2021年, 第34卷, 第6期　
刊出日期：2021-12-16

  

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Editorial
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  Integrated Structures and Materials Design of Mechanical Components

  Geng Chen, Lele Zhang, Christoph Broechmann, Chao Chang

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 132-132. https://doi.org/10.1186/s10033-021-00659-z

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Original Article
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  Numerical Modelling of the Powder Metallurgical Manufacturing Chain of High Strength Sintered Gears

  Ali Rajaei, Yuanbin Deng, Oliver Schenk, Soheil Rooein, Alexander Bezold, Christoph Broeckmann

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 143-143. https://doi.org/10.1186/s10033-021-00646-4

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  This paper presents a digital model for the powder metallurgical (PM) production chain of high-performance sintered gears based on an integrated computational materials engineering (ICME) platform. Discrete and finite element methods (DEM and FEM) were combined to describe the macroscopic material response to the thermomechanical loads and process conditions during the entire production process. The microstructural evolution during the sintering process was predicted on the meso-scale using a Monte-Carlo Model. The effective elastic properties were determined by a homogenization method based on modelling a representative volume element (RVE). The results were subsequently used for the FE modelling of the heat treatment process. Through the development of multi-scale models, it was possible obtain characteristics of the microstructural features. The predicted hardness and residual stress distributions allowed the calculation of the tooth root load bearing capacity of the heat-treated sintered gears.
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  RSDM: A Powerful Direct Method to Predict the Asymptotic Cyclic Behavior of Elastoplastic Structures

  Konstantinos V. Spiliopoulos, Ioannis A. Kapogiannis

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 140-140. https://doi.org/10.1186/s10033-021-00658-0

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  Mechanical engineering structures and structural components are often subjected to cyclic thermomechanical loading which stresses their material beyond its elastic limits well inside the inelastic regime. Depending on the level of loading inelastic strains may lead either to failure, due to low cycle fatigue or ratcheting, or to safety, through elastic shakedown. Thus, it is important to estimate the asymptotic stress state of such structures. This state may be determined by cumbersome incremental time-stepping calculations. Direct methods, alternatively, have big computational advantages as they focus on the characteristics of these states and try to establish them, in a direct way, right from the beginning of the calculations. Among the very few such general-purpose direct methods, a powerful direct method which has been called RSDM has appeared in the literature. The method may directly predict any asymptotic state when the exact time history of the loading is known. The advantage of the method is due to the fact that it addresses the physics of the asymptotic cycle and exploits the cyclic nature of its expected residual stress distribution. Based on RSDM a method for the shakedown analysis of structures, called RSDM-S has also been developed. Despite most direct methods for shakedown, RSDM-S does not need an optimization algorithm for its implementation. Both RSDM and RSDM-S may be implemented in any Finite Element Code. A thorough review of both these methods, together with examples of implementation are presented herein.
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  Statistical Analyses of the Strengths of Particulate Reinforced Metal Matrix Composites (PRMMCs) Subjected to Multiple Tensile and Shear Stresses

  Geng Chen, Shengzhen Xin, Lele Zhang, Christoph Broeckmann

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 142-142. https://doi.org/10.1186/s10033-021-00660-6

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  For design and application of particulate reinforced metal matrix composites (PRMMCs), it is essential to predict the material strengths and understand how do they relate to constituents and microstructural features. To this end, a computational approach consists of the direct methods, homogenization, and statistical analyses is introduced in our previous studies. Since failure of PRMMC materials are often caused by time-varied combinations of tensile and shear stresses, the established approach is extended in the present work to take into account of these situations. In this paper, ultimate strengths and endurance limits of an exemplary PRMMC material, WC-Co, are predicted under three independently varied tensile and shear stresses. In order to cover the entire load space with least amount of weight factors, a new method for generating optimally distributed weight factors in an n dimensional space is formulated. Employing weight factors determined by this algorithm, direct method calculations were performed on many statistically equivalent representative volume elements (SERVE) samples. Through analyzing statistical characteristics associated with results the study suggests a simplified approach to estimate the material strength under superposed stresses without solving the difficult high dimensional shakedown problem.
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  Delamination Testing of AlSi10Mg Sandwich Structures with Pyramidal Lattice Truss Core made by Laser Powder Bed Fusion

  M. Nuño, J. Bühring, M. N. Rao, K. -U. Schröder

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 126-126. https://doi.org/10.1186/s10033-021-00643-7

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  Sandwich structures possess a high bending stiffness compared to monolithic structures with a similar weight. This makes them very suitable for lightweight applications, where high stiffness to weight ratios are needed. Most common manufacturing methods of sandwich structures involve adhesive bonding of the core material with the sheets. However, adhesive bonding is prone to delamination, a failure mode that is often difficult to detect. This paper presents the results of delamination testing of fully additive manufactured (AM) AlSi10Mg sandwich structures with pyramidal lattice truss core using Laser Powder Bed Fusion (LPBF). The faces and struts are 0.5 mm thick, while the core is 2 mm thick. The inclination of the struts is 45°. To characterise the bonding strength, climbing drum peel tests and out-of-plane tensile tests are performed. Analytical formulas are derived to predict the expected failure loads and modes. The analytics and tests are supported by finite element (FE) calculations. From the analytic approach, design guidelines to avoid delamination in AM sandwich structures are derived. The study presents a critical face sheet thickness to strut diameter ratio for which the structure can delaminate. This ratio is mainly influenced by the inclination of the struts. The peel tests resulted in face yielding, which can also be inferred from the analytics and numerics. The out-of-plane tensile tests didn't damage the structure.
Research article
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  Influence of Ultrasonic Surface Rolling Process and Shot Peening on Fretting Fatigue Performance of Ti-6Al-4V

