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Modeling of Fatigue Crack Growth Closure Considering the Integrative Effect of Cyclic Stress Ratio,Specimen Thickness and Poisson's Ratio

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Chinese Journal of Mechanical Engineering 2012年第4期25卷 816-825页

作者： liu jiantao DU Pingan liu Xiaobao DU Qiang College of Mechanical and Electronic Engineering University of Electronic Science and Technology of China Chengdu 611731 China

Key components of large structures in aeronautics industry are required to be made light and have long enough fatigue *** is of vital importance to estimate the fatigue life of these structures *** the FCG process is affected by various factors,no universal model exists due to the complexity of the *** of the existing models are obtained by fitting the experimental data and could hardly describe the integrative effect of most existing factors *** order to account for the integrative effect of specimen parameters,material property and loading conditions on FCG process,a new model named integrative influence factor model（IIF） is proposed based on the plasticity-induced crack closure *** to the predictions of crack opening ratio（γ） and effective stress intensity factor range ratio（U） with different material under various loading conditions,predictions of γ and U by the IIF model are completely identical to the theoretical results from the plane stress state to the plane strain state when Poisson＇s ratio equals 1/*** Poisson＇s ratio equals 0.3,predictions of γ and U by the IIF model are larger than the predictions by the existing model,and more close to the theoretical *** addition,it describes the influence of R ratios on γ and U effectively in the whole region from-1.0 to ***,several sets of test data of FCG rates in 5 kinds of aluminum alloys with various specimen thicknesses under different loading conditions are used to validate the IIF model,most of the test data are situated on the predicted curves or between the two curves that represent the specimen with different thicknesses under the same stress *** of the test data slightly departure from the predictions by the IIF model due to the surface roughness and errors in ***,based on the analysis of the physical rule of crack opening ratios,a relative thickness of specimen is defined to describe the influence of mate

关键词： fatigue crack growth crack opening stress cyclic stress ratio constraint factor Poisson's ratio stress intensity factor

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A general model of fatigue crack growth under variable amplitude loading

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Science China(Technological Sciences) 2012年第3期55卷 673-683页

作者： liu jiantao DU PingAn ZHANG ZhenYu School of Mechatronies Engineering University of Electronic Science and Technology of China Chengdu 611731 China

A general model of fatigue crack growth(FCG) in ductile alloys under variable amplitude loading is proposed based on the passivation-lancet theory and the crack closure *** model can capture the interactions of single cycle overloading and underloading,sequential loading and spectrum loading ***,the retardation effect due to overloads and the acceleration effect due to underloading can be described quantitatively by a transition function of crack opening *** fatigue test data in 2024-T351,2024-T3 and 7075-T6 aluminum alloys under different types of variable amplitude loading and spectrum loading are used to validate the general model and the predictions by the general model are in good agreement with the test ***,the predictions are also compared with the existing models,including FASTRAN,AFGROW and the state-space model,and the comparison results show that the general model predicts the FCG process more accurately.

关键词： fatigue and fracture crack retardation effect variable loading crack closure effect plastic effect

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Machine learning and a computational fluid dynamic approach to estimate phase composition of chemical vapor deposition boron carbide

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Journal of Advanced Ceramics 2021年第3期10卷 537-550页

作者： Qingfeng ZENG Yong GAO Kang GUAN jiantao liu Zhiqiang FENG Science and Technology on Thermostructural Composite Materials Laboratory School of Materials Science and EngineeringNorthwestern Polytechnical UniversityXi’an 710072China MSEA International Institute for Materials Genome Gu’an 065500China School of Materials Science and Engineering South China University of TechnologyGuangzhou 510640China School of Mechanical Engineering Southwest Jiaotong UniversityChengdu 610031China eSchool of Mechanics and Engineering Southwest Jiaotong UniversityChengdu 610031China LMEE-UEVE UniversitéParis-SaclayEvry 91020France

Chemical vapor deposition is an important method for the preparation of boron *** of the correlation between the phase composition of the deposit and the deposition conditions (temperature,inlet gas composition,total pressure,reactor configuration,and total flow rate) has not been completely *** this work,a novel approach to identify the kinetic mechanisms for the deposit composition is *** leaning (ML) and computational fluid dynamic (CFD) techniques are utilized to identify core factors that influence the deposit *** has been shown that ML,combined with CFD,can reduce the prediction error from about 25% to 7%,compared with the ML approach *** sensitivity coefficient study shows that BHCl_(2 )and BCl_(3) produce the most boron atoms,while C_(2)H_(4) and CH_(4) are the main sources of carbon *** new approach can accurately predict the deposited boron-carbon ratio and provide a new design solution for other multi-element systems.

