Hasil untuk "Materials of engineering and construction. Mechanics of materials"

PENG Heng, DONG Minghui, ZHANG Maoqi, BAI Mingxian, GUO Jianwei

Sealing is a core factor for the safe operation of high-pressure proton exchange membrane electrolysis cells(PEMECs).To investigate the corrosion behavior of sealing polymer materials，two experimental methods were established: an accelerated high-temperature evaluation(100 ℃ acidic environment with H2 or O2 for 100 h) and a long-term high-pressure evaluation(80 ℃ acidic environment with 6－7 MPa H2 or O2 for 1 000 h)，to evaluate the corrosion behavior of five sealing polymer materials.Results showed that ethylene-propylene-diene monomer(EPDM) and fluoroelastomer(FKM) had chemical degradation and localized corrosion.In contrast，polyimide(PI)，polyetheretherketone(PEEK) and polytetrafluoroethylene(PTFE) had low corrosion rates and showed uniform corrosion characteristics.Specifically，PTFE showed excellent corrosion resistance，and its composite structure may help address corrosion and assembly issues in high-pressure PEMEC systems.

Sudheesh Parathakkatt, Vaisakh Kizhuveetil, Gokul G. K. et al.

Worm-like micelles (WLMs) are dynamic, self-assembling supramolecular structures that exhibit complex viscoelastic behaviour due to their ability to undergo reversible scission, fusion, branching, and sequence rearrangement. This review provides a comprehensive analysis of recent theoretical advances in modelling WLM rheology, from classical reptation–scission theories to modern stochastic simulations and multi-scale population-balance frameworks. A central challenge addressed is the rheological indistinguishability of competing models under linear conditions, which renders inverse modelling ill-posed and necessitates the integration of experimental data, such as cryogenic transmission electron microscopy (cryo-TEM), small-angle neutron scattering (SANS), and flow birefringence, to constrain theoretical predictions. The article further explores the limitations of conventional models in capturing nonlinear responses, including shear banding and extensional strain hardening, and emphasizes the need for spatially resolved, structurally informed constitutive equations. Emerging tools, including neural networks and hybrid modular frameworks, are identified as promising solutions for bridging microscopic rearrangement dynamics with macroscopic flow behaviour. Ultimately, the development of predictive, physically grounded WLM models will be essential for advancing applications in formulation science, smart materials, and industrial processing.

M. R. Kalibek, A. D. Ospanova, B. Suleimenova et al.

Erik Arévalo, Ramón Herrera Hernández, Dimitrios Katselis et al.

Direct current motors are widely used in a plethora of applications, ranging from industrial to modern electric (and intelligent) vehicle applications. Most recent operation methods of these motors involve drives that are designed based on an adequate knowledge of the motor dynamics and circulating currents. However, in spite of its simplicity, accurate discrete-time models are not always attainable when utilising the Euler method. Moreover, these inaccuracies may not be reduced when estimating the currents and rotor speed in sensorless direct current motors. In this paper, we analyse three discretisation methods, namely the Euler, second-order Taylor method and second-order Runge–Kutta method, applied to three common types of direct current motor: separately excited, series, and shunt. We also analyse the performance of two of the most simple Bayesian filtering methods, namely the Kalman filter and the extended Kalman filter. For the comparison of the models and the state estimation techniques, we performed several Monte Carlo simulations. Our simulations show that, in general, the Taylor and Runge–Kutta methods exhibit similar behaviours, whilst the Euler method results in less accurate models.

Jianghong Yuan, Xin Zhou, Xiangyu Li et al.

Abstract Patterns created by buckling of thin films on substrates have important applications in many fields such as functional devices and surface engineering. Introducing hierarchy to such patterns may further enhance their functionalities. However, unpredictable geometrical and material defects may disturb the formation of patterns. It is thus attractive to construct robust hierarchical buckling patterns that are insensitive to defects. Here, inspired by the construction of topologically protected localized states insensitive to defects in wave mechanics, a thin film of finite length bonded on a simple Winkler substrate is quantitatively designed by just varying its width continuously. Under the action of specific compressive stresses within such a continuous thin film owing to thermal mismatch between the film and substrate, there really exists a hierarchical film-buckling mode generated by topologically protected localization. Conditions under which the topologically protected localization exists are given explicitly, and the underlying mechanism is intuitively demonstrated from the mechanical point of view. Moreover, an analytical solution for the decay rate of localization is obtained as a satisfactory second-order approximation, from which the associated influencing factors are clearly identified. This work is expected to provide a theoretical guidance for the design and optimization of hierarchical patterns in film/substrate systems via the concept of topology.

