弹簧振子实验不确定度的分析研究

采用静力伸长法和振动周期法测量并计算弹簧振子的劲度系数,通过分析不确定度,比较了用静伸长法求弹簧劲度系数中逐差法和用最小二乘法作Excel直线拟合这两种数据处理方法的精确性差异,并通过计算得出测量弹簧劲度系数时静伸长精确度高于振动法的结论。实验结果具有一定的理论意义,并对于改进弹簧振子实验过程有重要的指导作用。     

基于ANSYS的共振频率分析及实验研究

由共振法测量杨氏模量的实验思想,采用有限元分析软件ANSYS14.0对铜质细长棒进行了模态分析及谐响应分析,获得了前三阶振动模态的共振频率及振型;通过施加载荷后的谐响应曲线,获得前三阶共振峰,将数值仿真结果与理论求解及实验结果进行对比,结果是一致的。     

弹簧等效质量和劲度系数示波器测量法

介绍了利用圆柱状弹簧作为电路电感元件,把弹簧振动信息转变为电信号,通过数字存储示波器的扫描模式显示,记录弹簧在一段时间内的振动过程,从而可对振动系统的振动周期进行比较直观的测量,进而测出弹簧等效质量、弹簧劲度系数.     

“鸡尾酒”弹弓橡皮筋劲度系数的测定

介绍了鸡尾酒弹弓的结构,设计了测量鸡尾酒弹簧劲度系数的实验方案,并通过图像确定了鸡尾酒弹簧的劲度系数.     

微型加速度传感器用于金属棒弹性模量测量

基于振动理论给出的悬臂梁弯曲自由振动的一阶固有频率与材料弹性模量的关系,提出用微型加速度传感器测量悬臂梁单端自由振动的频率,并在自行搭建的实验装置上对钢棒的弹性模量进行了测量,分析了影响测量结果准确性的因素.最终实验结果与手册查询到的对照值十分吻合,测量的相对不确定度为0.66%.本实验原理清晰、装置构成简单、操作简便、结果较精确,适于教学使用或工业现场检测之用.     

双光栅弹性模量测量实验方法

利用磁耦合双光栅法动态测量了材料的弹性模量,采用电磁能非接触耦合样品激振,激光光拍法微振动非接触检测,使测试样品处于完全自由振动状态,通过激光光拍微弱振动位移测量了样品的固有频率,再通过测量几何尺寸和质量即可计算出样品的弹性模量.     

传感器和Origin7.0软件在电脑控制韦伯福斯摆的实验研究中应用

研究用电脑控制韦伯福斯摆的实验中,用光电传感器、位移传感器和力传感器测量摆的振动周期和摆幅、角速度等及弹簧的劲度系数,由此来学习一种测量刚体转动惯量的方法。     

基于位移光栅尺的拉伸法弹性模量测量

基于光栅光学原理,利用位移光栅尺测量了弹性模量,建立了位移光栅尺拉伸法测量系统,通过实验获得金属丝在拉伸过程中的微小形变量数据,再利用拉伸法测量弹性模量与微小形变量之间的关系,最终实现弹性模量的测量.     

瞬态法测热导率

一、引言在普物实验中,热导率的测量通常都采用稳态法。该方法测量时间长,且不容易控制稳定。而瞬态法相对于稳态法,其测量时间短,散热损失小,且容易操作。下面介绍一个通过非平衡的瞬态测量方法测量良导体热导率的实验。二、原理在一处于平衡状态的细长棒状样品一端通以短时热脉冲,样品内任一点的温度随时间变化曲线与样品的热导率有关,通过测定该曲线便可确定样品的热导率。在t=0时,细长棒状良导体,处于平衡状态,在一端受一短时热脉冲。棒内距加热端距离为x处,温度随时间的变化如图1所示。从图中读出两对应温度相等的时刻t_1     

居家环境下运用光衍射法测量弹性模量实验的设计

居家环境下,利用生活材料搭建了基于光衍射法测量金属丝弹性模量的实验装置.并设计了简易螺旋测微器,提高了金属丝直径测量的精度.实验测得弹性模量的结果表明,此方案适合学生居家实验.该实验的完成,不仅锻炼了学生利用常见材料自主设计实验装置的能力,同时使学生对弹性模量及光衍射的理论知识有了更深刻的理解.     

