Overview of optical techniques that measure displacements: Murray lecture

Optical techniques that measure displacements play a very important role in current experimental mechanics, material sciences and metrology. This paper presents a survey of developments in these techniques from a personal experience point of view. Three main aspects are considered. Mathematical and numerical models used in the interpretation of fringe information and the corresponding data processing techniques. Optical and electro-optical developments that have taken place to improve the sensitivity, and the efficiency of these methods to make them competitive with purely numerical methods. Applications that have arisen from the synergy between advanced computational capabilities and optics are also presented.     

中应变率下材料动态拉伸关键参数测试方法

通过高速液压伺服材料试验机进行金属材料的中等应变率动态拉伸力学性能测试。为获取精确的动态拉伸载荷数据,提出了一种拉伸载荷的间接测量方法,在不改变试验机原有结构的情况下,解决了试验机自带载荷传感器测试数据在塑性段振荡导致材料真正动力学行为被掩盖的问题;通过数字图像相关的非接触测量方式进行动态拉伸应变的测量。实验验证表明,提出的载荷和应变测试方法可实现金属材料动态拉伸试验中的力学性能参数测试。     

DIC: A revolution in experimental mechanics

Experimental Techniques -     

Holographic-interferometry applications in experimental mechanics

Holographic-interferometry techniques were surveyed in several areas of application to experimental measurement. The principles of the technique were reviewed, and the theoretical basis for quantitative experimental measurement was developed and evaluated by controlled experiment on simple beam and plate structures in static loading. Subsequently, the effectiveness of the method in steady-state vibrations analyses was demonstrated by application to typical structures components. Nondestructive-testing potential was illustrated by the application to flaw detection in a bonded honeycomb, and some moiré procedures were examined. Immersion technique was employed to demonstrate the generation of surface elevation contours in opaque objects. In summary, experimental evidence is offered that holographic interferometry is a powerful and precise tool for experimental investigations.     

Optical methods in experimental mechanics

Experimental Techniques -     

Optical methods in experimental mechanics

Experimental Techniques -     

Optical methods in experimental mechanics

Experimental Techniques -     

Optical methods in experimental mechanics

Experimental Techniques -     

Optical methods in experimental mechanics

Experimental Techniques -     

材料超高温动态拉伸SHTB实验方法的有效性分析

针对高温拉伸分离式Hopkinson杆实验技术,通过数值模拟、实验验证以及几种典型材料的高温动态拉伸性能测试相结合的方法,对此实验技术中存在的几个关键问题进行了深入研究。结果表明:对于平板状钩挂式拉伸试样,通过标距段尺寸优化后,应力分布均匀,流动应力曲线与螺纹拉伸试样一致,且应力上升段后没有剧烈跳动;通过精确气动控制,在加载脉冲到来同时,可实现有效的试样快速同步组装和加载;当试样温度为1 200 ℃时,在冷加载杆与高温试样接触以及应力波加载试样的整个过程中,试样平均温度下降约1.3%,而加载杆端温升低于180 ℃。为了验证此实验技术,对3D打印TC4、镍基单晶高温合金DD6进行了最高温度约1 200 ℃时的高温动态拉伸力学性能实验测试。     

An experimental study of dynamic tensile properties of glass fiber at low-temperatures

Tensile impact experiments of EC8.0−24×7 glass fiber bundles at different low temperaturesT(14°C, −40°C and −10°C) and strain rates ɛ were carried out, and complete stress-strain curves were obtained. Within the range of the experiment temperatures and strain rates, it is found that the initial modulusE, the ultimate strength σ_max and the unstable strain ɛ _b of the glass fiber bundles all increase with ɛ at an identicalT. At an identical ɛ, with the decrease ofT, E and σ_max increase; but ɛ _b increases when 10°C>T>−40°C and decreases when −40°C>T>−100°C. The strain-rate- and temperature-dependent bimodal Weibull statistical constitutive theory was adopted for the statistical analysis of the experimental results, and the Weibull parameters of single fiber were obtained. The results show that the bimodal Weibull distribution function is suitable to represent the strength distribution of the glass fiber at low temperature and different strain rates. The differences in the mechanical properties between EC8.0−24×7 and EC5.5−12 ×14 glass fiber bundles were also discussed. Project supported by the National Natural Science Foundation of China (No. 19772058).     

