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

Ayyappan M, Muthiah A

In this paper, melting and solidification characteristics of composite PCM filled inside the shell and tube heat exchanger were investigated experimentally. ZnO nanoparticles (NPs) were synthesized using the sol–gel method. Myristic acid (MA) considered as the pure PCM and ZnO NPs serving as the supporting material. The morphology and crystal structure of ZnO particles were analyzed using Field Emission Scanning Electron Microscopy (FESEM) and x-ray Diffraction (XRD) techniques. ZnO nanoparticles at concentrations of 0.1, 0.3, and 0.5 wt% were individually dispersed in myristic acid to evaluate the heat transfer characteristics of nanocomposite phase change materials (NCPCMs) through phase change processes. Differential Scanning Calorimetry (DSC) analyses were used to assess the phase change behavior of PCM and nanocomposite PCMs in liquid and solid states. The phase change characteristics of the Myristic acid and nanocomposite PCMs were probed with regard to heat exchanger studies. The results show significant time savings, with a 68.04% reduction in complete melting time and a 42.73% reduction in solidification time when using 0.5 wt% ZnO NPs at a mass flow rate of 5 l min ^−1 . Furthermore, incorporating ZnO NPs at concentrations of 0.1, 0.3, and 0.5 wt% enhanced the thermal conductivity of the NCPCMs by 36.41%, 62.96%, and 82.71%, respectively, compared to pure MA.

Yongwen Liu, Lei Zhang, Pu Li et al.

This paper presents a twisting controller (TC) based on a high-order sliding mode observer (HOSMO) for linear induction motors (LIMs), accounting for dynamic end effects. Based on the LIM model in the field-oriented frame, two extended subsystems are developed: a velocity extended model and a flux extended model. Using these models, two HOSMOs are designed to estimate the disturbances in each subsystem. The HOSMO outputs are then used for disturbance rejection, resulting in two second-order systems with small bounded disturbances. Two TCs are subsequently implemented to achieve finite-time velocity and flux tracking of the LIM. The primary advantage of this strategy lies in its ability to reduce chattering through active disturbance rejection. Hardware-in-the-loop (HIL) experiments validate the effectiveness of the proposed TC-HOSMO scheme.

Z. Wang, L. Mei, X. Ma

<p>To improve the trajectory tracking performance and robustness for uncertain robot manipulators, a generalized sliding mode controller (GSMC) including an ideal controller and a continuous sliding mode controller (SMC) is proposed from the standpoint of motion constraints. First, the trajectory tracking requirements are formulated as the motion constraints, based on which an ideal controller is proposed to satisfy the motion constraints for robot manipulators whose dynamics are precisely known. Second, an additional continuous SMC is presented to compensate for the effects of uncertainty, and the chattering phenomenon that commonly exists in the SMC can be avoided by the introduction of a smoothing function. Third, Lyapunov analysis is conducted to verify that the proposed GSMC enables the tracking error restricted to a small region around zero. Finally, the numerical simulation and experiment are performed to verify the effectiveness and superiority of the proposed GSMC.</p>

Yao Meng, Xinyu Yang, Haitao Wang et al.

This paper proposes a new dual-stator hybrid-magnet flux modulation machine (DS-FMHMM) for direct-drive applications, which employs NdFeB magnet excitation and Ferrite magnet excitation on the rotor and outer stator sides, respectively. With this design, the proposed DS-FMHMM can not only fully use the bidirectional flux modulation effect, but also effectively alleviate the magnetic saturation issue. The machine configuration is described, together with the operating principle. Then, the design parameters of DS-FMHMM are globally optimized for obtaining high torque quality, and the influence of magnet dimensions on torque is analyzed. To evaluate the merits of the proposed DS-FMHMM, the electromagnetic performances of machines under different magnet excitation sources are analyzed, and a comprehensive electromagnetic performance comparison of DS-FMHMM and two existing dual-stator flux modulation machines (DSFMMs) is developed.

