Ta-based refractory alloys offer excellent high-temperature strength, but high W content significantly reduces room-temperature tensile ductility. Here for Ta-14W alloy with fracture strain of ∼5%, we demonstrate that a minor Hf addition significantly improves its ductility to over 30%. Firstly, Hf induces an asymmetric core structure of screw dislocation and reduces generalized stacking fault energy (GSFE), thereby promoting dislocation mobility and dislocation multiplication during plastic deformation. Secondly, Hf can strengthen grain boundaries (GBs) by preferentially segregating near GBs. Thirdly, Hf binds with O atoms to form HfO2 particles at GBs, lowering the risk of oxygen embrittlement. All these mechanisms offer insightful guide for the development of advanced Ta-W-based refractory alloys.
Materials of engineering and construction. Mechanics of materials
This study develops a progressive optimal fault-tolerant control method based on insufficient fault information. By combining passive and active fault-tolerant control manners during the process of fault diagnosis, insufficient fault information is fully used, and optimal fault-tolerant control effect is achieved. In addition, the fault-tolerant control method based on guaranteed robust cost control is introduced. The proposed progressive optimal fault-tolerant control method considers two aspects. First, as the amount of fault information continually increases, the performance index of the progressive optimal fault-tolerant controller improves. Second, at each moment, based on the corresponding insufficient fault information and prior knowledge, optimal fault-tolerant control is achieved according to current fault information. The process of progressive optimal fault-tolerant control converges to active fault-tolerant control when the fault is completely identified, and the optimal fault-tolerant controller is no longer reconfigured until no more useful fault information can be provided. Furthermore, a progressive optimal fault-tolerant control algorithm based on the grid segmentation in the parameter uncertainty domain and the selection of different auxiliary center points is introduced. Simulation results verified the feasibility of the proposed algorithm and the validity of the proposed theory.
Materials of engineering and construction. Mechanics of materials, Production of electric energy or power. Powerplants. Central stations
Lorenzo Bonetti, Daniele Natali, Stefano Pandini
et al.
This paper introduces a novel approach to 4D printing tailored structures with reversible two-way shape-memory effect (SME) through material extrusion technology. To this aim, methacrylated poly(ε-caprolactone) (PCL) was synthesized and evaluated from a rheological perspective to determine its suitability for extrusion-based printing. Following a printability assessment, an optimal set of parameters was identified to fabricate 3D structures, UV-crosslinked during printing. Subsequently, a physical and thermo-mechanical characterization of the printed structures was conducted to deepen the understanding of the fabrication process and properties of the obtained structures. To assess the shape-memory properties of the printed structures, both the one-way and two-way SME under load were investigated. Overall, this study opens the floodgates to implementing 4D printing via material extrusion technology, specifically targeting PCL-based semi-crystalline chemically crosslinked polymer networks with two-way SME. Because of its cost-effectiveness, versatility, and user-friendly nature, extrusion-based printing offers noteworthy advantages over other additive manufacturing approaches when reversible behavior of the printed structures is needed. Lastly, a glimpse of potential 4D printed structures from PCL-based semi-crystalline chemically crosslinked polymer networks is presented. The approach described holds significant promise across multiple research and industrial domains, including but not limited to smart actuators, soft robotics, and medical devices.
Materials of engineering and construction. Mechanics of materials
Islet transplantation is a promising strategy for diabetes mellitus treatment as it can recapitulate endogenous insulin secretion and provide long-term glycemic control. Islet models constructed in biomaterial scaffolds that reproduce biological characteristics of native islets is a feasible option to circumvent the dilemma of donor shortage and the requirement of chronic immunosuppression. Herein, we developed bioinspired artificial microcapsule-based islet models with microvessels for glycemic control using microfluidic electrospray strategy. Microfluidic electrospray can generate uniform hydrogel microcapsules with core-shell structure for encapsulating islet cells. The cell-laden microcapsules enabled the efficient transportation of nutrient, oxygen, and insulin; as well as the incorporation with microvessels for prompting glucose responsiveness and molecular exchange. We demonstrated by in vivo experiments that the blood glucose, food intake, and body weight of diabetic mouse models were alleviated, and the glucose tolerance was promoted after the engraftment of islet microcapsules. We further demonstrated the improved functionality of transplanted islet model in insulin secretion, immune escape, and microcirculation using standard histological and molecular analysis. These results indicated that the microcapsules with microvessels are promising artificial islet models and are valuable for treating diabetes.
