PSO algorithm for Young's modulus reconstruction

To get the quantitive value of abnormal biological tissues, an inverse algorithm about the Young＇s modulus based on the boundary extraction and the image registration technologies is proposed. With the known displacements of boundary tissues and the force distribution, the Young＇s modulus is calculated by constructing the unit system and the inverse finite element method （IFEM）. Then a tough range of the modulus for the whole tissue is estimated referring the value obtained before. The improved particle swarm optimizer （PSO） method is adopted to calculate the whole Yong＇s modulus distribution. The presented algorithm overcomes some limitations in other Young＇s modulus reconstruction methods and relaxes the displacements and force boundary condition requirements. The repetitious numerical simulation shows that errors in boundary displacement are not very sensitive to the estimation of next process; a final feasible solution is obtained by the improved PSO method which is close to the theoretical values obtained during searching in an extensive range.

A method to determine Young's modulus of soft gels for cell adhesion

A convenient technique is reported in this note for measuring elastic modulus of extremely soft material for cellular adhesion. Specimens of bending cylinder under gravity are used to avoid contact problem between testing device and sample, and a beam model is presented for evaluating the curvatures of gel beams with large elastic deformation. A self-adaptive algorithm is also proposed to search for the best estimation of gels＇ elastic moduli by comparing the experimental bending curvatures with those computed from the beam model with preestimated moduli. Application to the measurement of the property of polyacrylamide gels indi- cates that the material compliance varies with the concentrations of bis-acrylamide, and the gels become softer after being immersed in a culture medium for a period of time, no matter to what extent they are polymerized.

Probing the Young＇s modulus and Poisson＇s ratio in graphene/metal interfaces and graphite： A comparative study

By analyzing phonon dispersion, we have evaluated the average Young＇s modulus and Poisson＇s ratio in graphite and in graphene grown on Ru（0001）, Pt（111）, Ir（111）, Ni（111）, and BC3/NbB2（0001）. In both flat and corrugated graphene sheets and in graphite, we find a Poisson＇s ratio of 0.19 and a Young＇s modulus of 342 N/m. The unique exception is graphene/Ni（111）, for which we find different values because of the stretching of C-C bonds occurring in the commensurate overstructure （0.36 and 310 N/m for the Poisson＇s ratio and Young＇s modulus, respectively）. Such findings are in excellent agreement with calculations performed for a free-standing graphene membrane. The high crystalline quality of graphene grown on metal substrates leads to macroscopic samples with high tensile strength and bending flexibility for use in technological applications such as electromechanical devices and carbon-fiber reinforcements.

ELECTRIC FIELD EFFECTS ON YOUNG'S MOLULUS OF NANOWIRES

As an important component of nanodevices and nanomachine constructions, the mechanical performance of nanowires （NWs） has been a subject of intense research efforts due to gaining relevance in controlling functionality of nanoelectromechanical systems （NEMS）; meanwhile, one of the characteristics of the NEMS is the dependence of the functionality of the systems upon the applied electric field. The study of the electric effects on the Young＇s modulus of nanostructures is of certain usefulness in the design of NEMS and the precise measurement of mechanical properties of one-dimensional nanostructures. This paper reviews the origin of the size-dependence of the elastic property of NWs and the factors influencing the discrepancies and inconsistencies in the measured values of the Young＇s modulus for the NW, besides the surface effects, nonlinear effects, the electromechanical coupling effects as a possible effect responsible for the differences in quantitative and qualitative performance of the measured Young＇s modulus for the NWs versus the diameter are clarified.

CALCULATION OF THE YOUNG'S MODULUS OF AN ADSORBED POLYMER LAYER

Polymer layers adsorbed to a surface or in a confined environment often change their mechanical properties. There is even the possibility of solidification of the confined layer. To judge the stiffness of such a layer, we used the Hertz model to calculate the Young＇s modulus of the polymer layer in the confinement of AFM experiments with silicon nitride tip with a radius of curvature ofR ≈ 50 nm and a glass sphere attached to the cantilever R =5 μm. Since there is no visible indentation of the layer in the AFM experiments, the layer is either penetrated very easily, or the indentation is too small to be seen in a force curve. The latter would be the case for a polymer layer with a Young＇s modulus above 4 × 10^8 Pa in case of an experiment with a silicon nitride tip and 4×10^5 Pa in case of a glass sphere.

