纳米压痕仪的压头面积函数校准方法的比较研究

基于原子力显微镜的直接测量法和通过熔融石英标准样块校准的间接测量法对纳米压痕仪的压头面积函数及机架柔度进行校准,并将这2种方法的校准结果分别应用到熔融石英和聚碳酸酯2种标准样块的压痕测试。压痕实验结果表明,在较浅压入深度,直接测量法测得的硬度值和折合模量值比间接方法测得的结果准确,在较大压入深度,2种方法的测量结果相差不大。     

微纤丝取向对木材细胞壁力学性能的影响研究

以马尾松为研究对象,运用原位成像纳米压痕技术测试了两种不同微纤丝取向（微纤丝角）下马尾松细胞壁纵向弹性模量和硬度之间的差异,由此探索微纤丝角对其细胞壁力学性能的影响,结果表明,上述两种力学性能指标与微纤丝角之间存在负相关关系,微纤丝角从13.5°增加到21.7°,马尾松管胞细胞壁纵向弹性模量降低了18.77%,硬度减少了18.37%。纳米压针从细胞壁的纵向压入时,细胞壁变形机制以塑性变形为主,微纤丝角越大,最大压入深度也越大,残余变形量也越大,但残余变形占总变形的比例几乎相同,约为73%。     

弹丸在多层复合介质中的爆炸破坏效应研究

根据实验得到的运动弹丸在多层复合介质中不同深度爆炸时产生的弹坑形状、体积及破坏面积，对破坏效应进行了理论分析，建立了弹丸在多层复合介质中的爆炸破坏分区；考虑主要影响破坏效果因素条件下应用量纲分析方法，并结合实验数据得到了破坏参数与比炸深的无量纲关系式和关系曲线，由这些曲线能够方便地查找所需最佳破坏效果对应的比炸深，在相同条件下，该结果可推广到类似目标的爆炸破坏效应分析。     

A Straightforward Direct Traction Boundary Integral Method for Two-Dimensional Crack Problems Simulation of Linear Elastic Materials

This paper presents a direct traction boundary integral equation method (DTBIEM) for two-dimensional crack problems of materials. The traction boundary integral equation was collocated on both the external boundary and either side of the crack surfaces. The displacements and tractions were used as unknowns on the external boundary, while the relative crack opening displacement (RCOD) was chosen as unknowns on either side of crack surfaces to keep the single-domain merit. Only one side of the crack surfaces was concerned and needed to be discretized, thus the proposed method resulted in a smaller system of algebraic equations compared with the dual boundary element method (DBEM). A new set of crack-tip shape functions was constructed to represent the strain field singularity exactly, and the SIFs were evaluated by the extrapolation of the RCOD. Numerical examples for both straight and curved cracks are given to validate the accuracy and efficiency of the presented method.     

Identification of Parameters of a Nonlinear Material Model Considering the Effects of Viscoelasticity and Damage

This work deals with mechanical properties of a rubber material that is used in modern tram wheels as a damping element. Nonlinear static response as well as strain softening and hysteresis are captured in the material model that is selected. Method of identification of the model's parameters is developed. The identification method relies on successive minimizations with respect to different sets of parameters. Tests in tension, compression and simple shear are performed. Parameters of the material model are identified based on the tension and compression data, while the shear data are used for validation only.     

Analytical and experimental studies on the low-velocity impact response and damage of composite laminates under in-plane loads with structural damping effects

In this paper, low-velocity impact response and damage of composite laminates under in-plane loads are analytically and experimentally investigated. The authors recently proposed a modified displacement field of plate theory, considering the effect of initially loaded in-plane strain, and used a finite element program to analyze the structural behavior of the composite laminate. In this study, the program is upgraded to account for the structural damping effect of the laminate. A pendulum type impact test system and an in-plane loading fixture are constructed for the experimental study. The analytical and experimental impact behaviors are compared at different impact energy levels for cases with an initial in-plane tensile load and a compressive load, as well as cases without the initial in-plane load. The results show good correspondence between the analytical and experimental impact force histories. The effect of the initial in-plane load reduces for higher impact energies. The numerical estimation of the damaged area is in good agreement with the results from C-scanning experiments.     

