混凝土动态力学量的应变计直接测量法

本文介绍了用应变计直接测量混凝土动态应力一应变曲线的试验研究。讨论了分离式Hopkinson压杆装置间接测量混凝土材料动态应力一应变曲线存在的问题。试验分析了材料不均匀性和撞击端面接触不均匀对应变计记录信号的影响。在此基础上，用应变计直接测量应变法得到了无骨料钢纤维增强混凝土的两个应变率下的应力一应变曲线，并与传统方法的结果进行了分析比较。新方法适用于损伤演化较小的初始阶段，可以获得更可靠的加载应力一应变曲线。随着损伤的加剧，产生较大的随机应变，导致新方法的失效。     

电测虚拟实验探讨

介绍了自行研制的多媒体教学软件虚拟电测实验系统。该系统是在采集真实的实验图片和真实的实验数据基础上使用Visual Basic编制而成的。它完全模拟实际的实验环境和实验过程,能够完成电测的基本实验,如电阻应变片灵敏系数测定、材料弹性常数的测定、纯弯曲梁截面正应力分布的测定、主应力的测定等实验项目。制作该虚拟实验系统的目的是为了给学生提供一个预习的工具,让学生在进入实验室做实验之前就基本掌握实验的全过程,提高其对实验课的学习兴趣,同时也可以缓解实验教学设备不足与实验教学设备利用率低下的矛盾。实践证明:使用该系统教学与传统的教学过程有着明显的不同,它使学生由被动地参与教学过程变成主动地学习,这有利于知识的获取与掌握,此外,对于实验条件不足的困境也起到了一定的缓和作用。     

Measurement of Deformation and Strain in Nitinol

Phase shifted moiré interferometry is used to measure full-field strains during uniaxial tension and four-point bend loading of nitinol test samples. Optical resolution and grating coherence were exceptional and allowed simultaneous resolution of the strain fields within both the parent and transformed phases of the material. Evidence of localized and uniformly distributed phase transformation was observed for the samples tested in uniaxial tension while the bending results indicate a clear tension/compression asymmetry. The results further highlight the effect of the elasticity of the two phases and the complexity associated with competing martensite and R-phase transformations on the thermomechanical behavior of nitinol. Finally, the technique is applied to a nitinol implantable medical component to demonstrate the opportunities for improved end-use material characterization, numerical modeling and design validation.     

Time-of-Flight Diffraction Measurement Using Laser Ultrasound

We developed a new time-of-flight diffraction (TOFD) method based on laser ultrasound, which can use not only longitudinal waves but also shear waves. This method is more advantageous than the conventional TOFD method, because it enables us to obtain flaw depths accurately without knowing the longitudinal or shear wave velocity in the specimen or the distance between the transmitter and receiver, which are not easily obtained in complex-shaped objects. We applied the proposed method to estimate slit depths in aluminum alloy plates. The times of flight of the lateral wave, diffracted waves and the mode-converted shear wave at the flaw tip were measured and used to estimate the slit depth. As a result, an accurate estimation of flaw depth was achieved.     

一种新的全场应变光学测量方法

采用光栅衍射、光学全息、显微图像分析等技术，本文提出了一种用于固体表面应变直接测量的新的光学方法，并把这一方法应用于铝合金试件的单轴拉伸试验。实验结果表明：该方法的应变测量灵敏度为８×１０－５。     

Deformation and Rigid-body-motion Measurement by Multiple Interferometric Strain/Slope Rosettes

The multiple interferometric strain/slope rosette (Multi-ISSR) is a method extended from the interferometric strain/slope rosette (ISSR) to measure relative displacements of multiple strain gages and rigid-body-motion. The Multi-ISSR consists of more than three micro-indentations depressed onto a material surface. Upon laser beam illumination of the Multi-ISSR, light reflecting and diffracting from the Multi-ISSR indentations interfere to result in fringe patterns. The complicated patterns are analyzed to measure deformation and rigid-body-motion. Optical theory of the Multi-ISSR is developed and the governing equation for measuring deformation and rigid-body-motion is derived. Derivation of the general Multi-ISSR governing equation for the case of three indentations is presented and compared with the governing equation of the published ISSR.     

Strain Measurement Within a Single-lap Joint Using Embedded Strain Gages

Experimental Techniques -     

Deformation and Rigid-Body-Motion Measurement by Multiple Interferometric Strain/Slope Rosettes

The multiple interferometric strain/slope rosette (Multi-ISSR) is a method extended from the interferometric strain/slope rosette (ISSR) to measure relative displacements of multiple strain gages and rigid-body-motion. The Multi-ISSR consists of more than three micro-indentations depressed onto a material surface. Upon laser beam illumination of the Multi-ISSR, light reflecting and diffracting from the Multi-ISSR indentations interfere to result in fringe patterns. The complicated patterns are analyzed to measure deformation and rigid-body-motion. Optical theory of the Multi-ISSR is developed and the governing equation for measuring deformation and rigid-body-motion is derived. Derivation of the general Multi-ISSR governing equation for the case of three indentations is presented and compared with the governing equation of the published ISSR.     

刀具变形的在线散斑检测

散斑照相，防震要求低，光路简单，所需曝光时间短，符合连续激光对动态测量的要求。本文利用散斑照相法，测量了机床刀具的动态切削过程，并利用逐点分析和全场分析方法，分析了所拍摄的散斑图，得到了不同车速和不同切削用量条件下的位移场、应力场     

Load and Boundary Condition Calibration Using Full-field Strain Measurement

For critical load bearing structures, it is often necessary to experimentally determine the load distribution on the structure so that accurate finite element models can be developed for stress and fatigue life predictions. An inverse problem approach is presented here for computing or calibrating the loads and boundary conditions acting on a structure. This enables the creation of more accurate finite element models, especially for structures that have complicated load distribution and compliant boundary conditions. The method presented here involves minimizing the least square error between the strains computed using the finite element model and the strains and displacements obtained experimentally. The nodal loads and the compliance at fixed boundaries are treated as the variables in the optimization problem. The compliance is modeled as springs attached at the nodes that are on the boundary where the structure is restrained. The method is verified by computing the loads and boundary conditions when displacements, maximum shear strain or both are available at large number of points on the surface of the structure. The experimental data set was generated using the luminescent photoelastic coating (LPC) technique.     