Determination of reduced Young s modulus of thin films using indentation test

The flat cylindrical indentation tests with different sizes of punch radius were investigated using finite element method （FEM） aimed to reveal the effect of punch size on the indentation behavior of the film/substrate system. Based on the FEM results analysis, two methods was proposed to separate film＇s reduced Young＇s modulus from a film/substrate system. The first method was based on a new weight function that quantifies film＇s and substrate＇s contributions to the overall mechanical properties of the film/substrate system in the flat cylindrical indentation test. The second method, a numerical approach, including fitting and extrapolation procedures was put forward. Both of the results from the two methods showed a reasonable agreement with the one input FE model. At last, the effect of maximum indentation depth and the surface micro-roughness of the thin film on the reduced Young＇s modulus of the film/substrate system were discussed. The methods proposed in the present study provide some new conceptions on evaluating other properties of thin films, e.g. creep, for which a flat-ended punch is also employed.

The influence of nonparaxiality on the spectral behavior in Young's experiment illuminated by partially coherent light

Starting from the Rayleigh-Sommerfeld diffraction integral, this paper studies the spectral behavior in Young＇s experiment illuminated by nonparaxial partially coherent light and compares with the paraxial case, where the influence of nonparaxiality of partially coherent light on the spectral shifts and spectral switches is stressed. It is shown that there is a spectral shift in the nonparaxial case relative to the paraxial one and the critical position changes, at which the spectral switch occurs. The ratio of the waist width to the central wavelength ω0/λ0 and relative spatial correlation length △ affect the spectral difference. The smaller ω0/λ0 is, the larger the difference between the nonparaxial and paraxial results appears. The effect of relative spatial correlation length △ is relatively small.

Young＇s Modulus Enhancement and Measurement in CNT/Al Nanocomposites

Young＇s modulus is a critical parameter for designing lightweight structure, but Al and its alloys only demonstrate alimited value of 70-72 GPa. The introduction of carbon nanotubes （CNTs） is an effective way to make Al and its alloysstiffer. However, little research attention has been paid to Young＇s modulus of CNT/Al nanocomposites attributed to theuncertain measurement and unconvincing stiffening effect of CNTs. In this work, improved Young＇s modulus of 82.4 ± 0.4 GPa has been achieved in 1.5 wt% CNT/Al nanocomposite fabricated by flake powder metallurgy, which wasdetermined by resonance test and 13.5% higher than 72.6 ± 0.64 GPa of Al matrix. A comparative study and statisticalanalysis further revealed that Young＇s modulus determined by tensile test was relatively imprecise （83.1 ± 4.0 GPa） dueto the low-stress microplasficity or interface decohesion during tensile deformation of CNT/Al nanocomposite, while thevalue （98-100 GPa） was highly overestimated by nanoindentation due to the ＂pile-up＂ effect. This work shows an in-depthdiscussion on studying Young＇s modulus of CNT/Al nanocomposites.

An improved model for predicting effective Young's modulus of the twisted structure under cyclic loading:taking into account the untwisting effect

Twist structures have diverse applications, ranging from dragline, electrical cable, and intelligent structure. Among these applications, tension deformation can＇t be avoided during the fabrication and working processes, which often leads to the twist structure rotation （called untwisting effect） and twist pitch increasing. As a consequence, this untwisting behavior has a large effect on the effective Young＇s modulus. In this paper, we present an improved model based on the classical Costello＇s theory to predict the effective Young＇s modulus of the basic structure, twisted by three same copper strands under cyclic loading. Series of experiments were carried out to verify the present model taking into account the untwisting effect. The experimental results have better agreements with the presented model than the common Costello＇s model.

Measurement of Young's Modulus and Poisson's Ratio of Thermal Barrier Coatings

In gas turbines, thermal barrier coatings （TBCs） applied by air plasma spraying are widely used to lower the temperature of hot components. To analyze the characteristics of TBCs such as residual stress, bond strength, fracture toughness, and crack propagation ratio, the Young＇s modulus and Poisson＇s ratio are important parameters. For TBC is a brittle and thin film, it is desirable to evaluate those properties while the coatings are bonded to a substrate. An atmospheric plasma spray MCrAIY bond coat and Yttria stabilized zirconia （YSZ） top coat are deposited onto a nickel-base superalloy GH150 substrate. The Young＇s modulus and Poisson＇s ratio are measured by cantilever beam bending with NDI. The method will be developed to test the Young＇ s modulus and Poisson ratio of other multilayer systems.

