Hasil untuk "Mechanical engineering and machinery"

Nathalie Ronayette, Sonia Sousa Nobre, Sandrine Barthélémy et al.

New solar cells’ technologies such as silicon heterojunction and tandem solar cells raise new challenges such as temperature-induced degradations, which are problematic for the cells’ interconnection. Electrically Conductive Adhesives (ECAs), usually made of silver particles embedded in a polymeric matrix, seem a promising technology to allow low-temperature interconnection, but raise concern about a high consumption of silver in the manufacture of photovoltaic (PV) panels. In this work, the fabrication of copper-based ECAs is presented as an approach to reduce the silver consumption of the interconnection process. Core-shell copper-silver particles with dendritic shapes that showed resistant to oxidation up to 220°C were used as conductive fillers. Their integration into an acrylate fast-curing matrix was performed in ratios of 59 wt% and 69 wt% fillers, respectively accounting for silver contents of 3.0 wt% and 3.5 wt%. The resulting pastes have resistivities of 3.5 * 10‑3 Ω*cm and 9.0 * 10-4 Ω*cm respectively, globally similar to those of commercial ECAs dedicated to the interconnection of solar cells. Their fast-curing process was measured to occur upon heating at 105°C, and be completed upon heating at 160°C during 20 seconds, enabling high throughputs. First trials of these ECAs into strings of solar cells were made: the stencil-printed patterns had a good quality, but a poor adhesion between the solidified ECAs and the ribbons prevents their further use.

LI Lin, FAN Zhipeng, WANG Rugui

ObjectiveAiming at the problem of insufficient efficiency and spatial adaptability of flat plate antenna retracting and unfolding, a new type of planar deployable antenna mechanisms was proposed by modeling the unfolding motion of ferns during the growth process.MethodsFirstly, a modular design was adopted to design the shear fork module to realize the spiral-type closing and unfolding in the longitudinal plane. The folding and unfolding motion in the transverse plane was realized by combining a spherical four-bar mechanism, and its degree of freedom was calculated. Secondly, the kinematic analysis of the folding and unfolding mechanism was carried out to investigate the relation among the turning angle of the longitudinal unit, the turning angle of the transverse unit and the dihedral angle during its motion, the angular velocity and angular acceleration of the longitudinal unit's turning angle and each rod were deduced, and the rate of the mechanism's closing was analyzed. Finally, numerical calculations and simulations were carried out.ResultsThe designed bionic deployable mechanism has a simple driving system and high closing efficiency, which provides reference for the design and research of the flat antenna mechanism.

Pan Li, Jin Huang, Jie Zhang et al.

Ruggedized computers are the core of modern communication, guidance, control, and data-processing systems, and typically operate under extreme environmental conditions. However, under extreme service conditions such as temperature cycling, vibration, and mechanical shock, thermo–electro–mechanical (TME) multi-physics coupling in ball grid array (BGA) solder joints is particularly significant, severely affecting system reliability and signal integrity. To comprehensively elucidate the effects of thermal, electrical, and mechanical fields on solder joints and signal transmission, this study proposes a multiscale multi-physics modeling and analysis framework for BGA solder joints in microelectronic systems of ruggedized computers, covering the computer system level, motherboard level, solder joint level, and solder interconnect level. A model correlation study under ten thermal cycling conditions demonstrated an accuracy of 88.89%, confirming the validity and applicability of the proposed model. Based on this validated framework and model, the temperature distribution, stress–strain response, and signal integrity characteristics were further analyzed under combined conditions of thermal cycling, random vibration, and mechanical shock. The results indicate that a rise in temperature in solder joints induces thermal stresses and deformations, while variations in electrical conductivity under thermal loading trigger electromigration and concentration evolution, which further couple with stress gradients to form TME multi-physics interactions. Under such coupling, critical solder balls exhibit stress concentration at the metallurgical interfaces, with a maximum von Mises stress of 191.51 MPa accompanied by plastic strain accumulation. In addition, the PCIe high-speed interconnect experienced a maximum deformation of 16.104 μm and a voltage amplitude reduction of approximately 18.51% after 928 thermal cycles, exceeding the normal operating range. This research provides a theoretical basis and engineering reference for reliability assessment and optimization design of microelectronic systems in ruggedized computers in complex service environments.

