Verification of the duplex gauge using variable strains and temperatures

Four steel specimens were equipped with "duplex nances", a recently proposed transducer based on two different electrical resistance strain gauges, capable of correcting the effects induced by temperature. The examined innovative transducer, in comparison with traditional strain measuring systems, has the advantage of utilising two strain gauge channels of the same type, which significantly simplifies automatic measuring systems. The specimens were subjected to temperature and strain field variations in the ranges of=30–150°Cand=100–700μm/m respectively The temperature and strain values obtained from the duplex gauges were compared with those measured by means of traditional methodology, i.e. a strain gauge and a thermocouple.     

高温ITO薄膜应变计制备及压阻性能EI北大核心CSCD

高温薄膜应变计被广泛应用于极端条件热端构件的应变测量。ITO薄膜应变计通常能够应用于1000℃以上的应变测量,为了研究ITO薄膜的显微结构、XPS光谱、阻温特性及压阻响应,采用磁控溅射在陶瓷基底上制备了ITO薄膜应变计,并在高温纯N2中热处理ITO薄膜。结果表明,其电阻温度系数稳定在-750×10-6℃-1,在1200℃下测试其应变特性,测得电阻漂移率为0.0018 h-1,应变因子为16。ITO薄膜在高温下具有稳定的电阻温度系数和低漂移率,为高温端部件应变的测量提供了可能。     

GaN based high temperature strain gauges

Gallium Nitride based electronic devices have several unique properties such as robustness to high temperature, and both strong spontaneous and piezoelectric polarization fields. The polarization effects of Gallium Nitride are stable at high temperatures; therefore, it is an ideal material to fabricate high temperature strain gauges. In this work we have fabricated metal-insulator-semiconductor(MIS) capacitors to be used as a high temperature strain gauge. GaN based MIS capacitors were fabricated and tested both at room and high temperature. The gauge factor was measured to be 75 at room temperature. AlGaN/GaN heterostructures were also used to make MIS capacitors for testing at both room and high temperature. The gauge factors were measured on these devices to be 575 at room temperature, and 361 at 400 °C.     

Sensitivity calibration of post-yield strain gauges under cyclic plastic straining

A plastic sensitivity calibration procedure is outlined for strain gauges under cyclic, four point bending. Tests show that the gauge resistance changes in an approximately linear manner with longitudinal strain for the first quarter cycle of loading. Calibration curves for subsequent reversals to the direction of deformation display zero-shift and non-linearity. Under balanced strain cycling, there is evidence of a cyclically-stable, sensitivity calibration loop. Theoretical considerations are given in which it is proposed that separate sensitivity factors apply to the elastic and plastic components of strain. It is shown that the plastic sensitivity factor is a function of (i) plastic strain induced hardening and softening in the gauge foil and (ii) any apparent change to the gauge resistivity due to imperfect bonding. The elastic component sensitivity factor equals the manufacturer's value only in the absence of hardening. The two sensitivities may be combined to give a total sensitivity factor when a post-yield strain gauge suffers elastic-plastic straining.     

The measurement of thermal strain using self–temperature compensated strain gauges

The effect of a temperature change on a strain gauge installation may be to produce strain readings of a magnitude greater than the mechanical strain being recorded. This paper discusses some of the difficulties encountered in the measurement of strain. In particular, the selection of the most suitable type of self–temperature compensated strain gauge for a particular specimen and its associated wiring technique are considered.     

Microfabrication and characterization of spray-coated single-wall carbon nanotube film strain gauges

We present the design, fabrication, and characterization results of single-wall carbon nanotube (SWCNT) film strain gauges for potential applications as highly sensitive strain, weight, or pressure sensors on the macro-scale. A batch microfabrication process was developed for practical device construction and packaging using spray-coated SWCNTs and a conventional semiconductor process. The prototype was characterized using a commercial metal foil gauge with tensile and compressive testing on a binocular load cell. Our test results demonstrated that the proposed SWCNT film gauges have a linear relationship between resistance changes and externally applied strain. The gauge factor ranged from 7.0 to 16.4 for four different micro-grid configurations, indicating that the maximum strain sensitivity of the prototype was approximately eight times greater than that of commercial gauges.     

Protection of strain gauges for long-term stability

A strain gauge encapsulation and protection system is described which ensures the long term stability of resistance strain gauges. Protected gauges have been subjected to normal outdoor conditions for a period of 2 years together with over 40 temperature cycles to 60°C and 215 strain cycles to 800 micro-strain. Zero shift has not exceeded 40 microstrain.     

The effect of ambient temperature on the sensitivity of hot-cathode ionization gauges

We measured the sensitivities of five hot-cathode ionization gauges for ambient laboratory temperatures between 23 and 31 °C. All of the ionization gauges exhibited very similar behavior, and the sensitivity could be adequately modeled with a linear function of temperature. The slopes of the fits were smaller than one would expect due to changes in the calibration chamber number density. The thermal transpiration effect, due to local heating of the gauge structures, can account for this, and a characteristic gauge tube temperature can be inferred from the temperature dependence of the sensitivity. A recent comparison of the high vacuum standards of several National Metrology Institutes (NMIs) was performed over the range of 10⁻⁶-10⁻³ Pa using hot-cathode and spinning rotor gauges as transfer standards. Among the participants, laboratory temperatures varied by as much as 5 °C. It is necessary to know how laboratory temperature affects the sensitivity of the hot-cathode transfer standards (spinning rotor gauges explicitly account for the gas temperature) so that individual laboratory results can be corrected to a common temperature.     

