Complex Multiphase Materials Research Articles

Machine-learning-assisted deciphering of microstructural effects on ionic transport in composite materials: A case study of Li7La3Zr2O12-LiCoO2

The effective diffusivity of ionic species in multiphase materials is critical for the design and function of composite materials for electrochemical energy storage. In practice, effective diffusivity depends sensitively not only on the intrinsic diffusivities of constituting materials but also on their topological arrangement; nevertheless, these coupled contributions are oversimplified in most analytical models. Here, we combine atomistically informed mesoscale modeling and machine learning (ML) analysis to unravel how such features affect effective diffusivity in two-phase composites. Using the Li7La3Zr2O12-LiCoO2 composite solid-state battery cathode as a model system, we compute effective diffusivity for 600 distinct dense polycrystalline microstructures with different topological configurations of grains, grain boundaries, and heterointerfaces. We verify that in addition to atomic-scale variabilities, microstructural feature diversity can significantly impact effective transport properties. Across the ensemble of test microstructures, this often results in bimodal distributions of effective diffusivity that encompass two qualitatively distinct operating mechanisms, which we identify via flux analysis. An ML approach reveals that the most critical determining factors for effective diffusivity are the connectivity of bulk phases and their heterointerfaces. The role of ionic mobility at the heterointerfaces is also discussed. These insights highlight the combined importance of microstructure and interface engineering in tuning the transport properties of ionic species in composite materials. Our framework can also be extended for understanding generic microstructure-property relationships in other complex multiphase materials.

Pressure generation under deformation in a large-volume press

Abstract Deformation can change the transition pathway of materials under high pressure, thus significantly affects physical and chemical properties of matters. However, accurate pressure calibration under deformation is challenging and thereby causes relatively large pressure uncertainties in deformation experiments, resulting in the synthesis of complex multiphase materials. Here, pressure generations of three types of deformation assemblies were well calibrated in a Walker-type large-volume press (LVP) by electrical resistance measurements combined with finite element simulations (FESs). Hard Al2O3 or diamond pistons in shear and uniaxial deformation assemblies significantly increases the efficiency of pressure generation compared with the conventional quasi-hydrostatic assembly. The uniaxial deformation assembly using flat diamond pistons possess the highest efficiency in these deformation assemblies. This finding is further confirmed by stress distribution analysis based on FESs. With this deformation assembly, we found shear can effectively promote the transformation of C60 into diamond under high pressure and realized the synthesis of pure-phase diamond at relatively moderate pressure and temperature conditions. The present developed techniques will help improve pressure efficiencies in LVP and explore the new physical and chemical properties of materials under deformation in both science and technology.

A New Multiphase Apparatus for Testing Soil Permeated with Three Immiscible Fluids

Abstract Oil-contaminated unsaturated soil is a complex multiphase material. In this study, a new triaxial apparatus was developed to independently control/measure its air, oil, and water pressures. Therefore, the suctions associated with air–water, air–oil, and oil–water interfaces can be determined. The apparatus utilizes the hanging column and axis-translation techniques to control suctions in 0∼5 kPa and 5∼600 kPa. It is suitable for investigating water/oil retention, isotropic compression, and triaxial shear behavior of oil-contaminated soil. Using this new apparatus, five tests were conducted to analyze the saturation–pressure (S–P) relationship of sand and sandy silt at various oil and water contents and to evaluate the validity of the axis-translation technique for soil permeated with three nonimmersible fluids. Results showed that the artificial increase of air pressure in the axis-translation technique does not obviously alter the air–water and air–oil suctions at constant oil and water contents. A popular suction–saturation model, which was proposed based on test results of clean sands, showed a good prediction of the air–oil suction. However, the oil–water suction results of sandy silt do not align with the model prediction, suggesting that the model may need to be revised for soils with some silt and clay particles.

Effect of microstructure heterogeneity shapes on constitutive behaviour of encapsulated self-healing cementitious materials

Self-healing cementitious materials with microcapsules are complex multiscale and multiphase materials. The random microstructure of these materials governs their mechanical and transport behaviour. The actual microstructure can be represented accurately with a discrete lattice model, but computational restrictions mean that the size of domain that can be considered with this approach is limited. By contrast, a smeared approach, based on a micromechanical formulation, provides an approximate representation of the material microstructure with low computational costs. The aim of this paper is to compare simulations of a microcapsule-based self-healing cementitious system with discrete-lattice and smeared-micromechanical models, and to assess the relative strengths and weaknesses of these models for simulating distributed fracture and healing in this type of self-healing material. A novel random field generation technique is used to represent the microstructure of a cementitious mortar specimen. The meshes and elements are created by the triangulation method and used to determine the input required for the lattice model. The paper also describes the enhancement of the TUDelft lattice model to include self-healing behaviour. The extended micromechanical model considers both microcracking and healing. The findings from the study provide insight into the relative merits of these two modelling approaches.

