Frontiers of Mechanical Engineering

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Comprehensive analysis of the influence of structural and dynamic parameters on the accuracy of nano-precision positioning stages
Chengyuan LIANG, Fang YUAN, Xuedong CHEN, Wei JIANG, Lizhan ZENG, Xin LUO
Front. Mech. Eng.    2019, 14 (3): 255-272.   https://doi.org/10.1007/s11465-019-0538-x
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Nano-precision positioning stages are characterized by rigid-flexible coupling systems. The complex dynamic characteristics of mechanical structure of a stage, which are determined by structural and dynamic parameters, exert a serious influence on the accuracy of its motion and measurement. Systematic evaluation of such influence is essential for the design and improvement of stages. A systematic approach to modeling the dynamic accuracy of a nano-precision positioning stage is developed in this work by integrating a multi-rigid-body dynamic model of the mechanical system and measurement system models. The influence of structural and dynamic parameters, including aerostatic bearing configurations, motion plane errors, foundation vibrations, and positions of the acting points of driving forces, on dynamic accuracy is investigated by adopting the H-type configured stage as an example. The approach is programmed and integrated into a software framework that supports the dynamic design of nano-precision positioning stages. The software framework is then applied to the design of a nano-precision positioning stage used in a packaging lithography machine.

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Towards a next-generation production system for industrial robots: A CPS-based hybrid architecture for smart assembly shop floors with closed-loop dynamic cyber physical interactions
Qingmeng TAN, Yifei TONG, Shaofeng WU, Dongbo LI
Front. Mech. Eng.    2020, 15 (1): 1-11.   https://doi.org/10.1007/s11465-019-0563-9
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Given the multiple varieties and small batches, the production of industrial robots faces the ongoing challenges of flexibility, self-organization, self-configuration, and other “smart” requirements. Recently, cyber physical systems have provided a promising solution for the requirements mentioned above. Despite recent progress, some critical issues have not been fully addressed at the shop floor level, including dynamic reorganization and reconfiguration, ubiquitous networking, and time constrained computing. Toward the next generation production system for industrial robots, this study proposed a hybrid architecture for smart assembly shop floors with closed-loop dynamic cyber physical interactions. Aiming for dynamic reorganization and reconfiguration, the study also proposed modularized smart assembly units for the deployment of physical assembly processes. Enabling technologies, such as multiagent system (MAS), self-organized wireless sensor actuator networks, and edge computing, were discussed and then integrated into the proposed architecture. Furthermore, a multijoint robot assembly process was selected as a target scenario. Thus, an MAS was developed to simulate the coordination and negotiation mechanisms for the proposed architecture on the basis of the Java Agent Development Framework platform.

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Progress in terahertz nondestructive testing: A review
Shuncong ZHONG
Front. Mech. Eng.    2019, 14 (3): 273-281.   https://doi.org/10.1007/s11465-018-0495-9
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Terahertz (THz) waves, whose frequencies range between microwave and infrared, are part of the electromagnetic spectrum. A gap exists in THz literature because investigating THz waves is difficult due to the weak characteristics of the waves and the lack of suitable THz sources and detectors. Recently, THz nondestructive testing (NDT) technology has become an interesting topic. This review outlines several typical THz devices and systems and engineering applications of THz NDT techniques in composite materials, thermal barrier coatings, car paint films, marine protective coatings, and pharmaceutical tablet coatings. THz imaging has higher resolution but lower penetration than ultrasound imaging. This review presents the significance and advantages provided by the emerging THz NDT technique.

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Creep-fatigue crack growth behavior in GH4169 superalloy
Dianyin HU, Xiyuan WANG, Jianxing MAO, Rongqiao WANG
Front. Mech. Eng.    2019, 14 (3): 369-376.   https://doi.org/10.1007/s11465-018-0489-7
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This study aims to examine the crack growth behavior of turbine disc GH4169 superalloy under creep-fatigue loading. Crack growth experiments were performed on compact tension specimens using trapezoidal waveform with dwell time at the maximum load at 650 °C. The crack growth rate of GH4169 superalloy significantly increased with dwell time. The grain boundaries oxidize during the dwell process, thereby inducing an intergranular creep-fatigue fracture mode. In addition, testing data under the same dwell time showed scattering at the crack growth rate. Consequently, a modified model based on the Saxena equation was proposed by introducing a distribution factor for the crack growth rate. Microstructural observation confirmed that the small grain size and high volume fraction of the d phase led to a fast creep-fatigue crack growth rate at 650 °C, thus indicating that two factors, namely, fine grain and presence of the d phase at the grain boundary, increased the amount of weakened interface at high temperature, in which intergranular cracks may form and propagate.

