静电激振法测量微机械材料的杨氏模量

利用蚀刻硅技术制造的微机械构件 ,由于特殊的制作工艺而需要对其材料的机械性能如杨氏模量等进行测试。这是随微机械技术的产生而提出的一个新课题。文章综述了微机械材料杨氏模量的静态测试法。提出了微机械材料杨氏模量的动态测试法———静电激振法。这种方法具有测试装置简单、测量容易、适应性广等特点     

静电激振法测量微机械材料的杨氏模量

利用蚀刻硅技术制造的微机械构件,由于特殊的制作工艺而需要对其材料的机械性能如杨氏模量等进行测试。这是随微机械技术的产生而提出的一个新课题。文章综述了微机械材料杨氏模量的静态测试法,提出了微机械材料扬氏模量的动态测试法－静电激振法,这种方法具测试装置简单、测量容量、适应性广等特点。     

原子力显微镜微悬臂梁杨氏模量动态测试方法

原子力显微镜微悬臂梁是微纳米领域重要的微力传感器,而微悬臂梁的杨氏模量又是决定其力学性能的重要参数.由于微悬臂梁的尺寸处于微米级,有些特征尺寸甚至达到纳米级,常规的测试结构材料特性的检测方法已经难以满足需求,急需研究新的测试方法和装置对微悬臂梁的机械特性进行研究和分析.本文提出了一种基于微悬臂梁振动固有频率测试的杨氏模量测试方法.使用本方法时,首先建立待测微悬臂梁在空气中的振动模型,并使用数值仿真的方法计算结构尺寸相同但杨氏模量不同的各种微悬臂梁在空气中的振动固有频率,然后实际测量微悬臂梁的振动固有频率,和实验结果最接近的仿真结果所对应的杨氏模量参数就是待测微悬臂梁的杨氏模量.本文最后对Mikromaseh公司生产的NSC型探针的杨氏模量进行了测试,实验结果证实了本文提出的方法的正确性.     

基于印压法的软组织模体的杨氏模量测量

研制了基于印压法的软质材料杨氏模量的测量装置,通过有限元仿真方法确定杨氏模量与印压曲线的关系的系数,从而实现对仿组织弹性样本进行杨氏模量量值的标定;用瞬时弹性成像设备对仿组织弹性模体进行测量,其结果与印压法测量结果的一致性,验证了弹性量值传递的可行性。     

一种用微弯曲实验测定内禀材料长度的新方法

提出了一种用微弯曲实验测定材料的与应变梯度塑性相联系的内禀长度的新方法.由一组不同的加载时曲率半径Ri和对应的卸载后曲率半径RFi的比值与Ri的关系,求出屈服强度与杨氏模量的比和硬化系数与杨氏模量的比;再应用这两个比值求出不同样品厚度的无量纲弯曲力矩与表面应变的实验关系曲线,对曲线拟合求出材料的内禀长度.将这种方法用于测定铝的内禀材料长度,研究其弯曲强度的尺寸效应,所得结果与前人用微弯曲和微拉伸两种实验方法得到的结果符合得很好.     

基于中间层原理杨氏模量测量系统

阐述了基于声波通过中间层声波透过规律测量杨氏模量的理论和方法。通过建立合理的中间层进行声波透射实验,使用虚拟仪器调整声波信号发生器的频率,依据接收器接收到的声强变化确定声波在材料中的半波长,从而得出声波在中间层的行波速度,计算出材料的杨氏模量,测量结果表明,此测量系统可以满足测量的要求,并在一定程度上克服了传统声速法时间差的信号处理点容易引入误差的缺点。     

一种用于水声材料设计的动态参数测试方法

针对提高水声材料设计中动态参数输入精度的问题，提出了一种复杨氏模量及泊松比准确测试方法。对于复杨氏模量测试，通过将Williams-Landel-Ferry(WLF)方程引入到Havriliak-Negami(H-N)模型中，采用信赖域反射算法对未知参数进行拟合得到材料参数宽频域主曲线。对于泊松比测试，根据同一材料不同形状因子表观杨氏模量之比与泊松比存在唯一量化关系的特性，仅通过两种不同形状因子试样的准静态有限元模拟，获得表观杨氏模量比值与泊松比量化曲线。因此，根据橡胶样品表观杨氏模量测试结果，可以直接利用局部加权回归获得其泊松比。最后，将前述材料制成直径为55 mm、厚度为50 mm的声管样品，放置在水声管中进行吸声系数测试。同时，把橡胶的复杨氏模量和泊松比的测量结果输入到水-橡胶-水分层介质模型中进行吸声系数计算。结果表明两者吻合，验证了上述测试方法的正确性和有效性。     