关键词： machine learning(ML) computational fluid dynamic(CFD) chemical vapor deposition boron carbide B/C ratio kinetic mechanisms

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Automatic modeling together with numerical simulation of the different-scale microstructures of human tooth enamels

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Science China(Technological Sciences) 2017年第9期60卷 1381-1399页

作者： liu Tao DENG Qiang YANG Dan ZHENG Jing liu jiantao ZHOU ZhongRong School of Mechanical Engineering Southwest Jiaotong University Chengdu 610031 China

The present paper aims to develop an automatical strategy for generating accurate different-scale microstructures of human tooth enamels(HTEs),and to elaborate a numerical scheme for simulating their elastic *** first,the strong governing formulation of these microstructures is briefly constructed,and the relevant weak formulation is then deduced based on the virtual work ***,a subdividing approach,which cuts the elements intercepted by the interfaces between distinct phases automatically,is established with the aid of the level set method(LSM),and the discrete counterpart of the governing formula is obtained by combining the weak formulation derived and a discretized *** be noted,two silent merits are found when the elaborated strategy is applied:(1) the continents constituting the microstructures of different scales can be arbitrarily-shaped and conveniently reproduced;(2) the periodic boundary condition commonly employed can be enforced on the external surfaces of representative unit cells(RUCs) with no ***,a boundary value problem(BVP) involving a simplified HTE nanostructure is designed,analytically solved,and hereafter applied to verify the correctness of the proposed *** is observed that both the displacement and stress predictions by the computational approach are in good agreement with the relevant analytical results irrespective of the material combinations ***,discussions are made on the influence of material organizations of both the 2D and 3D HTE microstructures at the ultrastructural and repeated rod levels,and some concluding remarks are drawn.

关键词： tooth enamel level set method automatic modefing numerical simulation microstructure

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Hot deformation behavior of FGH96 superalloys

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Journal of University of Science and Technology Beijing 2006年第4期13卷 319-323页

作者： jiantao liu Guoquan liu Benfu Hu Yuepeng Song Ziran Qin Yiwen Zhang Materials Science and Engineering School University of Science and Technology Beijing Beijing 100083 Chin High Temperature Material Institute Central Iron ＆ Steel Research Institute Beijing 100081 China

The hot deformation behavior of FGH96 superalloys at 1070-1170℃ and 5×10^-4-2×10^-1 s^-1 were investigated by means of the isothermal compression tests at a Gleeble-1500 thermal mechanical simulator. The results show that dynamic recovery acts as the main softening mechanism below 2×10^-3 s^-1, whereas dynamic recrystallization acts as the main softening mechanism above 2× 10^-3 s^-1 during deformation; the temperature increase caused by the deformation and the corresponding softening stress is negligible; the thermal-mechanical constitutive model to describe the hot deformation behavior is given, and the value of the apparent deformation activation energy （Qdef） is determined to be 354.93 kJ/mol.