Lijuan LI, Beibei ZHANG, Zhaoda SUN

Under the background of the comprehensive implementation of the National Carbon Peak Carbon Neutralization Action, the superhard material industry energy consumption research was carried out. It aims to promote the superhard material industry to make new contributions to the green, low-carbon and high-quality development of the country. The energy consumption data of superhard material and product enterprises were summarized and analyzed, and the energy consumption of typical products in the inorganic non-metallic field was compared. The results show that from 2019 to 2021, the energy consumption per unit of gross industrial output value of superhard materials is 0.11, 0.10, and 0.08 tce/10 000¥; and that the energy consumption per unit of gross industrial output value of superhard materials products is 0.08, 0.07 and 0.05 tce/10 000¥ respectively. The reduction rate of energy consumption in superhard materials industry is far greater than the reduction percentage of national GDP energy consumption index. Compared with the typical products in the inorganic non-metallic field such as cement, ceramics and ordinary abrasives, the energy consumption in the superhard material industry is at a lower level. Finally, the paper makes suggestions on superhard industry policies and enterprise carbon reduction.

Mohd Izrul Izwan RAMLI, Siti Farahnabilah MUHD AMLI, Norainiza SAUD et al.

Hot Air Solder Leveling (HASL) is one of the most commonly used surface finishes in the industry. HASL is also one of the least expensive types of PCB surface finishes available. This study aims to examine the influence on the solder joint microstructure of dipping time and solder temperature. During soldering process, the temperature that used were 300°C and 400°C. The dipping time was split into three batches which is 20s, 60s, and 100s. The Sn-0.7Cu0.05Ni solder alloy was used in this analysis to shape the solder coating microstructure. In this analysis, an Optical Microscope (OM) was used to determine the microstructure of the shape of the solder coating microstructure. As dipping time and dipping speed increased, the interfacial IMC thickness was found to increase, grown up and getting thicker. This outcome results can be used as the basis in order to improve the solder joint properties.

Zhichao Tang, Jin Cui, Muzhi Yu et al.

The diffusion growth of intermetallic compounds in Al-Er alloys are closely related to the properties of the alloys. The current work aims at explaining the dominance of Al3Er in the Al-Er alloys precipitation phases and the interface thin layer phenomenon by diffusion couple technique, estimating the parabolic growth constant and diffusion activation energy of intermetallic compound in Al-Er diffusion couples to provide theoretical guidance for the design of new Al-Er alloys. In this work, Al-Er diffusion couples were successfully prepared by casting-cladding method in the atmosphere. The growth of Al-Er intermetallic compounds at diffusion couple interface during annealing were observed and recorded by High-Temperature Laser-Scanning Confocal Microscopy at 673, 698, 723 and 748 K respectively. The results show that the growth characteristics of Al-Er intermetallic compounds were accord with layer-terraced growth during annealing. The thickness of intermetallic compound was linear with the square root of time at experimental temperature. The intermetallic compound layer was composed of Al3Er and a very thin AlEr phase. The parabolic growth constants of Al3Er phase at 673, 698, 723 and 748 K were 1.017 × 10−14, 1.609 × 10−14, 3.111 × 10−14 and 4.76 × 10−14 respectively. The activation energy of Al3Er phase was (88.4 ± 5.3) kJ/mol and the pre-exponential factor was 7.126 × 10−8 m2/s.

ZHANG Sen, LIU Yi, SU Xiaolei et al.

In order to improve the microwave absorption performance of TiC powder, TiC/Ni composite powder was prepared by coating nickel particles with mass fraction of 10%, 20% and 30% on the surface of TiC by typical coarsening and sensitizing electroless nickel plating process. The composite powder was characterized by SEM and XRD, and the effect of nickel content on the microwave absorbing properties of TiC/Ni composite powder was analyzed. The results shows that the dielectric constant and permeability of TiC/Ni powder increases with the increase of nickel mass fraction. With -5 dB as the scale, the absorption bandwidth of the sample with a thickness of 3.0 mm increases from 0 to 3.34 GHz. When the thickness is 3.8 mm, the minimum reflection loss of TiC is -3.66 dB. For TiC/Ni samples with a thickness of 2.8 mm and a mass fraction of Ni of 30%, the minimum reflection loss value of -9.95 dB is obtained at 9.67 GHz. It can be seen that electroless nickel plating can improve the microwave absorption performance of TiC.

