Symmetry in Mechanical Engineering: Properties and Applications

A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Engineering and Materials".

Deadline for manuscript submissions: 31 May 2024 | Viewed by 3834

Special Issue Editors

School of Mechanical Engineering, Shandong University, Jinan 250061, China
Interests: reliability of electronic packaging; thermal management; friction and wear; advanced structural materials; computational materials
Special Issues, Collections and Topics in MDPI journals
College of Electrical Engineering, Henan University of Technology, Zhengzhou 450001, China
Interests: flexible electronics and sensors; thin film transistor; neuromorphic device; mechanical nondestructive testing technology
Centre for Advanced Laser Manufacturing (CALM), School of Mechanical Engineering, Shandong University of Technology, Zibo 255000, China
Interests: advanced functional materials and structures; thermal management; computational materials; ultrafast laser processing

Special Issue Information

Dear Colleagues,

Symmetry in mechanical engineering refers to the balanced arrangement of components and features in a system or design. Symmetrical properties, such as axial, radial, or planar symmetry, enable the uniform distribution of forces, vibrations, and loads, resulting in improved structural integrity and reduced wear. A symmetrical design often offers greater stability, ease of manufacturing, and cost-effectiveness, and it has diverse applications in mechanical engineering, e.g., in structural engineering, symmetrical shapes and arrangements enhance load-bearing capacity, minimizing stress concentrations; in fluid mechanics, symmetrical profiles reduce drag, enhance flow characteristics, and improve energy efficiency. On the other hand, asymmetry can offer unique advantages to  mechanical systems in specific scenarios: e.g., by introducing asymmetry via variations in material properties, surface textures, or geometry, a specialized thermal behavior could be performed, such as localized heat spreading, directed thermal gradients, or controlled temperature differentials. Therefore, constructing or modifying symmetry could provide properties that enhance the reliability, functionality and efficiency of mechanical systems, which is an effective approach in mechanical engineering to satisfy the requirements of performance and functions for different applications and under different conditions.

Prof. Dr. Yunqing Tang
Dr. Kun Xu
Dr. Bing Yang
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Symmetry is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • mechanical engineering
  • symmetric structure
  • asymmetric structure
  • mechanical design
  • machining
  • MEMS
  • structural reliability
  • thermal management
  • mass transfer
  • topology optimization

Published Papers (4 papers)