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Creative design inspired by biological knowledge: Technologies and methods
Runhua TAN, Wei LIU, Guozhong CAO, Yuan SHI
Front. Mech. Eng.    2019, 14 (1): 1-14.   https://doi.org/10.1007/s11465-018-0511-0
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Biological knowledge is becoming an important source of inspiration for developing creative solutions to engineering design problems and even has a huge potential in formulating ideas that can help firms compete successfully in a dynamic market. To identify the technologies and methods that can facilitate the development of biologically inspired creative designs, this research briefly reviews the existing biological-knowledge-based theories and methods and examines the application of biological-knowledge-inspired designs in various fields. Afterward, this research thoroughly examines the four dimensions of key technologies that underlie the biologically inspired design (BID) process. This research then discusses the future development trends of the BID process before presenting the conclusions.

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Modeling and optimization of an enhanced battery thermal management system in electric vehicles
Mao LI, Yuanzhi LIU, Xiaobang WANG, Jie ZHANG
Front. Mech. Eng.    2019, 14 (1): 65-75.   https://doi.org/10.1007/s11465-018-0520-z
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This paper models and optimizes an air-based battery thermal management system (BTMS) in a battery module with 36 battery lithium-ion cells. A design of experiments is performed to study the effects of three key parameters (i.e., mass flow rate of cooling air, heat flux from the battery cell to the cooling air, and passage spacing size) on the battery thermal performance. Three metrics are used to evaluate the BTMS thermal performance, including (i) the maximum temperature in the battery module, (ii) the temperature uniformity in the battery module, and (iii) the pressure drop. It is found that (i) increasing the total mass flow rate may result in a more non-uniform distribution of the passage mass flow rate among passages, and (ii) a large passage spacing size may worsen the temperature uniformity on the battery walls. Optimization is also performed to optimize the passage spacing size. Results show that the maximum temperature difference of the cooling air in passages is reduced from 23.9 to 2.1 K by 91.2%, and the maximum temperature difference among the battery cells is reduced from 25.7 to 6.4 K by 75.1%.

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Connected morphable components-based multiscale topology optimization
Jiadong DENG, Claus B. W. PEDERSEN, Wei CHEN
Front. Mech. Eng.    2019, 14 (2): 129-140.   https://doi.org/10.1007/s11465-019-0532-3
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The advances of manufacturing techniques, such as additive manufacturing, have provided unprecedented opportunities for producing multiscale structures with intricate latticed/cellular material microstructures to meet the increasing demands for parts with customized functionalities. However, there are still difficulties for the state-of-the-art multiscale topology optimization (TO) methods to achieve manufacturable multiscale designs with cellular materials, partially due to the disconnectivity issue when tiling material microstructures. This paper attempts to address the disconnectivity issue by extending component-based TO methodology to multiscale structural design. An effective linkage scheme to guarantee smooth transitions between neighboring material microstructures (unit cells) is devised and investigated. Associated with the advantages of components-based TO, the number of design variables is greatly reduced in multiscale TO design. Homogenization is employed to calculate the effective material properties of the porous materials and to correlate the macro/structural scale with the micro/material scale. Sensitivities of the objective function with respect to the geometrical parameters of each component in each material microstructure have been derived using the adjoint method. Numerical examples demonstrate that multiscale structures with well-connected material microstructures or graded/layered material microstructures are realized.

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Electromagnetic interference modeling and suppression techniques in variable-frequency drive systems
Le YANG, Shuo WANG, Jianghua FENG
Front. Mech. Eng.    2018, 13 (3): 329-353.   https://doi.org/10.1007/s11465-018-0466-1
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Electromagnetic interference (EMI) causes electromechanical damage to the motors and degrades the reliability of variable-frequency drive (VFD) systems. Unlike fundamental frequency components in motor drive systems, high-frequency EMI noise, coupled with the parasitic parameters of the trough system, are difficult to analyze and reduce. In this article, EMI modeling techniques for different function units in a VFD system, including induction motors, motor bearings, and rectifier-inverters, are reviewed and evaluated in terms of applied frequency range, model parameterization, and model accuracy. The EMI models for the motors are categorized based on modeling techniques and model topologies. Motor bearing and shaft models are also reviewed, and techniques that are used to eliminate bearing current are evaluated. Modeling techniques for conventional rectifier-inverter systems are also summarized. EMI noise suppression techniques, including passive filter, Wheatstone bridge balance, active filter, and optimized modulation, are reviewed and compared based on the VFD system models.