动态法测定石英杨氏模量的不确定度评定

按照分析测试中测量不确定度评定的方法,对利用弹性模量测试仪采用动态法测定石英杨氏模量时测量重复性、仪器准确度、样品质量测量、样品尺寸测量等引入的不确定度分量进行了评定,计算出石英杨氏模量的扩展不确定度。     

基于梯度滤波器的多尺度高精度微运动测量

微运动测量在微纳制造和生物医学等高技术领域担任了一个重要的角色,本文将梯度滤波器方法和多尺度方法相结合,提出了一种用于微运动测量的基于梯度滤波器的多尺度方法．在该方法中,利用多尺度金字塔迭代方法,对测量图像进行降采样和低通滤波,将较大像素的图像运动转化为多个小像素的图像运动进行估计,从而提高运动估计精度．提出的方法用于测量两个像素附近的MEMS微机械图像运动时,测量偏差达到了0．005个像素．模拟实验结果表明,这种基于梯度滤波器的多尺度方法能够实现高精度的微运动测量．     

用AFM力曲线技术测定聚合物微球的压缩杨氏模量

用无皂乳液聚合法制备了粒径为200-500nm的单分散聚苯乙烯(PS)微球。依靠正负电荷间作用力将样品分散在经过亲水处理的硅热氧化片刚性衬底上,借助原子力显微镜纳米压痕技术测定了PS颗粒样品的力学性质;依据样品的力-位移曲线,根据弹性力学接触模型,计算出PS微球样品的压缩杨氏模量为2-3 GPa(Hertz模型)和2-6 GPa(Sneddon模型)。结果表明,微球样品的杨氏模量计算值略低于PS块体材料,且随着粒径的增加而缓慢增大。Hertz模型更适于计算本文制备的亚微米级PS微球的压缩杨氏模量。     

Young's Modulus Measurement of Thin Films by Resonant Frequency Method Using Magnetostrictive Resonator

At present, there are many methods about Young's modulus measurement of thin films, but so far there is no recognized simple, non-destructive and cheaper standard measurement method. Considering thin films with various thicknesses were sputter deposited on the magnetostrictive resonator and monitoring the resonator's first-order longitudinal resonant frequency shift both before and after deposition induced by external magnetic field, an Young's modulus assessing method based on classical laminated plate theory is presented in this paper. Using the measured natural frequencies of Au, Cu, Cr, Al and SiC materials with various thicknesses in the literature, the Young's modulus of the five materials with various thicknesses are calculated by the method in this paper. In comparison with the Young's modulus calculated by the other methods, it is found that the calculated Young's modulus for various thicknesses are in good agreement with the Young's modulus values in the literature. Considering the simple and non-destructive characteristics of this method, which can effectively describe the effect of the thickness on the Young's modulus, it has the potential to become a standard assessing method of thin film Young's modulus.     

Measurement of elastic constants using vibrating wire strain gauges on disc and ring specimens

Useful methods of determining elastic constants employing diametrically–loaded disc and ring specimens have been proposed and applied by Durelli and Ferrer. Young's modulus may be measured from tests on a suitably dimensioned ring specimen. Subsequently Poisson's ratio may be found using a disc. The application of the methods described by the authors does not suit the case where the specimens are small and of stiff materials such as metals. In such a case sensitive means are required for measuring change in diameter with light loading. The paper indicates how this can be carried out for an aluminium alloy. The theory relating to the use of the disc for determining Poisson's ratio has been generalised to allow for measurement of change in length over part or all of a diameter. Poisson's ratio of the aluminium alloy was determined with a disc specimen 0.874 in (22.2 mm) diameter, vibrating wire strain gauges on either side of the specimen indicating change in diameter with loading. A ring was subsequently machined from the disc and similarly tested to confirm Young's modulus.     

Modifications of Surface Integrity during the Cutting of Copper

The required extreme surface quality of metallic parts made necessary investigation of different features of surface formed crystallites in polycrystalline materials. Every surface crystallite has different crystal plane orientation, so its reaction to the machine tool during cutting differs from that of other crystallites. These differences are reflected in the features of surface finish, especially when the surface is mirror like. The reason is that orientation of the crystallite determines the plastic and elastic deformation both of the machined surface and the chip. Elastic deformation perpendicular to the surface depends on the perpendicular compressive stress caused by the tool and Young's modulus, perpendicular to surface. After the passage of the tool, the elastic deformation disappears and its former values result in different levels of crystallite surfaces. Differences are determined by the orientation dependence of the Young's modulus. The ratio of highest to lowest modulus for copper is about 3, whereas for tungsten it is 1. The most important features of crystal structure and the reasons that cause deviations in surface finish in the machining of copper are reported.     