A Bicycle Design Model Based on Young Women＇s Fashion Combined With CAD and Statistical Science

Today, more people are riding bicycles than ever before--and the numbers keep growing. This is due in part to a greater awareness of environmental issues and growing health consciousness. Another factor driving the increasing number of women bicyclists today is many designer bicycles now available. Still, these bicycles reflect the subjective sensibilities of their designers, and there is no guarantee that they will always match an increasingly diverse array of consumer values. In response to this challenge, our study sets out to build a bicycle design model based on fashion styles popular with young women in their 20s. Fashion analysis and bicycle design analysis used statistical science, such as cluster analysis, principal component analysis, and analytic hierarchy process （AHP）. After that, we designed a new bicycle using computer-aided design （CAD） from the analysis results. Finally, the approach model developed in this study was confirmed to be effective by an interview with the company.

Surface-effects-dominated thermal and mechanical responses of zinc oxide nanobelts

t Molecular dynamics （MD） simulations are carried out to characterize the mechanical and thermal responses of [011^-1]-oriented ZnO nanobelts with lateral dimensions of 21.22A × 18.95 A, 31.02A× 29.42 A, and40.81A ×39.89A over the temperature range of 300-1000 K. The Young＇s modulus and thermal conductivity of the nanobelts are evaluated. Significant surface effects on properties due to the highsurface-to-volume ratios of the nanobelts are observed. For the mechanical response, surface-stress-induced internal stress plays an important role. For the thermal response, surface scattering of phonons dominates. Calculations show that the Young＇s modulus is higher than the corresponding value for bulk ZnO and decreases by -33% as the lateral dimensions increase from 21.22 A × 18.95A to 40.81 A × 39.89A. The thermal conductivity is one order of magnitude lower than the corresponding value for bulk ZnO single crystal and decreases with wire size. Specifically, the conductivity of the 21.22 A × 18.95 A belt is approximately （31-18）% lower than that of the 40.81 A × 39.89 A belt over the temperature range analyzed. A significant dependence of properties on temperature is also observed, with the Young＇s modulus decreasing on average by 12% and the conductivity decreasing by 50% as temperature increases from 300 K to 1000 K.

EXPERIMENTAL RESEARCHES ON MAGNETO-THERMO-MECHANICAL CHARACTERIZATION OF TERFENOL-D

The coupling effects of axial pre-stress, temperature and magnetic field on magne- tostrictive strain and magnetization as well as Young＇s modulus ofa Terfenol-D （Tbo.3Dyo.rFei.93） rod are tested to give a good understanding of magneto-thermal-mecha- nical characteristics of giant magnetostrictive materials. Results show that magneto-thermo-mechanical coupling of giant magnetostrictive materials is very strong; and the influences of pre-stress and temperature on magnetostrictive strain and Young＇s modulus vary with the intensity of magnetic field.

Design of a Biomimetic Skin for an Octopus-Inspired Robot - Part I： Characterising Octopus Skin

Octopus skin samples were tested under quasi-static and scissor cutting conditions to measure the in-plane material prop- erties and fracture toughness. Samples from all eight arms of one octopus were tested statically to investigate how properties vary from arm to arm. Another nine octopus skins were measured to study the influence of body mass on skin properties. In- fluence of specimen location on skin mechanical properties was also studied. Material properties of skin, i.e. the Young＇s modulus, ultimate stress, failure strain and fracture toughness have been plotted against the position of skin along the length of arm or body. Statistical studies were carried out to help analyzing experimental data obtained. Results of this work will be used as guidelines for the design and development of artificial skins for an octopus-inspired robot.

Compressive and energy absorption properties of closed-cell magnesium foams

The quasi-static compressive mechanical behavior and deformation mechanism of closed-cell magnesium foams were studied, and the ef- fects of the density of magnesium foams on the compressive and energy absorption properties were also discussed. The results show that the compressive process of closed-cell magnesium foams is characterized by three deformation stages： linear elastic stage, collapsing stage and densification stage. At the linear elastic stage, the peak compressive strength （t70） and Young＇s modulus （E0） increase as the density increases Magnesium foams can absorb energy at the collapsing stage. In a certain strain range, the energy absorption capacity also increases as the density of magnesium foams increases.