Materials of engineering and construction. Mechanics of materials
As an important means to study the mechanical properties and failure mechanism of rock materials and engineering mechanics, damage mechanics is often used to assist in the analysis of the failure process and mechanism of rock, metal, and other materials in the current research. In the use of damage mechanics to study the properties of rock materials and explore the deformation and failure law of rock, important research results have been achieved. The research methods of damage mechanics can be roughly divided into three types: statistical damage model, mesoscopic damage model, and continuous damage model. Based on the existing literature in hand, according to the division of damage mechanics research methods in the academic community, this paper collates and considers that the existing damage model construction can be summarized from the mechanical point of view. The pure theory is derived or fitted from the mathematical point of view. One of them is derived from the mechanism point of view, and the other is derived from the phenomenon point of view. The stress, strain, acoustic emission, and other data are analyzed and reconstructed, and both have advantages and disadvantages.
Alassane Compaoré, Moustapha Sawadogo, Youssouf Sawadogo
et al.
The paper describes lightweight-foamed concretes (LFC) that were formulated from cement, natural sand, and foam from a foaming agent with densities of 600 and 700 kg/m3. The identified mineral phases in the cement are alite, belite, Celite, ferrite, calcite, and gypsum. The obtained foamed concretes have a porosity varying from 29.17 to 37.14 vol%, a thermal conductivity below 0.2 W/m.K, and a mechanical strength greater than 2 MPa. At 28 days setting, the relative quantities of crystalline and amorphous phases were identified by XRD and DTA/TG. These techniques allowed to show the importance of the carbonation process and hydrated phases formation on the macroscopic strength increase. The microstructural characterization by image analyses evidences that when the density decreases, growth of both crystalline and amorphous phases in the bubble walls during setting is a mean of compensating the role of density in strength.
Materials of engineering and construction. Mechanics of materials
Georg Winkens, Alexander Kauffmann, Johannes Herrmann
et al.
Abstract Mo-Ti alloys form solid solutions over a wide range of compositions, with lattice misfit parameters increasing significantly with titanium content. This indicates a strong increase in the critical stress for edge dislocation motion. Here, we probe the transition from screw to edge dislocation-dominated strengthening in Mo-Ti solid solutions with titanium content up to 80 at%. The alloys were scale-bridging characterized to isolate the impact of substitutional solid solution strengthening. Mechanical testing yielded no significant influence of grain boundaries or grain orientation. The results were corrected for the strengthening by unavoidable interstitial oxygen. Modelling of screw and edge dislocation-controlled solid solution strengthening was applied to the results to evaluate the contributions of both dislocation types. The analysis reveals that screw dislocation motion controls the strength in allows with less than 40 at% titanium, while edge dislocation motion provides comparable strength for 60–80 at% titanium. These results in a system of reduced chemical complexity support the recent investigations of edge dislocation-controlled strengthening found in high-entropy alloys.
Materials of engineering and construction. Mechanics of materials
Johannes L. Otto, Lukas M. Sauer, Malte Brink
et al.
Nickel-based filler metals are frequently used in high temperature vacuum diffusion brazing for austenitic stainless-steel joints when components are subjected to high static or dynamic loads, corrosive environments and elevated temperatures. Due to melting point depressing metalloids such as silicon and boron, hard and brittle intermetallic phases are formed during the brazing process depending on the diffusion mechanisms. These brittle phases significantly affect mechanical and corrosive properties of the compounds. To quantify the influences of their amount, morphology and distribution, deep learning image segmentation was applied to segment these phases of the athermal solidification zone and the diffusion zone. Subsequently, characteristic microstructure parameters were calculated from these. The parameters of six different brazed joint variations were compared with their experimental characterization of mechanical and corrosive properties so that several correlations could be identified. Finally, a layer-by-layer removal of a brazed joint was performed using a focused ion beam, and a 3D model was reconstructed from the generated images to gain a mechanism-based understanding beyond the previous 2D investigations.