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A brief review on key technologies in the battery management system of electric vehicles
Kailong LIU, Kang LI, Qiao PENG, Cheng ZHANG
Front. Mech. Eng.    2019, 14 (1): 47-64.   https://doi.org/10.1007/s11465-018-0516-8
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Batteries have been widely applied in many high-power applications, such as electric vehicles (EVs) and hybrid electric vehicles, where a suitable battery management system (BMS) is vital in ensuring safe and reliable operation of batteries. This paper aims to give a brief review on several key technologies of BMS, including battery modelling, state estimation and battery charging. First, popular battery types used in EVs are surveyed, followed by the introduction of key technologies used in BMS. Various battery models, including the electric model, thermal model and coupled electro-thermal model are reviewed. Then, battery state estimations for the state of charge, state of health and internal temperature are comprehensively surveyed. Finally, several key and traditional battery charging approaches with associated optimization methods are discussed.

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Principle of maximum entropy for reliability analysis in the design of machine components
Yimin ZHANG
Front. Mech. Eng.    2019, 14 (1): 21-32.   https://doi.org/10.1007/s11465-018-0512-z
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We studied the reliability of machine components with parameters that follow an arbitrary statistical distribution using the principle of maximum entropy (PME). We used PME to select the statistical distribution that best fits the available information. We also established a probability density function (PDF) and a failure probability model for the parameters of mechanical components using the concept of entropy and the PME. We obtained the first four moments of the state function for reliability analysis and design. Furthermore, we attained an estimate of the PDF with the fewest human bias factors using the PME. This function was used to calculate the reliability of the machine components, including a connecting rod, a vehicle half-shaft, a front axle, a rear axle housing, and a leaf spring, which have parameters that typically follow a non-normal distribution. Simulations were conducted for comparison. This study provides a design methodology for the reliability of mechanical components for practical engineering projects.

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Cracking evolution behaviors of lightweight materials based on in situ synchrotron X-ray tomography: A review
Y. Luo, S. C. Wu, Y. N. Hu, Y. N. Fu
Front. Mech. Eng.    2018, 13 (4): 461-481.   https://doi.org/10.1007/s11465-018-0481-2
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Damage accumulation and failure behaviors are crucial concerns during the design and service of a critical component, leading researchers and engineers to thoroughly identifying the crack evolution. Third-generation synchrotron radiation X-ray computed microtomography can be used to detect the inner damage evolution of a large-density material or component. This paper provides a brief review of studying the crack initiation and propagation inside lightweight materials with advanced synchrotron three-dimensional (3D) X-ray imaging, such as aluminum materials. Various damage modes under both static and dynamic loading are elucidated for pure aluminum, aluminum alloy matrix, aluminum alloy metal matrix composite, and aluminum alloy welded joint. For aluminum alloy matrix, metallurgical defects (porosity, void, inclusion, precipitate, etc.) or artificial defects (notch, scratch, pit, etc.) strongly affect the crack initiation and propagation. For aluminum alloy metal matrix composites, the fracture occurs either from the particle debonding or voids at the particle/matrix interface, and the void evolution is closely related with fatigued cycles. For the hybrid laser welded aluminum alloy, fatigue cracks usually initiate from gas pores located at the surface or sub-surface and gradually propagate to a quarter ellipse or a typical semi-ellipse profile.

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A naive optimization method for multi-line systems with alternative machines
Weichang KONG, Fei QIAO, Qidi WU
Front. Mech. Eng.    2019, 14 (4): 377-392.   https://doi.org/10.1007/s11465-019-0544-z
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The scheduling of parallel machines and the optimization of multi-line systems are two hotspots in the field of complex manufacturing systems. When the two problems are considered simultaneously, the resulting problem is much more complex than either of them. Obtaining sufficient training data for conventional data-based optimization approaches is difficult because of the high diversity of system structures. Consequently, optimization of multi-line systems with alternative machines requires a simple mechanism and must be minimally dependent on historical data. To define a general multi-line system with alternative machines, this study introduces the capability vector and matrix and the distribution vector and matrix. A naive optimization method is proposed in accordance with classic feedback control theory, and its key approaches are introduced. When a reasonable target value is provided, the proposed method can realize closed-loop optimization to the selected objective performance. Case studies are performed on a real 5/6-inch semiconductor wafer manufacturing facility and a simulated multi-line system constructed on the basis of the MiniFAB model. Results show that the proposed method can effectively and efficiently optimize various objective performance. The method demonstrates a potential for utilization in multi-objective optimization.

