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State of the Art on Micromilling of Materials,a Review

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Journal of Materials Science & Technology 2012年第8期28卷 673-685页

作者： M.A.Cmara J.C. Campos Rubio A.M. Abro J.P. Davim Department of Mechanical Engineering Universidade Federal de Minas GeraisAv.Ant onio Carlos6627-Pampulha Belo Horizonte MGCEP:31.270-901Brazil Department of Mechanical Engineering University of AveiroCampus Universitrio de Santiago3810-193AveiroPortugal

The trend towards miniaturization has increased dramatically over the last decade, especially within the fields concerned with bioengineering, microelectronics, and aerospace. Micromillin8 is among the principal manu- facturing processes which have allowed the development of components possessing micrometric dimensions, being used to the manufacture of both forming tools and the final product. The aim of this work is to present the principal aspects related to this technology, with emphasis on the work material requirements, tool ma- terials and geometry, cutting forces and temperature, quality of the finished product, process modelling and monitoring and machine tool requirements. It can be noticed that size effect possesses a relevant role with regard to the selection of both work material （grain size） and tooling （edge radius）. Low forces and temper- ature are recorded during micromillin8, however, the specific cutting force may reach high values because of the ploughing effect observed as the uncut chip thickness is reduced. Finally, burr formation is the principal concern with regard to the quality of the finished part.

关键词： Micro-milling Micromachining size effect Miniaturization

Three-dimensionally nonlocal tensile nanobars incorporating surface effect: A self-consistent variational and well-posed model

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Science China(Technological Sciences) 2021年第11期64卷 2495-2508页

作者： ZHU XiaoWu LI Li School of Statistics and Mathematics Zhongnan University of Economics and LawWuhan 430073China State Key Laboratory of Digital Manufacturing Equipment and Technology School of Mechanical Science and EngineeringHuazhong University of Science and TechnologyWuhan 430074China

A naturally discrete nanobar implies that the continuum axiom fails, and the surface-to-volume ratio is very large. The nonlocal theory of elasticity releasing the continuum axiom and the surface theory of elasticity are therefore employed to model tensile nanobars in this work. As commonly believed in the current practice, the axial nonlocal effect is only taken into account to analyze the mechanical behaviors of nanobars, regardless of the three-dimensional inherent atomistic interactions. In this study,a three-dimensional nonlocal constitutive law is developed to model the true nonlocal effect of nanobars, and based on which,a self-consistent variational bar model is proposed. It has been revealed for the first time how both the cross-sectional nonlocal interactions and the axial nonlocality affect the tensile behaviors of nanobars. It is found that the nonlocal influence predicted by the currently axial nonlocal bar model is grossly underestimated. Both the nonlocal cross-sectional and axial interactions become significant when the length-to-height ratio of nanobars is small. If the length-to-height ratio is relatively large(slender bars), the main nonlocal effect stems, however, from the nonlocal cross-sectional effect, rather than the axial nonlocal effect. This work also shows that it is possible to overcome the ill-posed problem of the pure nonlocal integral elasticity by employing both the pure nonlocal integral elasticity and surface elasticity. A well-posed size-dependent governing equation has been established for modeling nanobars under tension, and closed-form solutions are derived for their displacements. Based on the closed-form solutions, the effective elastic modulus is obtained and will be useful for calibrating the physical quantities in the "discretecontinuum" transition region for a span-scale modeling approach. It is shown that the effective elastic modulus may be softening or hardening, depending on the competition between the surface(modulus

关键词： nonlocal integral elasticity tensile nanobar size effect surface elasticity

DEM Analysis of Single-Particle Crushing Considering the Inhomogeneity of Material Properties

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Acta Mechanica Solida Sinica 2022年第1期35卷 26-39页

作者： Tao Zhang Wenxiong Huang College of Mechanics and Materials Hohai UniversityNanjing 211100China

Crushing characteristics of single particles are the basis of granular material simulation with discrete element method(DEM).To improve the universality and precision of crushable DEM model,inhomogeneous stiffness and strength properties are introduced into the bonded particle method,with which the Weibull distribution and size effect of particle strength can be reproduced without deleting elementary *** issues of particle strength and carrying capacity under complex contact conditions are investigated in this work by symmetric loading tests,asymmetric loading tests,and ball-ball loading *** of numerical experiments indicate that particle carrying capacity is significantly influenced by coordination numbers,the symmetry of contact points,as well as the relative size of its *** conditions also show impact on single-particle crushing categories and the origin position of inner particle *** existing stress indexes and assumptions of particle crushing criterion are proved to be inappropriate for general loading *** the inherent inhomogeneity and contact conditions of particles should be taken into consideration in the simulation of granular materials.