  Ning Wang, Jinlong Zhu, Bai Liu, Xiancheng Zhang, Jiamin Zhang, Shantung Tu

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 90-90. https://doi.org/10.1186/s10033-021-00611-1

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  At present, there are many studies on the residual stress field and plastic strain field introduced by surface strengthening, which can well hinder the initiation of early fatigue cracks and delay the propagation of fatigue cracks. However, there are few studies on the effects of these key factors on fretting wear. In the paper, shot-peening (SP) and ultrasonic surface rolling process (USRP) were performed on Ti-6Al-4V plate specimens. The surface hardness and residual stresses of the material were tested by vickers indenter and X-ray diffraction residual stress analyzer. Microhardness were measured by HXD-1000MC/CD micro Vickers hardness tester. The effects of different surface strengthening on its fretting fatigue properties were verified by fretting fatigue experiments. The fretting fatigue fracture surface and wear morphology of the specimens were studied and analyzed by means of microscopic observation, and the mechanism of improving fretting fatigue life by surface strengthening process was further explained. After USRP treatment, the surface roughness of Ti-6Al-4V is significantly improved. In addition, the microhardness of the specimen after SP reaches the maximum at 80 μm from the surface, which is about 123% higher than that of the AsR specimen. After USRP, it reaches the maximum at 150 μm from the surface, which is about 128% higher than that of AsR specimen. It is also found that the residual compressive stress of the specimens treated by USRP and SP increases first and then decreases with the depth direction, and the residual stress reaches the maximum on the sub surface. The USRP specimen reaches the maximum value at 0.18 mm, about -550 MPa, while the SP specimen reaches the maximum value at 0.1 mm, about -380 MPa. The fretting fatigue life of Ti-6Al-4V effectively improved after USRP and SP. The surface integrity of specimens after USRP is the best, which has deeper residual compressive stress layer and more refined grain. In this paper, a fretting wear device is designed to carry out fretting fatigue experiments on specimens with different surface strengthening.
Original Article
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  Fatigue Property of Additively Manufactured Ti-6Al-4V under Nonproportional Multiaxial Loading

  Yuya Kimura, Fumio Ogawa, Takamoto Itoh

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 103-103. https://doi.org/10.1186/s10033-021-00626-8

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  The low cycle fatigue strength properties of the additively manufactured Ti-6Al-4V alloy are experimentally investigated under proportional and nonproportional multiaxial loading. The fatigue tests were conducted using hollow cylinder specimens with and without heat treatments, at room temperature in air. Two fatigue tests were conducted:one for proportional loading and one for nonproportional loading. The proportional loading was represented by a push-pull strain path (PP) and the nonproportional loading by a circle strain path (CI). The failure lives of the additively manufactured specimens were clearly reduced drastically by internal voids and defects. However, the sizes of the defects were measured, and the defects were found not to cause a reduction in fatigue strength above a critical size. The fracture surface was observed using scanning electron microscopy to investigate the fracture mechanisms of the additively manufactured specimens under the two types of strain paths. Different fracture patterns were recognized for each strain paths; however, both showed retention of the crack propagation, despite the presence of numerous defects, probably because of the interaction of the defects. The crack propagation properties of the materials with numerous defects under nonproportional multiaxial loading were clarified to increase the reliability of the additively manufactured components.
Research article
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  Nanoindentation Characterization of Creep-fatigue Interaction on Local Creep Behavior of P92 Steel Welded Joint

  Yuxuan Song, Yi Ma, Zhouxin Pan, Yuebing Li, Taihua Zhang, Zengliang Gao

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 131-131. https://doi.org/10.1186/s10033-021-00661-5

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  In modern fossil and nuclear power plants, the components are subjected to creep, fatigue, and creep-fatigue (CF) due to frequent start-up and shut-down operations at high temperatures. The CF interaction on the in-service P92 steel welded joint was investigated by strain-controlled CF tests with different dwell times of 30, 120, 300, 600 and 900 s at 650℃. Based on the observations of the fracture surface by scanning electron microscope (SEM), the characteristic microstructure of fatigue-induced damage was found for the CF specimens with short dwell times (30 and 120 s). The hardness, elastic modulus and creep deformation near the fracture edges of four typical CF specimens with 30, 120, 600 and 900 s dwell times were measured by nanoindentation. Compared to specimens with post-weld heat treatment (PWHT), lower hardness and creep strength were found for all CF specimens. In addition, significant reductions in hardness, elastic modulus, and creep strength were measured near the fracture edges for the CF specimens with short dwell times compared to the PWHT specimens. Compared to PWHT specimens (0.007), the increased strain rate sensitivities (SRS) of 0.010 to 0.17 were estimated from secondary creep. The increased values of SRS indicate that the room temperature creeps behavior is strongly affected by the decrease in dislocation density after the CF tests.
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  Numerical Study on Effect of Non-uniform CMAS Penetration on TGO Growth and Interface Stress Behavior of APS TBCs

  Zhenwei Cai, Zifan Zhang, Yingzheng Liu, Xiaofeng Zhao, Weizhe Wang

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 128-128. https://doi.org/10.1186/s10033-021-00654-4

