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关于负泊松比的材料力学课程教学拓展与探索

力学与实践 2024年第1期46卷 164-169页

作者：韦凯方棋洪湖南大学机械与运载工程学院长沙410082

泊松比是材料力学课程教学中的重要力学概念与材料弹性常数之一。本文对现有材料力学课程中泊松比教学内容进行了拓展和补充,引入了负泊松比效应概念,并介绍了常见的负泊松比材料及其力学性能优势。重点基于内凹蜂窝超材料,详细介绍了... 详细信息

泊松比是材料力学课程教学中的重要力学概念与材料弹性常数之一。本文对现有材料力学课程中泊松比教学内容进行了拓展和补充,引入了负泊松比效应概念,并介绍了常见的负泊松比材料及其力学性能优势。重点基于内凹蜂窝超材料,详细介绍了实现负泊松比效应的超材料力学理论分析及其教学实践;并借鉴虚拟仿真实验概念,应用有限元数值分析方法,对超材料的负泊松比效应进行仿真分析与讨论,直观地展示了超材料的力学变形模式及其负泊松比效应。从而以此为切入点,加深学生对弯曲内力、挠度、应变和泊松比等重点知识的理解与实践运用。

关键词：材料力学负泊松比超材料有限元分析

基于模拟-建模研究化学与温度对难熔高熵合金力学行为和变形机制的影响

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Acta Mechanica Sinica 2024年第2期40卷 103-115页

作者：李甲任思危刘彬 Peter K.Liaw 方棋洪 State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body College of Mechanical and Vehicle EngineeringHunan UniversityChangsha410082China State Key Laboratory of Powder Metallurgy Central South UniversityChangsha410083China Department of Materials Science and Engineering The University of TennesseeKnoxville37996USA

难熔高熵合金在高温下表现出优异的性能,突破了传统高温合金的工作温度上限.我们采用原子模拟研究了化学元素分布和温度对等原子比MoNbTaW难熔高熵合金变形机制的影响.根据微观结构演化,建立了基于微观结构的本构模型,定量评估多种强化... 详细信息

难熔高熵合金在高温下表现出优异的性能,突破了传统高温合金的工作温度上限.我们采用原子模拟研究了化学元素分布和温度对等原子比MoNbTaW难熔高熵合金变形机制的影响.根据微观结构演化,建立了基于微观结构的本构模型,定量评估多种强化机制的贡献.结果表明,应变硬化后,流动应力随应变呈锯齿状剧烈波动.由于退火结构的溶质浓度降低,温度升高降低了应变硬化率和流动应力波动幅度.变形孪晶在变形机制中起着关键作用,能够通过位错基塑性和晶粒中的非晶形核进一步调节局部变形.有序结构的存在强烈影响了应力和应变分配.固溶强化和晶界强化对流动应力的贡献很大,孪晶强化对流动压力的贡献很小.原子模拟和力学模型为深入理解难熔高熵合金变形行为及性能的精确预测提供依据.

关键词：流动应力固溶强化强化机制高温合金高熵合金变形机制晶界强化溶质浓度

A WEDGE DISCLINATION DIPOLE INTERACTING WITH A COATED CYLINDRICAL INHOMOGENEITY

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Acta Mechanica Solida Sinica 2015年第1期28卷 62-73页

作者： Yingxin Zhao qihong fang Youwen Liu State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body Hunan University College of Mechanical and Vehicle Engineering Hunan University

A three-phase composite cylinder model is utilized to study the interaction of a wedge disclination dipole with a coated cylindrical inhomogeneity. The explicit expression of the force acting on the wedge disclination dipole is calculated. The motilities and the equilibrium po- sitions of the disclination dipole near the coated inhomogeneity are discussed for various material combinations, relative thicknesses of the coating layer and the features of the disclination dipole. The results show that the material properties of the coating layer have a major part to play in alteringi the strengthening effect or toughening effect produced by the coated inhomogeneity.