Li Wei, Lei Zhao, Xun Zhu et al.

In this study, polylactic acid/graphene oxide/Dopamine (PLA/GO/DA) porous nanofiber membrane was prepared by electrospinning. L _16 (4 ^3 ) orthogonal experiment was designed to investigate the effects of reaction temperature, reaction time, and DA concentration on the adsorption performance of DA oxidized and self-polymerized on the fiber. Based on the characterization of scanning electron microscopy and the determination of the adsorption performance of the fiber membrane to methylene blue (MB) dye, data visualization analysis, variance analysis, and F-test were conducted to determine the optimal process parameters: reaction temperature of 45 °C, reaction time of 30 h, and DA concentration of 2 mg ml ^−1 . PLA/GO/PDA(Polydopamine) nanofiber was prepared and characterized under the optimal process parameters. The results showed that the average diameter of the PDA-loaded nanofiber increased from 737 nm to 996 nm, and a layer of PDA with a thickness of about 129 nm was loaded on the outer surface of the fiber, making the contact angle of the fiber membrane with 0° and becoming a hydrophilic material. In adsorption performance testing of MB, the PLA/GO/PDA nanofiber membrane prepared based on the PLA/GO/DA fiber membrane with an adsorption rate of 98.81 % in 24 h was superior to the PLA/GO/PDA nanofiber membrane prepared based on the PLA/GO fiber membrane.

Wonjun Shin, Ji Ye Lee, Jangsaeng Kim et al.

Abstract The need for understanding the low-frequency noise (LFN) of metal oxide semiconductor thin-film transistors (TFTs) is increasing owing to the substantial effects of LFN in various circuit applications. A focal point of inquiry pertains to the examination of LFN amidst bias stress conditions, known to compromise TFT reliability. In this study, we investigate the effects of hot carrier stress (HCS) on zinc tin oxide (ZTO) TFTs by low-frequency noise (LFN) analysis. Asymmetric damage caused by HCS is analyzed by measuring the power spectral density at the source and drain sides. The excess noise generated by the HCS is analyzed with consideration of trap density of states (DOS). It is revealed that the needle defects are generated during the HCS, significantly affecting the LFN characteristics of the ZTO TFTs. Additionally, we observe a self-recovery behavior in the devices and demonstrate the relevant changes in the LFN characteristics following this phenomenon. This study provides valuable insights into the LFN characteristics of ZTO TFTs under HCS conditions and sheds light on the underlying mechanisms.

Moses Robert W., C. Sang H., Park Cheol et al.

NASA envisions commercial operations will start with production of tens of metric tons of oxygen per year but will evolve into hundreds to thousands of metric tons of a variety of commodities including oxygen, water, propellants, construction, and manufacturing feedstock. NASA also envisions that commercial lunar mining and processing systems will adhere to the principles of ethical and responsible use of space, especially those identified in “Moon to Mars Objectives” and “Artemis, Ethics and Society: Synthesis from a Workshop” publications. NASA published in 2021 a system concept that illustrates the separation of oxygen and metals from lunar regolith by combining an electron beam (E-beam) with concentrated sunlight. Herein, that system concept has been analyzed in more detail using the current state of the art in E-beam system technology, known dissociation properties of some materials

B. Liu, Xiaoduan Zhang, Y. Garbatov

A micro-meso-macro analysis framework based on the multi-scale method was employed to analyse the mechanical behaviour of marine GFRP stiffened panels. The study aims to establish a procedure for assessing the impact of material composition and weave on the ultimate strength of GFRP stiffened panels. The ultimate strength assessment was an essential step in the design process, and the investigation of construction materials has a great benefit to the lightweight design of marine composite structures. The micro- and meso-scale RVE models of components used in GFRP materials are established, and their failure criteria and stiffness degradation models are created using the user-defined material subroutine VUMAT in ABAQUS. The equivalent material properties at the micro-scale (meso-scale) obtained by a homogenisation method are used to define the meso-scale (macro-scale) mechanical properties in the finite element analyses. The multi-scale method assesses the macro-mechanics of composites, and it is shown that the ultimate strength of GFRP stiffened panels is mainly determined by the failure of CSM fibre bundles and WR yarns. Parametric study of the meso-mechanics of composite materials can provide an analysis tool to obtain the optimal macro ultimate strength of the composite stiffened panel.