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  The penetration of CaO-MgO-Al₂O₃-SiO₂ (CMAS) is one of the most significant factors that induce the failure of air-plasma-sprayed thermal barrier coatings (APS TBCs). The direct penetration of CMAS changes the thermal/mechanical properties of the top coat (TC) layer, which affects the thermal mismatch stress behavior and the growth of thermally grown oxide (TGO) at the TC/bond coat (BC) interface, thereby resulting in a more complicated interface stress state. In the present study, a two-dimensional global model of APS TBCs with half of the TC layer penetrated by CMAS is established to investigate the effect of non-uniform CMAS penetration on the interface stress behavior. Subsequently, a local model extracted from the global model is established to investigate the effects of interface morphologies and CMAS penetration depth. The results show that non-uniform CMAS penetration causes non-uniform TGO growth in APS TBCs, which consequently causes the stress behavior to vary along the interface. Furthermore, the CMAS penetration depth imposes a significant effect on the TC/TGO interface stress behavior, whereas the interface roughness exerts a prominent effect on the stress level at the BC/TGO interface under CMAS penetration. This study reveals the mechanism associated with the effect of non-uniform CMAS penetration on the interface stress behavior in APS TBCSs.
Original Article
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  Novel Ring Compression Test Method to Determine the Stress-Strain Relations and Mechanical Properties of Metallic Materials

  Guangzhao Han, Lixun Cai, Chen Bao, Bo Liang, Yang Lyu, Maobo Huang, Xiaokun Liu

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 109-109. https://doi.org/10.1186/s10033-021-00622-y

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  Although there are methods for testing the stress-strain relation and strength, which are the most fundamental and important properties of metallic materials, their application to small-volume materials and tube components is limited. In this study, based on energy density equivalence, a new dimensionless elastoplastic load-displacement model for compressed metal rings with isotropy and constitutive power law is proposed to describe the relations among the geometric dimensions, Hollomon law parameters, load, and displacement. Furthermore, a novel test method was developed to determine the elastic modulus, stress-strain relation, yield and tensile strength via ring compression test. The universality and accuracy of the method were verified within a wide range of imaginary materials using finite element analysis (FEA), and the results show that the stress-strain curves obtained by this method are consistent with those inputted in the FEA program. Additionally, a series of ring compression tests were performed for seven metallic materials. It was found that the stress-strain curves and mechanical properties predicted by the method agreed with the uniaxial tensile results. With its low material consumption, the ring compression test has the potential to be as an alternative to traditional tensile test when direct tension method is limited.
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  Modeling and Experimental Analysis of Roughness Effect on Ultrasonic Nondestructive Evaluation of Micro-crack

  Zhe Wang, Zhichao Fan, Xuedong Chen, Yihua Kang, Jingwei Cheng, Wei Chen

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 114-114. https://doi.org/10.1186/s10033-021-00637-5

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  A high-precision evaluation of ultrasonic detection sensitivity for a micro-crack can be restricted by a corroded rough surface when the surface microtopography is of the same order of magnitude as the crack depth. In this study, a back-surface micro-crack is considered as a research target. A roughness-modified ultrasonic testing model for micro-cracks is established based on a multi-Gaussian beam model and the principle of phase-screen approximation. The echo signals of micro-cracks and noises corresponding to different rough front surfaces and rough back surfaces are obtained based on a reference reflector signal acquired from a two-dimensional simulation model. Further comparison between the analytical and numerical models shows that the responses of micro-cracks under the effects of different corroded rough surfaces can be accurately predicted. The numerical and analytical results show that the echo signal amplitude of the micro-crack decreases significantly with an increase in roughness, whereas the noise amplitude slightly increases. Moreover, the effect of the rough front surface on the echo signal of the micro-crack is greater than that of the rough back surface. When the root-mean-square (RMS) height of the surface microtopography is less than 15 μm, the two rough surfaces have less influence on the echo signals detected by a focused transducer with a frequency of 5 MHz and diameter of 6 mm. A method for predicting and evaluating the detection accuracy of micro-cracks under different rough surfaces is proposed by combining the theoretical model and a finite element simulation. Then, a series of rough surface samples containing different micro-cracks are fabricated to experimentally validate the evaluation method.
Research article
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  New Inverse Method for Determining Uniaxial Flow Properties by Spherical Indentation Test

  Guoyao Chen, Xiaocheng Zhang, Jiru Zhong, Jin Shi, Qiongqi Wang, Kaishu Guan

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 94-94. https://doi.org/10.1186/s10033-021-00617-9

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  The spherical indentation test has been successfully applied to inversely derive the tensile properties of small regions in a non-destructive way. Current inverse methods mainly rely on extensive iterative calculations, which yield a considerable computational costs. In this paper, a database method is proposed to determine tensile flow properties from a single indentation force-depth curves to avoid iterative simulations. Firstly, a database that contain numerous indentation force-depth curves is established by inputting varied Ludwic material parameters into the indentation finite elements model. Secondly, for a given experimental indentation curve, a mean square error (MSE) is designated to evaluate the deviation between the experimental curve and each curve in the database. Finally, the true stresses at a series of plastic strain can be acquired by analyzing these deviations. To validate this new method, three different steels, i.e. A508, 2.25Cr1Mo and 316L are selected. Both simulated indentation curves and experimental indentation curves are used as inputs of the database to inversely acquire the flow properties. The result indicates that the proposed approach provides impressive accuracy when simulated indentation curves are used, but is less accurate when experimental curves are used. This new method can derive tensile properties in a much higher efficiency compared with traditional inverse method and are therefore more adaptive to engineering application.
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  Approach for Obtaining Material Mechanical Properties in Local Region of Structure Based on Accurate Analysis of Micro-indentation Test

