Large-block Structure Research Articles

Enhancement of Microstructure and Mechanical Properties of High Nb-TiAl Alloys Prepared Using Laser Additive Manufacturing by Annealing Treatment

The microstructure, phase composition, hardness, and tensile properties of the Ti-48Al-2Cr-5Nb alloy have been systematically investigated using laser additive manufacturing technology. Results indicate that both the as-deposited and annealed microstructures contain both the α2 (Ti3Al) and γ (TiAl) phases. As the annealing temperature increased, the structure changed significantly from a large block structure to a fine equiaxed structure and finally to a large lamellar structure. Nevertheless, the amount and distribution of precipitation of α2 phase are obviously different, especially during the annealing at 1260 °C, where the fine α2 phases are evenly distributed on the γ phase matrix. The hardness value of the as-deposited sample is the highest, with a HV value of 484 at the room temperature, while the hardness value of the annealed sample at 1260 °C is the smallest, with a HV value of 344. An annealed sample at 1260 °C exhibits the highest tensile strength and elongation at room temperature, with values of 598 MPa and 2.1%, respectively. These values are increased by 1.15 times and 1.4 times compared to the as-deposited sample (519 MPa, 1.5%).

Interactive generation of new knowledge based on automatic means of logical inference

The work relates to the field of knowledge representation and algorithmization of their processing. To describe the subject of consideration by a set of statements and their processing, logical means of the first order type are used. Unlike the well-known achievements in the field of automatic proof (AP) in formal axiomatic theories, the automatic text synthesis of statements is complicated by the poor formalizability of the value of knowledge concept contained in the text. Based on the development of the calculus of positively-formed standardized formulas (pfs-formulas) the possibilities of analysis automation of the description of the subject matter and interactive generation of meaningful statements to improve this description are investigated. The proposed method of interactive knowledge generation integrates the capabilities of AP with algorithmized human-machine synthesis of new knowledge texts. AP in the calculus of pfs-formulas helps a person not only in the analysis of properties, but also in the choice of the required properties of the description of the subject matter. When the absence of a property desirable for a person in the analyzed knowledge is revealed by means of AP, the hypotheses is formed that logically guarantees the presence of the required property. Variants of hypotheses are automatically synthesized in a preliminary form, which are then refined interactively to improve the content of the generated text of new knowledge. The rules of synthesis are justified. Their application continues the inference in situations of inapplicability of the basic rule of inference in the calculus of pfs-formulas. The extension of calculus by the rules of synthesis transforms it as a first-order calculus of the deductive type into a means of deductive-abductive inference, which differs from the known works using abduction by the absence of a number of restrictions. Illustrative examples demonstrate the representation, analysis and generation of knowledge. These examples also show in interactive knowledge processing the importance of visualization of the processed text, provided by the large-block structure of pfs-formulas constructed from typical quantifiers. In conclusion, the results of the paper and possible directions for the development of the results are formulated.

Study on the in vitro digestion process of green wheat protein: Structure characterization and product analysis.

In this study, the in vitro digestion process of green wheat protein (GWP) was explored by simulating the gastrointestinal digestion. The digestibility of GWP was 65.23%, and was mainly digested by trypsin. During the digestion process of GWP, large‐size particles are digested by pepsin, and medium‐sized particles are digested by trypsin into smaller particles; irregular large block structure with smooth surface was gradually turned into smaller blocks with porous surface; and the spatial conformation was loosened mainly by the unfolding of β‐sheet structure. Gel electrophoresis demonstrated that HMW glutenin and ω‐gliadins in GWP were completely digested, while LMW glutenin and α/β/γ‐gliadins were partially digested. Additionally, the peptide lengths were relatively dispersed after pepsin digestion. Most of the peptides (76.5%) fell into the range 3–15 amino acid after pepsin and trypsin digestion. The molecular weight (MW) of most pepsin digestion products was above 2000 Da, whereas the MW of trypsin digestion products was mainly concentrated in 500–2000 Da. Besides, the sensitizing peptide sequence of wheat protein was detected in the final digestion products of GWP. This research provided a theoretical guidance for the development and application of GWP.