Materials of engineering and construction. Mechanics of materials
New building materials and products in construction and reconstruction, which improve the performance and efficiency characteristics of buildings, reduce material consumption, cost and labor intensity, are always relevant. A promising direction for further development of composite materials is the employment of pre-bound aggregate materials. Their production is a two-stage process, which involves at first creating an optimal aggregate mix and gluing the grains to each other and secondly filling the voids of the obtained aggregate framework with a high-workability matrix. Presented research is an experimental investigation of physical and technical properties of pre-bound aggregate composite materials. Composites with complex binders are also considered in this study. In such cases, the aggregate framework and the grouting matrix were made of binders of different nature, which are incompatible when the components are mixed ordinarily. When studying composites, a complex of physical and mechanical methods was used. Improvement of physical and mechanical properties of framework composites in comparison with composites obtained according to conventional techno- logy has been established. These advantages are identified primarily for such properties as deformability, impact strength, creep.
Nor Azirah Mohd Fohimi, Koay Mei Hyie, Salina Budin
et al.
Air pollution is a major environmental risk to health. The new building normally has a facing problem with indoor air pollutant. New construction materials and furniture will contribute higher contaminants compared to old materials. The effect of indoor air pollutants can result in human health problems, discomfort and reduces their productivity. The purpose of this present work is to experimental study the indoor air pollution status regarding carbon dioxide, carbon monoxide, volatile organic compounds, and formaldehyde concentration in an administration office at the new building faculty of mechanical engineering in Johor Bahru, Malaysia. The contaminants concentration values are investigated through field measurements and then compared to the limits stated in the Occupational Safety and Health Act standard. The field measurement of contaminant concentration level was conducted at the intersect plane between the vertical plane at the center of the air conditioning diffuser and the horizontal plane at 1.2 m from the floor. The contaminant concentration readings were taken at 6 locations inside the office. The data were conducted during actual working conditions. The reading of contaminants concentration is taken in 30 minutes. One minute is equal to one number of samples. It was found that only the formaldehyde concentration is exceeding the maximum limit.
Advances in multi-material 3D printing technologies are enabling the construction of advantageous engineering structures for diverse applications. Multi-material printing allows the combination of contrasting engineering materials in a single part to gain synergistic performance increases. Cellular structure such as honeycomb structures provide high-energy absorption to weights ratio that could benefit through multi-material strategies for tailored responses in applications such as design of helmets and prosthetics. In this study, we investigate the compressive response and the energy absorption for combinations of acrylonitrile butadiene styrene (ABS) and thermoplastic polyurethane (TPU) printed lattices. Results demonstrate energy absorption increases from pure TPU samples of 2.18kN.mm in a non-linear fashion to pure ABS samples of 11.47kN.mm as bands of TPU are added to ABS. Splitting a single band of TPU into multiple bands with the same total thickness changes the behavior of first and second peak before densification. Testing with in-plane loading demonstrated more similar behavior among the differently designed multi-material lattices, with collapsing occurring with sequential failures of unit cell rows. These results demonstrate the feasibility in constructing multi-material lattice systems with ABS and TPU combinations, while highlighting their benefits for enabling controlled energy absorption and deformation responses based on designed material combinations.