关键词： Bonded particle method Inhomogeneous properties size effect Coordination number Symmetry Relative size

Unconventional dislocation starvation behavior of medium-entropy alloy single crystal pillars containing pre-existing dislocations

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Journal of Materials Science & Technology 2023年第11期142卷 60-75页

作者： Luling Wang Bin Liu Jianqiu Zhou Yang Cao Feng Zhang Yonghao Zhao Department of Mechanical and Power Engineering Nanjing Tech UniversityNanjing 210009China Nano and Heterogeneous Materials Center School of Materials Science and EngineeringNanjing University of Science and TechnologyNanjing 210094China School of Mechanical Engineering Nanjing Institute of TechnologyNanjing 211167China

The excellent dislocation storage ability of bulk multi-principal element alloys(MPEAs)has been widely *** date,however,the underlying mechanisms of dislocation escape behavior in small-size facecentered cubic(FCC)MPEAs have rarely been ***,we quantitatively control the initial dislocation densities(-10^(15) m^(-2) and -10^(16) m^(-2))by large-scale molecular dynamics(MD)simulations and perform uniaxial compression simulations to compare the dislocation starvation behavior of CrCoNi with pure Cu single crystal pillars(SCPs).The analysis reveals that the CrCoNi SCPs with low initial dislocation density(-10^(15) m^(-2))can continuously accommodate mobile dislocations,and the critical dimension for dislocation starvation is about 30 *** particular,the CrCoNi SCPs with chemical short-range ordering(SRO)exhibit better dislocation storage and multiplication abilities than the random solid solution(RSS)samples even when the initial dislocation density is ***,the presence of a large number of pre-existing dislocation locks governs the strong dislocation multiplication ability of the small-size RSS CrCoNi SCPs,in obvious contrast to the deformation of all pure Cu SCPs which is completely dominated by intermittent mobile dislocation *** importantly,we reveal the fundamental physics for the good dislocation storage of CrCoNi SCPs at small sizes from the perspective of chemical *** new phenomena reported in this work provide a unique atomic-scale perspective for understanding the microscopic physical origin of the mechanical behavior of MPEAs and the discovery of extremely slow dislocation escape behavior in small-scaled pillars,providing a reliable basis for the development of the dislocation starvation model.

关键词： Molecular dynamics Medium entropy alloy Single crystal pillar Dislocation starvation Chemical short-range order size effect

Frictional Behavior of a Micro-sized Superconducting Fiber in a Low-Temperature Medium： Experimental and Computational Analysis

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Acta Mechanica Solida Sinica 2018年第4期31卷 405-415页

作者： Shiren La Jun Wang Xingyi Zhang Youhe Zhou Department of Mechanics and Engineering Sciences College of Civil Engineering and Mechanics Lanzhou University Lanzhou 730000 China Key Laboratory of Mechanics on Disaster and Environment in Western China Attached to the Ministry of Education of China Lanzhou University Lanzhou 730000 China

The purpose of the current study is to explore the frictional behavior of a micro- sized superconducting fiber at the low-temperature condition. At first, a highly precise tribometer composed of a superconducting fiber wrapping around a cylinder made of pure Cu was immersed in liquid nitrogen. The force and displacement resolutions of the experimental system were as high as 0.01 mN and 0.03 ~m, respectively. The NbTi fibers with diameters ranging from 22.9 to 115 ~m were used in the experiments, and their frictional behaviors in three media, i.e., liquid nitrogen, air and water, were systemically investigated. It was found that the frictional force in air showed a remarkable size effect. The existence of water medium could significantly reduce the frictional force, but could not eliminate the size effect. For the samples with the same diameter, the frictional force in liquid nitrogen was about 1.4 times of that in air, accompanied with remark- able stick-slip phenomenon. Notably, the fiber＇s frictional behavior in liquid nitrogen showed no dependence on diameter. In order to interpret these phenomena, the frictional behaviors of the fibers in air, water and liquid nitrogen were simulated using a modified spring-slider model, by taking into account the influence of hydrophilicity on surface roughness, and the influence of surface roughness on the fiber＇s frictional behavior. The simulation results were consistent with the experimental data qualitatively.