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Research

15 pages, 13929 KiB  
Article
Effects of KoBo-Processing and Subsequent Annealing Treatment on Grain Boundary Network and Texture Development in Laser Powder Bed Fusion (LPBF) AlSi10Mg Alloy
by Przemysław Snopiński
Symmetry 2024, 16(1), 122; https://doi.org/10.3390/sym16010122 - 19 Jan 2024
Viewed by 596
Abstract
It is well known that the properties of polycrystalline metals are related to grain boundaries (GBs), which are fundamental structural elements where crystallographic orientations change abruptly and often exhibit some degree of symmetry. Grain boundaries often exhibit unique structural, chemical, and electronic properties [...] Read more.
It is well known that the properties of polycrystalline metals are related to grain boundaries (GBs), which are fundamental structural elements where crystallographic orientations change abruptly and often exhibit some degree of symmetry. Grain boundaries often exhibit unique structural, chemical, and electronic properties that differ from bulk crystalline domains. Their effects on material properties, including mechanical strength, corrosion resistance, and electrical conductivity, make grain boundaries a focus of intense scientific investigation. In this study, the microstructural transformation of an AlSi10Mg alloy subjected to KoBo extrusion and subsequent annealing is investigated. A notable discovery is the effectiveness of a strain-annealing method for grain boundary engineering (GBE) of the LPBF AlSi10Mg alloy. In particular, this study shows a significant increase in the population of coincidence site lattice boundaries (CSL), which embody the symmetry of the crystal lattice structure. These boundaries, which are characterised by a high degree of symmetry, contribute to their special properties compared to random grain boundaries. The experimental results emphasise the crucial role of strain-induced boundary migration (SIBM) in the development of a brass texture in the microstructure of the alloy after annealing. In addition, the presented results demonstrate the feasibility of applying GBE to materials with high stacking fault energy (SFE), which opens up new possibilities for optimizing their properties. Full article
(This article belongs to the Special Issue Symmetry in Mechanical Engineering: Properties and Applications)
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24 pages, 9481 KiB  
Article
Distributed Rotational Inertia Load Excitation Model and Its Impact on High-Speed Jointed Rotor Dynamic Response
by Fayong Wu, Jie Hong and Xueqi Chen
Symmetry 2023, 15(11), 2009; https://doi.org/10.3390/sym15112009 - 01 Nov 2023
Viewed by 655
Abstract
Contemporary aero-engines aim for enhanced efficiency and weight reduction. They are designed to increase rotor operational speed while reducing rotor bending stiffness. This may result in bending deformation in rotor systems within the operational speed range. Such deformation can change the relative positions [...] Read more.
Contemporary aero-engines aim for enhanced efficiency and weight reduction. They are designed to increase rotor operational speed while reducing rotor bending stiffness. This may result in bending deformation in rotor systems within the operational speed range. Such deformation can change the relative positions of rotor components, potentially causing increased mass asymmetry or unbalance. Traditional rotor dynamic models typically assume a constant rotor state. They approximate unbalance using constant mass eccentricities at certain rotor cross-sections. However, this approach has its limitations. This paper focuses on a high-speed jointed rotor system. A distributed rotational inertia load excitation model is proposed. This model explicitly considers the rotor’s variable unbalance state at different operational speeds. The study involves both simulations and experimental investigations. The results show that at high speeds, bending deformation causes the unbalance and rotational inertia load to shift from a concentrated to a distributed state. Notably, the localized rotational inertia moment from thin-disk components like turbine disks becomes significant at high speeds. This results in a rapid increase in bearing load with rotational speed. It also profoundly affects the rotor’s joints, causing interfacial slip and sudden changes in rotor vibration characteristics. Full article
(This article belongs to the Special Issue Symmetry in Mechanical Engineering: Properties and Applications)
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22 pages, 7587 KiB  
Article
Analysis of High-Speed Rotor Vibration Failure Due to Sudden Angular Deformation of Bolt Joints
by Fayong Wu, Jie Hong, Xueqi Chen and Yanhong Ma
Symmetry 2023, 15(10), 1937; https://doi.org/10.3390/sym15101937 - 19 Oct 2023
Viewed by 817
Abstract
As the efficiency of advanced aero engines improves, the operational speed of their rotors increases. This heightened operational speed makes the rotor dynamics highly sensitive to changes in the rotor’s mass asymmetry state, or unbalance state. During the use of a dual-spool turbofan [...] Read more.
As the efficiency of advanced aero engines improves, the operational speed of their rotors increases. This heightened operational speed makes the rotor dynamics highly sensitive to changes in the rotor’s mass asymmetry state, or unbalance state. During the use of a dual-spool turbofan engine, when its supercritical high-pressure rotor (HPR) exceeds a certain operational speed, the rotor’s vibration spikes and continues to increase with the operational speed until it drops sharply near the maximum operational speed. Analysis of the bolt joints in the faulty rotor reveals various phenomena such as joint interface damage, changes in bolt loosening torque distribution, and alterations in rotor initial unbalance. This paper proposes that at high operational speeds, the bolt joint of the HPR undergoes sudden angular deformation, resulting in the slanting of the principal axis of inertia of the turbine disk. This slant leads to changes in the unbalanced state of the HPR. The additional unbalance causes a sudden rotational inertia load excitation, triggering the rotor vibration failure. Subsequently, a rotor dynamic model that incorporates the angular deformation of the joints is established to simulate how this joint deformation influences the dynamic response of the rotor. The simulation results align well with the observed failure phenomenon and validate the proposed failure mechanism. Finally, troubleshooting measures are proposed and implemented in the faulty engine, effectively mitigating the vibration fault. Full article
(This article belongs to the Special Issue Symmetry in Mechanical Engineering: Properties and Applications)
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34 pages, 12809 KiB  
Article
System Modeling and Simulation for Investigating Dynamic Characteristics of Geared Symmetric System Based on Linear Analysis
by Joo-Mi Bahk, Sun-Hak Kim and Jong-Yun Yoon
Symmetry 2023, 15(10), 1904; https://doi.org/10.3390/sym15101904 - 11 Oct 2023
Viewed by 1029
Abstract
Complex vibrational phenomena, such as gear impacts and mesh stiffness excitations, often require a significant amount of effort to be revealed using nonlinear analytical methods. However, key parameters for addressing vibrational problems can often be identified through simplified approaches based on linear analysis [...] Read more.
Complex vibrational phenomena, such as gear impacts and mesh stiffness excitations, often require a significant amount of effort to be revealed using nonlinear analytical methods. However, key parameters for addressing vibrational problems can often be identified through simplified approaches based on linear analysis models. In light of these considerations, this study aimed to propose linear analytical methods to investigate the influences of various key parameters within symmetric systems. To achieve the main goal of this study, system modeling and eigensolutions were first implemented, focusing on a specific manual transmission with a front-engine/front-wheel configuration. Second, analytical techniques to reduce the number of degrees of freedom from the original symmetric system were suggested, and the reduced model was validated. Third, the system responses in the time domain were examined, along with key system parameters, such as gear mesh stiffness and clutch dampers, using state–variable equations. As a result, the findings from the linear system model demonstrated the fundamental dynamic characteristics of the torsional system within specific frequency regimes relevant to noise and vibration problems. Furthermore, the reduced lumped linear model employing the state–variable formula established its reliability in determining key parameters for mitigating noise and vibration problems. Full article
(This article belongs to the Special Issue Symmetry in Mechanical Engineering: Properties and Applications)
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