Measurement of Strain/Load Transfer in Parallel Seven-wire Strands with Neutron Diffraction

The elastic strains induced in the constituent wires of parallel wire strands under tensile loading were measured using neutron diffraction. The elastic strains carried by the individual wires depended very strongly on the boundary conditions at the grips and on radial clamping forces. The friction forces between the wires were quite significant and should not be neglected in analytical or numerical formulations of strain partitioning in parallel wire cables.     

A Procedure for Accurate One-Dimensional Strain Measurement Using the Grid Method

This paper deals with the accurate calculation of strain using the grid method. The strain field is first directly deduced from the fringe pattern without calculating the displacement field. This procedure is validated with two numerical examples. Two types of experiment are then carried out: a translation and a tensile test. It is observed that some additional fictitious strains appear in both cases. They are due to two main reasons which interact with each other: the grid defects and the displacement of the grid lines during testing. A suitable procedure is proposed to cancel out these fictitious strains. This procedure is successfully applied in two cases of fringe patterns.     

Stress Wave Analysis and Optical Force Measurement of Servo-Hydraulic Machine for High Strain Rate Testing

Based on fundamental mechanical principles, a force measurement method for a servo-hydraulic tensile machine at strain rates from quasi-static up to 10³/s is proposed in this paper. Analytical and numerical stress wave analyses were performed at first to understand the principles of the force signal oscillation. The result of this FEM simulation indicates that the elastic vibration within the tensile specimen has a higher frequency and much lower amplitude than at the piezoelectric force sensor of the test machine. Based on this finding, a noncontact optical force measurement method was developed, which provides a fast and reliable force measurement directly on the specimen with little disturbance from the system ringing effect at strain rates up to 10³/s.     

Overview of High-temperature Deformation Measurement Using Digital Image Correlation

Background

Developments in digital image correlation (DIC) in the last decade have made it a practical and effective optical technique for displacement and strain measurement at high temperatures.

Objective

This overview aims to review the research progress, summarize the experience and provide valuable references for the high-temperature deformation measurement using DIC.

Methods

We comprehensively summarize challenges and recent advances in high-temperature DIC techniques.

Results

Fundamental principles of high-temperature DIC and various approaches to generate thermal environment or apply thermal loading are briefly introduced first. Then, the three primary challenges presented in performing high-temperature DIC measurements, i.e., 1). image saturation caused by intensified thermal radiation of heated sample and surrounding heating elements, 2) image contrast reduction due to surface oxidation of the heated sample and speckle pattern debonding, and 3) image distortion due to heat haze between the sample and the heating source, and corresponding countermeasures (i.e., the suppression of thermal radiation, fabrication of high-temperature speckle pattern and mitigation of heat haze) are discussed in detail. Next, typical applications of high-temperature DIC at various spatial scales are briefly described. Finally, remaining unsolved problems and future goals in high-temperature deformation measurements using DIC are also provided. 

Conclusions

We expect this review can guide to build a suitable DIC system for kinematic field measurements at high temperatures and solve the challenging problems that may be encountered during real tests.

     

Integrated Measurement Technique for Curing Process-Dependent Mechanical Properties of Polymeric Materials Using Fiber Bragg Grating

We propose an integrated technique to measure critical mechanical properties of polymeric materials. The method is based on a fiber Bragg grating (FBG) sensor. A polymer of interest is cured around a glass FBG and the Bragg wavelength (BW) shift is measured and documented while polymerization progresses at the curing temperature. After complete polymerization, the BW shift is monitored continuously as the temperature of the cured polymer changes. The desired material properties are then found inversely from the relationship between the Bragg wavelength shift and the deformation of the polymer caused by the changes in the material properties.     

Universal Calibration Constants for Strain Gauge Hole-Drilling Residual Stress Measurements

Experimental Mechanics - There is a large geometrical variation among the commercially available strain gauge rosettes used for hole-drilling residual stress measurements. Detailed calibration data...     

应变式压杆压力传感器在冲击波载荷测试中的应用

在近区爆炸冲击波载荷测量中,压电式压力传感器因上升时间短且强度高的高频压力脉冲作用而可能产生疲劳和过载失效。本文根据应力波在细长圆柱弹性杆中的传播特性,设计了一种应变式压杆压力传感器,当圆柱杆的一端受到压力波作用时,产生的弹性应力波沿杆轴向传播,通过测量杆的轴向应变可计算出杆中传播的应力波,从而得到作用在杆端的压力波。为了检验压杆压力传感器的性能,采用一个厚壁圆柱形爆炸容器,并将传感器安装在容器壁面不同位置上,测量中心装药产生的爆炸冲击波载荷,经反复试验,结果表明这种传感器性能是稳定可靠的。     

干涉型光纤应变测试方法的感应光纤

本文讨论了干涉型光纤应变测试方法中感应光纤的基本测量原理，对直线形和圆弧形栅状感应光纤进行了分析，同时介绍了直线形栅状感应光纤的制作方法。利用马赫－泽德干涉光纤应变测试系统和直线形栅状感应光纤测量了等强度悬臂梁的应变，测试结果与理论应变值进行了比较，相对误差为１．６７％。