关键词： Micro-sized superconducting fiber Frictional behavior Surface roughness Hydrophilic-ity Stick-slip size effect Modified spring-slider model

The intrinsic nature of materials failure and the global non-equilibrium energy criterion

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Science China(Physics,Mechanics & Astronomy) 2020年第12期63卷 80-91页

作者： Biao Wang School of Physics and Sino-French Institute of Nuclear Engineering and Technology Sun Yat-sen UniversityGuangzhou 510275China

Materials failure under some sort of loading is a well-known natural phenomenon,and the reliable prediction of materials failure is the most important key issue for many different kinds of engineering structures based on their safety *** this research,instead of establishing empirical models,the material failure process was modeled as a nonequilibrium process based on the microstructural ***,the evolution equations were established and the stability analysis was carried out to obtain the critical conditions for the materials *** was found that the material strength was a global property in nature,and the commonly used local criteria based on the most dangerous point failure were not the rational *** on the idea,some examples were considered,such as the size effect of the material strength,the strength of the polycrystalline metals,the stress-strain relationship of the ultrafine crystalline metal with nanoscale growth twins,the strength of lithium niobite crystal specimens with *** of the theoretical predictions gave reasonable results compared with the experimental data.

关键词： strength theory nonequilibrium thermodynamics stability analysis size effect nanomaterials

Nonlocal stress gradient formulation for damping vibration analysis of viscoelastic microbeam in thermal environment

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Applied Mathematics and Mechanics(English Edition) 2023年第5期44卷 773-786页

作者： Hai QING Huidiao SONG State Key Laboratory of Mechanics and Control for Aerospace Structures Nanjing University of Aeronautics and AstronauticsNanjing 210016China

An integral nonlocal stress gradient viscoelastic model is proposed on the basis of the integral nonlocal stress gradient model and the standard viscoelastic model,and is utilized to investigate the free damping vibration analysis of the viscoelastic BernoulliEuler microbeams in thermal ***'s principle is used to derive the differential governing equations and corresponding boundary *** integral relations between the strain and the nonlocal stress are converted into a differential form with constitutive *** size-dependent axial thermal stress due to the variation of the environmental temperature is derived *** Laplace transformation is utilized to obtain the explicit expression for the bending deflection and *** the boundary conditions and constitutive constraints,one can get a nonlinear equation with complex coefficients,from which the complex characteristic frequency can be determined.A two-step numerical method is proposed to solve the elastic vibration frequency and the damping *** effects of length scale parameters,viscous coefficient,thermal stress,vibration order on the vibration frequencies,and critical viscous coefficient are investigated numerically for the viscoelastic Bernoulli-Euler microbeams under different boundary conditions.

关键词： damping vibration size effect integral nonlocal stress gradient model standard viscoelastic model Laplace transformation

Linear and nonlinear torsional free vibration of functionally graded micro/nano-tubes based on modified couple stress theory

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Applied Mathematics and Mechanics(English Edition) 2016年第6期37卷 725-740页

作者： A.R.SETOODEH M.REZAEI M.R.ZENDEHDEL SHAHRI Faculty of Mechanical and Aerospace Engineering Shiraz University of Technology

The linear and nonlinear torsional free vibration analyses of functionMly graded micro/nuno-tubes （FGMTs） are analytically investigated based on the couple stress theory. The employed non-classical continuum theory contains one material length scale parameter, which can capture the small scale effect. The FGMT model accounts for the through-radius power-law variation of a two-constituent material. Hamilton＇s principle is used to develop the non-classical nonlinear governing equation. To study the effect of the boundary conditions, two types of end conditions, i.e., fixed-fixed and fixed-free, are considered. The derived boundary value governing equation is of the fourthorder, and is solved by the homotopy analysis method （HAM）. This method is based on the Taylor series with an embedded parameter and is capable of providing very good approximations by means of only a few terms, if the initial guess and the auxiliary linear operator are properly selected. The analytical expressions are developed for the linear and nonlinear natural frequencies, which can be conveniently used to investigate the effects of the dimensionless length scale parameter, the material gradient index, and the vibration amplitude on the natural frequencies of FGMTs.

关键词： torsional vibration nonlinear vibration micro/nano-tube functionallygraded material (FGM) couple stress theory size effect

Nonlinear Bending of FCC Nanoplates Based on a Quasi-Continuum Model

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Acta Mechanica Solida Sinica 2022年第6期35卷 1030-1039页

作者： Wenjing Zhan Yaqi Guo Ying Zhao Guohua Nie School of Aerospace Engineering and Applied Mechanics Tongji UniversityShanghai200092China

A quasi-continuum model of plate-type nanomaterials with the face-centered cubic crystal structures is proposed in this *** fundamental governing equations for the nonlinear bending of the nanoplates are given by using the principle of minimum potential ***,the analytical solution is derived for cylindrical bending deformation of the structure under uniform transverse loading fixed at two sides based on the modified iterative method.A lattice finite element model is established to verify the present quasi-continuum ***,the corresponding solution by adopting the classical continuous plate theory is presented,in which two cases are considered for use of bulk values(limit values)and nanovalues of both elastic modulus and Poisson's *** difference among the quasi-continuum and continuous models are discussed by computation.

关键词： FCC Nanoplates Quasi-continuum model size effect Nonlinear bending