An efficient and accurate numerical method for the heat conduction problems of thermal metamaterials based on edge-based smoothed finite element method

Thermal metamaterials are a class of artificial composite structures with special thermal conduction properties. Due to the existence of complex multi-phase materials arrangement and interfaces in the thermal metamaterials, an efficient and accurate numerical method is on-demand to predict their temperature distribution and performances. In this paper, we studied the edge-based smoothed finite element method (ES-FEM) for simulating the heat conduction of thermal metamaterials in both steady-state and transient circumstances. Benefit from the adopted smoothing technique, the numerical errors caused by the complex interface are further eliminated. The most significant advantage of the proposed method is that one can directly use the automatically generated coarse triangle mesh to reduce the computational costs while ensuring accuracy. Two numerical examples are presented, in which two typical thermal metamaterials, the thermal cloak and thermal concentration device, are considered respectively in both steady-state and transient cases. The results illustrate that the ES-FEM based approach has good efficiency and accuracy in the heat conduction simulation of the thermal metamaterials.

Electron work function: an indicative parameter towards a novel material design methodology

Electron work function (EWF) has demonstrated its great promise in materials analysis and design, particularly for single-phase materials, e.g., solute selection for optimal solid-solution strengthening. Such promise is attributed to the correlation of EWF with the atomic bonding and stability, which largely determines material properties. However, engineering materials generally consist of multiple phases. Whether or not the overall EWF of a complex multi-phase material can reflect its properties is unclear. Through investigation on the relationships among EWF, microstructure, mechanical and electrochemical properties of low-carbon steel samples with two-level microstructural inhomogeneity, we demonstrate that the overall EWF does carry the information on integrated electron behavior and overall properties of multiphase alloys. This study makes it achievable to develop “electronic metallurgy”—an electronic based novel alternative methodology for materials design.

Effect of micro-aeration on the mechanical behaviour of chocolates and implications for oral processing.

Aeration in foods has been widely utilised in the food industry to develop novel foods with enhanced sensorial characteristics. Specifically, aeration at the micron-sized scale has a significant impact on the microstructure where micro-bubbles interact with the other microstructural features in chocolates. This study aims to determine the effect of micro-aeration on the mechanical properties of chocolate products, which are directly correlated with textural attributes such as hardness and crumbliness. Uniaxial compression tests were performed to determine the mechanical properties such as Poisson's ratio, Young's modulus and macroscopic yield strength together with fracture tests to estimate the fracture toughness. In vivo mastication tests were also conducted to investigate the link between the fracture properties and fragmentation during the first two chewing cycles. The uniaxial stress-strain data were used to calibrate a viscoplastic constitutive law. The results showed that micro-aeration significantly affects mechanical properties such as Young's modulus, yield and fracture stresses, as well as fracture toughness. In addition, it enhances the brittle nature of the chocolate, as evidenced by lower fracture stress but also lower fracture toughness leading to higher fragmentation, in agreement with observations in the in vivo mastication tests. As evidenced by the XRT images and the stress-strain measurements micro-aeration hinders the re-arrangement of the microscopic features inside the chocolate during the material's deformation. The work provides a new insight of the role of bubbles on the bulk behaviour of complex multiphase materials, such as chocolates, and defines the mechanical properties which are important input parameters for the development of oral processing simulations.

Design of single-phase chiral metamaterials for broadband double negativity via shape optimization

Double negative elastic metamaterials are a kind of novel artificial materials with unique ability to manipulate elastic wave propagation in the subwavelength scale. They are generally designed by inducing the combination of multiple resonance with different negative effective parameters. However, due to the limitation of empirical structural shape and design tools, these metamaterials are made by complex multiphase materials but possess a relatively narrow frequency range with double negativity, which is unsuitable for practical engineering applications. In this work, a shape optimization and single-phase chiral elastic metamaterials (EMMs) based strategy is presented for designing the EMMs with a broadband double negativity (negative mass density and bulk modulus). Several numerical examples are presented to validate the method by considering different initial shapes, target frequency ranges and design variables. Besides, numerical simulations related to double negativity including negative refraction and imaging are investigated by using the optimized chiral EMMs. Interestingly, elastic wave mode conversion and super-resolution imaging of 0.28λ are observed. The proposed metamaterial combined with the design approach is a very efficient way to obtain double negativity over a broad frequency band and it may thus have great potential for designing new elastic metamaterials.