  He Xue, Jinxuan He, Jianlong Zhang, Yuxuan Xue

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 130-130. https://doi.org/10.1186/s10033-021-00644-6

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  The hot or cold processing would induce the change and the inhomogeneous of the material mechanical properties in the local processing region of the structure, and it is difficult to obtain the specific mechanical properties in these regions by using the traditional material tensile test. To accurately get actual material mechanical properties in the local region of structure, a micro-indentation test system incorporated by an electronic universal material test device has been established. An indenter displacement sensor and a group of special micro-indenter assemblies are established. A numerical indentation inversion analysis method by using ABAQUS software is also proposed in this study. Based on the above test system and analysis platform, an approach to obtaining material mechanical properties in the local region of structures is proposed and established. The ball indentation test is performed and combined with the energy method by using various changed mechanical properties of 316L austenitic stainless steel under different elongations. The investigated results indicate that the material mechanical properties and the micro-indentation morphological changes have evidently relevance. Compared with the tensile test results, the deviations of material mechanical parameters, such as hardness H, the hardening exponent n, the yield strength σ_y, and others are within 5% obtained through the indentation test and the finite element analysis. It provides an effective and convenient method for obtaining the actual material mechanical properties in the local processing region of the structure.
Research Highlight
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  Greentelligence: Smart Manufacturing for a Greener Future

  Xingyu Li, Baicun Wang, Tao Peng, Xun Xu

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 116-116. https://doi.org/10.1186/s10033-021-00656-2

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Review
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  Opportunities and Challenges: Classification of Skin Disease Based on Deep Learning

  Bin Zhang, Xue Zhou, Yichen Luo, Hao Zhang, Huayong Yang, Jien Ma, Liang Ma

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 112-112. https://doi.org/10.1186/s10033-021-00629-5

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  Deep learning has become an extremely popular method in recent years, and can be a powerful tool in complex, prior-knowledge-required areas, especially in the field of biomedicine, which is now facing the problem of inadequate medical resources. The application of deep learning in disease diagnosis has become a new research topic in dermatology. This paper aims to provide a quick review of the classification of skin disease using deep learning to summarize the characteristics of skin lesions and the status of image technology. We study the characteristics of skin disease and review the research on skin disease classification using deep learning. We analyze these studies using datasets, data processing, classification models, and evaluation criteria. We summarize the development of this field, illustrate the key steps and influencing factors of dermatological diagnosis, and identify the challenges and opportunities at this stage. Our research confirms that a skin disease recognition method based on deep learning can be superior to professional dermatologists in specific scenarios and has broad research prospects.
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  Effect of Machined Surface Integrity on Fatigue Performance of Metal Workpiece: A Review

  Guoliang Liu, Chuanzhen Huang, Bin Zhao, Wei Wang, Shufeng Sun

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 118-118. https://doi.org/10.1186/s10033-021-00631-x

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  Fatigue performance is a serious concern for mechanical components subject to cyclical stresses, particularly where safety is paramount. The fatigue performance of components relies closely on their surface integrity because the fatigue cracks generally initiate from free surfaces. This paper reviewed the published data, which addressed the effects of machined surface integrity on the fatigue performance of metal workpieces. Limitations in existing studies and the future directions in anti-fatigue manufacturing field were proposed. The remarkable surface topography (e.g., low roughness and few local defects and inclusions) and large compressive residual stress are beneficial to fatigue performance. However, the indicators that describe the effects of surface topography and residual stress accurately need further study and exploration. The effect of residual stress relaxation under cycle loadings needs to be precisely modeled precisely. The effect of work hardening on fatigue performance had two aspects. Work hardening could increase the material yield strength, thereby delaying crack nucleation. However, increased brittleness could accelerate crack propagation. Thus, finding the effective control mechanism and method of work hardening is urgently needed to enhance the fatigue performance of machined components. The machining-induced metallurgical structure changes, such as white layer, grain refinement, dislocation, and martensitic transformation affect the fatigue performance of a workpiece significantly. However, the unified and exact conclusion needs to be investigated deeply. Finally, different surface integrity factors had complicated reciprocal effects on fatigue performance. As such, studying the comprehensive influence of surface integrity further and establishing the reliable prediction model of workpiece fatigue performance are meaningful for improving reliability of components and reducing test cost.
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  A Review on Friction Stir Welding of Steels

  Dhanesh G Mohan, ChuanSong Wu

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 137-137. https://doi.org/10.1186/s10033-021-00655-3

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  Friction Stir Welding (FSW) is the most promising solid-state metals joining method introduced in this era. Compared to the conventional fusion welding methods, this FSW can produce joints with higher mechanical and metallurgical properties. Formerly, FSW was adopted for low melting metals like aluminum alloys. In recent years it has made significant progress in friction stir welding of steels since unfavourable phase transformations occurred in welds due to the melting of the parent and filler metals in fusion welding can be eliminated. The main advantage of FSW over traditional fusion welding is the reduction in the heat-affected zone (HAZ), and the joints exhibit excellent mechanical and corrosion resistance properties. This article reviews the progress in the relevant issues such as the FSW tool materials and tool profiles for joining steels, microstructure and mechanical properties of steels joints, special problems in joining dissimilar steels. Moreover, in-situ heating sources was used to overcome the main limitations in FSW of hard metals and their alloys, i.e., tool damages and insufficient heat generation. Different in-situ heating sources like laser, induction heat, gas tungsten arc welding assisted FSW for various types of steels are introduced in this review. On the basis of the up-to-date status, some problems that need further investigation are put forward.
Original Article
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  Subsurface Defect Evaluation of Selective-Laser-Melted Inconel 738LC Alloy Using Eddy Current Testing for Additive/Subtractive Hybrid Manufacturing