Pan-Fu Ouyang, D. Li, Jia Xie

Abstract The auxetic structure with negative Poisson’s ratio has broad application prospects in many engineering fields. Although it is often simplified as a linear elastic problem in theoretical models, the generally used slender structure, such as the reentrant honeycombs, will inevitably undergo large deformation resulting in significant non-conservative load effects in the service conditions. Therefore, a numerical framework for modeling nonlinear deformation of the auxetic structures under follower loads with the complex variable element-free Galerkin method is developed in this paper. The application of the complex variable meshfree method is to deal with the numerical difficulties caused by mesh distortion that may occur in large deformation problems, and at the same time, it can improve the construction efficiency of meshfree shape functions through the complex variable moving least-squares approximation. The Galerkin weak form of the incremental total Lagrangian formula for large deformation problems with the enforced essential boundary conditions using the penalty method is derived and then discretized in the complex variable meshless implementation. Five numerical examples are presented with detailed convergence study to demonstrate the accuracy of the proposed approach in dealing with non-conservative large deformation of the slender auxetic structures.

T. Ayadat

Abstract. An expansive soil expands when water is added, and shrinks when it dries out. On construction sites, expansive soils can pose geotechnical engineering challenges. More financial loss is caused by expansive soil damage than by floods, hurricanes, tornadoes, and earthquakes combined. The aim of this study is to analyze the effect of stabilization of an expansive soil using three different chemical additives, in this case: white cement and nano-silica as admixture, waste granite dust, and a new liquid polymer soil stabilizer (i.e. liquid granite). This study investigated the effect of these stabilizing agents on the variation of soil consistency, linear shrinkage, and soil swelling behaviour. Three groups of tests were carried out as part of the experimental program. As part of the first group, tests were performed on expansive soil reinforced with 2%, 4%, 8%, and 10% of white cement combined with 2% of nano-silica. Another group of tests consisted of samples mixed with different percentages of granite powder (5%, 10%, 15%, and 20%). In the third group, liquid granite as a soil stabilizer was blended with soil specimens at various concentrations (1%, 2%, 3%, and 4%). For all admixtures, the results showed a marked improvement in soil consistency, an important decrease in linear shrinkage, and a considerable reduction on the expansion index. Compared with the original bentonite clay, the swelling behaviour (expansion index) was reduced considerably by adding these three different chemical additives. Moreover, a correlation between the expansion index and the dosage of the different stabilizers was proposed.

Batool Al-Shorman, Mousa I. Bani Baker, T. Ayadat

Abstract. Soil stabilization is a technique that is used in most construction projects to enhance the geotechnical and engineering properties of soil. There is a wide range of research studies related to soil stabilization techniques and agents, these studies discussed the effects of the different types of soil stabilization on soil, the most suitable agent type regarding soil classification, and the challenges that were founded during the application of these processes. Stabilization agents include traditional and non-traditional additives with their different categories were reviewed and discussed in this paper by presenting the results of the recent studies concerned with various types of soil stabilization agents in different laboratories and project tests with highlights on the enhancement of soil properties. In addition to increasing the compressive and shear strength parameters, Maximum Dry Density (MDD), and California Bearing Ratio (CBR) of the soil, the soil stabilization agents play a great role in decreasing the soil plasticity index, swelling, compressibility, porosity, permeability, and Optimum Moisture Content (OMC).