Two-dimensional nanomaterials and their derivatives for laser protection

To achieve simultaneous protection against both pulsed and continuous wave (CW) or quasi-CW lasers, significant research effort has been devoted to the state-of-the-art optical limiting (OL) materials and processes in an attempt to achieve some measures of protection against such laser beams in the past decades. Two-dimensional (2D) nanomaterials with a lot of unique properties, including graphene, transition metal dichalcogenides, black phosphorus and others, have aroused the extensive research interest of many researchers. In this review paper, we describe systematically the OL mechanisms and the recent achievements in the 2D nanomaterials and their organic/polymeric derivatives for laser protection. In an effort to sustain the advantage of 2D nanomaterials, one can not only introduce the functional molecules or polymers to blend with them to form a complex multi-phase material system, but also embed the soluble 2D nanosheets covalently functionalized with organic/polymeric materials in a polymer host to form host-guest composite materials that are expected to improve the OL performance of the whole system. All in all, an optimized complex multi-component nanomaterial system enormously enhances the performance and applicability of OL devices. In addition, the fundamental studies of the photophysical and photonic properties of 2D nanomaterials and their derivatives in various solid hosts are of significance for modifying the nanomaterials at a molecular level.

On Osmotic Pressure in Hyperelastic Biphasic Fiber‐Reinforced Articular Cartilage

AbstractArticular cartilage belongs to the group of connective tissues and ensures a low‐friction performance of the human musculoskeletal system. It is a complex multiphase material with two main components: a collagen fiber‐reinforced porous solid and a liquid phase. The mechanical behavior of articular cartilage is decisively determined by the interaction between the highly anisotropic, inhomogeneously distributed collagen fiber network, the isotropically distributed proteoglycans and the interstitial fluid. The electrically negatively charged proteoglycans generate an electrical gradient that creates an osmotic negative pressure on the fluid which causes swelling of the cartilage. This leads to mechanically prestressed collagen fibers resulting in a decrease of total pressure occurring inside the cartilage. An increasingly common joint disease is osteoarthritis (OA), which severely impairs everyday life, especially in the elderly population. It is characterized by a loss of matrix stiffness as well as by a reduced tension stiffness and viscoelasticity of the collagen fibers. The aim of the developed model is to describe the previously mentioned material properties of cartilage as precisely as possible. The biphasic model uses the Theory of Porous Media for homogenization and contains an incompressible poroelastic solid matrix reinforced with collagen fibers and an incompressible pore fluid. By including the occurring osmotic pressure, the correct initial stress state of the imaged configuration is considered.

A novel optical method for measuring 3D full-field strain deformation in geotechnical tri-axial testing

Soil is a complex multiphase material and has anisotropic properties; meanwhile, soil behaviour is typically evaluated in tri-axial testing. Until now, there have still been some challenges in measuring the total strain, the local strain deformation and the volume changes during tri-axial testing. In conventional geotechnical testing, it cannot acquire enough deformation characteristics. To improve the situation, a digital image measurement system has been constructed and calibrated on a geotechnical tri-axial apparatus. In the digital image measurement system, the three-dimensional digital image correlation (3D-DIC) technique was applied to measure the soil specimen’s 3D large deformation and reconstruct the 3D surface topography of the specimen. To improve the measurement accuracy, a standard spatial calibration procedure to rectify the 3D reconstruction data in tri-axial testing is proposed to improve the effect of the projective transformation in stereovision. Through rectification, the root-mean-squared error in terms of displacement measurement in the tri-axial testing was reduced by more than half. Furthermore, a subpixel edge detector was applied to estimate the volume changes based on the 3D-DIC results. Finally, comparing the results between the image measurement system and the conventional measurement method, the proposed method not only can obtain the specimen’s distribution of 3D full-field deformation, volume strain and so on, but also can provide a method for rectifying the 3D data measured by the image measurement technique in tri-axial testing. The results from 3D reconstruction can describe directly the characteristics of anisotropy and non-uniformity in geotechnical materials. The results can provide more information than conventional testing when establishing a constitutive model in soil mechanics.