  Sai Guo, Guanhui Ren, Bi Zhang

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 111-111. https://doi.org/10.1186/s10033-021-00633-9

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  New materials and manufacturing technologies require applicable non-destructive techniques for quality assurance so as to achieve better performance. This study comprehensively investigated the effect of influencing factors including excitation frequency, lift-off distance, defect depth and size, residual heat, and surface roughness on the defect EC signals of an Inconel 738LC alloy produced by selective laser melting (SLM). The experimental investigations recorded the impedance amplitude and phase angle of EC signals for each defect to explore the feasibility of detecting subsurface defects by merely analyzing these two key indicators. Overall, this study revealed preliminary qualitative and roughly quantitative relationships between influencing factors and corresponding EC signals, which provided a practical reference on how to quantitively inspect subsurface defects using eddy current testing (ECT) on SLMed parts, and also made solid progress toward on-line ECT in additive/subtractive hybrid manufacturing (ASHM) for fabricating SLMed parts with enhanced quality and better performance.
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  Fatigue Life Prediction of Rolling Bearings Based on Modified SWT Mean Stress Correction

  Aodi Yu, Hong-Zhong Huang, Yan-Feng Li, He Li, Ying Zeng

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 110-110. https://doi.org/10.1186/s10033-021-00625-9

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  The existing engineering empirical life analysis models are not capable of considering the constitutive behavior of materials under contact loads; as a consequence, these methods may not be accurate to predict fatigue lives of rolling bearings. In addition, the contact stress of bearing in operation is cyclically pulsating, it also means that the bearing undergo non-symmetrical fatigue loadings. Since the mean stress has great effects on fatigue life, in this work, a novel fatigue life prediction model based on the modified SWT mean stress correction is proposed as a basis of which to estimate the fatigue life of rolling bearings, in which, takes sensitivity of materials and mean stress into account. A compensation factor is introduced to overcome the inaccurate predictions resulted from the Smith, Watson, and Topper (SWT) model that considers the mean stress effect and sensitivity while assuming the sensitivity coefficient of all materials to be 0.5. Moreover, the validation of the model is finalized by several practical experimental data and the comparison to the conventional SWT model. The results show the better performance of the proposed model, especially in the accuracy than the existing SWT model. This research will shed light on a new direction for predicting the fatigue life of rolling bearings.
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  Fault Diagnosis Based on BP Neural Network Optimized by Beetle Algorithm

  Maohua Xiao, Wei Zhang, Kai Wen, Yue Zhu, Yilidaer Yiliyasi

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 119-119. https://doi.org/10.1186/s10033-021-00648-2

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  In the process of Wavelet Analysis, only the low-frequency signals are re-decomposed, and the high-frequency signals are no longer decomposed, resulting in a decrease in frequency resolution with increasing frequency. Therefore, in this paper, firstly, Wavelet Packet Decomposition is used for feature extraction of vibration signals, which makes up for the shortcomings of Wavelet Analysis in extracting fault features of nonlinear vibration signals, and different energy values in different frequency bands are obtained by Wavelet Packet Decomposition. The features are visualized by the K-Means clustering method, and the results show that the extracted energy features can accurately distinguish the different states of the bearing. Then a fault diagnosis model based on BP Neural Network optimized by Beetle Algorithm is proposed to identify the bearing faults. Compared with the Particle Swarm Algorithm, Beetle Algorithm can quickly find the error extreme value, which greatly reduces the training time of the model. At last, two experiments are conducted, which show that the accuracy of the model can reach more than 95%, and the model has a certain anti-interference ability.
Research article
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  Measurement and Characterisation of a Diffuse Acoustic Field Using a Phased Array

  Jingwei Cheng

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 129-129. https://doi.org/10.1186/s10033-021-00657-1

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  A diffuse acoustic field has been increasingly used to infer temporal changes in the structures, such as early dislocations and microcracking. This study explores three different techniques to characterise acoustic field by using a single ultrasonic phased array. The first two techniques are proposed to measure spatial uniformity of wave field by examining differences in the integral of energy and the maximum energy respectively at multiple inspection locations. The third one is developed to evaluate the degree of phase coherence between propagating waves transmitted sequentially by two neighbouring array elements. The efficacy of these techniques are investigated by examining their metrics on simulations and well-known samples. The results suggest that two selected metrics can be used to quantitatively estimate the diffuse field start time as well as the field size by comparing their value with the idealised diffuse state (15% for the energy integral metric, η_area and 1 for the phase coherence metric, η_phase) and identifying the convergence start point.
Original Article
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  Raising the Speed Limit of Axial Piston Pumps by Optimizing the Suction Duct

  Yu Fang, Junhui Zhang, Bing Xu, Zebing Mao, Changming Li, Changsheng Huang, Fei Lyu, Zhimin Guo

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 105-105. https://doi.org/10.1186/s10033-021-00624-w

