Visco-Elastic Properties of Semi-Solid Alloys

Oscillation and creep experiments have been performed with Semi-Solid Material (SSM) AlSi7 with 35% solid fraction to investigate the early visco-elastic properties after shearing of the material in a Searle Rheometer. The preparation of the SSM has been done in situ using a standard procedure to guarantee for all experiments the same initial properties of the material. First, oscillation experiments at low amplitude allowed to study the evolution of material structure with time. Subsequently, creep experiments have been performed changing the resting period based on previous results. Creep experiments are characterized by exposing the material to a sudden increase of shear stress. The resolution in time has been 0.01 seconds, which allows observing the dynamics of the development of visco-elastic properties.The material exhibits viscoelastic properties that are becoming more pronounced with longer resting time. This is in accordance with previous experiments where the ratio between elastic and viscous properties increases with increasing resting time. The development of the elastic properties follows the increase of the yield stress due to the creation of an internal structure of the material, which starts immediately after stopping shearing. The investigation of the short-term response of SSM can be particularly relevant for industrial practice, where material deformation during die filling is very fast and the material flow does not take place in steady-state condition.

Hypothesis Relating the Structure, Biochemistry and Function of Active Zone Material Macromolecules at a Neuromuscular Junction

This report integrates knowledge of in situ macromolecular structures and synaptic protein biochemistry to propose a unified hypothesis for the regulation of certain vesicle trafficking events (i.e., docking, priming, Ca2+-triggering, and membrane fusion) that lead to neurotransmitter secretion from specialized “active zones” of presynaptic axon terminals. Advancements in electron tomography, to image tissue sections in 3D at nanometer scale resolution, have led to structural characterizations of a network of different classes of macromolecules at the active zone, called “Active Zone Material’. At frog neuromuscular junctions, the classes of Active Zone Material macromolecules “top-masts”, “booms”, “spars”, “ribs” and “pins” direct synaptic vesicle docking while “pins”, “ribs” and “pegs” regulate priming to influence Ca2+-triggering and membrane fusion. Other classes, “beams”, “steps”, “masts”, and “synaptic vesicle luminal filaments’ likely help organize and maintain the structural integrity of active zones. Extensive studies on the biochemistry that regulates secretion have led to comprehensive characterizations of the many conserved proteins universally involved in these trafficking events. Here, a hypothesis including a partial proteomic atlas of Active Zone Material is presented which considers the common roles, binding partners, physical features/structure, and relative positioning in the axon terminal of both the proteins and classes of macromolecules involved in the vesicle trafficking events. The hypothesis designates voltage-gated Ca2+ channels and Ca2+-gated K+ channels to ribs and pegs that are connected to macromolecules that span the presynaptic membrane at the active zone. SNARE proteins (Syntaxin, SNAP25, and Synaptobrevin), SNARE-interacting proteins Synaptotagmin, Munc13, Munc18, Complexin, and NSF are designated to ribs and/or pins. Rab3A and Rabphillin-3A are designated to top-masts and/or booms and/or spars. RIM, Bassoon, and Piccolo are designated to beams, steps, masts, ribs, spars, booms, and top-masts. Spectrin is designated to beams. Lastly, the luminal portions of SV2 are thought to form the bulk of the observed synaptic vesicle luminal filaments. The goal here is to help direct future studies that aim to bridge Active Zone Material structure, biochemistry, and function to ultimately determine how it regulates the trafficking events in vivo that lead to neurotransmitter secretion.

Development of Biological E-Module Based on Contextual Teaching and Learning (CTL) Learning on Structure and Function of Plants and Animal Networks to Improve Critical Thinking Skills of Class XI MIPA SMA Students

In the field of education, the presence of technology has helped teachers a lot in carrying out learning. Future education cannot only focus on cognitive aspects. To face various problems and challenges of the times in the future, students are expected to have much better attitudes, skills, and knowledge competencies, to be more creative, innovative, and productive. The purpose of this research is to analyze the feasibility and effectiveness of the development e-module Biology based on Contextual Teaching and Learning (CTL) on the material structure and function of plant and animal tissues to improve the critical thinking skills of students in class XI MIPA SMA that are valid, practical, and effective. The results showed that the e-module Biology based on Contextual Teaching and Learning (CTL) on the structure and function of plant and animal tissues to improve critical thinking skills of students in class XI MIPA SMA has a very valid category with a validator value of 89.33%, very practical 93.33% by Biology teachers and students with a score of 87.52% and the results of the effectiveness test of the CTL - based e-module showed that it was very effective, there was a significant difference between classes that used CTL - based e-modules and classes that did not use CTL - based e-modules . So, it can be concluded that the CTL-based Biology e-module that has been developed is very valid, very practical, and very effective.

Analysis of Damage Evolution in Concrete under Fatigue Loading by Acoustic Emission and Ultrasonic Testing

The fatigue process of concrete under compressive cyclic loading is still not completely explored. The corresponding damage processes within the material structure are especially not entirely investigated. The application of acoustic measurement methods enables a better insight into the processes of the fatigue in concrete. Normal strength concrete was investigated under compressive cyclic loading with regard to the fatigue process by using acoustic methods in combination with other nondestructive measurement methods. Acoustic emission and ultrasonic signal measurements were applied together with measurements of strains, elastic modulus, and static strength. It was possible to determine the anisotropic character of the fatigue damage caused by uniaxial loading based on the ultrasonic measurements. Furthermore, it was observed that the fatigue damage seems to consist not exclusively of load parallel oriented crack structures. Rather, crack structures perpendicular to the load as well as local compacting are likely components of the fatigue damage. Additionally, the ultrasonic velocity appears to be a good indicator for fatigue damage beside the elastic modulus. It can be concluded that acoustic methods allow an observation of the fatigue process in concrete and a better understanding, especially in combination with further measurement methods.