On the contact mechanics of a rolling cylinder on a graded coating. Part 1: Analytical formulation

In this paper, the fully coupled rolling contact problem of a graded coating/substrate system under the action of a rigid cylinder is investigated. Using the singular integral equation approach, the governing equations of the rolling contact problem are constructed for all possible stick/slip regimes. Applying the Gauss–Chebyshev numerical integration method, the governing equations are converted to systems of algebraic equations. A new numerical algorithm is proposed to solve these systems of equations. Both the coupled and the uncoupled solutions to the problem are found through an implemented iterative procedure. In Part I of this paper, the analytical formulation of the rolling contact problem and the discretization of the governing equations are introduced for all assumed stick/slip regimes. A detailed discussion of the proposed numerical algorithm, the iteration procedure and the numerical results, obtained using the analytical formulation, are given in Part II.     

弹性转子—轴承—基础系统的非线性振动研究

以转子动力学和非线性动力学理论为基础,针对非线性转子－轴承系统的具体特点,建立了采用短轴承模型的弹性转子－轴承－基础系统模型,并用数值积分和庞加莱映射方法对其在某些参数域中进行了非线性振动研究。对系统动力学特性随转速及偏心质量变化时的非线性行为进行了分析,计算结果显示,系统在某些参数域中可能发生倍周期分叉、概周期及混沌运动。用数值方法得到系统在特殊参数域中的分叉图、频谱图、相图、轴心轨迹、及率加莱映射图,并用分形几何理论对混沌系统的状态进行了判断。数值分析结果为该类转子－轴承系统的设计和安全运行提供了理论思考。     

Nonlinear shear properties of spruce softwood: Numerical analyses of experimental results

Determination of material parameters from experimental tests often rely on simplifying assumptions like the existence of uniform stress and strain fields within the considered part of the test specimen. However, more detailed analyses usually show that the stress and strain fields differ from the assumed (nominal) uniform distributions. In order to utilize the potential of numerical analyses of wooden structures by the FEM method, the nominal material parameters measured directly from tests need to be re-evaluated in order to make them more useful for FEM models and to make FEM models more reliable.Experimental data from shear testing of clear wood from Norway spruce was analysed numerically with a bilinear material law in shear. The inherent material parameters were fitted to the experimental behaviour by means of optimization methods in conjunction with FEM analyses. The study included six Arcan test configurations comprising the three orthotropic material planes of wood, and covered the whole loading range until failure. Compared to numerical results, it was found that stiffness values measured were too high, and that downward adjustments in the range of 5–30% were required. Linear limit stresses between 40% and 60% of the nominal shear strengths were found, whilst the tangent moduli ranged between 30% and 70% of the linear elastic shear moduli. The rolling shear plane RT showed most nonlinearity and the LT plane least. Analyses with modified bilinear parameters showed good correspondence with experimental findings. The parameters were found to be relatively well adapted by Weibull distributions.     

Nonlinear Dynamical Analysis in Incompressible Transversely Isotropic Nonlinearly Elastic Materials: Cavity Formation and Motion in Solid Spheres

In this paper, the problem of cavity formation and motion in an incompressible transversely isotropic nonlinearly elastic solid sphere, which is subjected to a uniform radial tensile dead load on its surface, is examined in the context of nonlinear elastodynamics. The strain energy density associated with the nonlinearly elastic material may be viewed as the generalized forms of some known material models. It is proved that some determinate conditions must be imposed on the form of the strain energy density such that the surface tensile dead load has a finite critical value. Correspondingly, as the surface tensile dead load exceeds the critical value, a cavity would form in the interior of the sphere and the motion of the formed cavity with time would present a class of singular nonlinear periodic oscillations. The effects of constitutive parameters on cavity formation and motion are discussed in detail, and the corresponding numerical examples are given simultaneously.     