Junping Hu, Youxing Liu

Exploiting non-noble metals catalysts with excellent performance for hydrogen evolution reaction (HER) has aroused gigantic interest, but still challenges. Herein, we reported the graphene oxide (GO) supported Fe doped Ni(OH) _2 hexagonal nanosheets (GO-Fe,Ni HHNs) for HER firstly. SEM and XRD were carried out to investigate the morphology and crystal structure of the GO-Fe,Ni HHNs systematically. The elements and bonding of the sample were measured via using XPS. In addition, we found that the recrystallization treatment could significantly improve the morphology and crystallinity of the nanosheets. Most important, the GO-Fe,Ni HHNs possessed exceptional catalytic performance and stability in PBS solution. The overpotential (10 mA cm ^−2 ) and Tafel slope were 190 mV and 110 mV dec ^−1 , respectively, significantly better than that of other non-noble metal catalysts reported before.

Minglong Kang, Li Zhou, Yunlai Deng et al.

Multilayer brazeable aluminum alloy sheet is prone to collapse during high-temperature brazing process. The sagging resistance of the aluminum composite sheet needs to be further improved for quality control. Effects of annealing and rate of reduction on sagging resistance, microstructure, and Si diffusion of a hot-rolled, four-layered Al clad sheet (4343/3003/6111/3003) were investigated by means of a sagging device, OM, SEM, and TEM. Results showed that once annealed at 360°C, the sagging distance was increased from 3 to 15.7 mm as the reduction rate changed from 10% to 40%. By increasing annealing temperature to 410°C, those were changed from 3.1 to 20.8 mm accordingly. At 360°C/40% and 410°C/40%, specimens exhibited weak sagging resistance, whereas fine recrystallized grains were formed in the core promoting Si penetration along grain boundaries. While the specimens were treated at 360°C/10% and 410°C/10%, better sagging resistance was observed due to the formation of coarse recrystallized grains that can suppress erosion of Si. At the same reduction rate, the sagging resistance was higher for the sample annealed at a lower temperature as more precipitates appeared in the core (at 360°C), thus leading to an increase in strength.

Denis A Romanov

This article describes increasing wear resistance of 5CrNiMo die steel by more than 5 times. This effect is achieved by creating TiC-Ti-Al and TiB _2 -Ti-Al coatings on the surface of 5CrNiMo die steel. The microhardness of the formed coatings depends on which part of the structure is measured. The microhardness differs by more than 12 times in the matrix material and in the inclusions of titanium carbides and borides. However, the combination of metal matrix composites and the reinforcing inclusions suggests a high complex of properties of the formed coatings. The formation of wear-resistant coatings of these systems is carried out by two-stage treatment. At the first stage, electro-explosive spraying of TiC-Ti-Al or TiB _2 -Ti-Al coatings is performed. At the second stage, electron-beam treatment of these coatings is carried out. The structure uniformity during electro-explosive spraying is enforced by specially designed composite conductors, which are electrically exploded. The reason for wear resistance increase is the formation of a multiphase finely dispersed structure in coatings based on TiC, Al _3 Ti, Ti and Ti _3 Al phases for TiC-Ti-Al system and TiB _2 , TiB and AlTi _3 phases for TiB _2 -Ti-Al system. The structure was also studied in detail at the interface between the coatings and the substrate using transmission electron microscopy. The studies of the structure of electro-explosive coatings were compared with the structural features of TiC-Ti-Al composite coatings obtained by the laser cladding technique on the surface of TiAl alloy. Comparison of the findings of the structure obtained by these two different spraying methods revealed both general patterns and characteristic features for each of the coating methods. They relate to features at the interface between the coatings and the substrate, as well as characteristic unitary coating layers.

Wei Wei, Qiang Li, Fangchao Xu et al.