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Damage mechanism and evaluation model of compressor impeller remanufacturing blanks: A review
Haiyang LU, Yanle LI, Fangyi LI, Xingyi ZHANG, Chuanwei ZHANG, Jiyu DU, Zhen LI, Xueju RAN, Jianfeng LI, Weiqiang WANG
Front. Mech. Eng.    2019, 14 (4): 402-411.   https://doi.org/10.1007/s11465-019-0548-8
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The theoretical and technological achievements in the damage mechanism and evaluation model obtained through the national basic research program “Key Fundamental Scientific Problems on Mechanical Equipment Remanufacturing” are reviewed in this work. Large centrifugal compressor impeller blanks were used as the study object. The materials of the blanks were FV520B and KMN. The mechanism and evaluation model of ultra-high cycle fatigue, erosion wear, and corrosion damage were studied via theoretical calculation, finite element simulation, and experimentation. For ultra-high cycle fatigue damage, the characteristics of ultra-high cycle fatigue of the impeller material were clarified, and prediction models of ultra-high cycle fatigue strength were established. A residual life evaluation technique based on the “b-HV-N” (where b was the nonlinear parameter, HV was the Vickers hardness, and N was the fatigue life) double criterion method was proposed. For erosion wear, the flow field of gas-solid two-phase flow inside the impeller was simulated, and the erosion wear law was clarified. Two models for erosion rate and erosion depth calculation were established. For corrosion damage, the electrochemical and stress corrosion behaviors of the impeller material and welded joints in H2S/CO2 environment were investigated. KISCC (critical stress intensity factor) and da/dt (crack growth rate, where a is the total crack length and t is time) varied with H2S concentration and temperature, and their variation laws were revealed. Through this research, the key scientific problems of the damage behavior and mechanism of remanufacturing objects in the multi-strength field and cross-scale were solved. The findings provide theoretical and evaluation model support for the analysis and evaluation of large centrifugal compressor impellers before remanufacturing.

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Fatigue crack initiation of magnesium alloys under elastic stress amplitudes: A review
B. J. WANG, D. K. XU, S. D. WANG, E. H. HAN
Front. Mech. Eng.    2019, 14 (1): 113-127.   https://doi.org/10.1007/s11465-018-0482-1
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The most advantageous property of magnesium (Mg) alloys is their density, which is lower compared with traditional metallic materials. Mg alloys, considered the lightest metallic structural material among others, have great potential for applications as secondary load components in the transportation and aerospace industries. The fatigue evaluation of Mg alloys under elastic stress amplitudes is very important in ensuring their service safety and reliability. Given their hexagonal close packed structure, the fatigue crack initiation of Mg and its alloys is closely related to the deformation mechanisms of twinning and basal slips. However, for Mg alloys with shrinkage porosities and inclusions, fatigue cracks will preferentially initiate at these defects, remarkably reducing the fatigue lifetime. In this paper, some fundamental aspects about the fatigue crack initiation mechanisms of Mg alloys are reviewed, including the 3 followings: 1) Fatigue crack initiation of as-cast Mg alloys, 2) influence of microstructure on fatigue crack initiation of wrought Mg alloys, and 3) the effect of heat treatment on fatigue initiation mechanisms. Moreover, some unresolved issues and future target on the fatigue crack initiation mechanism of Mg alloys are also described.

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Influence of the field humiture environment on the mechanical properties of 316L stainless steel repaired with Fe314
Lianzhong ZHANG, Dichen LI, Shenping YAN, Ruidong XIE, Hongliang QU
Front. Mech. Eng.    2018, 13 (4): 513-519.   https://doi.org/10.1007/s11465-018-0503-0
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The mechanical properties of 316L stainless steel repaired with Fe314 under different temperatures and humidities without inert gas protection were studied. Results indicated favorable compatibility between Fe314 and 316L stainless steel. The average yield strength, tensile strength, and sectional contraction percentage were higher in repaired samples than in 316L stainless steel, whereas the elongation rate was slightly lower. The different conditions of humiture environment on the repair sample exerted minimal influence on tensile and yield strengths. The Fe314 cladding layer was mainly composed of equiaxed grains and mixed with randomly oriented columnar crystal and tiny pores or impurities in the tissue. Results indicated that the hardness value of Fe314 cladding layer under different humiture environments ranged within 419–451.1 HV0.2. The field humiture environment also showed minimal impact on the average hardness of Fe314 cladding layers. Furthermore, 316L stainless steel can be repaired through laser cladding by using Fe314 powder without inert gas protection under different temperatures and humidity environments.