Substrate-dependent cell elasticity measured by optical tweezers indentation

In the last decade, cell elasticity has been widely investigated as a potential label free indicator for cellular alteration in different diseases, cancer included. Cell elasticity can be locally measured by pulling membrane tethers, stretching or indenting the cell using optical tweezers. In this paper, we propose a simple approach to perform cell indentation at pN forces by axially moving the cell against a trapped microbead. The elastic modulus is calculated using the Hertz-model. Besides the axial component, the setup also allows us to examine the lateral cell–bead interaction. This technique has been applied to measure the local elasticity of HBL-100 cells, an immortalized human cell line, originally derived from the milk of a woman with no evidence of breast cancer lesions. In addition, we have studied the influence of substrate stiffness on cell elasticity by performing experiments on cells cultured on two substrates, bare and collagen-coated, having different stiffness. The mean value of the cell elastic modulus measured during indentation was 26±9 Pa for the bare substrate, while for the collagen-coated substrate it diminished to 19±7 Pa. The same trend was obtained for the elastic modulus measured during the retraction of the cell: 23±10 Pa and 13±7 Pa, respectively. These results show the cells adapt their stiffness to that of the substrate and demonstrate the potential of this setup for low-force probing of modifications to cell mechanics induced by the surrounding environment (e.g. extracellular matrix or other cells).     

Passive-active vibration isolation systems to produce zero or infinite dynamic modulus: theoretical and conceptual design strategies

The application of mechanical springs connected in parallel and/or in series with active springs can produce dynamical systems characterised by infinite or zero value stiffness. This mathematical model is extended to more general cases by examining the dynamic modulus associated with damping, stiffness and mass effects. This produces a theoretical basis on which to design an isolation system with infinite or zero dynamic modulus, such that stiffness and damping may have infinite or zero values. Several theoretical designs using a mixture of passive and active systems connected in parallel and/or in series are proposed to overcome limitations of feedback gain experienced in practice to achieve an infinite or zero dynamic modulus. It is shown that such systems can be developed to reduce the weight supported by active actuators as demonstrated, for example, by examining suspension systems of very low natural frequency or with a very large supporting stiffness or with a viscous damper or a self-excited vibration oscillator. A more general system is created by combining these individual systems allowing adjustment of the supporting stiffness and damping using both displacement and velocity feedback controls. Frequency response curves show the effects of active feedback control on the dynamical behaviour of these systems. The theoretical design strategies presented can be applied to design feasible hybrid vibration control systems displaying increased control performance.     

螺旋测微计在测量金属杨氏模量中的应用

本根据拉伸法测量金属杨氏模量的原理,对利用螺旋测微计测量金属杨氏模量的方法做了可行性分析,并在此基础上设计出一套完整的借助螺旋测微计测量金属杨氏模量的方法。     

Cyclic stress-strain curves and internal friction of steel at ultrasonic frequencies

A new interpretation of some characteristics of material push-pull loaded at a frequency of 23 kHz can be evaluated by measuring the internal friction and elasticity modulus defect at different strain amplitudes. It is possible to obtain interesting relations describing the material's cyclic microplasticity response. The paper presents some basic relationships between the ‘plastic’ internal friction, elasticity modulus defect, hysteresis loop area, plastic strain amplitude and the cyclic deformation hardening coefficient, for low carbon steel with different grain sizes.     

