Large Compositional Space Research Articles

Explicit tangent stiffness matrix for the geometrically nonlinear analysis of laminated composite frame structures

In this paper, based on Von Kármán’s nonlinear theory and the classical lamination theory, a closed form expression is derived for the tangent stiffness matrix of a laminated composite beam element undergoing large deformation and rotation under mechanical and hygrothermal loads. Stretching, bending and torsion have been considered. A co-rotational element reference frame is used as the Updated Lagrangian (UL) formulation. The model has been verified in different problems by comparison with the results of Nastran and ANSYS composite laminate tools, and the difference in the resulting large deformations is less than 5%. The major advantage of the proposed approach is that the composite structure is modeled using 1D beam elements rather than 2D shell or 3D solid elements as in the case of Nastran and ANSYS where laminates are defined over surfaces or 3D solids. The availability of an explicit expression for the tangent stiffness matrix makes the proposed model highly efficient specially when dealing with large composite space frame structures. The saving in computational time could reach 93% compared to regular FE software packages. The developed model is very useful for modeling and designing flexible composites used in new applications such as morphing aerospace structures and flexible robots.

Designing High-Efficiency Nanostructured Two-Phase Heusler Thermoelectrics

Nanostructured systems formed by two distinct phases are particularly promising for high efficiency thermoelectrics due to the reduction in thermal conductivity afforded by the nanostructured phase. However, the choice of the matrix and nanostructured phases represents a challenging materials discovery problem due to the large compositional space involved. Heusler phase thermoelectrics are particularly promising candidates for nanostructuring since these compounds often possess favorable electronic thermoelectric properties but relatively high thermal conductivity. Here, we have developed a high-throughput screening strategy to predict promising candidates for nanostructuring systems based on two Heusler phases. Our search includes all two-phase systems involving full, half, and inverse Heusler in the Open Quantum Materials Database, in total a search space of ∼1011 possible combinations of two Heusler compounds. To reduce this space, our screening approach starts with a set of known thermoelectrics as ma...

Computationally-driven engineering of sublattice ordering in a hexagonal AlHfScTiZr high entropy alloy

Multi-principle element alloys have enormous potential, but their exploration suffers from the tremendously large range of configurations. In the last decade such alloys have been designed with a focus on random solid solutions. Here we apply an experimentally verified, combined thermodynamic and first-principles design strategy to reverse the traditional approach and to generate a new type of hcp Al-Hf-Sc-Ti-Zr high entropy alloy with a hitherto unique structure. A phase diagram analysis narrows down the large compositional space to a well-defined set of candidates. First-principles calculations demonstrate the energetic preference of an ordered superstructure over the competing disordered solid solutions. The chief ingredient is the Al concentration, which can be tuned to achieve a D019 ordering on the hexagonal lattice. The computationally designed D019 superstructure is experimentally confirmed by transmission electron microscopy and X-ray studies. Our scheme enables the exploration of a new class of high entropy alloys.

Alloy Design Based on Computational Thermodynamics and Multi-objective Optimization: The Case of Medium-Mn Steels

A new alloy design methodology is presented for the identification of alloy compositions, which exhibit process windows (PWs) satisfying specific design objectives and optimized for overall performance. The methodology is applied to the design of medium-Mn steels containing Al and/or Ni. By implementing computational alloy thermodynamics, a large composition space was investigated systematically to map the fraction and stability of retained austenite as a function of intercritical annealing temperature. Alloys exhibiting PWs, i.e., an intercritical annealing range, which when applied satisfies the given design objectives, were identified. A multi-objective optimization method, involving Pareto optimality, was then applied to identify a list of optimum alloy compositions, which maximized retained austenite amount and stability, as well as intercritical annealing temperature, while minimized overall alloy content. A heuristic approach was finally employed in order to rank the optimum alloys. The methodology provided a final short list of alloy compositions and associated PWs ranked according to their overall performance. The proposed methodology could be the first step in the process of computational alloy design of medium-Mn steels or other alloy systems.

