One-dimensional nanostructured materials are often used as beams in many applications such as ultrahigh-frequency resonators and ultrasensitive sensors.Compared with usual macroscopic beams,nanobeams have much higher surface/volume ratios so that their surface energies may play a significant role.Besides,they often bear large deflections due to their typically large slenderness ratios and larger elastic ranges.There is,however,lack of a theory that takes into account of both the above two features owned by nanobeams.In this paper,we present such a theory and give applied examples to show that surface energy and large deflection may individually or jointly have notable effects.
Dujuan Zeng Quanshui Zheng 1(Department of Engineering Mechanics,Tsinghua University,Beijing 100084,China)
In this review,a critical look at the research progress of experimental solid mechanics in China for the past years is presented.Issues are discussed of the discovery and development of new fundamental methods and techniques versus performance benchmarking for many of their applications.Included herein are photoelasticity and various forms of modern photomechanics,acoustical techniques,image processing and videometrics,radial and spectrum techniques,and experimental mechanics on micro/nano scale.It is also noticed that both the ever developed instrumentation and specialized synthetical techniques have played important roles in advancing experimental mechanics in scientific researches and industrial applications.Finally,an attempt is made to look into the future of experimental solid mechanics with personal opinions offered on what the future trends will be for the researches in the field.
To simulate the nonlinear behavior of ferroelectric structures and devices under non-uniform electromechanical loadings,a domain-switching embedded electromechanical finite element method is developed in this paper.Following continuum assumption,the electromechanical behavior of each representative material point can be obtained by averaging the behavior of the local corresponding microstructure,e.g.42 domains used in this work.A new Double Gibbs free energy criterion for domain-switching is proposed to ensure the convergence and stability of the simulations on ferroelectrics under non-uniform field.Several computational examples are given to demonstrate that this nonlinear finite element method can yield reasonable and stable simulation results which can be used to explain some experimental results and assist the design of ferroelectric devices.
A temporal approach to fast shape measurement is presented.In principle,the rotational object method is used in combination with the sequence pulse counting method (SPCM) to determine the height of the object through calculating the related phase.Two specimens are tested to demonstrate the validity of the approach.One is an object covered by a Chinese character (tea) with a height variety of 0.3 mm,and the other is an object surface with a relatively large fluctuation of 3.5 mm.The experimental results are compared with mechanical measurements.An axis shifting method is also proposed to determine shapes with relatively large fluctuations.Effects of such parameters on the height measurement as incident angle of the dual light beams,tilting angle of the object,and azimuth angle of the measured point are discussed as well.
In this paper,the force-distance curves have been employed to investigate the force sensing properties of the probe-type microforce sensors.In the preliminary studies,two kinds of probe-type microforce sensors have been used to load the objects with dry and wetted surfaces.One is a developed piezoresistive cantilever force sensor with sensitivity of 35 μN/V and the other an atomic force microscope(AFM) cantilever beam probe with sensitivity of 10.4 nN/V.The force outputs corresponding to the regimes of approaching,indenting,and loading are obtained,and the properties of the stability in the approaching regime of the sensors,local mechanical behavior of the tested objects in the indenting regime,and the force sensing of the global samples are analyzed.Experimental results of this analysis are also presented.
Two kinds of clamping in micro/nano scale experiments are investigated in this paper,one based on electron-beam-induced deposition,and the other on the van der Waals interaction.The clamping strength and mechanism are analyzed both theoretically and experimentally.The influence of relative humidity on the micro/nano clamping and the method of electrostatic clamping are discussed.The clamping strength and performance of different clamping methods are compared considering the size and material of the clamped objects,and the application environments.