Xuefeng Li, Shibo Wang, Yu Chen

This article investigates the fragmentation of rock during the indentation process with a conical pick. The study explores the impact of indentation dip angle, indentation spacing, and confining pressure on rock fragmentation through simulation using the discrete element method. Rock models of coal and red sandstone are created and calibrated for the simulation. The findings indicate that the indentation force increases exponentially with the increase of indentation dip angle for both coal and red sandstone. The specific energy increases first and then decreases with the increase of indentation dip angle. The maximum specific energy is found in the condition of indentation dip angle of 25° for red sandstone, while it is 20° for coal. The indentation force increases logarithmically with the increase of indentation spacing tending to be an unrelieved indentation condition. The optimal indentation spacing with the lowest specific energy is determined to be 50 mm for breaking coal and 34 mm for breaking red sandstone. Additionally, the indentation force increases exponentially for coal while it increases linearly for red sandstone with the increase of the confining pressure. For both coal and red sandstone, specific energy increases with the increase of the confining pressure.

LUO Jiman, SONG Yide, SONG Yucheng et al.

ObjectiveTo increase the obstacle crossing performance of robots and enhance their terrain adaptability, a “walking jumping dual purpose” robot with a composite jumping mechanism on wheeled robots was designed and studied.MethodsThe bouncing mechanism was designed with a combination of springs and cylinder sliders, where energy was stored in the springs to enable bouncing. Firstly, a rebound mechanism scheme was designed and a virtual simulation prototype was built. Then, in order to study the relation between the sliding rod length and the motion, the relation between the sliding rod of the mechanism and the swing angle of the jumping leg was obtained through the kinematic modeling of the mechanism, and the velocity and acceleration of the mechanism were analyzed. Thirdly, a mechanism dynamics model was established based on the Lagrangian dynamics method, and the influence of the rotation angle and angular acceleration on the torque of each member was obtained. Further analysis through the oblique upward throwing motion model, the relation between the robot’s takeoff angle and its bounce performance was studied.ResultsJumping simulations were conducted on the robot using Adams software to verify the accuracy of the theoretical modeling, as well as the good jumping performance and smoothness of the robot.

Dong Trong Nguyen, Christian Lindahl Elseth, Jakob Rude Øvstaas et al.

As aquaculture expands to meet global food demand, it remains dependent on manual, costly, infrequent, and high-risk operations due to reliance on high-end Remotely Operated Vehicles (ROVs). Scalable and autonomous systems are needed to enable safer and more efficient practices. This paper proposes a cost-effective autonomous inspection framework for the monitoring of mooring systems, a critical component ensuring structural integrity and regulatory compliance for both the aquaculture and floating offshore wind (FOW) sectors. The core contribution of this paper is a modular and scalable vision-based inspection pipeline built on the open-source Robot Operating System 2 (ROS 2) and implemented on a low-cost Blueye X3 underwater drone. The system integrates real-time image enhancement, YOLOv5-based object detection, and 4-DOF visual servoing for autonomous tracking of mooring lines. Additionally, the pipeline supports 3D reconstruction of the observed structure using tools such as ORB-SLAM3 and Meshroom, enabling future capabilities in change detection and defect identification. Validation results from simulation, dock and sea trials showed that the underwater drone can effective inspect of mooring system critical components with real-time processing on edge hardware. A cost estimation for the proposed approach showed a substantial reduction as compared with traditional ROV-based inspections. By increasing the Level of Autonomy (LoA) of off-the-shelf drones, this work provides (1) safer operations by replacing crew-dependent and costly operations that require a ROV and a mothership, (2) scalable monitoring and (3) regulatory-ready documentation. This offers a practical, cross-industry solution for sustainable offshore infrastructure management.

Hyun-Ki Kang, Hyungsoo Lee, Chang-Seok Oh et al.

The aim of this work is to study the phase transformations, microstructures, and mechanical properties of martensitic stainless steel (MSS) 410 deposits produced by laser powder-directed energy deposition (LP-DED) additive manufacturing. The LP-DED MSS 410 deposits underwent post-heat treatment, which included austenitizing at 980 °C for 3 h, followed by different tempering treatments at the temperatures of 250, 600, and 750 °C for 5 h, respectively. The analyses of phase transformations and microstructural evolutions of LP-DED MSS 410 were carried out using X-ray diffraction, SEM-EDS, and EBSD. Vickers hardness and tensile strength properties were also measured to analyze the effects of the different tempering heat treatments. It revealed that the as-built MSS 410 has very fine lath martensite, high hardness of about 480 HV_1.0, and tensile strength of about 1280 MPa, but elongation was much lower than the post-heat-treated ones. Precipitations of chromium carbide (Cr₂₃C₆) were most commonly observed at the grain boundaries and the entire matrix at the tempering temperatures of 600 °C and 750 °C. In general, the tensile strength decreased from 1381 MPa to 688 MPa as tempering temperatures increased to 750 °C from 250 °C. Additionally, as the tempering temperature increased, the chromium carbide and tempered martensite structures became coarser.