Identification of High-CO2-Capacity Cationic Zeolites by Accurate Computational Screening

Solid porous materials such as cationic zeolites have shown great potential in energy-efficient separation processes. Conventional adsorbent design involves ad-hoc and inefficient experimental evaluation of a large structural and compositional space. We developed a computational methodology to screen cationic zeolites for CO2 separation processes with quantitative accuracy, and identified a number of novel high-performing materials. This study enabled us to develop an intuitive design workflow for selecting optimal materials and dramatically accelerate the development of industrially relevant separation processes.

Nepheline Crystallization in High-Alumina High-Level Waste Glass

ABSTRACTThe understanding of the crystallization of aluminosilicate phases in nuclear waste glasses is a major challenge for nuclear waste vitrification. Robust studies on the compositional dependence of nepheline formation have focused on large compositional spaces with hundreds of glass compositions. However, there are clear benefits to obtaining complete descriptions of the conditions under which crystallization occurs for specific glasses, adding to the understanding of nucleation and growth kinetics and interfacial conditions. The focus of this work was the investigation of the microstructure and composition of one simulant high-level nuclear waste glass crystallized under isothermal and continuous cooling schedules. It was observed that conditions of low undercooling, nepheline was the most abundant aluminosilicate phase. Further undercooling led to the formation of additional phases such as calcium phosphate. Nepheline composition was independent of thermal history.

High-Throughput Development of Amphiphile Self-Assembly Materials: Fast-Tracking Synthesis, Characterization, Formulation, Application, and Understanding

Amphiphile self-assembly materials, which contain both a hydrophilic and a hydrophobic domain, have great potential in high-throughput and combinatorial approaches to discovery and development. However, the materials chemistry community has not embraced these ideas to anywhere near the extent that the medicinal chemistry community has. While this situation is beginning to change, extracting the full potential of high-throughput approaches in the development of self-assembling materials will require further development in the synthesis, characterization, formulation, and application domains. One of the key factors that make small molecule amphiphiles prospective building blocks for next generation multifunctional materials is their ability to self-assemble into complex nanostructures through low-energy transformations. Scientists can potentially tune, control, and functionalize these structures, but only after establishing their inherent properties. Because both robotic materials handling and customized rapid characterization equipment are increasingly available, high-throughput solutions are now attainable. These address traditional development bottlenecks associated with self-assembling amphiphile materials, such as their structural characterization and the assessment of end-use functional performance. A high-throughput methodology can help streamline materials development workflows, in accord with existing high-throughput discovery pipelines such as those used by the pharmaceutical industry in drug discovery. Chemists have identified several areas that are amenable to a high-throughput approach for amphiphile self-assembly materials development. These allow an exploration of not only a large potential chemical, compositional, and structural space, but also material properties, formulation, and application variables. These areas of development include materials synthesis and preparation, formulation, characterization, and screening performance for the desired end application. High-throughput data analysis is crucial at all stages to keep pace with data collection. In this Account, we describe high-throughput advances in the field of amphiphile self-assembly, focusing on nanostructured lyotropic liquid crystalline materials, which form when amphiphiles are added to a polar solvent. We outline recent progress in the automated preparation of amphiphile molecules and their nanostructured self-assembly systems both in the bulk phase and in dispersed colloidal particulate systems. Once prepared, we can structurally characterize these systems by establishing phase behavior in a high-throughput manner with both laboratory (infrared and light polarization microscopy) and synchrotron facilities (small-angle X-ray scattering). Additionally, we provide three case studies to demonstrate how chemists can use high-throughput approaches to evaluate the functional performance of amphiphile self-assembly materials. The high-throughput methodology for the set-up and characterization of large matrix in meso membrane protein crystallization trials can illustrate an application of bulk phase self-assembling amphiphiles. For dispersed colloidal systems, two nanomedicine examples highlight advances in high-throughput preparation, characterization, and evaluation: drug delivery and magnetic resonance imaging agents.