S. Saputo

Abstract. Thin-walled mechanical components, such as beams, plates and shells, are widely used as structural components in several engineering fields, in particular mechanical, aeronautical and aerospace sectors. The purpose of this work is to analyse the cross-ply bending behaviour of cylindrical and spherical shell structures using the finite element method. Hence, numerical models, realized using commercial software, were realized using the shell and solid approaches and were compared with numerical and analytical methods to appreciate their advantages. In this research, a Navier solution in close form for high-order theories, developed using the Carrera Unified Formulation (CUF) approach, has been reported, where the high-order elastic shell model has been developed using the variational principle of virtual work for three-dimensional linear theory equations and the analytical results were obtained using the Mathematica software. The results furnished by the numerical method such as the elasticity solutions given in the literature using Navier’s method are used as a benchmark for comparing the finite element method results in terms of maximum displacement and stress distribution along the principal structure direction. However, the numerical shell model cannot provide sufficient data to describe the tensional and deformational state at all points and especially along the laminate thickness. Wishing to obtain a complete description of the plate's mechanical behaviour, it is necessary to use a three-dimensional approach with the associated increase in calculation time. In contrast, the numerical solution based on the CUF approach shows a very efficient description of the composite structure behaviour and its use should be preferred to the classical lamination approach if an accurate description of the structure is necessary.

L. Jradi

Abstract. Cellular glass aggregates made from recycled glass are increasingly being used in civil engineering and infrastructure applications. This contemporary material is relatively new in civil engineering applications. This paper investigates the effect of shearing conditions and initial aggregates’ state on the mechanical properties of cellular glass foam. A series of monotonic large-scale triaxial tests (300 mm diameter and 600 mm height) was performed in order to investigate the influence of initial dry density, initial aggregates’ state (i.e. flawless, weathered, and compacted), and consolidation stresses on the mechanical behavior of cellular glass foam. The material’s behaviour observed under monotonic shear is of contracting type, with significant evolution of the material during shear (grain crushing) and a strongly strain-hardening character. The failure criterion of the studied material is similar to the failure criterion used for granular soils for which a shearing resistance angle and apparent cohesion is perceived.

HOU YanYan, CHANG Qing, HU XiWen et al.

Active gear design is a method that can pre-control gear meshing performance directly. In order to study the influence of active gear design on the bearing characteristics of tooth surface, the relationship between active modification parameters of the face gear and bearing characteristics of tooth surface is studied. Firstly, the contact model of the gear pair is established by the finite element method, and then different groups of active modification parameters are designed for simulation analysis. The results show that the geometric transmission error greatly influences gear transmission stability and contact strength, and controlling its amplitude can control bearing transmission error amplitude. Pre-designed contact path inclination angle within 30° neighborhood, bearing contact characteristics are better. The contact ellipse length mainly affects the contact strength of tooth surface and bending strength of tooth root. According to the simulation results, when it takes 0.5～0.75 times of tooth width, face gear pair has better bearing contact characteristics.

Gamze Bilgen, Omer Faruk Altuntas

The amount of waste materials such as dredged materials (DM) and waste glass (WG) have been growing exponentially since the middle of the 20th century. The most important problem created by them is the lack of space to be used for storage beside ecological, economic, and environmental problems. The purpose of the presented study is to contribute to the elimination of the mentioned problems by assessing the re-use of related wastes as pavement material. Therefore initially, DM was treated with additives at various contents that are powdered waste glass (GP) (5 %, 10 %, 15 %, 20 %, 25 %), lime (5 %) and cement (5 %). Following, a series of experimental studies and calculations such as Proctor, California bearing ratio (CBR), resilient modulus (MR) were carried out on the blends to define the geotechnical properties of them. Additionally, a cost analysis was made according to the obtained test results and the design inputs for a typical flexible pavement to determine the effect of the additives on the cost of the road construction. The underlying mechanism process of determined effects was defined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The obtained results indicate that CBR of the DM is 5.6 % which means has sufficient strength and stiffness for being used as a subgrade. Increasing the GP content in the blends contributes to achieving more desired results both geotechnically and indirectly economically. Combined use of cement and GP on DM increases the CBR value up to 83 %. This translates to an 89 % reduction in the structural number (SN) and 170 % decrease in cost index. The results of microstructural analysis indicate that the geotechnical improvement of treated DM was provided by CSH and CAH formations. Consequently, the additives used improve index and stiffness properties of DM which means a decrease in the layer thickness in road construction and therefore a decrease in the cost. The presented study confirms the usability of cement, PG, and lime-treated DM as pavement material, according to criteria specified by the Federal Highway Administration.