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  The maximum delivery pressure and the maximum rotational speed determine the power density of axial piston pumps. However, increasing the speed beyond the limit always accompanies cavitation, leading to the decrease of the volumetric efficiency. The pressure loss in the suction duct is considered a significant reason for the cavitation. Therefore, this paper proposes a methodology to optimize the shape of the suction duct aiming at reducing the intensity of cavitation and increasing the speed limit. At first, a computational fluid dynamics (CFD) model based on the full cavitation model (FCM) is developed to simulate the fluid field of the axial piston pump and a test rig is set to validate the model. Then the topology optimization is conducted for obtaining the minimum pressure loss in the suction duct. Comparing the original suction duct with the optimized one in the simulation model, the pressure loss in the suction duct gets considerable reduction, which eases the cavitation intensity a lot. The simulation results prove that the speed limit can increase under several different inlet pressures.
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  Tribological Properties of Cylinder Block/Valve Plate Interface of Axial Piston Pump on the Tribometer

  Jiahai Huang, Zhenhua Dou, Zhenglei Wang, Long Quan, Linkai Niu

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 122-122. https://doi.org/10.1186/s10033-021-00647-3

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  The tribological properties of cylinder block/valve plate is an important consideration in the design of axial piston pump. The effect of materials and heat treatment on friction and wear properties has been studied in depth. Engineering experiences show that the speed and load also affect the tribological properties, but these have not been systematically analyzed. The purpose of this paper is to evaluate the tribological properties of the commonly used materials (CuPb15Sn5 and 38CrMoAl/42CrMo) for cylinder block/valve plate with different heat treatment and contact pressure at different speed. During the test, tribometer is used to simulate the contact pattern between the valve plate/cylinder block in axial piston pump, the friction coefficient, wear rate and surface topography are analyzed to evaluate the tribological properties of different types of friction samples at different speed. Results indicate that:(1) contact surface of the samples at 1800 r/min is more prone to adhesive wear than those at 500 r/min; (2) in the terms of wear resistance, quench-tempered and nitrided 38CrMoAl (38CrMoAl QTN for short) is better than quench-tempered and nitrided 42CrMo, although they are all commonly used materials in the axial piston pump; (3) 2.5 MPa is the critical contact pressure of the interface between valve plate made of 38CrMoAl QTN and cylinder block made of CuPb15Sn5 on the tribometer, which implies the pressure bearing area at the bottom of the cylinder block should be carefully designed; (4) the valve plate/cylinder block made of 38CrMoAl QTN/CuPb15Sn5 exhibits good tribological properties in a real axial piston pump. This research is useful for the failure analysis and structural optimization design of the valve plates/cylinder block.
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  Investigation on the Flow Behavior of Side Channel Pumps Based on Vortex Identification

  Fan Zhang, Desmond Appiah, Ke Chen, Shouqi Yuan, Kofi Asamoah Adu-Poku, Lufeng Zhu

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 120-120. https://doi.org/10.1186/s10033-021-00649-1

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  The momentum flow exchange between the impeller and side channel produces highly turbulent flows in side channel pumps. The turbulent flows feature complex patterns of vortex structures that are partly responsible for the dissipation of energy losses and unsteady pressure pulsations. The concept of turbulent flows in side channel pumps requires a reliable vortex identification criterion to capture and predict the effects of the vortex structures on the performance. For this reason, the current study presents the application of the new Ω-criterion to a side channel pump model in comparison with other traditional methods such as Q and λ₂ criteria. The 3D flow fields of the pump were obtained through unsteady Reynolds-averaged Navier-Stokes (RANS) simulations. Comparative studies showed that the Ω-criterion identifies the vortex of different intensities with a standard threshold, Ω=0.52. The Q and λ₂ criteria required different thresholds to capture vortex of different intensities thus leads to subjective errors. Comparing the Ω-criterion intensity on different planes with the entropy losses and pressure pulsation, the longitudinal vortex plays an important role in the momentum exchange development which increases the head performance of the pump. However, the rate of exchange is impeded by the axial and radial vortices restricted in the impeller. Therefore, the impeller generates the highest entropy loss and pressure pulsation intensities which lower the output efficiency. Finally, the findings provide a fundamental background to the morphology of the vortex structures in the turbulent flows which can be dependent upon for efficiency improvement of side channel pumps.
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  Medical Grabbing Servo System with Friction Compensation Based on the Differential Evolution Algorithm

  Yeming Zhang, Kaimin Li, Meng Xu, Junlei Liu, Hongwei Yue

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 107-107. https://doi.org/10.1186/s10033-021-00619-7

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  This paper introduces a pneumatic finger cylinder servo control system for medical grabbing. First, according to the physical structure of the proportional directional valve and the pneumatic cylinder, the state equation of the gas in the servo system was obtained. The Stribeck friction compensation model of a pneumatic finger cylinder controlled by a proportional valve was established and the experimental platform built. To allow the system output to better track the change in the input signal, the flow-gain compensation method was adopted. On this basis, a friction compensation control strategy based on a differential evolution algorithm was proposed and applied to the position control system of a pneumatic finger cylinder. Finally, the strategy was compared with the traditional proportional derivative (PD) strategy and that with friction compensation. The experimental results showed that the position accuracy of the finger cylinder position control system can be improved by using the friction compensation strategy based on the differential evolution algorithm to optimize the PD parameters.
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  Effects of Vibration Characteristics on the Atomization Performance in the Medical Piezoelectric Atomization Device Induced by Intra-Hole Fluctuation