关键词： three-phase composite disclination dipole coating layer complex variable function method

INTERACTION OF A DISLOCATION DIPOLE WITH A MODE III INTERFACE CRACK

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Acta Mechanica Solida Sinica 2007年第1期20卷 50-56页

作者： Jin Bo fang qihong Liu Youwen College of Civil Engineering Hunan University Changsha 410082 China College of Mechanics and Aerospace Hunan University Changsha 410082 China

Interaction between a screw dislocation dipole and a mode III interface crack is investigated. By using the complex variable method, the closed form solutions for complex potentials are obtained when a screw dislocation dipole lies inside a medium. The stress fields and the stress intensity factors at the tip of the interface crack produced by the screw dislocation dipole are given. The influence of the orientation, the dipole arm and the location of the screw dislocation dipole as well as the material mismatch on the stress intensity factors is discussed. The image force and the image torque acting on the screw dislocation dipole center are also calculated. The mechanical equilibrium position of the screw dislocation dipole is examined for various material property combinations and crack geometries. The results indicate that the shielding or anti-shielding effect on the stress intensity factor increases abruptly when the dislocation dipole approaches the tip of the crack. Additionally, the disturbation of the interface crack on the motion of the dislocation dipole is also significant.

关键词： dislocation dipole interface crack image force image torque

A SCREW DISLOCATION IN A THREE-PHASE COMPOSITE CYLINDER MODEL WITH INTERFACIAL RIGID LINES

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Acta Mechanica Solida Sinica 2005年第4期18卷 283-294页

作者： fang qihong Liu Youwen Jiang Chiping Department of Engineering Mechanics Hunan University Changsha 410082 China Solid Mechanics Research Center Beijing University of Aeronautics and Astronautics Beijing 100083 China

The problem of the elastic interaction between a screw dislocation and a three-phase circular inclusion with interracial rigid lines （anti-cracks） is investigated. An efficient and concise method for the complex multiply connected region is developed, with which explicit series form solutions of the complex potentials in the matrix, and the interphase layer and inclusion regions are derived. Based on the complex potentials, the image force on the screw dislocation is then calculated by using the Peach-Koehler formula. The equilibrium position of the dislocation is discussed in detail for various rigid line geometries, interphase layer thicknesses and material property combinations. The main results show that the interracial rigid lines exert a significant perturbation effect on the motion of the screw dislocation near the circular inclusion surrounded by an interphase layer.

关键词： screw dislocation interfacial rigid lines interphase layer complex potential method,image force

Effect of lattice distortion on solid solution strengthening of BCC high-entropy alloys

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Journal of Materials Science & Technology 2018年第2期34卷 349-354页

作者： Zhipeng Wang qihong fang Jia Li Bin Liu Yong Liu State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body Hunan University State Key Laboratory for Powder Metallurgy Central South University

An analytical model is established to study the influence of lattice distortion and fraction of Hf on the yield strength of the BCC TiNbTaZrHfx multi-component high entropy alloys （HEAs）. Meanwhile, the mechanism of solid solution strengthening caused by lattice distortion is also discussed in the HEA. The distorted unit cell is introduced to indicate the lattice distortion effects induced by the differences of the atomic size and shear modulus by doping other elements in Ti-based metal. The results show that the calculated values of the alloying yield strength considering the path of least resistance are obtained with regard to various grain sizes for the equiatomic TiNbTaZrHf HEA, which is well in line with the experimental results. Furthermore, it is predicted that the alloying yield strength is the largest value in the case of the same grain size for the Hf atomic fraction of 0.122. The meaningful modeling could provide a theoretical method to investigate the yield strength and alloying design of other BCC HEAs in the future.