弹性基础隔振系统的简化性能指标和有源控制力

系统研究了基础弹性对单层隔振系统、双层隔振系统及浮筏隔振系统隔振性能的影响。分析了不同隔振系统与不同弹性基础间的振动耦合特性,讨论了不同隔振系统的振级落差和力传递率特性,给出了振级落差和力传递率的简化计算方法。针对不同隔振系统的有源隔振问题,比较了不同作动器安装方式所需的控制力。研究表明,对于所有隔振系统,增加基础的刚度和阻尼有利于提高振级落差和力传递率;对于浮筏隔振系统,增加筏架的刚度和阻尼有利于提高隔振性能和减少有源隔振所需的控制力。      

Simplified performance indices and active control force of vibration isolation systems with elastic base

Influence of the elasticity of the base on vibration isolation performances of single layer, double layer and floating raft vibration isolation systems is investigated systematically.Characteristics of vibration coupling between different vibration isolation systems and different elastic bases are analyzed. Moreover the characteristics of vibration acceleration level difference and force transmissibility of different vibration isolation systems are discussed and their simplified expressions are given. In addition the required control forces of active vibration isolation under different installations of actuators for different vibration isolation systems are compared.The results show that for all vibration isolation systems, the addition of the stiffness and damping of the base can enhance their vibration acceleration level difference and force transmissibility.Moreover for floating raft vibration isolation system, the addition of the stiffness and damping of the raft can enhance its vibration isolation performance and reduce the control force required by active vibration isolation.     

Choice of thickness ratio of a coated beam used for investigating the complex modulus of viscoelastic materials

The coated beam method has been widely used for investigating the complex modulus of elasticity of relatively soft viscoelastic materials; e.g., materials for vibration damping. With this method a rectangular section metal beam is coated with the viscoelastic material on one side, or symmetrically on both sides, and the resonances of the bending vibration of the beam are investigated. In this paper a procedure is described for finding the ratio of coating thickness to metal thickness required to obtain accurate results for the complex modulus in such investigations. The contradiction experienced earlier—that a relatively large thickness ratio is required for precision while the nature of the resonance method is such as to demand a small one—is analyzed mathematically. The relationships derived serve as a basis for optimizing the choice of the ratio. Diagrams and a procedure for this are worked out and presented. Finally, a few experimental results obtained with suitable and unsuitable thickness ratios are discussed.     

强迫振动方法确定黏弹性细棒的复杨氏模量

提出了一种方法--强迫纵振动法(该计算方法不同于以前的梁振动法)来确定黏弹性样品细棒的杨氏模量。在室温下,对长度分别为108 mm,100 mm,90 mm,83.5 mm,80 mm,74.5 mm,70 mm的聚碳酸酯细棒,实验测试得到了棒两端的振幅比与激励频率之间的关系曲线,并由曲线的3 dB带宽计算得到损耗因子,进一步得到棒的储能和耗能杨氏模量。依照这种方法,只要能得到足够多的数据,用最小二乘算法,可得到在感兴趣的频段内该材料相应的杨氏模量随频率变化的曲线。若测试频率步长减小到5 Hz,则测试最大误差可小于6%。与现有测试方法相比较,本方法计算简单,物理意义清晰。      

Experimental Cosserat elasticity in open-cell polymer foam

Reticulated open-cell polymer foams exhibit substantial size effects in torsion and bending: slender specimens are more rigid than anticipated via classical elasticity. Such size effects are predicted by Cosserat (micropolar) elasticity, which allows points to rotate as well as translate and incorporates distributed moments (couple stresses). The Cosserat characteristic length is larger than the cell size. The Cosserat coupling coefficient is larger than in dense closed-cell foams and approaches 1 for foam with 0.4 mm cells.     

Effect of surface layer thickness on buckling and vibration of nonlocal nanowires

In this Letter, the buckling and vibration behavior of nonlocal nanowires by incorporating surface elasticity is investigated. A modified core–shell model is developed to depict the size effect of Youngʼs modulus and validated by the reported experimental data. Our results show that the buckling load and natural frequency of nanowires increase when the effect of surface layer thickness is taken into account. Moreover, as the diameter of nanowires is smaller than 50 nm, the influence of surface layer thickness becomes obvious. This work can be helpful in characterizing and predicting the buckling and vibration behavior of NWs.