Microrheology of biomaterial hydrogelators

Microrheology uses the motion of dispersed colloidal probe particles to measure the viscosity or viscoelastic moduli of soft materials. The distinct advantages of microrheology include small sample volume requirements, access to a large range of time scales for the dynamic response and short acquisition times. These advantages make microrheology important for studies of biomaterial hydrogelators. Recent advances have enabled the precise characterization of hydrogelator sol–gel transitions, measurements of rare and scarce materials and high-throughput screening of hydrogel rheology over a large composition space. In this review, we focus on multiple particle tracking microrheology, including the considerations that define its operating regimes and its recent applications. Those interested in biomaterial rheology will find these methods as accessible as bulk rheological measurements and straightforward to implement in their own work.

Research on Manufacture and Test of Advanced Composite Material Flange

Due to the problems of potential corrosion and thermal expansion differences between traditional metal connecting pieces and carbon fiber poles, it is difficult for them to meet the operating requirements of truss structures in the environment of stratosphere. Based on the large scale composite space truss structure of stratosphere aerostats, the carbon fiber flange connection joints were studied in the present paper. Adopting the three-dimensional full five- directional braiding technology, Toray T700S - 12K carbon fiber is used as the raw material to manufacture flange joint preform, and to manufacture flange forming by RTM(resin transfer molding) process. As demonstrated by tensile and bending tests, the composite flange joints have better mechanical properties than flanges manufactured by aviation aluminum alloy, and meet requirements of stratosphere truss structure connecting pieces. In conjunction with the results of finite element analysis, mechanical properties can be further enhanced by the improvements of the braiding process, the forming process and the physical dimension.

Epitaxial growth of CoxMnySiz (111) thin films in the compositional range around the Heusler alloy Co2MnSi

Epitaxial growth and structural properties of CoxMnySiz thin films on Ge (111) substrates, including the Heusler alloy Co2MnSi (111), have been studied using combinatorial molecular beam epitaxy (MBE) techniques. In situ reflection high energy electron diffraction and ex situ x-ray diffraction experiments show that high quality coherent MBE growth with fcc (111) stacking can be achieved over a relatively large composition space that includes Co2MnSi. The highest structural and chemical ordering is observed near the composition of Co0.63Mn0.14Si0.23 rather than that at the Heusler stoichiometry of Co2MnSi. The in-plane crystallographic axis of the fcc film exhibits a 60° rotation with respect to that of the Ge substrate. The rotation appears to be originated at the film-substrate interface, as a result of the symmetry and stacking of the Ge (111) surface reconstruction.

New Compounds Consisting of Turbostratic Intergrowths: Ultra-low Thermal Conductivities and Tunable Electric Properties

ABSTRACTA recently discovered synthetic route to new kinetically stable [(MSe)y]m[TSe2]n layered intergrowths has been applied to prepare several different compositions (M = Pb or Sn, T = Ta, Nb, Mo, or W) with m = n = 1, in thin film form. Scanning transmission electron microscopy and synchrotron X-ray diffraction show the nanostructure of these materials is characterized by a combination of in-plane component crystallinity with misregistration and rotational mis-orientation between adjacent layers. Extremely low cross-plane thermal conductivity as low as 0.1 W m-1 K-1 are attributed to the turbostratic nanostructure. By appropriate choice of M and T, we demonstrate that a range of electrical transport properties are possible, from metallic to semiconducting. Annealing (PbSe)0.99WSe2 and (PbSe)1.00MoSe2 specimens in a controlled atmosphere of PbSe or WSe2 is observed to systematically influence carrier properties, and is interpreted in terms of reduction of the concentration of electrically active defects. Considering these observations and the large composition and structural space that can be explored in such [(MSe)y]m[TSe2]n intergrowths, these materials are of interest for further investigation as potential thermoelectric materials.