WAAM process for metal block structure parts based on mixed heat input

Additive manufacturing based on robotic welding is used for the manufacture of metal parts by applying an arc as a heat source and wire as feedstock. The process is known as wire arc additive manufacturing (WAAM). However, the current WAAM process has a limitation in fabricating block structure components with high geometry accuracy and consistent welding due to the process complexity and the lack of appropriate process planning methods. Furthermore, common defects such as voids, gaps, and collapse decrease the mechanical properties of the final product. This paper presents a novel process planning method based on a mixed heat input (MHI) strategy to minimize voids and collapse defects that occur in fabricating large block structure components while maintaining a high manufacturing efficiency. By separating each layer into boundary layers and inner layers, the MHI method applies various heat input conditions at different positions of the layer allowing the construction of defect-free components. The performance of this method is shown in a validation study considered as the fabrication of a regular structure component. To evaluate the mechanical properties of the deposited sample, the hardness and microstructure are reported and compared with the conventional WAAM process. Then, the MHI strategy is applied to the manufacturing of a large block structure component with a similar structure as the validation study. Furthermore, the robustness of the proposed MHI strategy in fabricating complex geometric parts is evaluated by two case studies. The results show that such strategy succeeds in achieving high production efficiency and quality simultaneously.

In a Field of Party Walls

When Deng Xiaoping initiated market reforms in 1978, reopening the country and inviting the newest phase of foreign investment in Chinese cities, the structure and scale of these cities changed dramatically. Today, the governing process rewards the official who can most rapidly transform his or her city into guoji dadushi , a “great international city.”1 With an unprecedented release of capital,2 China has built more—more skyscrapers and high-rises, more housing and malls, more rail systems and highways—than any other country in a thirty-year period.3 In Shanghai, the traditional lilong (alleyway or lane) housing compounds are being replaced by new gated communities of luxury housing towers surrounded by landscaped parks or paved parking (Figure 1). Widened streets, elevated highways, and spiraling approach ramps to suspension bridges impose a new, vehicular, logic on the city (Figure 2). On its expanding edges, rows upon rows of repetitive housing blocks are organized by an economic logic of mass reproduction and the strict daylight standards that govern the spacing of buildings to ensure that sunlight penetrates residential spaces. Along what were once tow roads running beside canals, new shopping malls have organized their indoor public spaces according to the logic of retailing rather than that of public streets. Figure 1 Aerial view of Shanghai, 2004 (author’s photo) Figure 2 Aerial view of Puxi from Pudong, 2012. The sense of the Huangpu River in the city is now understood only from the heights of new skyscrapers (author’s photo) Developers, to ensure that each project announces itself as an icon, intentionally dissociate it from its surrounding context. Each building is a discrete object whose separation from other buildings is more important than the relation between them. Spaces between buildings are undefined and cars dominate public space. Urbanism is fragmented as identity is transferred from the city to its …

Structure and evolution of the Earth’s crust in the region of junction of the Central Asian Fold Belt and the Siberian Platform: Skovorodino–Tommot profile

An integrated geological and geophysical study was performed to investigate the region of junction of the eastern part of the Central Asian Fold Belt and the Siberian Platform in the Skovorodino–Tommot 3-DV reference profile line (52°–60° N, 122°–129° E), where the belt is separated from the Aldan–Stanovoi Shield of the Platform by a series of deep faults. The main results are as follows: Seismic, density, and geoelectric characteristics of rocks were obtained and used to determine (refine) the intracrustal boundaries of tectonic structures; large-block structure of the Earth’s crust, caused by mantle faults, and the difference between the layered structure of the crust for the shield and fold regions were established; and available paleomagnetic data were used to perform palinspastic reconstructions for 180 and 140 million years, the most productive metallogenic epoch in the region, coeval with collision processes at the closure of the Mongol-Okhotsk paleobasin.

Studying defect structure of GaN epilayers by means of three-beam X-ray diffraction analysis

X-ray multiple diffraction in epitaxial films of GaN with various densities of dislocations has been measured using Renninger scans for a primary forbidden (0001) reflection. The angular widths of three-beam diffraction peaks measured in both φ scans (rotation about the normal to the sample surface) and θ scans (rotation about the Bragg angle) have been analyzed. It is established that the three-beam Renninger diffraction peaks exhibit splitting due to a large-block structure of epilayers. For some three-beam combinations, the half-width (FWHM) of θ scan peaks is highly sensitive to the dislocation density.

