, in a silicon-nitride (Si3N4) matrix to obtain continuous fibre SiC-Si3N4 ceramic composites (CFCCs) with maximum high temperature strength and high temperature creep resistance. This investigation shows how models with different dimensions and input design variables can be handled and integrated efficiently by the trust region model management framework, while significantly reducing design cycle times in application to the design of multiphase composite materials.

Probing the improbable: imaging C atoms in alumina

The ability to probe the three-dimensional atomic structure of materials is an essential tool for material design and failure analysis. Atom-probe tomography has proven very powerful to analyze the detailed structure and chemistry of metallic alloys and semiconductor structures while ceramic materials have remained outside its standard purview. In the current work, we demonstrate that bulk alumina can be quantitatively analyzed and microstructural features observed. The analysis of grain boundary carbon segregation – barely achievable by electron microscopy – opens the possibility of understanding the mechanistic effects of dopants on mechanical properties, fracture and wear properties of bulk oxides.

A Variable Fidelity Model Management Framework for Designing Multiphase Materials

Research applications involving design tool development for multi phase material design are at an early stage of development. The computational requirements of advanced numerical tools for simulating material behavior such as the finite element method (FEM) and the molecular dynamics (MD) method can prohibit direct integration of these tools in a design optimization procedure where multiple iterations are required. One, therefore, requires a design approach that can incorporate multiple simulations (multiphysics) of varying fidelity such as FEM and MD in an iterative model management framework that can significantly reduce design cycle times. In this research a material design tool based on a variable fidelity model management framework is presented. In the variable fidelity material design tool, complex “high-fidelity” FEM analyses are performed only to guide the analytic “low-fidelity” model toward the optimal material design. The tool is applied to obtain the optimal distribution of a second phase, consisting of silicon carbide (SiC) fibers, in a silicon-nitride (Si3N4) matrix to obtain continuous fiber SiC–Si3N4 ceramic composites with optimal fracture toughness. Using the variable fidelity material design tool in application to two test problems, a reduction in design cycle times of between 40% and 80% is achieved as compared to using a conventional design optimization approach that exclusively calls the high-fidelity FEM. The optimal design obtained using the variable fidelity approach is the same as that obtained using the conventional procedure. The variable fidelity material design tool is extensible to multiscale multiphase material design by using MD based material performance analyses as the high-fidelity analyses in order to guide low-fidelity continuum level numerical tools such as the FEM or finite-difference method with significant savings in the computational time.

State-Space Constitutive Model for Magnetization and Magnetostriction of Galfenol Alloys

We present a thermodynamic model that quantifies the magnetization and magnetostriction of annealed or unannealed Galfenol alloys subjected to magnetic fields and mechanical stresses. The model requires a small number of parameters directly related to physical properties of the data, thus providing a useful tool for material characterization and design. Furthermore, the model is formulated in state-space form, which simplifies computations for design and control of Galfenol devices.

Grain boundary disordering in binary alloys

This letter reports a grain boundary (GB) premelting/prewetting model based on the Miedema model and computational thermodynamics, predicting that GB disordering can start at as low as 60%–85% of the bulk solidus temperatures in selected systems. This model quantitatively explains the long-standing mystery of subsolidus activated sintering in W–Pd, W–Ni, W–Co, W–Fe and W–Cu, and it has broad applications for understanding GB-controlled transport kinetics and physical properties. Furthermore, this study demonstrates the necessity of developing GB “phase” diagrams as a tool for material design.

Evolutionary crystal structure prediction as a tool in materials design

Ab initio methods allow a more or less straightforward prediction of numerous physicalproperties of solids, but require the knowledge of their crystal structure. The evolutionaryalgorithm USPEX, developed by us in 2004–2006, enables reliable prediction of thestable crystal structure without relying on any experimental data. Numerous tests(mostly for systems with up to 28 atoms in the unit cell, and a few tests with up to128 atoms/cell) showed a success rate of nearly 100%. USPEX has resulted in a number ofpredictions of hitherto unknown stable structures. We give a short overview ofthe method, introducing some new developments and results, and discuss a fewalternative approaches. The method is illustrated by a test on an 80 atom supercell ofMgSiO3 and by the search for new materials with compositionsAl13K and Al12C.

