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Direct simulation of thermo-coupled fatigue failure for metals

ZAMM-ZEITSCHRIFT FUR ANGEWANDTE MATHEMATIK UND MECHANIK 2018年第6期98卷 856-869页

作者： Zhan, Lin Wang, Si-Yu Xi, Hui-Feng Xiao, Heng Shanghai Univ Shanghai Inst Appl Math & Mech Yanchang Rd 149 Shanghai 200072 Peoples R China Jinan Univ Sch Mech & Construct Engn Guangzhou 510632 Guangdong Peoples R China Jinan Univ MOE Key Lab Disaster Forecast & Control Engn Guangzhou 510632 Guangdong Peoples R China

A new finite strain elastoplastic J2-flow model with thermo-coupled effects is proposed for the purpose of simulating cyclic and non-cyclic thermo-coupled fatigue failure behavior of metals. Novelties in four respects are incorporated in the proposed model: (i) the usual notion of yielding is rendered irrelevant with a smooth transition from the elastic to the plastic state;(ii) the thermodynamic consistency stipulated by the second law is identically ensured;(iii) asymptotic loss of the strength in cyclic and non-cyclic thermomechanical processes is incorporated as inherent constitutive features;and, accordingly, (iv) the fatigue failure behavior may be derived as direct consequences of the proposed model, without involving any additional failure criteria and any additional variables. Thermo-coupled responses of a metal bar with two fixed ends under cyclic heating and cooling over various temperature ranges are studied based on a simple case of the proposed model. Results are obtained for the maximum tensile and compressive stresses changing with the cycle number and, in particular, for the thermal fatigue life versus the temperature amplitude. Model predictions compare well with test data.

关键词： direct simulation elastoplasticity fatigue failure metals thermomechanical processes

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Safety monitoring in construction site based on unmanned aerial vehicle platform with computer vision using transfer learning techniques 7

Safety monitoring in construction site based on unmanned aer...

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7th Asia-Pacific Workshop on Structural Health Monitoring, APWSHM 2018

作者： Guo, Yapeng Niu, Haowei Li, Shunlong Harbin Institute of Technology School of Transportation Science and Engineering Harbin China Key Lab of Intelligent Disaster Mitigation Ministry of Industrial and Information Technology Harbin China Key Lab of Structures Dynamic Behaviour and Control Ministry of Education Harbin China

ISBN: (纸本)9783000603594

Safety is an inevitable issue in all kinds of construction sites. The most effective way to insure human's safety is wearing safety helmet, thus whether wearing or not is a main problem of safety monitoring. This paper proposed an approach using deep learning-based computer vision techniques to detect workers (i.e., not wearing safety helmet) from image sequences shot by unmanned aerial vehicle (UAV). Firstly training and testing dataset were created using label tools as a size of 300×300. Then a fine-tune method based on single shot multibox detector network was employed to get high accuracy of detection. The effectiveness and accuracy of methods were validated and discussed. Finally, some visualization work has been done for a deeper understanding of the network. © APWSHM 2018. All rights reserved.

关键词： Computer vision

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Numerical Study of a Southwest Vortex Rainstorm Process Influenced by the Eastward Movement of Tibetan Plateau Vortex

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ADVANCES IN METEOROLOGY 2018年第1期2018卷

作者： Liu, Xiaoli Ma, Endian Cao, Zhibin Jin, Shuanglong Nanjing Univ Informat Sci & Technol Key Lab Aerosol Cloud Precipitat Minist Educ Key Lab Meteorol DisasterChina Meteorol Adm Nanjing 210044 Jiangsu Peoples R China Nanjing Univ Informat Sci & Technol Collaborat Innovat Ctr Forecast & Evaluat Meteoro Nanjing 210044 Jiangsu Peoples R China Purple Mt Observ Nanjing 210008 Jiangsu Peoples R China China Elect Power Res Inst State Key Lab Operat & Control Renewable Energy & Beijing 100192 Peoples R China

A number of studies revealed the possible eastward movement of the Tibetan Plateau low-pressure system in summer and indicated the enhancement effect of this process on the southwest vortex in the Sichuan Basin, which can induce strong convective precipitation and flood events in China. In this study, a numerical simulation of a southwest vortex rainstorm process was performed. The results show that the low-pressure system originated from the Tibetan Plateau affects the southwest vortex mainly at the middle level, causing the strength increase of southwest vortex (SWV), and acts as a connection between the positive vorticity centers at the upper and lower layers. For the microscopic cloud structure, the vertical updraft of the cloud cluster embedded in the SWV increases as the low-pressure system from the plateau arrives at the Sichuan Basin. Vapor and liquid cloud water at the lower level are transported upward, based on which the ice cloud at the upper level and the warm cloud at the lower level are joined to create favorable conditions for the growth of ice crystals. As the ice crystals grow up, snow and graupel particles form, which substantially elevates the precipitation. This effect leads to the rapid development of SWV rainstorm clouds and the occurrence of precipitation. In addition to the effect of the plateau vortex, the subsequent merging of the convective clouds is another important factor for heavy rainfall because it also leads to development of convective clouds, causing heavy rainfall.