毛刷电接触对的插拔力研究

针对现有毛刷电接触对插拔力控制方法的缺乏,提出了基于插拔深度控制毛刷电接触对插拔力的方法,在插拔过程中建立毛刷电接触对的结构力学模型和有限元仿真模型,并对毛刷电接触对进行插入力试验.将结构力学模型、有限元仿真模型、插拔力试验所得的插入力随插入深度变化曲线进行对比分析,评估了随机插合等因素对结构力学模型的影响,进行了线簧孔、麻花针和毛刷电接触对在不同插拔深度的插拔力对比试验.结果表明,毛刷电接触对插入力大小与插拔深度成幂函数关系,当典型毛刷电接触对插拔深度为1.8~2.4mm时,插拔力明显较同规格线簧孔、麻花针电接触对的小.基于插拔深度控制插拔力的方法为毛刷电接触对系列化扩展及参数设计提供了一定的参考.     

Weibull Stress Solutions for 2-D Cracks in elastic and Elastic-Plastic Materials

The Weibull stress is widely used as a measure of the probability of cleavage failure. In this work analytical and semi-analytical expressions for the Weibull stress are developed in terms of the remote loading parameters, J or K, and material properties. Results are presented for sharp cracks and notches in elastic and elastic-plastic materials under plane stress and plane strain conditions. The proposed relations enable Weibull stress estimates to be obtained without the need for costly finite element analyses and provide insight into the use of the Weibull stress as a parameter for the prediction of cleavage failure of cracked bodies. The expressions have been verified using finite element techniques and good agreement has been found throughout. The results of the analyses have been used to interpret the mesh size dependence of Weibull stress values obtained from finite element calculations. This revised version was published online in August 2006 with corrections to the Cover Date.     

一种钠钙硅酸盐玻璃的纳米压痕测试分析

采用纳米压痕测试技术对一种钠钙硅酸盐玻璃进行微观力学性能的测试分析.测得加载-卸载过程载荷与压入深度曲线,发现被测玻璃的最大压深、残余深度和弹性回复量随最大加载力的增加而增大,但其相对弹性回复率系数基本稳定,平均值为58.2%.通过电子显微镜观察了不同最大载荷下的压痕形貌,发现压痕区域出现了边界沉陷现象.当最大加载力为1 000 mN左右时,三棱锥工具头测试的压痕区域出现了较明显的微裂纹;采用四棱锥工具头时出现微裂纹的最大加载力要小于该值,且裂纹取向均与金刚石工具头的棱角取向一致.利用非线性有限元软件MSC.Marc对纳米压痕过程进行了仿真分析,得到载荷与压入深度的仿真曲线,该曲线与试验结果基本相符;分析了载荷作用下材料内部的应力分布.利用Oliver-Pharr模型得到不同压入深度下被测玻璃的接触刚度值,该值随压入深度的增加而增大.     

旋转型行波超声电机理论模型的仿真研究

建立了旋转型行波超声电机定、转子间的摩擦驱动模型，不仅考虑了接触界面上的纵向分布力，而且分析接触力沿周向和径向上的分量，在此基础上结合定子和转子的动力学模型得到了整个电机的机电耦合模型。文章分析了预压力影响电机驱动频率的本质原因，说明该频率不能直接通过分析自由定子得到，最后通过数值计算分析了接触界面力对电机工作频率的影响，取得了与实验一致的结果。     

Numerical study of the structural behaviour of impacted composite laminates subjected to compression load

Composite materials allow all the benefits which a high specific strength involves, in a design process their application involves many critical problems. Currently, these problems, such as environmental conditions, notch sensitivity, damaging under low velocity impacts, are taken into account by means of the application of conservative design safety factors regarding the ultimate tensile strength. In order to try to reduce these safety factors, this work aimed to study and to understand the impact damage growing mechanisms due to compression loads. To this purpose, compression tests have been experimentally performed on composite panels, which have been previously subjected to low velocity impact phenomena, considering impact energies of 6 J, 10 J and 13 J respectively. Moreover, numerical model able to simulate Low Velocity Impacts (LVI) and Compression After Impacts (CAI) onto CFRP panels is proposed. A single explicit finite element analysis has been carried out by using the Abaqus^® finite element code; the need to build a numerical model, which allows simulation in only one analysis both LVI and CAI steps, depends on the difficulty to import the impact damage distribution into a separate compression analysis. In fact, in only one analysis the compression step can occur directly onto the impacted plate, which allows to consider the effective impact damage distribution as the starting configuration for quasi static analysis under operating loads.     