This paper proposes an electromagnetic actuator that concurrently realizes two working functions of vibration suppression and energy regeneration. The actuator consists of four permanent magnetic rings, three soft iron rings, three coils, and three springs. The design of the electromagnetic actuator is based on finite element method (FEM) analysis, and the prototype is based on this analysis. Based on the prototype, the characteristics of the electromagnetic actuator, which has an output force–current coefficient of 39.49 N/A, are explored. A control algorithm with a position controller and an acceleration controller are applied to the actuator. When an impulse excitation is input to the electromagnetic actuator, the acceleration of the controlled object decreases from 114.26 m/s² to 3.14 m/s² here. Moreover, when the sinusoidal excitation with a 3 mm amplitude and 5 Hz frequency is input to the electromagnetic actuator, the vibration amplitude of the controlled object is 0.045 mm, suppressed within 1.46% when compared with the input signal. The peak value of the regenerated electromotive force is 1.97 V here, and the actuator efficiency for regenerating energy is 11.59%. The experimental results with multiple frequencies and amplitudes also show that the amplitude of the controlled object can be suppressed within 5.5%, and that the ratio of the electromotive force (EMF) to the input amplitude is 0.13. The results indicate that this electromagnetic actuator can suppress vibrations effectively and regenerate energy from vibrations.

Phillip Won, Seung Hwan Ko, Carmel Majidi et al.

Living systems have evolved to survive in a wide range of environments and safely interact with other objects and organisms. Thus, living systems have been the source of inspiration for many researchers looking to apply their mechanics and unique characteristics in engineering robotics. Moving beyond bioinspiration, biohybrid actuators, with compliance and self-healing capabilities enabled by living cells or tissue interfaced with artificial structures, have drawn great interest as ways to address challenges in soft robotics, and in particular have seen success in small-scale robotic actuation. However, macro-scale biohybrid actuators beyond the centimeter scale currently face many practical obstacles. In this perspective, we discuss the challenges in scaling up biohybrid actuators and the path to realize large-scale biohybrid soft robotics.

G Carbajal-Franco, E Rendón-Lara, I M Abundez-Barrera et al.

The finding of a material with the precise properties needed to solve a specific issue is the first topic that needs unraveling when an application is projected. One approach to find a material with a specific property value is to study a different but linked property. The aim of this research is to find materials with similar Electronic Band Structures (EBS); which in a simulation typically contain more than 1,000 ordered pairs of data. Our approach is, instead of calculating the similarities between the EBS of different materials, to calculate the similarity between their crystalline structures, and then the similarity between the EBS of the resulting similar compounds is tested. The software system developed in this research finds materials with similar crystallography, then the similarity of the compounds is tested by comparing the DFT modeled Electronic Band Diagrams (EBDs). The crystallographic data was mined from the Crystallography Open Database (COD) in the form of CIF files; that were used to calculate the x-ray diffraction (XRD) data using REFLEX, a component of Materials Studio. The plane presence, position and intensity of the peaks from the XRD data, were used to calculate the similarity between materials. With the list of similar materials from the previous process and the correspondent CIF files, the CASTEP code (from Materials Studio) was used to calculate the EBDs. In this work, three different materials were analyzed: CdTe, CdSe and GaAs. As results, 2D maps showing 50 compounds with the highest similarities are shown and for the EBD analysis, the 6 + most similar compounds were computed and analyzed by means of the first derivative. It is shown that the EBDs of the similar materials share the same shape, but with different values, making the system a useful tool for Materials Integration.

Mengda Li, Yutian Cheng, Tongjun Yu et al.

Stress-induced self-separation is one of the most efficient process for preparing native GaN substrate. The control of GaN film thickness is the key point for GaN film separating from substrate completely. Considering the bowing of bilayer, we studied the radial stress in GaN film before separation. A shrunken circular delamination front model was proposed to derive the unrelaxed stress after separation, and the energy release rate for GaN/sapphire systems of different thicknesses was investigated during the whole separation process. A critical thickness about 500–700 μm was determined for separating 2-inch (5.08 cm) GaN film from a sapphire substrate. By precisely controlling the GaN film thickness around such critical thickness, the complete separation rate could be increased greatly to 74%, which is of great importance in realizing the industrialization of GaN substrate. Keywords: GaN, Stress-induced self-separation, Bilayer thick film, Residual stress, Fracture

Oriane Baulin, Thierry Douillard, Damien Fabrègue et al.