Application of an ultrasonic technique to creep cavitation in silicon nitride

A non-destructive method based on measurements of ultrasonic wave velocities and Young's modulus is proposed for quantification of creep cavitation in silicon nitride. Tensile creep tests of silicon nitride were conducted at 1400°C in air and the tests were periodically interrupted to measure the longitudinal and transverse ultrasonic wave velocities and Young's modulus. The velocities and Young's modulus decreased linearly with tensile creep strain. The volume fraction of cavities was estimated from the values of the ultrasonic wave velocities and Young's modulus, and compared with the cavity volume predicted from tensile creep strain. The dependence of Young's modulus on volume fraction of cavities is discussed.     

A novel strategy for developing α+β dual-phase titanium alloys with low Young's modulus and high yield strength

In this study,a novel strategy for developing α+β dual-phase titanium alloys with low Young's modulus and high yield strength was proposed,and a Ti-15Nb-5Zr-4Sn-1Fe alloy was developed through theoret-ical composition design and microstructure manipulation.After hot-rolling and subsequent annealing,a high volume fraction of ultrafine grained α phase embedded in metastable β-matrix was formed in the microstructure as intended.Consequently,this alloy exhibits both low Young's modulus(61 GPa)and high yield strength(912 MPa).The experimental results prove that the proposed strategy is appropriate for developing titanium alloys with superior yield strength-to-modulus ratio than those of conven-tional metallic biomedical materials.Present study might shed light on the research and development of advanced biomedical titanium alloys with low Young's modulus and high yield strength.     

Frequency dependency of Young's modulus of dental cocomposites

The Young's modulus of 15 commercial dental particulate filled composites was measured with three different methods. The materials were tested with static, low-frequency, and high-frequency elastic deformations. The analysis of the results shows that the frequency dependence of the Young's modulus of elasticity follows the same empirical law for all frequencies. Furthermore, knowledge of the Young's modulus for the resin component at all frequencies suffices to predict the Young's modulus of any particulate-filled composite.     

Internal stress relaxation based method for elastic stiffness characterization of very thin films

Accurate measurement of the Young's modulus of films with thickness smaller than a few hundreds of nanometers remains extremely challenging. The present method disclosed here is based on the combined measurements of the internal stress using the Stoney method and of the corresponding elastic strain obtained by releasing microstructures. Experimental validation is presented for silicon nitride films. The Young's moduli of the 100, 300, and 500 nm-thick films are equal to 193 ± 20 GPa, 226 ± 22 GPa, and 208 ± 18 GPa, respectively, in good agreement with nanoindentation test results. This very simple method can potentially be used for much thinner films and extended to materials involving no internal stress.     

Feasibility of Estimation Methods for Measuring Young's Modulus of Wood by Three-Point Bending Test

We examined the feasibility of estimation methods for measuring Young's modulus of wood by the three-point bending test using spruce specimens (Picea sitchensis Carr.). By measuring the deflections at the midspan and at the midpoint between the loading and supporting points, Young's moduli were determined according to elementary and Timoshenko's beam theory. Additionally, longitudinal strain at the midspan was measured independently of measuring the deflections, and Young's modulus was also determined from the load-strain relation. The values of Young's modulus obtained by the different procedures were compared with each other, and the following results were obtained: (1) Measurement of two-point deflections was effective for obtaining Young's modulus while reducing the influence of shear deformation when the specimen had a small depth. (2) In the measurement of two-point deflections, the specimen configuration should be regarded as more important than the contact at the loading and supporting points. (3) The use of strain gauges should be taken into account as a standardized method for measuring Young's modulus by bending.     

Study of the mechanical properties of Nd:YVO4 crystal by use of laser interferometry and finite-element analysis

A hybrid method that combines experimental and numerical approaches for determining the material properties of Nd:YVO(4) is reported. In the experimental investigations a laser interferometer is proposed for measuring the physical deformation of lasing materials at the end-pump surface. By matching with the measured end bulging, we have implemented a numerical solution with finite-element analyses to determine the Poisson ratio and Young's modulus of the crystal. The accuracy interval of the evaluated Poisson ratio of 0.33 and Young's modulus of 133 GPa is discussed numerically. Based on the mechanical properties obtained, the end effect is separated from thermal effects, and it shows that the end effect results in an approximate equal thermal lensing effect compared with the index parts for end-pumped Nd:YVO(4) lasers.