Structure and microhardness of rapidly solidified Al-Ni-Cr alloys

Al-Ni-Cr foils prepared by rapid quenching from the liquid state are studied. The surface of the foils is found to have a cellular morphology, with a microcrystalline, large-block structure and (111) texture. The effect of annealing on the microhardness of the foils is analyzed. The aging behavior of the microhardness is shown to depend on the Ni/Cr ratio.

Navier-Stokes Computations for Body/Cruciform Grid Fin Configuration

A grid fin is an unconventional aerodynamic lifting and control device consisting of an outer frame with internal grid framework of small chord. The present study performs the Navier-Stokes computations of turbulent flowspast 1) a grid fin alone and 2) fin/body combination shapes at Mach numbers of 2.5 and 0.7. This work designs a procedure to generate a structure grid with a simple and efficient algorithm combining block-off and multiblock methods for the complex configurations. Full Navier-Stokes equations with a pointwise version of the Baldwin-Barth one-equation turbulence model are discretized into finite difference form and solved by an algorithm in a fully coupled, implicit, and large block structure, and the solution algorithm achieves satisfactory convergence. The comparisons between computations and experimental data are made, and the detailed flow structure near grid fins can be obtained and examined.

Computations using the preconditioning BI-CGSTAB algorithm in chemical non-equilibrium problems

A robust method for solving the chemical non-equilibrium Navier-Stokes equations, including all of the species conservation and energy production equations, is developed. The algorithm is embodied in a fully coupled, implicit, large block structure. Van Leer flux splitting for inviscid terms and central differencing for viscous terms in the explicit operators are applied in the numerical algorithm. The fully-coupled system is solved implicitly and the bi-conjugate gradient stable (Bi-CGSTAB) method with a preconditioner of incomplete lower-upper (LU)-factorization (ILU) is used for solving large block structure and diagonal dominate matrix equations. The computations are performed for the hypersonic inflow over blunt bodies including half cylinder, double ellipse and blunt nose. The adaptive grid constructed by moving grid method is employed to capture the shock location. Computational results in the present study are compared with other calculated data and exhibit good agreement. Convergence histories of the mean flow variables and species equations demonstrate that the fast convergent rate can be achieved by the preconditioned Bi-CGSTAB method

Earthquakes and large block monumental structures

A review of a research program developed in the last fen years into the dynamics of large block structure is presented. The many aspects which characterize the structural behaviour and determine the complexity of the consequent dynamics are briefly discussed. The preliminary mechanical models and first results obtained are also analyzed; they allow to define the direction of the main object of the research in progress.

Flux-split algorithms for flows with non-equilibrium chemistry and vibrational relaxation

The numerical computation of gas flows with non-equilibrium thermodynamics and chemistry is considered. Several thermodynamic models are discussed, including an equilibrium model, a general non-equilibrium model, and a simplified model based upon vibrational relaxation. Flux-splitting procedures are developed for the fully-coupled inviscid equations involving fluid dynamics, chemical production, and internal energy relaxation processes. New forms of flux-vector split and flux-difference split algorithms valid for non-equilibrium flow, are embodied in a fully coupled, implicit, large-block structure. Several numerical examples in one space dimension are presented, including high-temperature shock tube and nozzle flows.

The computation of non-equilibrium, chemically-reacting flows

A finite-volume method for the numerical computation of flows with non-equilibrium thermodynamics and chemistry is presented. Flux-splitting procedures are developed for the fully-coupled equations involving fluid dynamics, chemical production and thennodynamic relaxation processes. An analysis of the governing equations is performed, whereby theoretical conditions are developed under which the Euler equations retain the homogeneity property, F = AQ, where F is the flux-vector, Q is the vector of conservative dependent variables (including all the species densities and vibrational energies), and A is the Jacobian matrix ∂F/ ∂Q. This property, previously only shown to exist for thermally perfect gases, is utilized in the development of flux-split algorithms for non-equilibrium flows. These algorithms have been recently shown to give very accurate and robust solutions for high speed flows in chemical equilibrium. The analysis presented here develops new forms of flux-vector-split and flux-difference-split algorithms for flows with non-equilibrium thermodynamics and chemistry. The algorithms may be embodied in a fully-coupled, implicit, large-block structure, including all the species conservation and energy production equations. Several numerical examples are presented, including high-temperature shock tube and nozzle flows. The methodology is compared to other existing techniques, including spectral, implicit central-differenced and uncoupled procedures, and favorable comparisons are shown regarding accuracy, shock-capturing and convergence rates.