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Ultimate Strength Analysis of Three-Way Pipe Considering Plastic Reinforcement Effect

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Journal of Physics: Conference Series 2020年第2期1650卷

作者： Wei Su Wenhao Luo Xianshan Dong Renhuai Liu MOE Key lab of Disaster Forecast and Control in Engineering Guangzhou 510632 China. Science and Technology on Reliability Physics and Application Technology of Electronic Component Laboratory China Electronic Product Reliability and Environmental Testing Research Institute Guangzhou 510610 China. School of Mechanics and Construction Engineering Jinan University Guangzhou 510632 China

Considering the plastic reinforcement effect in materials, the plastic limit load of the three-way structure is analyzed. ANSYS commercial finite element software is used for numerical simulation. According to the results, the paper discusses the influence of the plastic reinforcement effect on the pipe's plastic ultimate load and failure mode. And the structure is further analyzed to verify the theory and design ideas in actual engineering. For improving the design and safety assessment of the three-way structure, the results provide a theoretical basis and a numerical reference, and the finite element method is economical than the experimental method. At last, it satisfies the accuracy requirements of engineering.

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Ultimate Strength Analysis of Local Thinning Tee Pipe Considering Plastic Strengthening Effect

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Journal of Physics: Conference Series 2020年第2期1650卷

In this paper, the locally thinned three-way structure under internal pressure is analyzed based on the theory of plastic strengthening effect and limit analysis. A finite element model is presented through ANSYS commercial software to simulate the mechanical properties of orthogonal and oblique three-way structures. This paper systematically analyses how the shape and size of the thinning effect the plastic limit load of the pipe and what is the typical failure mode of plastic failure. Some valuable conclusions are drawn, which provide a useful reference for the design and production of the tee pipe.

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Wave Soldering Structure Optimization Simulation of Multi-layer Ceramic Capacitors

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Journal of Physics: Conference Series 2020年第3期1650卷

作者： Wei Su Wenhao Luo Junkui Li Renhuai Liu MOE Key lab of Disaster Forecast and Control in Engineering Guangzhou 510632 China. Science and Technology on Reliability Physics and Application Technology of Electronic Component Laboratory China Electronic Product Reliability and Environmental Testing Research Institute Guangzhou 510610 China. School of Mechanics and Construction Engineering Jinan University Guangzhou 510632 China

In this paper, the thermal analysis and structural analysis of MLCC are carried out by using the commercial finite element software ANSYS. By comparing the thermal-mechanical analysis results of the structural optimization models of different schemes, the optimal optimization scheme is found. The model calculated the time required for MLCC to reach temperature stability considering thermal convection and heat conduction, and obtained the thermal deformation and thermal stress distribution of MLCC element. Based on the analysis results of MLCC original model, the thermal analysis under different wave soldering temperatures was carried out. Based on the simulated transient results, the structure and materials of MLCC key components were optimized. The results provide a basis for the optimal design of MLCC.

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Indirect inverse substructuring identification method for coupling dynamic stiffness of vibrational structures

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Chinese Journal of Acoustics 2018年第2期37卷 241-256页

作者： LU Guangqing WANG Minqing WANG Bo CAO Renjing GUO Zhiwei PENG Wenbin LIU Yujun MOE Key Lab of Disasters Forecast and Control in Engineering Jinan University Guangzhou 510632 Research Institute of Shenzhen Northwestern Polytechnical University Shenzhen 518057 School of Marine Science and Technology Northwestern Polytechnical University Xi'an 710072

Coupling dynamic stiffness is a key parameter in vibrational analysis of complex coupled structures, for both estimation of structural vibrational characteristics and design of vibration control. An indirect method of inverse substructuring analysis to identify the stiffness is studied further by using frequency response functions that are tested on the models of coupled structures. The theoretical effectiveness of this method is here verified by two ＇mass-rubber＇ ex- perimental models constructed as two-level substructures with mono-coupling and tri-coupling connections, and the identification error is also analyzed. The coincidence of numerical and experimental results show that the indirect method has better feasibility and effectiveness than the existing direct method of inverse substructuring analysis, and with more applicable con- ditions and higher acceptable precision in determining the stiffness. It provides more solid theoretical basis for the stiffness identification by inverse substructuring analysis.