  Qiufeng Yan, Wanting Sun, Lei Zhang, Hongmei Wang, Jianhui Zhang

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 123-123. https://doi.org/10.1186/s10033-021-00635-7

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  Oral inhalation of aerosolized drugs has be widely applied in healing the affected body organs including lesions of the throat and lungs and it is more efficient than those conventional therapies, such as intravenous drip, intramuscular injection and external topical administration in the aspects of the dosage reduction and side effects of drugs. Nevertheless, the traditional atomization devices always exhibit many drawbacks. For example, non-uniformed atomization particle distribution, the instability of transient atomization quantity and difficulties in precise energy control would seriously restrict an extensive use of atomization inhalation therapy. In this study, the principle of intra-hole fluctuation phenomenon occurred in the hole is fully explained, and the produced volume change is also estimated. Additionally, the mathematical expression of the atomization rate of the atomizing device is well established. The mechanism of the micro-pump is further clarified, and the influence of the vibration characteristics of the atomizing film on the atomization behavior is analyzed theoretically. The curves of sweep frequency against the velocity and amplitude of the piezoelectric vibrator are obtained by the Doppler laser vibrometer, and the corresponding mode shapes of the resonance point are achieved. The influence of vibration characteristics on atomization rate, atomization height and atomization particle size are also verified by experiments, respectively. Both the experimental results and theoretical calculation are expected to provide a guidance for the design of this kind of atomization device in the future.
Research article
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  Simulation and Experimental Study on a New Successive Forming Process for Large Modulus Gears

  Yao Lin, Tao Wu, Guangchun Wang

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 127-127. https://doi.org/10.1186/s10033-021-00653-5

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  A successive tooth forming process for producing large modulus spur gears (m>2.5 mm) is firstly proposed in this paper to break the restrictions of large forming load and large equipment structure of traditional plastic forming. It contains the preforming stage and the finishing stage. In the first stage, the die with a single-tooth preforms gear teeth one by one through several passes. In the second stage, the other die with multi-teeth refines the preformed teeth into required shape. The influence of total pressing depth and feed distribution in preforming stage on final forming quality is analyzed by numerical simulation, and the reasonable process parameters are presented. Successive tooth forming experiments are carried out on the self-designed gear forming device to verify the optimal simulation results. Gears without fold defects are well formed both in simulations and experiments, proving the feasibility of this method. Compared with the whole die forging process, the new technology has advantages of smaller load and simpler tooling, which shows a good potential for manufacturing large modulus and large size spur gears.
Original Article
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  Effect of Thermal Cyclic Loading on Stress-Strain Response and Fatigue Life of 3D Chip Stacking Structure

  Liang Zhang, Weimin Long, Sujuan Zhong

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 115-115. https://doi.org/10.1186/s10033-021-00640-w

  摘要 ( ) PDF全文 ( )   可视化   收藏

  The thermo-mechanical reliability of IMCs (Ni₃Sn₄, Cu₃Sn, Cu₆Sn₅) solder joints and Sn-3.9Ag-0.6Cu solder joints was investigated systematically in 3D chip stacking structure subjected to an accelerated thermal cyclic loading based on finite element simulation and Taguchi method. Effects of different control factors, including high temperature, low temperature, dwell time of thermal cyclic loading, and different IMCs on the stress-strain response and fatigue life of solder joints were calculated respectively. The results indicate that maximum stress-strain can be found in the second solder joint on the diagonal of IMC solder joints array; for Sn-3.9Ag-0.6Cu solder joints array, the corner solder joints show the obvious maximum stress-strain, these areas are the crack propagated locations. The stress-strain and fatigue life of solder joints is more sensitive to dwell temperature, especially to high temperature; increasing the high temperature, dwell time, or decreasing the low temperature, can reduce the stress-strain and enlarge the fatigue life of solder joints. Finally, the optimal design in the 3D-IC structure has the combination of the Cu₆Sn₅/Cu₃Sn, 373 K high temperature, 233 K low temperature, and 10 min dwell time. The fatigue lives of Sn-3.9Ag-0.6Cu under 218-398 K loading in the 3D assembly based on the creep strain are 347.4 cycles, which is in good agreement with experimental results (380 cycles).
Research article
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  Heat Transfer Performance of a Novel Microchannel Embedded with Connected Grooves

  Ding Yuan, Wei Zhou, Ting Fu, Qingyu Dong

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 145-145. https://doi.org/10.1186/s10033-021-00632-w

  摘要 ( ) PDF全文 ( )   可视化   收藏

  To improve the heat transfer performance of microchannels, a novel microchannel embedded with connected grooves crossing two sidewalls and the bottom surface (type A) was designed. A comparative study of heat transfer was conducted regarding the performances of type A microchannels, microchannels embedded with grooves on their bottom (including types B and C), or on the sidewalls (type D) as well as smooth rectangular microchannels (type E) via a three-dimensional numerical simulation and experimental validation (at Reynolds numbers from 118 to 430). Numerical results suggested that the average Nusselt number of types A, B, C, and D microchannels were 106, 73.4, 50.1, and 12.6% higher than that of type E microchannel, respectively. The smallest synergy angle β and entropy generation number N_s,a were determined for type A microchannels based on field synergy and nondimensional entropy analysis, which indicated that type A exhibited the best heat transfer performance. Numerical flow analysis indicated that connected grooves induced fluid to flow along two different temperature gradients, which contributed to enhanced heat transfer performance.
Original Article
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  Optimum Seeking of Redundant Actuators for M-RCM 3-UPU Parallel Mechanism