Naoki Yamashita, Tomoko Hirayama

In boundary lubrication, adsorbed molecular films formed by lubricant additives on the metal surfaces of sliding parts effectively reduce friction and wear. A method is presented for simultaneously measuring friction and the gap at a metal–lubricant interface under boundary lubrication conditions using atomic force microscopy. In this method, line-and-space patterns are microfabricated in Cu films on Si substrates, and the gap is evaluated from the step height change when scanning in base oil and in base oil with an additive. Neutron reflectometry showed that whereas both stearic acid and stearyl alcohol formed molecular film about 2 nm thick on Cu film in a static state, the gap increased only with stearic acid due to maintaining a molecular film on the Cu film. This demonstrates the feasibility of the proposed method as means for visualizing the gap and shows that there is a difference between the two additives in their film-forming ability in a static state and their durability against friction. The proposed method for simultaneously measuring friction and the gap at a metal–lubricant interface is thus an effective way to investigate the tribological performance of additives under boundary lubrication conditions.

Islam M Elbaz, MA Sohaly, H El-Metwally

In this paper, we study a stochastic SIS epidemic model with distributed delays. The positiveness of the solutions is established. We obtain sufficient conditions for the extinction of the disease through the study of stochastic stability of the disease-free equilibrium and stability of the same equilibrium in the mean. Compared to many works on the deterministic and stochastic SIS models and their stability, the distributed delays involved in the model offer new conditions with much more boundedness on the rate of losing immunity. The disease is extinct for small and large enough values of the intensity of noise and regardless of the initial history functions and the magnitude of the basic reproductive number R 0 .

Siming Zhao, Baoshun Wang, Na Zhu et al.

Abstract Smart windows refer to those which can dynamically modulate the transmitted light by changing their colors. Dual‐band electrochromic materials (ECMs) refer to materials that can change their colors and regulate light transmission in both visible (VIS) and infrared (IR) regions under different voltages. The dual‐band ECMs‐based building windows can thus regulate the indoor temperature to reduce the energy consumption for heating and air‐conditioning systems. Therefore, the wide application of ECMs in building windows will contribute a lot to establishing an energy‐saving society. During the past decades, enormous efforts have been made to improve the performance of dual‐band ECMs. This review presents a summary of the recent progress of dual‐band ECMs, focusing on their modulation mechanism, material design, and performance optimization. Finally, the challenges and outlook of dual‐band ECMs are also discussed.

Xiaoqiang Du, Yangyang Ding, Xiaoshuang Zhang

Water electrolysis is a promising technology to produce hydrogen but it was severely restricted by the slow oxygen evolution reaction (OER). Herein, we firstly reported an advanced electrocatalyst of MOF-derived hollow Zn–Co–Ni sulfides (ZnS@Co9S8@Ni3S2-1/2, abbreviated as ZCNS-1/2) nanosword arrays (NSAs) with remarkable hydrogen evolution reaction (HER), OER and corresponding water electrolysis performance. To reach a current density of 10 mA cm−2, the cell voltage of assembled ZCNS-1/2//ZCNS-1/2 for urea electrolysis (1.314 V) is 208 mV lower than that for water electrolysis (1.522 V) and stably catalyzed for over 15 h, substantially outperforming the most reported water and urea electrolysis electrocatalysts. Density functional theory calculations and experimental result clearly reveal that the properties of large electrochemical active surface area (ECSA) caused by hollow NSAs and fast charge transfer resulted from the Co9S8@Ni3S2 heterostructure endow the ZCNS-1/2 electrode with an enhanced electrocatalytic performance.

S. Haque, A. K. Bhurjee, P. Kumar

Transportation-based models are widely used to solve real-life problems such as supply chain problems, inventory level problems, business models, management problems, etc. The parameters of these problems have been conventionally measured as deterministic. However, these parameters have vagueness due to the uncertainty in the data sets. Such uncertainty of the parameters is generally measured using randomness (probability theory) or fuzziness (fuzzy theory), with certain assumptions and limitations. Closed intervals interpretation is another concept to deal with the uncertainties of real-world issues in recent decades, avoiding the limitations in probability theory and fuzzy set theory. This study formulates a fixed-charged multi-objective non-linear solid transportation with parameters such as availability of items, conveyance capacity, transportation cost, requirement, and budget for destinations in the form of closed intervals, where objectives are minimization of total transportation cost and action of time under the restriction over budget. An efficient solution procedure is developed with the help of interval analysis based on the parametric perception of intervals. Initially, the objective functions are converted into a crisp function using multiple integrations, and as a result, the problem is converted into a deterministic multi-objective non-linear programming problem. In addition, a real-world numerical problem is considered for testing the developed solution process for greater comprehension and clarity.