Phonon band structure and thermal transport correlation in a layered diatomic crystal

To elucidate the relationship between a crystal's structure, its thermal conductivity, and its phonon dispersion characteristics, an analysis is conducted on layered diatomic Lennard-Jones crystals with various mass ratios. Lattice dynamics theory and molecular dynamics simulations are used to predict the phonon dispersion curves and the thermal conductivity. The layered structure generates directionally dependent thermal conductivities lower than those predicted by density trends alone. The dispersion characteristics are quantified using a set of novel band diagram metrics, which are used to assess the contributions of acoustic phonons and optical phonons to the thermal conductivity. The thermal conductivity increases as the extent of the acoustic modes increases, and decreases as the extent of the stop bands increases. The sensitivity of the thermal conductivity to the band diagram metrics is highest at low temperatures, where there is less anharmonic scattering, indicating that dispersion plays a more prominent role in thermal transport in that regime. We propose that the dispersion metrics (i) provide an indirect measure of the relative contributions of dispersion and anharmonic scattering to the thermal transport, and (ii) uncouple the standard thermal conductivity structure-property relation to that of structure-dispersion and dispersion-property relations, providing opportunities for better understanding of the underlying physical mechanisms and a potential tool for material design.

Digital image analysis and microstructure modeling tools for microstructure sensitive design of materials

Microstructures contain features at length scales ranging from nanometers to millimeters. These features have complex geometry, their locations and orientations are often non-uniform, and spatial correlations usually exist. In such complex microstructures, deformation and fracture processes are governed by several types of microstructural features present at different length scales, multiple fracture micro-mechanisms contribute to the overall fracture, and spatial correlations and microstructural gradients affect the fracture path. These microstructural complexities provide opportunities and challenges for microstructure sensitive design of materials. In this contribution, we present digital image analysis and microstructure modeling tools that can provide useful input for microstructure sensitive design of materials through incorporation of the detailed microstructural geometry in the simulations of materials behavior. Digital image analysis and microstructure modeling based methodologies are presented for performing finite elements (FE) based simulations on the realistic microstructure models and two- and three-dimensional microstructural digital images, and for linking the interactions among microstructural features at different length scales.

Design of smart composite materials using topology optimization

The topology optimization method is used to find the distribution of material phases that extremizes an objective function (e.g., thermal expansion coefficient, piezoelectric coefficients etc) subject to constraints, such as elastic symmetry and volume fractions of the constituent phases, within a periodic base cell. The effective properties of the material structures are found using a numerical homogenization method based on a finite-element discretization of the base cell. The optimization problem is solved using sequential linear programming. We review the topology optimization procedure as a tool for smart materials design and discuss in detail two recent applications of it to design composites with extreme thermal expansion coefficients and piezocomposites with optimal hydrophone characteristics.

Wear by surface fatigue on a new foundation part II. particle detachment mechanisms and quantitative aspects

An alternative model of wear produced by surface fatigue (SFW) was suggested. Surface cracks control the process of wear particle generation by SFW. New models of contact mechanics based on material microstructure and its evolution with time type, different from those models based on surface topography, were formulated. During dry sliding, the stress is exerted by pressure spots originated from groupings of harder material. A new quantitative investigation was set up to evaluate the contribution of SFW to the total wear loss produced during dry sliding. It was found that SFW is a major contributor to the overall wear loss generated during dry sliding. For cast irons and ceramic coating. SFW controls the amount of the total wear loss during dry sliding. SFW has a secondary contribution to the total wear loss for ceramic materials and sintered steels. Practical tools for design of materials that withstand SFW were suggested.

A comparative study of failure criteria in probabilistic fields and stochastic failure envelopes of composite materials

One of the major objectives of this paper is to offer a practical tool for materials design of unidirectional composite laminates under in-plane multiaxial load. Design-oriented failure criteria of composite materials are applied to construct the evaluation model of probabilistic safety based on the extended structural reliability theory. Typical failure criteria such as maximum stress, maximum strain and quadratic polynomial failure criteria are compared from the viewpoint of reliability-oriented materials design of composite materials. The new design diagram which shows the feasible region on in-plane strain space and corresponds to safety index or failure probability is also proposed. These stochastic failure envelope diagrams which are drawn in in-plane strain space enable one to evaluate the stochastic behavior of a composite laminate with any lamination angle under multi-axial stress or strain condition. Numerical analysis for a graphite/epoxy laminate of T300/5208 is shown for the comparative verification of failure criteria under the various combinations of multi-axial load conditions and lamination angles. The stochastic failure envelopes of T300/5208 were also described in in-plane strain space.

Stochastic materials design of composite materials. Stochastic failure envelope of unidirectional laminates subjected to in-plane multiaxial loads.

One of the major objectives of this paper is to offer a practical tool for stochastic materials design of unidirectional composite laminates under the in-plane multiaxial load. Quadratic polynomial failure criteria and fist order reliability method (FORM) are applied to construct the evaluation model of probabilistic safety of composite laminates. From the numerical analysis of T300/5208, the relation between the applied stress vector and safety indices β is discussed. A new design diagram which corresponds to safety index or failure probability is proposed. The stochastic failure envelope diagrams, which are drawn in the in-plane strain space, enable one to evaluate the stochastic behavior of composite laminate with any lamination angle under multiaxial stress or strain condition.