Complex modulus modeling of asphalt concrete mixes using the Non-Smooth Contact Dynamics method

Asphalt mixtures are complex multiphase materials showing a viscoelastic behavior. To assess the mechanical response of these materials, a typical practice is to perform a complex modulus test. An alternative to laboratory characterization is to simulate numerically this test by means of a discrete approach. These approaches are able to reproduce the mechanical performances of asphalt mixtures, but are still time-consuming. In this paper, the complex modulus test is reproduced numerically for a viscoelastic granular material by means of 3D Non-Smooth Contact Dynamics simulations. A viscoelastic phase surrounding the rigid particles is simulated by a contact model acting between them. This contact law was implemented in the LMGC90 software, based on the Burger’s model. The developed contact model handles larger time step lengths to reduce the computational time. Experimental and numerical testing campaigns were conducted for the complex modulus test on trapezoidal samples in a 2PB configuration. The numerical model was able to reproduce the mechanical performances obtained during experimental tests, regarding the material properties such as the complex modulus norm and the associate phase angle. The proposed model can be used to simulate the mechanical response of road structures under traffic loading concerning rutting, crack propagation and fatigue damage.

Modelling of novel polymer materials through atomistic molecular dynamics simulations

Molecular simulation methodologies are nowadays very important tools for the prediction of structure-properties relations of molecular systems, and, more general, for the computational design of novel materials. Here, we demonstrate that the atomistic molecular dynamic simulations can be successfully used to design well-defined polymer systems as well as to examine their structural and dynamical properties. More specifically, we study the behaviour of graphene-based nanocomposites and nanostructured polymer materials. We provide a detailed analysis adapted to every system with a special focus on detecting the local heterogeneities in the material. Our carefully developed method allows us to shed light on the relation between the local structure and final properties of the desired material. The obtained information can be applied in the development of novel complex multi-phase polymeric materials with a broad range of possible applications, as for instance in energy storage and electronics.

Variations in ultrasonic transmission behavior along seagrass leaf blades

Seagrass is a complex multi-phase material, and an effective method for connecting acoustic propagation through seagrass meadows to internal or external characteristics of the seagrass would be beneficial for acoustic remote sensing applications. To investigate some of these connections, ultrasonic (1, 2.25, and 5 MHz) time-of-flight measurements through individual leaf blades of the endemic Mediterranean seagrasses Posidonia oceanica and Cymodocea nodosa are presented. Acoustic measurements were made at multiple points along the leaf blades and the sound speed and signal attenuation varied significantly within a single blade depending on measurement location. The measured acoustic variations are compared to external blade features such as discoloration, epiphyte coverage, and thickness. Microscopy images of blade cross-sections each taken at each acoustic measurement location are used to compare the void fraction to acoustic behavior. [Work supported by ONR, ONR Global.]

Physico-mechanical properties and micromechanisms of local deformation in thin near-surface layers of complex multiphase materials

Size effects in the local mechanical properties of multiphase materials are studied by means of micro- and nanoindentation. The numerical values of the elasticity modulus, hardness, and crack resistance of single phases and interphase boundaries in several rock samples (polycrystalline banded iron formations, granite, anthracite, sandstone, marble, and serpentine marble) are determined. The strongest and weakest intergrowth boundaries in the investigated materials are established. Thermal activation analysis is performed, and the activation and energy characteristics of local deformation in a material under an indenter are identified. The predominant micromechanisms of plasticity in single phases and inclusions in rocks under the action of high local stresses are identified.

Concurrent determination of nanocrystal shape and amorphous phases in complex materials by diffraction scattering computed tomography

Advanced functional materials often contain multiple phases which are (nano)crystalline and/or amorphous. The spatial distribution of these phases and their properties, including nanocrystallite size and shape, often drives material function yet is difficult to obtain with current experimental techniques. This article describes the use of diffraction scattering computed tomography, which maps wide-angle scattering information onto sample space, to address this challenge. The wide-angle scattering signal contains information on both (nano)crystalline and amorphous phases. Rietveld refinement of reconstructed diffraction patterns is employed to determine anisotropic nanocrystal shapes. The background signal from refinements is used to identify contributing amorphous phases through multivariate curve resolution. Thus it is demonstrated that reciprocal space analysis in combination with diffraction scattering computed tomography is a very powerful tool for the complete analysis of complex multiphase materials such as energy devices.