Mechanical Characterization of Electroplated Ni Films by Micro-tensile Testing

Mechanical properties of structural materials are particularly important for design, performance realization and reliability analysis of microelectromechanical systems （MEMS）. Furthermore, accurate database of mechanical properties at the micro scale can provide indispensable reference for establishing MEMS standard. Electroplated nickel film is one of the most favored structural materials used in MEMS, thus its mechanical properties has been studied for many years. However, the measured values show large scatter in Yotmg＇s modulus of nickel film. Young＇s modulus and yield stress of electroplated nickel film are measured by using a micro-tensile testing instrument. The tensile load applied on the specimen is measured by a load cell with accuracy 0.25 mN directly, without additional friction. Through measuring the axial stiffness coefficient of the tensile instnunent in situ, the tensile strain of the specimen is obtained by using two-serial spring model. The electroplated nickel films were fabricated from sulfarnate baths, and the gauge section is 500μm long and 10μm wide nominally, and thickness range between 25 μm and 50μm. The obtained Young＇s modulus from tensile testing is 83＋6 GPa for nickel specimens electroplated at current density of 20 mA/cm2 and it increases to 124＋5 GPa as current density is decreased to 10 mA/cm2. The phenomena are interpreted in terms of porosity of microstructure. The higher current density produced rnicrostucture with low density and high volume fraction of pores, and the microstructure of high porosity corresponds to a lower modulus. The measured values of Young＇s modulus are consistent with those of calculated from the exponential empirical formula between Young＇s modulus and porosity. The micro-tensile testing instrument can also be used for mechanical measurement of other MEMS films.

A molecular mechanics approach for analyzing tensile nonlinear deformation behavior of single-walled carbon nanotubes

In this paper, by capturing the atomic information and reflecting the behaviour governed by the nonlinear potential function, an analytical molecular mechanics approach is proposed. A constitutive relation for single-walled carbon nanotubes （SWCNT＇s） is established to describe the nonlinear stress-strain curve of SWCNT＇s and to predict both the elastic properties and breaking strain of SWCNT＇s during tensile deformation. An analysis based on the virtual internal bond （VIB） model proposed by P. Zhang et al. is also presented for comparison. The results indicate that the proposed molecular mechanics approach is indeed an acceptable analytical method for analyzing the mechanical behavior of SWCNT＇s.

Experimental study on dynamic elastic parameters of coal samples

Dynamic elastic parameters of coal are closely linked to crack characteristics and are lithology indicators in seismic exploration. This experimental study measured ultrasonic wave velocity of coal samples considering both parallel(90°) and perpendicular(0°) to bedding planes, and then calculated the dynamic elastic parameters(Edand ld) and their anisotropy values(AEdand Ald). The variations of Edand ld,as well as AEdand Aldwere analyzed under various confining stresses. The results show that: Firstly, a critical confining pressure exists, and significant variation in the parameters can be seen below this point and weak variation appears above it. Secondly, a positive correlation exists between Edand the square of P-wave velocity(VP2), and between AEdand the P-wave velocity anisotropy(AEP) as well; however, there is no clear correlation between ldand P-wave velocity(VP). Thirdly, according to the major controlling factors of anisotropy, the coal samples with different Edand ldas well as AEdand Aldcan be divided into two types: one is mainly controlled by bedding and cracks and the other one is mainly controlled by differences of mineral compositions in directions. Consequently, this study can provide theoretical basis for future research on the dynamic elastic parameters and anisotropy of coal.

Molecular Dynamics Study of Effects of Si-Doping Upon Structure and Mechanical Properties of Carbon Nanotube

In this paper, a Si-doped single-walled carbon nanotube （SWCNT） （7,7） and several perfect armchair SWCNTs are investigated using the classical molecular dynamics simulations method. The inter-atomic short-range interaction is represented by empirical Tersoff bond order potential. The computational results show that the axial Young＇s modulus of the perfect SWCNTs are in the range of 1.099 ± 0.005 TPa, which is in good agreement with the existing experimental results. From our simulation, the Si-doping decreases the Young＇s modulus of SWCNT, and with the increased strain levels, the effect of Si-doped layer in enhancing the local stress level increases. The Young＇s modulus of armchair SWCNTs are weakly affected by tube radius.

NANOMECHANICAL MAPPING OF CARBON BLACK REINFORCED NATURAL RUBBER BY ATOMIC FORCE MICROSCOPY

Atomic force microscopy （AFM） has the advantage of obtaining mechanical properties as well as topographic information at the same time. By analyzing force-distance curves measured over two-dimensional area using Hertzian contact mechanics, Young＇s modulus mapping was obtained with nanometer-scale resolution. Furthermore, the sample deformation by the force exerted was also estimated from the force-distance curve analyses. We could thus reconstruct a real topographic image by incorporating apparent topographic image with deformation image. We applied this method to carbon black reinforced natural rubber to obtain Young＇s modulus distribution image together with reconstructed real topographic image. Then we were able to recognize three regions; rubber matrix, carbon black （or bound rubber） and intermediate regions. Though the existence of these regions had been investigated by pulsed nuclear magnetic resonance, this paper would be the first to report on the quantitative evaluation of the interfacial region in real space.