关键词： FGH96 superalloys hot deformation hot deformation activation energy dynamic recovery dynamic recrystallization

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Particle size dependence of the microsegregation and microstructure in the atomized Ni-based superalloy powders:Theoretical and experimental study

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Journal of Materials Science & Technology 2024年第4期171卷 54-65页

作者： Jikang Li Mingsheng Yang Yunfei Cai Yuanyuan Zhang Qingshuai Feng jiantao liu Tong liu Key Laboratory of Aerospace Materials and Performance(Ministry of Education)School of Materials Science and Engineering Beihang UniversityBeijing 100191China Central Iron and Steel Research Institute Beijing 100081China

The microstructure and microsegregation of atomized powder,which depend on their sizes,are of great importance to the mechanical properties of the consolidated bulk ***,it is necessary to reveal the relationship between particle size and powder *** effects of particle size on the so-lidification characterization of the atomized Ni-based superalloy powders were studied via finite element *** on the simulations,a model was developed to predict the microsegregation and mi-crostructure of atomized powders with different sizes and study the influence of thermal history on the powder attributes during the atomization *** radiation heat transfer and temperature gradi-ent within the rapid solidification alloy powders were taken into account in this *** validating the accuracy of the model,the predictions of the present model were compared with the microsegregation and microstructure of the specific size powder close to the screen mesh *** results showed that mi-crostructure depended primarily on the temperature gradient within the powder,while the solidification rate had a more significant effect on the *** model predicted microstructure features in agreement with the experiment,and for microsegregation,the deviations of prediction for most ele-ments were less than 10%.This work provides a new model to precisely predict the microsegregation and microstructure of the atomized alloy powders and sets a foundation to control the powder features for various engineering applications.

关键词： Particle size Solidification microstructure Microsegregation Numerical simulation

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Winter wheat mapping using a random forest classifier combined with multi-temporal and multi-sensor data

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International Journal of Digital Earth 2018年第8期11卷 783-802页

作者： jiantao liu Quanlong Feng Jianhua Gong Jieping Zhou Jianming Liang Yi Li State Key Laboratory of Remote Sensing Science Institute of Remote Sensing and Digital EarthChinese Academy of SciencesBeijingPeople’s Republic of China University of Chinese Academy of Sciences BeijingPeople’s Republic of China Beijing Piesat Information Technology Co. Ltd.BeijingPeople’s Republic of China Zhejiang-CAS Application Center for Geoinformatics JiashanPeople’s Republic of China School of Life Sciences Arizona State UniversityTempeAZUSA

Wheat is a major staple food crop in *** and cost-effective wheat mapping is exceedingly critical for food production management,food security warnings,and food trade policy-making in *** reduce confusion between wheat and non-wheat crops for accurate growth stage wheat mapping,we present a novel approach that combines a random forest(RF)classifier with multi-sensor and multi-temporal image *** study aims to(1)determine whether an RF combined with multi-sensor and multi-temporal imagery can achieve accurate winter wheat mapping,(2)to find out whether the proposed approach can provide improved performance over the traditional classifiers,and(3)examine the feasibility of deriving reliable estimates of winter wheat-growing areas from medium-resolution remotely sensed *** wheat mapping experiments were conducted in Boxing *** experimental results suggest that the proposed method can achieve good performance,with an overall accuracy of 92.9%and a kappa coefficient(κ)of *** winter wheat acreage was estimated at 33,895.71 ha with a relative error of only 9.3%.The effectiveness and feasibility of the proposed approach has been evaluated through comparison with other image classification *** conclude that the proposed approach can provide accurate delineation of winter wheat areas.

关键词： Winter wheat random forest phenology Landsat-8 GF-1

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Deep reinforcement learning and 3D physical environments applied to crowd evacuation in congested scenarios

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International Journal of Digital Earth 2023年第1期16卷 691-714页

作者： Dong Zhang Wenhang Li Jianhua Gong Guoyong Zhang jiantao liu Lin Huang Heng liu Haonan Ma National Engineering Research Center for Geoinformatics Aerospace Information Research InstituteChinese Academy of SciencesBeijingPeople’s Republic of China University of Chinese Academy of Sciences BeijingPeople’s Republic of China Zhejiang-CAS Application Center for Geoinformatics JiaxingPeople’s Republic of China School of Surveying and Geo-Informatics Shandong Jianzhu UniversityJinanPeople’s Republic of China