The Manufacture and Test of Advanced Composite Material Flange

Due to the problems of potential corrosion and thermal expansion differences between traditional metal connecting pieces and carbon fiber poles, it is difficult for them to meet the operating requirements of truss structures in the environment of stratosphere. Based on the large scale composite space truss structure of stratosphere aerostats, the carbon fiber flange connection joints were studied in the present paper. Adopting the three-dimensional full five-directional braiding technology, Toray T700S – 12K carbon fiber is used as the raw material to manufacture flange joint preform, and to manufacture flange forming by RTM(resin transfer molding) process. As demonstrated by tension tests, the composite flange joints have equivalent mechanical properties with flanges manufactured by common aviation aluminum alloy, and meet requirements of stratosphere truss structure connecting pieces.

Alloys-By-Design: Application to nickel-based single crystal superalloys

Design rules are proposed by which the compositions of nickel-based single crystal superalloys can be chosen systematically, using models for the most important characteristics: creep resistance, microstructural stability, castability, density and cost. Application of the rules allows the very large compositional space to be reduced to just a few ideal compositions, which are likely to be close to the optimal ones. The procedures have the potential to remove much of the traditional reliance placed upon empiricism and trial-and-error-based testing. It appears that trade-offs must be accepted, however; for example, the most creep-resistant alloys are more dense, more costly and more inherently susceptible to casting-related defects such as freckles during processing. Compositions suitable for both jet propulsion and land-based applications are proposed, for future experimental testing.

A novel combinatorial approach for understanding microstructural evolution and its relationship to mechanical properties in metallic biomaterials

The new generation of metallic biomaterials for prosthesis implantation (orthopedic and dental) typically have a Ti base with fully biocompatible alloying additions such as Nb, Ta, Zr, Mo, Fe and Sn. While the binary Ti–Ta and the ternary Ti–Nb–Ta systems are promising, the large composition space afforded by these systems offers tremendous scope in terms of alloy design via optimization of alloy composition and thermomechanical treatment. In the present paper a novel combinatorial approach has been developed for rapidly exploring the microstructural evolution and microstructure–microhardness (or elastic modulus) relationships in these systems. Using directed laser deposition, compositionally graded alloy samples have been fabricated and subsequently heat-treated to affect different microstructures in terms of the volume fraction and distribution of the α phase in the β matrix as a function of composition. Subsequently, composition-specific indentation-based hardness and modulus information has been obtained from these graded samples, and the resulting data have been used to develop relationships between the composition, microstructure and mechanical properties. Such rapid combinatorial assessments can be very useful in optimizing not only the alloy composition but also the desired microstructure for achieving the best combination of properties for specific orthopedic or dental applications.

Combinatorial study of Ni–Ti–Pt ternary metal gate electrodes on HfO2 for the advanced gate stack

The authors have fabricated combinatorial Ni–Ti–Pt ternary metal gate thin film libraries on HfO2 using magnetron co-sputtering to investigate flatband voltage shift (ΔVfb), work function (Φm), and leakage current density (JL) variations. A more negative ΔVfb is observed close to the Ti-rich corner than at the Ni- and Pt-rich corners, implying smaller Φm near the Ti-rich corners and higher Φm near the Ni- and Pt-rich corners. In addition, measured JL values can be explained consistently with the observed Φm variations. Combinatorial methodologies prove to be useful in surveying the large compositional space of ternary alloy metal gate electrode systems.

Applications of combinatorial methods in catalysis

With rising economic demands for higher efficiency and productivity in research and development, combinatorial catalysis is increasingly being implemented to bring more catalysts per unit time to the marketplace. High-throughput automated synthesis and advanced screening technologies are now being applied to the discovery of more efficient homogeneous as well as heterogeneous catalysts and materials. The combinatorial process allows the exploration of large and diverse compositional and parameter spaces by establishing an integrated workflow of rapid parallel or combinatorial synthesis of large numbers of catalytic materials, subsequent high-throughput assaying of these compounds and large-scale data analysis. The number of experiments that can be screened has risen by orders of magnitude resulting in a much higher probability of discovering new catalysts or materials. The goal of this review is to provide an overview of selected advances that have been made in this rapidly growing field in both academia and industry over the past several years.

Finite-element model for the thermoelastic analysis of large composite space structures

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.