Currently, the construction of buildings made of monolithic concrete and reinforced concrete is becoming increasingly relevant. The use of innovative technologies, minimum construction time, durability, reliability, the ability to perform work in various climatic conditions, architectural individuality contribute to the development of monolithic construction. Concrete and reinforced concrete are the main materials of modern construction. The quality of structures depends not only on the composition of concrete, the amount of portland cement, the chemical additives used, the water-cement ratio, the quality of fillers, etc., but also significantly on the heat and humidity regime of concrete holding. To ensure the necessary temperature conditions for hardening and strength gain of concrete, various methods of heating structures are used. One of the methods of concrete care is thermal processing during the hardening period and the acquisition of critical or design strength. The aim of the study is to improve the technology of erection of monolithic concrete and reinforced concrete structures using thermal processing of concrete by means of infrared radiation. The technology of thermal processing of the laid and compacted concrete mixture using infrared heating and a two-chamber transparent shelter for infrared rays has been developed. The obtained results permit us to provide conditions for the normal course of the chemical reaction of hydration, hardening and strength gain. This allows successfully solve the problems of concreting in the erection of buildings and structures made of monolithic concrete and reinforced concrete.
Relevance. In recent years, composite materials have become widespread in the construction of reinforced concrete structures for industrial, civil and transport structures. It is proposed to strengthen the reinforced concrete structures of hydraulic structures with prestressed basalt composite rebar. It took an experimental and theoretical substantiation of technical solutions to strengthen the reinforced concrete structures of hydraulic structures with prestressed basalt composite reinforcement. The aim of the work was to carry out a set of experimental and theoretical studies of the stress-strain state and internal forces in low-reinforced concrete structures of hydraulic structures reinforced with prestressed basalt composite rebar. Methods. Experimental studies of the stress-strain state and internal forces were carried out on the basis of low-reinforced concrete beam-type models with interblock construction joints, harden with prestressed basalt composite reinforcement in the stretched (compressed) zones of the models. Theoretical studies of the stress-strain state and internal forces were carried out on the basis of the theory of reinforced concrete and structural mechanics. Results. As a result of the research carried out on typical low-reinforced concrete structures of hydraulic structures with interblock construction joints, the main stages of the stress-strain state of hydraulic reinforced concrete structures were formulated. Based on the data of experimental and theoretical studies, taking into account the reinforcement with prestressed basalt composite rebar, as well as with prestressed clamps in the shear zone, a method was developed for calculating the strength of low-reinforced hydrotechnical reinforced concrete structures with interblock construction joints.
Sina Sadighikia, Albert Grau‐Carbonell, Tom A.J. Welling
et al.
Abstract Understanding the chemical structure of rod‐shaped silica colloidal particles is attainable by investigating their etching mechanism in solution. Liquid Cell (Scanning) Transmission Electron Microscopy (LC‐(S)TEM) is a promising technique through which the etching of these particles can be observed in real time, and at the single particle level, without possible deformations induced by the surface tension of dried particles. However, the presence of high energy electrons, and the different geometry in LC experiments may alter the conditions of in situ experiments compared to their ex situ counterparts. Here we present a controlled low‐dose LC‐STEM study of the basic etching process of micron‐sized silica rods that are immobilized on the SiN window of a liquid cell. The results show that using low‐dose imaging conditions, combined with a low accumulated electron dose, and optimized flow rates of solutions allow for investigation of the chemical etching mechanism of silica colloidal particles using the LC‐(S)TEM technique with negligible effects of the electron beam. A comparison of ex situ etching experiments with LC‐STEM observations show that the LC geometry can play a crucial role in LC‐STEM experiments where the diffusion of the etching particles is important, which should be considered during the interpretations of LC‐STEM results.
Materials of engineering and construction. Mechanics of materials
António J. Arsénio, Francisco Ferreira da Silva, João F. P. Fernandes
et al.
This document presents a study on the optimization of the 3D geometry of a horizontal axis radial levitation bearing with zero-field cooled (ZFC) high-temperature superconductor (HTS) bulks in the stator, and radially magnetized permanent magnet (PM) rings in the rotor. The optimization of component dimensions and spacing to minimize the volume or cost concerning only the maximization of the levitation force was previously studied. The guidance force and guiding stability depend on the spacing between PM rings in the rotor and between the rings of HTS bulks in the stator. This new optimization study aims to find the optimum spacing that maximize the guidance force with given HTS bulk and PM ring dimensions while maintaining the minimum required levitation force. Decisions are taken using the non-dominated sorting genetic algorithm (NSGA-II) over 3D finite element analysis (FEA). A simplified electromagnetic model of equivalent relative permeability is used on 3D FEA to reduce numerical processing and optimization time. Experimental prototypes were built to measure magnetic forces and validate appropriate values of equivalent magnetic permeability. An analysis of stable and unstable geometry domains depending on the spacing between rings of HTS bulks and PM rings is also done for two HTS bulk sizes.