To avoid crowd evacuation simulations depending on 2D environments and real data,we propose a framework for crowd evacuation modeling and simulation by applying deep reinforcement learning(DRL)and 3D physical environments(3DPEs).In 3DPEs,we construct simulation scenarios from the aspects of geometry,semantics and physics,which include the environment,the agents and their interactions,and provide training samples for *** DRL,we design a double branch feature extraction combined actor and critic network as the DRL policy and value function and use a clipped surrogate objective with polynomial decay to update the *** a unified configuration,we conduct evacuation *** scenarios with one exit,we reproduce and verify the bottleneck effect of congested crowds and explore the impact of exit width and agent characteristics(number,mass and height)on *** scenarios with two exits and a uniform(nonuniform)distribution of agents,we explore the impact of exit characteristics(width and relative position)and agent characteristics(height,initial location and distribution)on agent exit selection and ***,interactive 3DPEs and unified DRL enable agents to adapt to different evacuation scenarios to simulate crowd evacuation and explore the laws of crowd evacuation.

关键词： Virtual geographic environments crowd evacuation crowd evacuation simulation deep reinforcement learning 3D physical environments

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A Two-Layer Active Power Optimization and Coordinated Control for Regional Power Grid Partitioning to Promote Distributed Renewable Energy Consumption

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Energy Engineering 2024年第9期121卷 2479-2503页

作者： Wentao Li jiantao liu Yudun Li GuoxinMing Kaifeng Zhang Kun Yuan Key Laboratory of Measurement and Control of CSE Southeast UniversityNanjing210096China China Electric Power Research Institute Nanjing210003China State Grid Shandong Electric Power Research Institute Jinan250003China

With the large-scale development and utilization of renewable energy,industrial flexible loads,as a kind of loadside resource with strong regulation ability,provide new opportunities for the research on renewable energy consumption problem in power *** paper proposes a two-layer active power optimization model based on industrial flexible loads for power grid partitioning,aiming at improving the line over-limit problem caused by renewable energy consumption in power grids with high proportion of renewable energy,and achieving the safe,stable and economical operation of power ***,according to the evaluation index of renewable energy consumption characteristics of line active power,the power grid is divided into several partitions,and the interzone tie lines are taken as the optimization ***,on the basis of partitioning,a two-layer active power optimization model considering the power constraints of industrial flexible loads is *** upper-layer model optimizes the planned power of the inter-zone tie lines under the constraint of the minimum peak-valley difference within a day;the lower-layer model optimizes the regional source-load dispatching plan of each resource in each partition under the constraint of theminimumoperation cost of the partition,so as to reduce the line overlimit phenomenon caused by renewable energy consumption and save the electricity cost of industrial flexible ***,through simulation experiments,it is verified that the proposed model can effectively mobilize industrial flexible loads to participate in power grid operation and improve the economic stability of power grid.

关键词： Renewable energy consumption active power optimization power grid partitioning industrial flexible loads line over-limit

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Additive manufacturing alumina components with lattice structures by digital light processing technique

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Journal of Materials Science & Technology 2019年第12期35卷 2751-2755页

作者： Qjngfeng Zeng Changhao Yang Dingyi Tang Jiayao Li Zhiqiang Feng jiantao liu Kang Guan Science and Technology on Thermostructural Composite Materials Laboratory School of Materials Science and EngineeringNorthwestern Polytechnical University.Xi'an 710072China International Center for Materials Discovery School of Materials Science and EngineeringNorthwestern Polytechical UniversityXi'an 710072China MSEA International Institute for Materials Genome Gu'an065500China School of Mechanics and Engineering Southwest Jiaotong UniversityChengdu 610031China LMEE-UEVE Universiti Paris-SaclayEvry 91020France School of Mechanical Engineering Southwest Jiaotong UniversityChengdu 610031China School of Materials Science and Engineering South China University of TechnologyGuangzhou 510640China

Digital light processing technique was applied to manufacture alumina ceramic parts with two types of lattice structure units, i.e. vertex interconnect structure and edge structure. The internal porosity of the unit is 40%. The printed parts were sintered and the grain size is about 1.1 μm. The bending strength of the vertex interconnect structure is much larger than that of the edge structure. Materials genome initiative(MGI) aims to digital design and intelligent manufacture for advanced components. This research shows us an example to achieve this goal.

关键词： Additive manufacturing Ceramics DLP Lattice structure

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