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Finite element modeling of counter-roller spinning for large-sized aluminum alloy cylindrical parts
Dawei ZHANG, Fan LI, Shuaipeng LI, Shengdun ZHAO
Front. Mech. Eng.    2019, 14 (3): 351-357.   https://doi.org/10.1007/s11465-019-0528-z
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Counter-roller spinning (CRS), where the mandrel is replaced by rollers, is an effective means of manufacturing large-sized, thin-walled, cylindrical parts with more than 2500 mm diameter. CRS is very complex because of multi-axis rotation, multi-local loading along the circumference, and radial-axial compound deformation. Analytical or experimental methods cannot fully understand CRS. Meanwhile, numerical simulation is an adequate approach to investigate CRS with comprehensive understanding and a low cost. Thus, a finite element (FE) model of CRS was developed with the FORGE code via meshing technology, material modeling, determining the friction condition, and so on. The local fine mesh moving with the roller is one of highlights of the model. The developed 3D-FE model was validated through a CRS experiment by using a tubular blank with a 720 mm outer diameter. The developed 3D-FE model of CRS can provide a basis for parameter optimization, process control, die design, and so on. The data on force and energy predicted by the 3D-FE model can offer reasonable suggestions for determining the main mechanical parameters of CRS machines and selecting the motors. With the predicted data, an all-electric servo-drive system/machine with distributed power was designed in this work for CRS with four pairs of rollers to manufacture a large-sized, thin-walled, cylindrical part with 6000 mm diameter.

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Real-time task processing method based on edge computing for spinning CPS
Shiyong YIN, Jinsong BAO, Jie LI, Jie ZHANG
Front. Mech. Eng.    2019, 14 (3): 320-331.   https://doi.org/10.1007/s11465-019-0542-1
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Spinning production is a typical continuous manufacturing process characterized by high speed and uncertain dynamics. Each manufacturing unit in spinning production produces various real-time tasks, which may affect production efficiency and yarn quality if not processed in time. This paper presents an edge computing-based method that is different from traditional centralized cloud computation because its decentralization characteristics meet the high-speed and high-response requirements of yarn production. Edge computing nodes, real-time tasks, and edge computing resources are defined. A system model is established, and a real-time task processing method is proposed for the edge computing scenario. Experimental results indicate that the proposed real-time task processing method based on edge computing can effectively solve the delay problem of real-time task processing in spinning cyber-physical systems, save bandwidth, and enhance the security of task transmission.

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Recent development on innovation design of reconfigurable mechanisms in China
Wuxiang ZHANG, Shengnan LU, Xilun DING
Front. Mech. Eng.    2019, 14 (1): 15-20.   https://doi.org/10.1007/s11465-018-0517-7
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Reconfigurable mechanisms can deliberately reconfigure themselves by rearranging the connectivity of components to meet the different requirements of tasks. Metamorphic and origami-derived mechanisms are two kinds of typical reconfigurable mechanisms, which have attracted increasing attention in the field of mechanisms since they were proposed. Improving the independent design level, innovation, and international competitive powers of reconfigurable mechanical products is important. Summarizing related significant innovation research and application achievements periodically will shed light on research directions and promote academic exchanges. This paper presents an overview of recent developments in innovation design of reconfigurable mechanisms in China, including metamorphic and origami mechanisms and their typical applications. The future development trends are analyzed and forecasted.