Recently, the high ductility of Cu-based bulk metallic glasses (BMGs) has been directly linked to the presence of Y2O3 precipitates, and surrounding crystallized areas. Nevertheless, the formation of the precipitates remains to be defined. In this work, the structure of Y2O3 precipitates and crystallized zones of the BMG are investigated at the nanoscale in three-dimensions, shining light on their spatial distribution and their origin. Two kinds of precipitates were observed: small solid ones and large hollow ones. The mechanism proposed to explain the formation of hollow-precipitates is based on the Kirkendall effect. A model was implemented to assess the feasibility of this mechanism with the experimental results. Moreover, our results suggest that micro and nano-crystallized areas within the BMG are induced by the presence of yttria precipitates, with a correspondence between the size of the precipitate and the size of the crystallized areas. Keywords: Bulk metallic glasses, Microscopy, Kirkendall effect, Yttrium, Y2O3 precipitates

Kazuhei AOYAGI, Eiichi ISHII, Tsuyoshi ISHIDA

In the construction of a deep underground facility, the hydromechanical properties of the rock mass around an underground opening are changed significantly due to stress redistribution. This zone is called an excavation damaged zone (EDZ). In high-level radioactive waste disposal, EDZs can provide a shortcut for the escape of radionuclides to the surface environment. Therefore, it is important to develop a method for predicting the detailed characteristics of EDZs. For prediction of the EDZ in the Horonobe Underground Research Laboratory of Japan, we conducted borehole televiewer surveys, rock core analyses, and repeated hydraulic conductivity measurements. We observed that niche excavation resulted in the formation of extension fractures within 0.2 to 1.0 m into the niche wall, i.e., the extent of the EDZ is within 0.2 to 1.0 m into the niche wall. These results are largely consistent with the results of a finite element analysis implemented with the failure criteria considering failure mode. The hydraulic conductivity in the EDZ was increased by 3 to 5 orders of magnitude compared with the outer zone. The hydraulic conductivity in and around the EDZ has not changed significantly in the two years following excavation of the niche. These results show that short-term unloading due to excavation of the niche created a highly permeable EDZ.

Alexander N. Ionov, Tiecheng Lu, Yossi Gofer et al.

The influence of fast neutron irradiation on the structure and spatial distribution of Ge nanocrystals (NC) embedded in an amorphous SiO2 matrix has been studied. The investigation was conducted by means of laser Raman Scattering (RS), High Resolution Transmission Electron Microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). The irradiation of Ge- NC samples by a high dose of fast neutrons lead to a partial destruction of the nanocrystals. Full reconstruction of crystallinity was achieved after annealing the radiation damage at 8000C, which resulted in full restoration of the RS spectrum. HR-TEM images show, however, that the spatial distributions of Ge-NC changed as a result of irradiation and annealing. A sharp decrease in NC distribution towards the SiO2 surface has been observed. This was accompanied by XPS detection of Ge oxides and elemental Ge within both the surface and subsurface region.

Jagadeesh Babu Veluru, Satheesh K. K., Trivedi D.C. et al.

Electrospinning is one of the simplest techniques for obtaining polymer nano fibers. Nanofibers have large surface area to volume ratio and hence have excellent application potential in sensors, filter design etc. Polyaniline (PANI) is the well-known and widely studied conducting polymer, which however, is insoluble in many common organic solvents and hence difficult to process. PANI in its base form is non conductive but it can be made conducting by protonating with an acids such as hydrochloric acid (HCl) or camphor sulphonic acid (CSA). However, it is difficult to electrospin PANI by itself since we need preferably the polymer in solution form. In this study we have formed nanofibers of PANI (CSA) dispersed in Poly Methyl Methacrylate (PMMA) solution in chloroform. The morphology of the electrospun conducting PMMA-PANI composite fibers is studied using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The DC and AC conductivities of these fibers are measured and the results are discussed.

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