关键词： High entropy alloy Solid solution strengthening Least resistance Yield strength Alloying design

Effect of cold working and annealing on microstructure and properties of powder metallurgy high entropy alloy

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Science China(Technological Sciences) 2018年第2期61卷 197-203页

作者： LIU Bin XU LiYou LIU Yong WANG JingShi WANG JiaWen fang qihong State Key Lab of Powder Metallurgy Central South UniversityChangsha 410083China College of Mechanical and Vehicle Engineering Hunan UniversityChangsha 410082China

An equiatomic CoCrFeNiMn high entropy alloy （HEA） was produced by powder metallurgy method. Cold rolling followed by subsequent annealing was conducted to further optimize the microstructure and mechanical properties. The results show that the SPSed CoCrFeNiMn HEA has an equiaxed single fcc phase microstructrue. Cold rolling results in extensive dislocation pile-up and twinning within the grains. The 80% cold-rolled alloy shows very high yield strength of 1292 MPa, but a limited elongation of 3%. Subsequent annealing produces recrystallization and precipitation of fine a particles with particle size of 30-100 nm. The annealed alloy has a yield strength of 540 MPa, which is about two to three times of the cast CoCrFeNiMn HEA, while still maintains a high tensile ductility of 41%. The improvement of the tensile properties is caused by the grain boundary strengthening, solid solution strengthening, and precipitation strengthening.

关键词： powder metallurgy high entropy alloy annealing cold rolling mechanical properties

Effects of grain boundary on irradiation-induced zero-dimensional defects in an irradiated copper

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Applied Mathematics and Mechanics(English Edition) 2022年第2期43卷 233-246页

作者： Jing PENG Shiyong CUI Yuanyuan TIAN qihong fang Jia LI P.K.LIAW State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body College of Mechanical and Vehicle EngineeringHunan UniversityChangsha410082China Department of Materials Science and Engineering The University of TennesseeKnoxvilleTennessee37996U.S.A

Grain boundaries(GBs)can serve as effective sinks for radiation-induced defects,thus notably influencing the service performance of ***,the effect of GB structures on the zero-dimensional defects induced by irradiation has not been fully ***,the evolution of cascade collision in the single-crystal(SC),bicrystalline(BC),and twinned crystalline(TC)copper is studied by atomic simulations during *** spatial distributions of vacancies and interstitials are closely related to the GB at a certain primary knock-on atom(PKA)*** with the TC,the BC displays a more obvious segregation of the interstitial atoms near GB,due to the characteristic of the greater interstitial binding *** evolution of Frenkel pairs is more sensitive to the change of the GB position in the BC.A more prominent defect annihilation rate is caused by the effect of the GB than that of the twin boundary(TB).The marked secondary emission phenomenon has been observed in the BC,which promotes the formation of an inverted pagoda-like defect *** are similar sub-conical defect distributions and microstructures induced by cascade collision in the TC and the *** has been found that the influence range of the GB is wider in the ***,the average flow stress of the irradiated copper is quantitatively calculated by establishing a physical strengthening *** contribution of vacancy to the average flow stress in the irradiated BC and TC is obvious than that in the SC,due to the formation of many *** study provides a theoretical basis for further understanding and customization of the metal-based equipment with good radiation resistance.

关键词： irradiation cascade collision grain boundary(GB) interstitial and vacancy molecular dynamics(MD)simulation physical strengthening model

High-throughput simulation combined machine learning search for optimum elemental composition in medium entropy alloy

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Journal of Materials Science & Technology 2021年第9期68卷 70-75页

作者： Jia Li Baobin Xie qihong fang Bin Liu Yong Liu Peter K.Liawc State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body Hunan UniversityChangsha410082.China State Key Laboratory of Powder Metallurgy.Central South University Changsha410083China Department of Materials Science and Engineering The University of TennesseeKnoxvilleTN37996USA

In medium/high entropy alloys, their mechanical properties are strongly dependent on the chemicalelemental composition. Thus, searching for optimum elemental composition remains a critical issue to maximize the mechanical performance. However, this issue solved by traditional optimization process via "trial and error" or experiences of domain experts is extremely difficult. Here we propose an approach based on high-throughput simulation combined machine learning to obtain medium entropy alloys with high strength and low cost. This method not only obtains a large amount of data quickly and accurately,but also helps us to determine the relationship between the composition and mechanical *** results reveal a vital importance of high-throughput simulation combined machine learning to find best mechanical properties in a wide range of elemental compositions for development of alloys with expected performance.

关键词： Medium entropy alloy Optimum elemental composition High-throughput simulation Machine learning