Ernest C. Nwosu, Godswill N. Nwaji, Chibuike Ononogbo et al.

The demand for freshwater has continued to soar amidst an increasing population, industrialization, and environmental pollution. The continuous shrinkage of this important resource has necessitated the need for a concerted effort on seawater desalination. Solar-powered desalination occupies a strategic position in the water-energy nexus and offers an alternative to taking off pressure from the already stressed freshwater sources. A numerical study with experimental validation of a single-slope double-effect solar still integrated with paraffin wax is thus presented. A transient mathematical model considering the humid air media in the upper and lower chambers was developed. Previous works in this area ignored the thermal analysis of the humid air medium, and as such, adopted the evaporation theory in the estimation of the freshwater yield. However, this study considers the thermal resistance offered by the humid air in the computation of the yield using the condensation theory. The energy-balance equations were discretized using the finite element method and solved with the aid of version 7.12 of the FlexPDE numerical solver. The model was validated with data from the experimental study. The correlation coefficients between the predicted and experimental data showed good agreement with values in the range of 0.97≤r≤0.99, and values of root mean square percent deviation of 3.2%≤e≤16.8%. The system achieved its best performance in November with a daily yield of 4.06 kg/m2 and a mean efficiency of 33.7%. The upper basin contributed an average of 52% of the total yield with a greater percentage of its yield occurring during the nocturnal phase. The effects of the upper basin and the PCM on the diurnal performance of the system were evaluated.

Ying Han, Jielai Yang, Weiwei Zhao et al.

The occurrence of osteoarthritis (OA) is highly associated with the reduced lubrication property of the joint, where a progressive and irreversible damage of the articular cartilage and consecutive inflammatory response dominate the mechanism. In this study, bioinspired by the super-lubrication property of cartilage and catecholamine chemistry of mussel, we successfully developed injectable hydrogel microspheres with enhanced lubrication and controllable drug release for OA treatment. Particularly, the lubricating microspheres (GelMA@DMA-MPC) were fabricated by dip coating a self-adhesive polymer (DMA-MPC, synthesized by free radical copolymerization) on superficial surface of photo-crosslinked methacrylate gelatin hydrogel microspheres (GelMA, prepared via microfluidic technology), and encapsulated with an anti-inflammatory drug of diclofenac sodium (DS) to achieve the dual-functional performance. The tribological test and drug release test showed the enhanced lubrication and sustained drug release of the GelMA@DMA-MPC microspheres. In addition, the functionalized microspheres were intra-articularly injected into the rat knee joint with an OA model, and the biological tests including qRT-PCR, immunofluorescence staining assay, X-ray radiography and histological staining assay all revealed that the biocompatible microspheres provided significant therapeutic effect against the development of OA. In summary, the injectable hydrogel microspheres developed herein greatly improved lubrication and achieved sustained local drug release, therefore representing a facile and promising technique for the treatment of OA.

Jabbar Mohammed L.

Dopamine is considered an important molecule that plays several essential roles in the human body, and herein lies the key to this paper on the electronic and optical properties of dopamine and its derivatives, such as quinone and L-dihydroxyphenylalanine (L-DOPA), using DFT and TD-DFT methods, respectively. Our findings show that dopamine has a dielectric behavior, whereas quinone and L-DOPA have semiconductor behaviors in the ground and excited states. By computing the optical properties, we disclose that the electronic transition spectrum of dopamine, quinone and L-DOPA are observed in the ultra-violet region, visible spectrum, and (ultraviolet and visible regions), respectively. Other properties, such as ionization potential, electronic affinity, hardness and softness are also calculated due to their importance in sensor applications and sensing.

Liu Yang, Zhongyang Zhao, Yi Zhang et al.