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Review of materials used in laser-aided additive manufacturing processes to produce metallic products
Xiaodong NIU, Surinder SINGH, Akhil GARG, Harpreet SINGH, Biranchi PANDA, Xiongbin PENG, Qiujuan ZHANG
Front. Mech. Eng.    2019, 14 (3): 282-298.   https://doi.org/10.1007/s11465-019-0526-1
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Rapid prototyping (RP) or layered manufacturing (LM) technologies have been extensively used to manufacture prototypes composed mainly of plastics, polymers, paper, and wax due to the short product development time and low costs of these technologies. However, such technologies, with the exception of selective laser melting and sintering, are not used to fabricate metallic products because of the resulting poor life, short cycle, poor surface finish, and low structural integrity of the fabricated parts. The properties endowed by these parts do not match those of functional parts. Therefore, extensive research has been conducted to develop new additive manufacturing (AM) technologies by extending existing RP technologies. Several AM technologies have been developed for the fabrication of metallic objects. These technologies utilize materials, such as Ni-, Al-, and Ti-based alloys and stainless steel powders, to fabricate high-quality functional components. The present work reviews the type of materials used in laser-based AM processes for the manufacture of metallic products. The advantages and disadvantages of processes and different materials are summarized, and future research directions are discussed in the final section. This review can help experts select the ideal type of process or technology for the manufacturing of elements composed of a given alloy or material (Ni, Ti, Al, Pb, and stainless steel).

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Isomorphism analysis on generalized modules oriented to the distributed parameterized intelligent product platform
Shasha ZENG, Weiping PENG, Tiaoyu LEI
Front. Mech. Eng.    2020, 15 (1): 12-23.   https://doi.org/10.1007/s11465-019-0555-9
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The distributed parameterized intelligent product platform (DPIPP) contains many agents of a product minimum approximate autonomous subsystem (generalized module). These distributed agents communicate, coordinate, and cooperate using their knowledge and skills and eventually accomplish the design for mass customization in a loosely coupled environment. In this study, a new method of isomorphism analysis on generalized modules oriented to DPIPP is proposed. First, on the basis of the bill of material partition and generalized module mining, the parameters of the main characteristics are extracted to construct the main characteristic parameter matrix. Second, similarity calculation of generalized modules is realized by improving the clustering using representatives algorithm, and isomorphism model sets are obtained. Generalized modules with a similar structure are combined to complete the isomorphism analysis. The effectiveness of the proposed method is verified by taking high- and medium-pressure valve data as an example.

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Nonlinear dynamics of a wind turbine tower
A. GESUALDO, A. IANNUZZO, F. PENTA, M. MONACO
Front. Mech. Eng.    2019, 14 (3): 342-350.   https://doi.org/10.1007/s11465-019-0524-3
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The recent proliferation of wind turbines has revealed problems in their vulnerability under different site conditions, as evidenced by recent collapses of wind towers after severe actions. Analyses of structures subjected to variable actions can be conducted through several methods with different accuracy levels. Nonlinear dynamics is the most reliable among such methods. This study develops a numerical procedure to obtain approximate solutions for rigid-plastic responses of structures subjected to base harmonic pulses. The procedure’s model is applied to a wind turbine tower subjected to inertial forces generated by harmonic ground acceleration, and failure is assumed to depend on the formation of shear hinges. The proposed approach provides an efficient representation of the post-elastic behavior of the structure, has a low computational cost and high effectiveness, and uses a limited number of mechanical parameters.

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Robust topology optimization of multi-material lattice structures under material and load uncertainties
Yu-Chin CHAN, Kohei SHINTANI, Wei CHEN
Front. Mech. Eng.    2019, 14 (2): 141-152.   https://doi.org/10.1007/s11465-019-0531-4
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Enabled by advancements in multi-material additive manufacturing, lightweight lattice structures consisting of networks of periodic unit cells have gained popularity due to their extraordinary performance and wide array of functions. This work proposes a density-based robust topology optimization method for meso- or macro-scale multi-material lattice structures under any combination of material and load uncertainties. The method utilizes a new generalized material interpolation scheme for an arbitrary number of materials, and employs univariate dimension reduction and Gauss-type quadrature to quantify and propagate uncertainty. By formulating the objective function as a weighted sum of the mean and standard deviation of compliance, the tradeoff between optimality and robustness can be studied and controlled. Examples of a cantilever beam lattice structure under various material and load uncertainty cases exhibit the efficiency and flexibility of the approach. The accuracy of univariate dimension reduction is validated by comparing the results to the Monte Carlo approach.

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An application of game theory in distributed collaborative decision making
Angran XIAO
Front. Mech. Eng.    2019, 14 (1): 85-101.   https://doi.org/10.1007/s11465-019-0523-4
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In a distributed product realization environment, new paradigms and accompanying software systems are necessary to support the collaborative work of geographically dispersed engineering teams from different disciplines who have different knowledge, experience, tools and resources. To verify the concept of collaboration by separation, we propose a generic information communication medium to enable knowledge representation and exchange between engineering teams, a digital interface. Across digital interfaces, each engineering team maintains its own perspective towards the product realization problem, and each controls a subset of design variables and seeks to maximize its own payoff function subject to individual constraints. Hence, we postulate the use of principles from game theory to model the relationships between engineering teams and facilitate collaborative decision making without causing unnecessary information exchange or iteration across digital interfaces. A product design and manufacturing scenario is introduced to demonstrate the efficacy of using game theory to maintain a clean interface between design and manufacturing teams.