Major and Trace Element Analysis of Natural and Experimental Igneous Systems using LA-ICP-MS.

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) enables spatially resolved quantitative measurements of major, minor and trace element abundances in igneous rocks and minerals with equal or better precision than many other in situ techniques, and more rapidly than labour-intensive wet chemistry procedures. Common applications for LA-ICP-MS in the Earth sciences centre on investigating the composition of natural and experimental geological materials, including: analysis of whole rock silicate glasses, flux-free pressed powder tablets and/or fused aliquots of materials; in situ probing of individual minerals, xenocrysts, fluid and melt inclusions, experimental run products, and siderophile-rich micronuggets; and multidimensional chemical mapping of complex (multiphase) materials.

Intermetallic titanium aluminides in aerospace applications – processing, microstructure and properties

After more than 30 years of fundamental research and development activities intermetallic titanium aluminides based on the ordered γ-TiAl phase have found applications in aerospace and automotive industries. The advantages of this class of innovative high-temperature lightweight materials are their low density, their good strength and creep properties, as well as their oxidation resistance up to 750 °C. A drawback, however, is their limited ductility at room temperature, which is reflected by a low plastic strain at fracture. Advanced engineering TiAl alloys, such as the β-solidifying so-called TNM alloy with a nominal composition of Ti-43.5Al-4Nb-1Mo-0.1B (in atomic percent), are complex multi-phase materials which can be processed by ingot or powder metallurgy, precision casting methods as well as additive manufacturing. Each production process leads to specific microstructures which can be altered and optimised by thermomechanical processing and/or subsequent heat treatments, whereby the knowledge of the occurring solidification processes and phase transformation sequences is essential. Therefore, thermodynamic calculations were conducted to predict the phase fraction diagrams. After experimental verification, these phase diagrams provided the base for the development of heat treatments to adjust balanced mechanical properties. To determine the influence of deformation and kinetic aspects, sophisticated ex- and in situ methods have been employed. Finally, the application of TiAl alloys in aerospace is reported.

Stability and failure mass of unsaturated heterogeneous slopes

Rainfall infiltration in an unsaturated soil slope induces loss of suction (and even positive pore-water pressures), which can eventually lead to failure. This paper investigates the probability and the size of failure of an unsaturated slope with spatially variable void ratio, subjected to a constant intensity rainfall. The random finite element method is employed in conjunction with a Monte Carlo simulation to stochastically evaluate the factor of safety and the size of the sliding mass. The results indicate that the mean value and the variability of these two quantities depend on both correlation length and coefficient of variation of the void ratio field. This dependency is more prominent during the transient regime than at steady states. Notably, the factor of safety in some cases can be low but the corresponding sliding mass is relatively small, while in other instances, the factor of safety might remain large though the associated sliding mass is very sizeable. The correlation between the factor of safety and the size of the sliding mass shifts from positive to negative as the rainfall progresses. A simple quadrant plot is suggested to assess the risk associated with slope failure, taking into account both the factor of safety and the size of failure, rather than the factor of safety alone as it is usually the case. The study also demonstrates an application of a numerical approach to assess stability of geostructures composed of complex multiphase materials such as unsaturated soils or frozen soils.

Analysis of Thermal Evolution of Si2U3/Al Calcined Miniplates

As part of a process called cerus for the conditioning of spent fuel elements from research reactors (which is about its immobilization in a sintered ceramic matrix of uranium oxide) were performed calcinations and sintering on an aluminum miniplate that representing a real plate from MTR fuel type, but containing natural Si2U3instead of enriched. Product of heat treatments it results a complex multi-phase material, it was studied its behavior during and after heat treatments involved in the cerus process. There were performed differential thermal analysis (DTA) in air to 1250°C, and X-ray diffraction at high temperature (700-1100°C) to elucidate which compounds were generated during the calcination and sintering and the moment when these transformations occur, and as a result there were obtained complex alloys of Al-U, and the formation of oxides of aluminum and uranium. On the other hand, tests were carried out on compacted powder of calcined miniplates in a high temperature microscope (HSM) and dilatometry to know their linear and surface response to the heating and sintering in order to characterize their individual contributions to the final material, resulting in an important expansion of about 25% which was attributed to oxidants interactions and/or formation of uranium aluminides and silicides. Several intermetallic of Si-U and Al as well as the generation of oxides of aluminum and uranium were found.