Research on Heat Dissipation of Multi-Chip LED Filament Package

By studying the substrate material, structure, chip distribution, and array form of the multi-chip light-emitting diode (LED) package, the heat-dissipation capacity of the LED package is improved. Finite element analysis and steady-state thermal analysis are used to simulate and analyze LED packages with different materials and structures. Using the theory of LED illuminance and uniformity, the illuminance of some structures is computed. The results show that the change of substrate material and structure can greatly impact heat dissipation, while changing array forms has little effect on heat dissipation. By improving the spatial distribution of the chip, the temperature superposition problem of the substrate is solved, and the illuminance and uniformity are improved while dissipating heat. The LED filaments of the combined, equidistant, chip-distribution mode have improved heat dissipation. The S-type equal difference has the highest illumination and high illumination uniformity.

Two-level mathematical models for determining the stress state and life plate with a hole

Modern trends in the development of mechanical engineering and other industries related to the production of materials and structures with a given set of physical, mechanical, and technological properties are aimed at reducing material consumption, energy consumption, increasing accuracy, reliability, and competitiveness of the manufactured product. Therefore, the creation of mathematical methods for assessing the stress state of structural elements based on the analysis of the elastic characteristics of a material, taking into account the peculiarities of its internal microstructure, is an actual task. The considered algorithm includes the following stages: identification of strength parameters using data obtained from images of the material microstructure; study of the stress-strain state of the model based on the variational-difference finite element method; formation of a system of linear algebraic equations for solving the problem of analyzing the elastic properties of a material using the plane problem of the theory of elasticity; construction of the material yield surface for a series of tests based on the strength criteria of composite materials, taking into account the different resistance of the material under tensile and compressive loads. Based on the developed mathematical model, the SSS and the yield surface of the plate with a hole are estimated. Structural analysis is performed at the macro and micro levels. The occurrence of plastic deformations at the micro-level can lead to the development of cracks and structural damage at the macro level. As a result of the study, the probability of plastic deformation in the plate is determined, and the critical zones of the model are established. The practical significance of the results obtained is to create an approach to assessing the mechanical properties of a material, such as elastic modulus, shear modulus, Poisson's ratio, and their probabilistic characteristics following the internal material structure. The proposed approach contributes to the expansion of knowledge about the material and allows to increase the valuable information obtained by modeling. To assess the probability of plastic deformations, the generated method uses the entire set of probabilistic characteristics of the yield surface.

Structure and Properties of Mixed Former Aluminum Borate Glasses Modified With Silver Oxide

The current study focuses on glass preparation and characterization in the xAl2O3 (35-x) Ag2O.65B2O3 system (0≤x≤35 mol%), where Ag2O is replaced with Al2O3. To examine a wide range of both structure and morphology of the produced glasses, nuclear magnetic resonance (NMR) of 27Al nuclei, X-ray diffraction (XRD) spectroscopy, and transmission electron microscopy (TEM) are used. Changing the Al2O3 and Ag2O molar ratios reveals a substantial change in material structure. In Al2O3-rich glass, the well-formed AlO6, AlO5, and AlO4 structured groups are the well-formed units. In samples of (20 and 30 mol % Al2O3), tetrahedral AlO4 and traces from AlO6 units may be detected. At lower concentrations of Al2O3 (10 mol%), the dominant unit is only AlO4 groups containing non-bridging oxygen bonds (NBO). The XRD and EDP spectra confirm the amorphous nature of the glasses of Al2O3 ˂ 20 mol%. Glasses of higher Al2O3 concentrations contain crystalline Ag2Al2B2O7 which are formed due to the higher oxygen packaging of the mixed AlO5 and AlO4 compared with that of glasses containing only AlO4 species. The amount of higher coordinated Al species AlO5 and AlO6 are gradually increased in response to an increase in the ratios of Al2O3/Ag2O. The morphology of crystalline units is confirmed from TEM to differ from that of an amorphous composition. The conductivity decreases and the activation energy for ionic conduction increase with increasing Al2O3. The hardness number of the studied glasses is highly increased with increasing Al2O3 content. The increase of activation energy and the hardness number of the glasses led to an increase in the durability of the investigated glasses.

Friction Stir Processing of Additively Manufactured Ti-6Al-4V Alloy: Structure Modification and Mechanical Properties

This work explores the possibility of using friction stir processing to harden the Ti-6Al-4V titanium alloy material produced by wire-feed electron beam additive manufacturing. For this purpose, thin-walled workpieces of titanium alloy with a height of 30 cm were printed and, after preparation, processed with an FSW-tool made of heat-resistant nickel-based superalloy ZhS6U according to four modes. Studies have shown that the material structure and properties are sensitive to changes in the tool loading force. In contrast, the additive material’s processing direction, relative to the columnar grain growth direction, has no effect. It is shown that increasing the axial load leads to forming a 𝛽-transformed structure and deteriorates the material strength. At the same time, compared to the additive material, the ultimate tensile strength increase during friction stir processing can achieve 34–69%.

Reliability improvement of steel storage tanks for phosphoric acid

The paper describes the one-sided welding method for steel structures based on the rational choice of the inverse angle of butt-welded elements of Belgian steel for the manufacture of tank bottom elements of intended for phosphoric acid storage in a construction site. It is shown that the most expedient method for ensuring the design geometry of the tank with a minimum stress of 1.4507 of the material structure, is the bottom sheets preset for welding at a reverse angle of 12 degrees.The proposed method improves the tank reliability for storing aggressive products, its trouble-free and technical safety during the operation. The need is shown for studying the replacement of imported steel by Russian steel to manufacture tanks from alternative nonmetallic materials.