Materials of engineering and construction. Mechanics of materials, Production of electric energy or power. Powerplants. Central stations
YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-δ</sub>(YBCO) bulk material prepared by high temperature solid state reaction was milled and dispersed through ultrasonic process in ethanol to prepare nanoscale YBCO/ethanol sol. Then it was mixed with aniline or O-phenylenediamine and the organic/YBCO hybrid materials were obtained after concentration and being dried in vacuum. The influence of the organic on YBCO’s chemical composition, phase, elemental valence and magnetic properties was studied by Fourier transform infrared spectroscopy(FT-IR), X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS) and vibrating sample magnetometer(VSM). The results show that the infrared absorption of YBCO is not affected by the aniline or O-phenylenediamine within 0.05%-5%(mass fraction, the same below), however the intensity of the XRD peaks is significantly increased. The interaction between the N atom in aniline or O-phenylenediamine and the Y atom in YBCO is stronger compared with N-Ba or N-Cu. The superconducting transition temperature <i>T</i><sub>c</sub> and magnetization <i>M</i> of YBCO are significantly affected by the content of N element in the hybrid materials. When the content of N element exceeds 1%, <i>T</i><sub>c</sub> is significantly decreased and <i>M</i><sub>min</sub> is increased accordingly.
Materials of engineering and construction. Mechanics of materials
In this paper, a simplified approach for the design of thin-walled laminated composite beam structures is presented. For this purpose, structural efficiency metrics have been developed that allow for the integrated selection of layup sequence, materials of construction, and cross-sectional shape of laminated composite beams. The structural efficiency metrics are plotted in design charts for axial, bending (in both cross-section’s principal directions), and torsional loading conditions. The design charts provide the designer with an accurate and efficient approach for the selection of the optimum fiber direction, number of layers in the laminate, and mass of the overall structure. The results are generated for two different sizes of envelopes to analyze various cross-sectional types and sizes. It is shown that the design charts can be applied to single open and closed loop cross sections as well as multi-cell sections. The proposed simplified approach and developed design charts have been used for increasing the bending and torsional stiffness of a laminated composite robotic arm. The results show that the design charts can be used to accurately predict stiffnesses and deformations and assist the designer in selecting the various parameters that govern the performance of laminated composite beams.
Formulation of the problem. Many structures today require floor structures to meet increased requirements for strength, span coverage and surface quality. Steelcrete structures often fit the bill. However, despite a long history of success, the industry is still not fully understood, in particular, the behavior of this structure in the early stages of construction is not unambiguous. Due to the impossibility of creating a composite section, various effects and a complex stress-strain state immediately arise in the time interval between the combination of different materials in space and the combination of different materials in the work. Thus, the stage of erection of a structure before it became reinforced concrete is of interest for a complete understanding of the mechanics of the work of composite sections. The purpose of the study is to investigate the features of the operation of the steelcrete sections at the stage of installation and operation, as a composite structure that combines the advantages and disadvantages of steel and concrete. As a result of the research, it was found that the study of the stress-strain state, which affects the circumstances, both at the operation stage and at the construction stage, is an important task for further understanding the work of reinforced concrete. , and increasing its durability. In particular, at the time of erection, a complex stress-strain state occurs, which can lead to unpredictable changes in shape. This state is unstable up to the inclusion of the concrete shelf of the reinforced concrete section in the work due to the hardening of concrete in the area of the anchors and its subsequent inclusion in work. These issues require further study in order to better understand the work of concrete and steel as a single composite material at various stages of the life cycle of structures.