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Viscoelastic shear lag model to predict the micromechanical behavior of tendon under dynamic tensile loading

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JOURNAL OF THEORETICAL BIOLOGY 2018年 437卷 202-213页

作者： Wu, Jiayu Yuan, Hong Li, Longyuan Fan, Kunjie Qian, Shanguang Li, Bing Jinan Univ Inst Appl Mech MOE Key Lab Disaster Forecast & Control Engn Guangzhou 510632 Guangdong Peoples R China Univ Plymouth Sch Engn Plymouth PL4 8AA Devon England Kunming Met Coll Architecture Engn Fac Kunming 650033 Yunnan Peoples R China Imperial Coll London Blackett Lab South Kensington Campus London SW7 2AZ England

Owing to its viscoelastic nature, tendon exhibits stress rate-dependent breaking and stiffness function. A Kelvin-Voigt viscoelastic shear lag model is proposed to illustrate the micromechanical behavior of the tendon under dynamic tensile conditions. Theoretical closed-form expressions are derived to predict the deformation and stress transfer between fibrils and interfibrillar matrix while tendon is dynamically stretched. The results from the analytical solutions demonstrate that how the fibril overlap length and fibril volume fraction affect the stress transfer and mechanical properties of tendon. We find that the viscoelastic property of interfibrillar matrix mainly results in collagen fibril failure under fast loading rate or creep rupture of tendon. However, discontinuous fibril model and hierarchical structure of tendon ensure relative sliding under slow loading rate, helping dissipate energy and protecting fibril from damage, which may be a key reason why regularly staggering alignment microstructure is widely selected in nature. According to the growth, injury, healing and healed process of tendon observed by many researchers, the conclusions presented in this paper agrees well with the experimental findings. Additionally, the emphasis of this paper is on micromechanical behavior of tendon, whereas this analytical viscoelastic shear lag model can be equally applicable to other soft or hard tissues, owning the similar microstructure. (C) 2017 Elsevier Ltd. All rights reserved.

关键词： Tendon Biocomposites Shear lag model Kelvin-Voigt viscoelastic model Mechanical response

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An improved nelder-mead algorithm for optimization problem on structural damage detection 24th

An improved nelder-mead algorithm for optimization problem o...

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24th Australasian Conference on the Mechanics of Structures and Materials, ACMSM 2016

作者： Chen, Zepeng Yu, Ling Department of Mechanics and Civil Engineering Jinan University Guangzhou China MOE Key Lab of Disaster Forecast and Control in Engineering Jinan University Guangzhou China

ISBN: (纸本)9781138029934

Structural Damage Detection (SDD) is one of fundamental objectives in the field of structural health monitoring. Usually, the SDD problem can be transformed into an optimal problem by introducing objective functions mathematically. Many methodologies have been developed and achieved great success in the last few decades. However, their calculation efficiency and accuracy are still required to be improved. In this study, an Improved Nelder-Mead (INM) simplex algorithm is proposed for the SDD optimal problem by embedding the Nelder-Mead process into Particle Swarm Optimization (PSO) algorithm. The hybrid algorithm is named PSO-INM. In order to get better results, two filter strategies are proposed based on fitness values and index stability factor. Numerical simulations of a thin-walled hollow simply-supported beam are conducted to assess effectiveness of both PSO-INM and two proposed strategies. The results show that the PSO-INM algorithm and strategies proposed herein are able to locate structural damages as well as to quantify extents of damages with a good noise immunity. Some related issues are discussed as well. © 2017 Taylor & Francis Group, London.

关键词： Structural health monitoring

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Analysis of the Generating and Influencing Factors of Vertical Cracking in Abutments during Construction

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ADVANCES IN MATERIALS SCIENCE AND engineering 2018年第1期2018卷 1-13页

作者： Xue, Xingwei Zhou, Junlong Hua, Xudong Li, Hongnan Shenyang Jianzhu Univ Sch Traff Engn Shenyang 110168 Liaoning Peoples R China Jinan Univ MOE Key Lab Disaster Forecast & Control Engn Guangzhou 510618 Guangdong Peoples R China

In order to analyze the causes of cracking in abutments subject to concrete shrinkage and temperature variation during the construction process and to determine factors affecting the mechanical properties of the abutment, nonlinear calculations capturing abutment behavior are conducted with Midas/FEA software. Using these calculations, the cracking mechanism is identified, and the influence of the evaluated factors is analyzed. It is concluded that the deformation between the pile cap and abutment backwall as constrained by a pile foundation when subjected to concrete shrinkage and temperature changes is the basic cause of abutment cracks during construction;these cracks form over the piles and develop upward. For a given reinforcement ratio, the distribution of horizontal crack-control steel using small, closely spaced bars is more beneficial. When pile-bearing capacity meets the standard, the width of the generated cracks tends to decrease with the decrease in the diameter of the piles. The existence of a postcast strip in the abutment backwall also contributes to the decrease in the depth of the crack. Finally, the impact of age difference between the pile cap concrete and abutment backwall concrete on cracking is inconsequential.

关键词： EXPANSION & contraction of concrete FINITE element method CRACKING of concrete CONSTRUCTION projects TEMPERATURE effect

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