The peel test in experimental adhesive-fracture mechanics

Several test specimens have been proposed for obtaining adhesive-fracture energy, γa, in bond systems. These tests include blister, cone, lap-shear and peel tests. Peel tests have been used for many years to compare relative strengths of different adhesives, different surface-preparation techniques, etc. This paper demonstrates the potential use of peel tests in obtaining γa values. There are several reasons for devloping the peel test for fracture-mechanics work. First, most laboratories have facilities for preparing peel specimens. In addition, the adhesivefracture energy has recently been shown to be a function of loading mode. In peel tests, various combinations of Mode I and Mode II loadings can be applied by varying the peel angle. Peel-test-analysis methods discussed include closed-form solutions for particular peel-specimen geometries loaded with a given force and numerical techniques for general peel-specimen analysis. This paper also points out the difference between debond load and maximum peel load. The debond-load to maximum-load ratio is shown to depend upon adhesive type but independent of load rate over three decades of time for two different adhesive systems tested.     

Recent research activities in experimental mechanics in China

A brief review is presented of the recent activities in the field of experimental mechanics in the People's Republic of China. The current research work covers the following subjects: (1) photoelastic phenomena, such as the classical three-dimensional photoelasticity, the scattered-light technique, birefringent coatings, birefringent materials; (2) holography, holographic interferometry, speckle interferometry and their applications; (3) moiré method; (4) strain-gage techniques and strain indicators.     

固体力学跨尺度计算若干问题研究

本文展示了固体力学领域跨尺度计算的若干问题和研究概况。（1）建立位错动力学与有限元耦合DDD-FEM的计算模型,实现了能够基于纳米尺度离散位错运动机制计算分析连续介质有限变形晶体塑性问题,提出微纳尺度（200 nm~10 μm）晶体塑性流动应力解析公式,结合试验数据揭示了在无应变梯度下强度和变形的尺寸效应;（2）建立具有微相分离结构的纳米尺度粗粒化分子动力学模型CG-MD,计算获得聚脲材料在时域和频域下的存储模量和损耗模量,通过动态加载分析的DMA试验和超声波试验的数据验证,解决了连续介质尺度下微相分离高分子共聚物的设计难题;（3）通过数据驱动关联高分辨率的微米尺度CT影像和临床低分辨率的毫米尺度CT影像的特征值,建立了围关节松质骨小梁的等效模量和结构张量,为骨组织增材制造点阵结构设计和实现个性化骨缺损重建奠定了基础。     

In-situ tensile testing of nano-scale specimens in SEM and TEM

We present a new experimental method for the mechanical characterization of freestanding thin films with thickness on the order of nanometers to micrometers. The method allows, for the first time, in-situ SEM and TEM observation of materials response under uniaxial tension, with measurements of both stresses and strains under a wide variety of environmental conditions such as temperature and humidity. The materials that can be tested include metals, dielectrics, and multi-layer composites that can be deposited/grown on a silicon substrate. The method involves lithography and bulk micromachining techniques to pattern the specimen of desired geometry, release the specimen from the substrate, and co-fabricate a force sensor with the specimen. Co-fabrication provides perfect alignment and gripping. The tensile testing fits an existing TEM straining stage, and a SEM stage. We demonstrate the proposed methodology by fabricating a 200 nm thick, 23.5 μm wide, and 185 μm long freestanding sputter deposited aluminum specimen. The testing was done in-situ inside an environmental SEM chamber. The stress-strain diagram of the specimen shows a linear elastic regime up to the yield stress σ _y MPa, with an elastic modulusE=74.6 GPa.     

Design and evaluation of a testing machine for determining tensile properties of materials at moderate strain rates

A test fixture was designed and built to evaluate tensile properties at a specific rate of strain in the region from 0.01 to 25 in./in./sec. The specimen is of tubular section and loaded internally by fluid pressure. Details of the design and instrumentation are presented. Test results for annealed 1018 steel are given and compared with results of other investigators. This steel is shown to be strain-rate sensitive in the region tested.     

The future role of experimental mechanics in international aspects

The present and future role of measurement and experimental techniques in analyzing displacements, strain and stress in structures, structural elements as well as in technical systems is considered. There are more reasons and much wider fields to apply methods of experimental mechanics nowadays than ever before. New advanced modern techniques, new measurement equipment,automatization of the measuring and evaluating processes are available. Hybrid techniques, i.e. the combination of advanced measurement and computer techniques have been developed. Such methods allow optimization of structures and products, saving energy and raw materials, improving the quality of products and the reliability and safety of structures and technical systems, controlling the production processes as well as supervising the safety of operating systems. They can and have to contribute to minimizing risks of technical systems, and detractions of environment. To transfer knowledge on new developments in more or less advanced methods of experimental mechanics is of increasing importance to those developing countries, which are at the threshold of economic development.     

A novel tensile device for in situ scanning electron microscope mechanical testing

Experimental Techniques - To facilitate the study of deformation mechanisms and mechanical properties of bulk materials with feature size of centimeter level, a novel tensile device compatible with...