电连接器接触件应力场的数值分析与试验验证

利用ANSYS对某型号电连接器接触件应力场进行分析,以寻找应力变化规律.对接触件应力场分布特点、插孔形变、接触压力随温度升高的变化规律进行了仿真研究,并进行数据分析与接触压力的试验验证.结果表明:随着温度升高,插孔最大形变量增加,最大接触压力和接触压力区域都有所减少;尺寸较小的接触件插孔槽缝底部最大等效应力随温度升高增幅较大,交变载荷作用时易出现疲劳、破裂等,属产品失效薄弱点.通过分析得知最大等效应力值随温度上升而变化的趋势取决于温度软化效应和热应力增强作用的综合结果;仿真结果能较好地反映电连接器的工作应力状态,接触压力试验验证了有限元仿真方法的可行性.     

Numerical Study on the Effects of Equi-biaxial Residual Stress on Mechanical Properties of Nickel Film by Means of Nanoindentation

In this paper,mechanical properties of Nickel film under residual stress have been systematically examined by finite element method in nanoindentation.It was found that load-displacement curves shifted under elastic residual stress and residual stress exceeded the yield stress for fixed indentation depth.Indentation profiles changed monotonously with compressive and tensile stresses at peak force which determinates contact area observed directly by finite element modeling (FEM).The elastic residual stress h...     

AgSnO2触头材料及其添加剂的研究与发展

综述了银基氧化物电触头材料的种类和发展状况,主要阐述了银基二氧化锡电触头材料的特性以及添加氧化物添加剂的重要作用,简述了纳米复合触头材料的制备方法,介绍了国内外研究者对纳米复合AgMeO触头材料的研究进展.     

Thermal Postbuckling Analysis of Imperfect Reissner-Mindlin Plates on Softening Nonlinear Elastic Foundations

A thermal postbuckling analysis is presented for a simply supported, moderately thick rectangular plate subjected to uniform or nonuniform tent-like temperature loading and resting on a softening nonlinear elastic foundation. The initial geometrical imperfection of the plate is taken into account. The formulations are based on the Reissner-Mindlin plate theory considering the first-order shear-deformation effect, and including plate-foundation interaction and thermal effects. The analysis uses a deflection-type perturbation technique to determine the thermal buckling loads and postbuckling equilibrium paths. Numerical examples are presented that relate to the performances of perfect and imperfect, moderately thick plates resting on softening nonlinear elastic foundations. The effects played by foundation stiffness, transverse shear deformation, plate aspect ratio, thermal load ratio and initial geometrical imperfections are studied. Typical results are presented in dimensionless graphical form and exhibit interesting imperfection sensitivity.     

Computation of the maximum torque of a cap liner using a power‐law friction and finite element analysis

In the ‘filled closed’ containers, the cap removal torque and the sealing of the contents are two crucial criteria in the closing quality, and the consumer perceives these two parameters as constituting a guarantee of packaging integrity. This work looks at the experimental study and the finite element analysis of the maximum torque of a metal cap with a liner over a glass bottle. For studying parameters influencing the cap removal torque (twist‐off torque), several experiments and simulations were conducted in order to evaluate the maximum torque of a loose crown cap. A test bench was built to measure the torque required to slide a cap liner on the top of a glass bottle, and the result of the experiment is compared with the predicted torque given by an axisymmetric finite element (FE) analysis. Since the behaviour of the cap liner is hyperelastic, compression and friction tests were conducted to evaluate the elastic properties and the non‐linear static friction behaviour of the elastomer seal. Contact regions, material non‐linear elasticity for the liner and large displacement options are included in the FE model in order to describe the evolution of the contact area and the distribution of contact pressure as a function of the applied force. The predicted maximum torque is then calculated by a numerical integration scheme over the contact surface, using an experimental coefficient of static friction as a function of the normal pressure. The predicted torque shows good agreement with that measured through experiments, thereby making it possible to understand the influence of the liner on the cap removal torque of a glass bottle. Copyright © 2010 John Wiley & Sons, Ltd.