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An exploratory study for predicting component reliability with new load conditions
Zhengwei HU, Xiaoping DU
Front. Mech. Eng.    2019, 14 (1): 76-84.   https://doi.org/10.1007/s11465-018-0522-x
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Reliability is important to design innovation. A new product should be not only innovative, but also reliable. For many existing components used in the new product, their reliability will change because the applied loads are different from the ones for which the components are originally designed and manufactured. Then the new reliability must be re-evaluated. The system designers of the new product, however, may not have enough information to perform this task. With a beam problem as a case study, this study explores a feasible way to re-evaluate the component reliability with new loads given the following information: The original reliability of the component with respect to the component loads and the distributions of the new component loads. Physics-based methods are employed to build the equivalent component limit-state function that can predict the component failure under the new loads. Since the information is limited, the re-evaluated component reliability is given by its maxi- mum and minimum values. The case study shows that good accuracy can be obtained even though the new reliability is provided with the aforementioned interval.

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An improved artificial bee colony algorithm with MaxTF heuristic rule for two-sided assembly line balancing problem
Xiaokun DUAN, Bo WU, Youmin HU, Jie LIU, Jing XIONG
Front. Mech. Eng.    2019, 14 (2): 241-253.   https://doi.org/10.1007/s11465-018-0518-6
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Two-sided assembly line is usually used for the assembly of large products such as cars, buses, and trucks. With the development of technical progress, the assembly line needs to be reconfigured and the cycle time of the line should be optimized to satisfy the new assembly process. Two-sided assembly line balancing with the objective of minimizing the cycle time is called TALBP-2. This paper proposes an improved artificial bee colony (IABC) algorithm with the MaxTF heuristic rule. In the heuristic initialization process, the MaxTF rule defines a new task’s priority weight. On the basis of priority weight, the assignment of tasks is reasonable and the quality of an initial solution is high. In the IABC algorithm, two neighborhood strategies are embedded to balance the exploitation and exploration abilities of the algorithm. The employed bees and onlooker bees produce neighboring solutions in different promising regions to accelerate the convergence rate. Furthermore, a well-designed random strategy of scout bees is developed to escape local optima. The experimental results demonstrate that the proposed MaxTF rule performs better than other heuristic rules, as it can find the best solution for all the 10 test cases. A comparison of the IABC algorithm and other algorithms proves the effectiveness of the proposed IABC algorithm. The results also denote that the IABC algorithm is efficient and stable in minimizing the cycle time for the TALBP-2, and it can find 20 new best solutions among 25 large-sized problem cases.

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A family of non-conforming crack front elements of quadrilateral and triangular types for 3D crack problems using the boundary element method
Guizhong XIE, Fenglin ZHOU, Hao LI, Xiaoyu WEN, Fannian MENG
Front. Mech. Eng.    2019, 14 (3): 332-341.   https://doi.org/10.1007/s11465-019-0540-3
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This study focuses on establishing non- conforming crack front elements of quadrilateral and triangular types for 3D crack problems when the dual boundary element method is applied. The asymptotic behavior of the physical variables in the area near the crack front is fully considered in the construction of the shape function. In the developed quadrilateral and triangular crack front elements, the asymptotic term, which captures the asymptotic behavior of the physical variable, is multiplied directly by the conventional Lagrange shape function to form a new crack front shape function. Several benchmark numerical examples that consider penny-shaped cracks and straight-edge crack problems are presented to illustrate the validity and efficiency of the developed crack front elements.

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Robust topology optimization of hinge-free compliant mechanisms with material uncertainties based on a non-probabilistic field model
Junjie ZHAN, Yangjun LUO
Front. Mech. Eng.    2019, 14 (2): 201-212.   https://doi.org/10.1007/s11465-019-0529-y
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This paper presents a new robust topology optimization framework for hinge-free compliant mecha- nisms with spatially varying material uncertainties, which are described using a non-probabilistic bounded field model. Bounded field uncertainties are efficiently represented by a reduced set of uncertain-but-bounded coefficients on the basis of the series expansion method. Robust topology optimization of compliant mechanisms is then defined to minimize the variation in output displacement under constraints of the mean displacement and predefined material volume. The nest optimization problem is solved using a gradient-based optimization algorithm. Numerical examples are presented to illustrate the effectiveness of the proposed method for circumventing hinges in topology optimization of compliant mechanisms.