Piezoelectric actuators (PEAs), as a smart material with excellent characteristics, are increasingly used in high-precision and high-speed nano-positioning systems. Different from the usual positioning control or fixed frequency tracking control, the more accurate rate-dependent PEA nonlinear model is needed in random signal dynamic tracking control systems such as active vibration control. In response to this problem, this paper proposes a Hammerstein model based on fractional order rate correlation. The improved Bouc-Wen model is used to describe the asymmetric hysteresis characteristics of PEA, and the fractional order model is used to describe the dynamic characteristics of PEA. The nonlinear rate-dependent hysteresis model can be used to accurately describe the dynamic characteristics of PEA. Compared with the integer order model or linear autoregressive model to describe the dynamic characteristics of the PEA Hammerstein model, the modeling accuracy is higher. Moreover, an artificial bee colony algorithm (DE-ABC) based on differential evolution was proposed to identify model parameters. By adding the mutation strategy and chaos search of the genetic algorithm into the previous ABC, the convergence speed of the algorithm is faster and the identification accuracy is higher, and the simultaneous identification of order and coefficient of the fractional model is realized. Finally, by comparing the simulation and experimental data of multiple sets of sinusoidal excitation with different frequencies, the effectiveness of the proposed modeling method and the accuracy and rapidity of the identification algorithm are verified. The results show that, in the wide frequency range of 1–100 Hz, the proposed method can obtain more accurate rate-correlation models than the Bouc-Wen model, the Hammerstein model based on integer order or the linear autoregressive model to describe dynamic characteristics. The maximum error (Max error) is 0.0915 μm, and the maximum mean square error (RMSE) is 0.0244.

Shultoni Mahardika

Steel is a type of material that is widely used as a main material in the manufacture of various kinds of industrial and automatic machinery spare parts. Some mechanical properties of steel that are often used in design are hardness, ductility and toughness. Often in a design, we have difficulty getting steel with mechanical properties that are appropriate with the design. For this reason, engineering carried out mechanical properties engineering, to obtain steel in accordance with design calculations. AISI 4140 steel is a medium alloy steel. This steel is often used for industrial and automotive machinery parts. This research engineered the mechanical properties of the steel, namely the hardness and ductility of the material. The process is carried out by conducting steel hardening at 850 °C followed by rapid cooling with water media. After that, tempering at temperatures of 300 ᵒC, 400ᵒC and 500ᵒC by cooling together with the furnace. The result is hardness and tensile strength of the material has increased, when compared with untreated material. This method is effectively used to obtain mechanical strength values in accordance with technical planning calculations. . Keywords: Tempering, AISI 4140, Mechanical Properties Engineering

P. Sofer, Michale Sofer, J. Gebauer et al.

Department of Control Systems and Instrumentation, Faculty of Mechanical Engineering, VŠB — Technical University of Ostrava, 17. listopadu 15/2127, 708 33 Ostrava-Poruba, Czech Republic Department of Applied Mechanics, Faculty of Mechanical Engineering, VŠB — Technical University of Ostrava, 17. listopadu 15/2127, 708 33 Ostrava-Poruba, Czech Republic Department of Thermal Machinery, Czestochowa University of Technology, Faculty of Mechanical Engineering and Computer Science, Armii Krajowej 21, 42-201 Czestochowa, Poland Faculty of Production Engineering and Materials Technology, Częstochowa University of Technology, Armii Krajowej 19, 42-200 Częstochowa, Poland

D. Blinov, M. Morozov

One of the tendencies in mechanical engineering is the transition from sliding friction to rolling friction in part joints moving under load, motor assemblies and machinery. For the present time, planetary roller screws (PRS), which are rolling mechanisms, possess the biggest potential as converters of rotational motion to linear motion. However production of high-precision parts for PRS requires special expensive equipment. The emerging world tendency for reduction of technological costs is to develop nutless roller screws (NRS), which is the most complex PRS part to manufacture. Its production requires an additional machine tool or a universal grinding machine for external and internal grinding. The new rolling NRS has been developed in line with this tendency. This paper focuses on the design and operation of the mechanism and on theoretical studies. A test model and a testing rig have been developed to confirm the results of the theoretical studies and to determine operation parameters of the new NRS. The experiments showed that the newly developed NRS loses to PRS in some parameters, while outperforming it in other. It is also simpler and cheaper to produce and after additional studies and tests rational applications for the newly developed NRS can be found.

Yilang Liu, Yuhao Chen, Hongyi Li et al.

This paper describes the process of a team of mechanical engineering students in designing and simulating an easy to wear augmentation exoskeleton device. The goal of the project is to develop a fundamental technology associate with the design and control of an upper-body exoskeleton that augments human arm strength and endurance during lifting motion. The technology is intended to be used by military soldiers who are required to frequently lift more than 100 pounds objects, such as heavy machinery, tank ammunition, etc. This proof of concept design focuses on using a wearable device to provide and support both arms with considerable strength to lift more than 100 pounds objects. Some of the features of this upper body exoskeleton include easy to wear, light weight, portable, sturdy, and easy to control. The exoskeleton device mainly consists of two sections: wearable body vest and EMG sensors and Arduino control system. This paper also discussed the range of basic motion of the arms, how the wearable exoskeleton device is developed, and how the performance and efficiency of such device are evaluated.