Jiaquan Li, Kai Wang, Yijiao Jiang et al.

Single‐atom catalysts (SACs) composed of atomically dispersed metal‐active sites embedded in supporting substrates are attracting increasing attention in liquid‐phase selective oxidation reactions with joint merits of both advanced catalytic efficiency and high stability. Co‐based SACs present superior performance in several model oxidative reactions against many other metals, thus they are recognized as a promising solution to the current high‐cost noble‐metal catalysts required for the synthesis of fine chemicals. In this review, the up‐to‐date research on the synthesized Co–SACs in selective oxidation applications is summarized. The strategies of the preparation of Co–SACs with diverse Co‐loading levels and well‐tuned morphologies and chemical structures are showcased, as well as the characterization techniques of the SACs. The applications of Co–SACs in a series of selective oxidation reactions and the influence of different oxidants on the overall reaction efficiency are discussed. In addition, the progress of the mechanism exploration involving active‐site identification, catalytic activation of oxidants, and oxidation pathway elucidation is highlighted. Meanwhile, the existing challenges and the future efforts for the development of the Co–SAC reaction system in selective oxidation processes are outlined.

Zhen Zhang, Kenan Shi, Pan Ge et al.

This paper proposes a kinesthetic–tactile fusion feedback system based on virtual interaction. Combining the results of human fingertip deformation characteristics analysis and an upper limb motion mechanism, a fingertip tactile feedback device and an arm kinesthetic feedback device are designed and analyzed for blind instructors. In order to verify the effectiveness of the method, virtual touch experiments are established through the mapping relationship between the master–slave and virtual end. The results showed that the average recognition rate of virtual objects is 79.58%, and the recognition speed is improved by 41.9% compared with the one without force feedback, indicating that the kinesthetic–tactile feedback device can provide more haptic perception information in virtual feedback and improve the recognition rate of haptic perception.

S. Kashtanova, A. V. Rzhonsnitskiy

This paper studies the issue of determination and influence of natural boundary conditions in the problem of buckling of a thin plate with an elliptical inclusion under tension. First, the naturalness of the boundary conditions of the “free edge” type for a plate with a hole is proved. Then a plate with welded inclusion is considered and natural boundary conditions are derived. The limit cases are checked for an absolutely soft inclusion and for an absolutely rigid one. It is shown that the first case leads to a problem with a hole and the corresponding natural boundary conditions, and in the second case, to the absence of natural conditions, since a problem with a clamped edge occurs. The authors conclude that the use of additional restrictions will lead to the construction of a basis that will rapid up the convergence of the method. Variational methods are widely used in all fields of mechanics, including in the field of machine, aircraft, and rocket engineering. An exact solution to the problems of elasticity theory and structural mechanics is not always possible to construct, therefore, in practice, great importance is attached to various approximate methods. Among them a special place is occupied by variational methods based on the direct minimization of the corresponding energy of the body and making it possible to build approximate analytical solutions in the form of a functional series. The goal of variational methods is to construct a partial sum of this series, which, with a sufficient number of terms, will be maximum close to the solution. However, the issue of convergence is influenced by many factors, and one of them is the natural boundary conditions, which are derived in this paper for the problem of the stability loss of the plate with the elliptical inclusion under tension.

V. Zimnyukov, M. Zborovskaya

In the 1950s, the construction of hydropower facilities began in the regions of Siberia and the Far East, characterized by harsh climatic conditions, which should be taking into account to predict the stress state of dams. The aim of the study is an assessment of the conditions for the formation of temperature cracks in concrete dams and their influence on the further operation of the structure, as well as measures and technologies to combat cracking in massive concrete. Thermal stresses often exceed the stresses caused by the action of external loads and lead to the appearance of cracks in the concrete. Almost all modern concrete dams are subject to thermal cracking today. Appropriate design and technological measures must be provided for. When studying the thermally stressed state of lightweight concrete dams, the method of direct reproduction of thermal deformations on models made of brittle materials and computational methods oriented towards computer methods of solving problems are used. The results of modeling and computational studies of massive buttress dams are presented and the influence of the main influencing factors is considered, taking into account the effect of cracking on the operation of such dams.