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Review on mechanism and process of surface polishing using lasers
Arun KRISHNAN, Fengzhou FANG
Front. Mech. Eng.    2019, 14 (3): 299-319.   https://doi.org/10.1007/s11465-019-0535-0
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Laser polishing is a technology of smoothening the surface of various materials with highly intense laser beams. When these beams impact on the material surface to be polished, the surface starts to be melted due to the high temperature. The melted material is then relocated from the ‘peaks to valleys’ under the multidirectional action of surface tension. By varying the process parameters such as beam intensity, energy density, spot diameter, and feed rate, different rates of surface roughness can be achieved. High precision polishing of surfaces can be done using laser process. Currently, laser polishing has extended its applications from photonics to molds as well as bio-medical sectors. Conventional polishing techniques have many drawbacks such as less capability of polishing freeform surfaces, environmental pollution, long processing time, and health hazards for the operators. Laser polishing on the other hand eliminates all the mentioned drawbacks and comes as a promising technology that can be relied for smoothening of initial topography of the surfaces irrespective of the complexity of the surface. Majority of the researchers performed laser polishing on materials such as steel, titanium, and its alloys because of its low cost and reliability. This article gives a detailed overview of the laser polishing mechanism by explaining various process parameters briefly to get a better understanding about the entire polishing process. The advantages and applications are also explained clearly to have a good knowledge about the importance of laser polishing in the future.

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Balancing method without trial weights for rotor systems based on similitude scale model
Ruiduo YE, Liping WANG, Xiaojie HOU, Zhong LUO, Qingkai HAN
Front. Mech. Eng.    2018, 13 (4): 571-580.   https://doi.org/10.1007/s11465-018-0478-x
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A balancing method without trial weights based on the dynamic similitude scale model was proposed as a solution to the balancing problem of a large-scale rotor system. This method could be used to directly obtain the required coefficients for the balancing problem of the prototype system through a similarity model test without a prototype test. Thus, the weight test process of the prototype system was effectively eliminated in the proposed balancing method. First, with the rotor system as the research object, the analytical expression of the influence coefficient was derived on the basis of rotor dynamics theory. Then, through calculation and dimensional analysis methods, the similitude relationships of the rotor system and the influence coefficient were deduced on the basis of dynamic similitude theory. The correctness of the proposed similitude relationships was verified through numerical simulation and experiment. The balancing method without trial weights was proposed based on the similitude relationship of the influence coefficient. The effect of the balancing method without trial weights was compared with that of the traditional influence coefficient method through numerical simulation, and the results verified the correctness and effectiveness of the proposed balancing method. The results of this study provide theoretical supplements for the balancing method and the similitude design of the rotor system.

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Robust optimization of the billet for isothermal local loading transitional region of a Ti-alloy rib-web component based on dual-response surface method
Ke WEI, Xiaoguang FAN, Mei ZHAN, Miao MENG
Front. Mech. Eng.    2018, 13 (3): 376-384.   https://doi.org/10.1007/s11465-018-0500-3
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Billet optimization can greatly improve the forming quality of the transitional region in the isothermal local loading forming (ILLF) of large-scale Ti-alloy rib-web components. However, the final quality of the transitional region may be deteriorated by uncontrollable factors, such as the manufacturing tolerance of the preforming billet, fluctuation of the stroke length, and friction factor. Thus, a dual-response surface method (RSM)-based robust optimization of the billet was proposed to address the uncontrollable factors in transitional region of the ILLF. Given that the die underfilling and folding defect are two key factors that influence the forming quality of the transitional region, minimizing the mean and standard deviation of the die underfilling rate and avoiding folding defect were defined as the objective function and constraint condition in robust optimization. Then, the cross array design was constructed, a dual-RSM model was established for the mean and standard deviation of the die underfilling rate by considering the size parameters of the billet and uncontrollable factors. Subsequently, an optimum solution was derived to achieve the robust optimization of the billet. A case study on robust optimization was conducted. Good results were attained for improving the die filling and avoiding folding defect, suggesting that the robust optimization of the billet in the transitional region of the ILLF was efficient and reliable.

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