  Chen Zhao, Jingke Song, Xuechan Chen, Ziming Chen, Huafeng Ding

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 121-121. https://doi.org/10.1186/s10033-021-00651-7

  摘要 ( ) PDF全文 ( )   可视化   收藏

  The singularity problem brings troubles to the design and application for the parallel mechanism. Currently, redundant actuation is one of the useful methods to solve this singularity problem. However, faced to the numerous joints in a parallel mechanism, how to make a quantitative criterion of seeking the most efficient joints added actuators for letting the mechanism passes through singularity is a necessarily open issue. This paper focuses on a 2R1T 3-UPU (U for universal joint and P for prismatic joint) parallel mechanism (PM) with two rotational and one translational (2R1T) degrees of freedom (DOFs) and the ability of multiple remote centers of motion (M-RCM). The singularity analysis based on the indexes of motion/force transmissibility and constraint shows that this PM has transmission singularity, constraint singularity, mixed singularity and limb singularity. To solve these singular problems, the quantifiable redundancy transmission index (RTI) and the redundancy constraint index (RCI) are proposed for optimum seeking of redundant actuators for this PM. Then the appropriate redundant actuators are selected and the working scheme for redundant actuators near the corresponding singular configuration are given to help the PM passes through the singularity. This research proposes a quantitative criterion to optimum seeking of redundant actuators for the parallel mechanism to solve its singularity.
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  Tooth Position and Deformation of Flexspline Assembled with Cam in Harmonic Drive Based on Force Analysis

  Yunpeng Yao, Xiaoxia Chen, Jingzhong Xing, Liteng Shi, Yuqi Wang

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 104-104. https://doi.org/10.1186/s10033-021-00621-z

  摘要 ( ) PDF全文 ( )   可视化   收藏

  Deformation of the flexspline is the basis of analyzing tooth trajectory and designing tooth profile. Considering the tooth influence on the position of equivalent neutral layer, a piecewise method for calculating the deformation of flexspline assembled with a cam wave generator is presented in this paper. Firstly, a mechanic model of a ring of uniform thickness in contact with a rigid cam is established. The displacements of the ring inside and outside an unknown wrapping angle are determined by the geometric constraints of the cam profile and the equilibrium relationship, respectively. Meanwhile, the wrapping angle is solved according to the boundary conditions. The assembly forces are derived to investigate the circumferential elongation and strain. Then, considering the tooth effects on the neutral layer of flexspline, the tooth is positioned on the equivalent neutral layer, which is the non-elongation layer within one gear pitch but offset from the geometric mid-layer. The equivalent neutral layer is positioned by the empirical formula of the offset ratio, which is summarized by the orthogonal simulation on finite element models of racks. Finally, finite element models of a ring-shaped and a cup-shaped flexspline assembled with elliptical cam are established to verify the effectiveness and accuracy of the piecewise method. The results show that, compared with the geometric method, the tooth positioning deviation calculated by the piecewise method can be reduced by about 70% with a more accurate deformation description from the geometric condition and mechanic condition inside and outside the wrapping angle.
Research article
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  Integrated Optimization of Structure and Control Parameters for the Height Control System of a Vertical Spindle Cotton Picker

  Xingzheng Chen, Congbo Li, Rui Hu, Ning Liu, Chi Zhang

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 136-136. https://doi.org/10.1186/s10033-021-00662-4

  摘要 ( ) PDF全文 ( )   可视化   收藏

  Vertical picking method is a predominate method used to harvest cotton crop. However, a vertical picking method may cause spindle bending of the cotton picker if spindles collide with stones on the cotton field. Thus, how to realize a precise height control of the cotton picker is a crucial issue to be solved. The objective of this study is to design a height control system to avoid the collision. To design it, the mathematical models are established first. Then a multi-objective optimization model represented by structure parameters and control parameters is proposed to take the pressure of chamber without piston, response time and displacement error of the height control system as the optimization objectives. An integrated optimization approach that combines optimization via simulation, particle swarm optimization and simulated annealing is proposed to solve the model. Simulation and experimental test results show that the proposed integrated optimization approach can not only reduce the pressure of chamber without piston, but also decrease the response time and displacement error of the height control system.
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  Competitive Failure of Bolt Loosening and Fatigue under Different Preloads

  Guangwu Yang, Long Yang, Jingsong Chen, Shoune Xiao, Shilin Jiang

  Chinese Journal of Mechanical Engineering. 2021, 34(6): 141-141. https://doi.org/10.1186/s10033-021-00663-3

  摘要 ( ) PDF全文 ( )   可视化   收藏

  Existing research on the competitive failure relationship, failure mechanism, and influencing factors of bolt loosening and fatigue under different preloads is insufficient. This study analyzes the competitive failure relationship between bolt loosening and fatigue under composite excitation through competitive failure tests of bolt loosening and fatigue under different preloads. The results indicated that the failure mode of the bolt is only related to the load ratio (R) and is unrelated to the initial preload and excitation amplitude, which only determine the failure life of the bolt. The small axial loads of composite excitation can restrain bolt failure, and the significant degree of this restraining effect is different for different preloads. Subsequently, a fracture analysis of the bolt was performed to verify the competitive failure relationship of the bolt from a microscopic perspective, and the competitive failure mechanism of the bolt was determined. Based on the findings, we propose a calculation equation for the optimal preload of 8.8 grade high-strength bolts that can serve as a reference for engineering applications.