Measurement of long-term dimensional stability with electrical resistance strain gauges

Sheet materials with low thermal expansion are employed in the construction of certain precision components and must display excellent dimensional stability. Measurement of small dimensional changes in sheet materials over long periods of time (of the order of two parts per million per year) poses severe experimental problems when conventional measuring techniques such as interferometry are used. To avoid these difficulties, experiments were conducted to explore the usefulness of bonded electrical resistance strain gauges for measuring the dimensional stability of sheet specimens. Based on the results obtained, it is concluded that the strain gauge method is capable of detecting gradual length changes as small as about 1 or 2 parts per million over time periods approaching one year.     

Correcting for the effects of temperature on strain gauges —-use of computer–logger on Milford Haven Bridge project

The effects of temperature changes on strain gauge readings depend partly on the characteristics of the gauge and measuring equipment, and partly on the thermal properties of the structure being tested. The effect on the gauge can be numerically corrected, or compensated for by experimental techniques, and if required, the effect of temperature changes on the structure can be reduced by careful selection of the time of reading. Correction of Demec, vibrating wire and electrical resistance strain gauge outputs is discussed.
Experience with a computer controlled data logger used to correct for thermal effects on a 1/4-bridge electrical resistance strain gauge installation is described. The use of this system on the Milford Haven Bridge is estimated to have reduced potential temperature errors from between ±100 to 200 μstrain to about ±20 to 30 μstrain.     

The behaviour of post yield strain gauges

The calibration of post yield electrical resistance strain gauges in tension shows that their behaviour is strongly dependent upon gauge construction, bond strength, the presence of instability and the mechanism of plastic deformation. For medium tensile strains in the range 0-5% the calibrations reveal that the gauge sensitivity factor consists of separate elastic and plastic components which are respectively identified with recoverable and irrecoverable strain components.     

Development of temperature compensated high elongation resistance strain gauges for use up to 250°C

The paper describes the development and evaluation of temperature compensated high elongation resistance strain gauges for use from room temperature to 250°C. These gauges could be temperature-compensated on steels with coefficient of thermal expansion α = 11 ppm/°C. Thermal output within 250°C was about 1 μm/m/°C and maximum standard deviation of 5 gauges was 34 μm/m. Strain limit was > 4% at room temperature and at 250°C. Gauge factors of different strain ranges at R.T. and at 250°C are tabulated. Some applications are stated.     

Embedded Strain Gauges: Effect of the Stress Normal to the Grid

Abstract:  In general, a strain gauge embedded in a model is subjected to a stress normal to the grid, whereas a gauge on the external surface is free from such a stress. This paper concerns the effect of the stress normal to the grid on the output of the strain gauge; usually, the influence of such a stress has a negligible effect, however, in some cases a notable influence has been noted. Therefore, the output of the strain gauge is determined in function of the strains in the plane of the gauge, ɛ _l and ɛ _t, and of the stress, σ _n, normal to the grid. The analysis shows that the output of the strain gauge is influenced by the coupled effect of transverse sensitivity and pressure sensitivity of the strain gauge. In particular, the analysis shows that, for Constantan gauges compensated for steel, the influence of the transverse sensitivity is in general prevailing on that one due to the pressure sensitivity. The results reported in this paper explain the experimental data obtained by various researchers.     

High strain rate torsional testing of a high manganese steel: Design and simulation

In this study, some less-discussed aspects of designing a high strain rate torsional testing machine adapted from the Kolsky bar setup are surveyed with an emphasis on the clamping system design. Dynamic torsional experiments with true strain rates in the range of ∼500–1700 /s are conducted on specimens of a high-Mn TRIP/TWIP steel. Deformation characteristics of torsional specimens with different geometries are studied through coupled field thermo-mechanical finite element analyses using ANSYS commercial software package. The effect of specimen geometry on the stress and strain distributions and accuracy of the experimental results is also studied. Using the FEM analysis, deformation temperature rise is attained over the specimen gauge zone and its influence on the stacking fault energy and mechanical behavior of the steel is investigated.     

Method for computing temperature characteristic of a wire-wound strain gauge

Summary Both the theoretical and experimental data show that it is possible to apply the above technique in a general case for calculating, without the necessity of testing, the temperature characteristic of a strain gauge glued to any material providing it is supplied with a certificate indicating in the given temperature range the properties of the wire ( _R, ₁) and of the wire network (S, R). Such a condition will exist if the manufacture of strain gauges with differing characteristics is centralized.     

液氮低温环境下电阻应变片测试性能的试验研究

分别采用低温电阻应变片及拉线式位移传感器的电测技术,该文开展了液氮浸泡下的悬臂梁结构在静载条件下的应变测量。对两种实验测试结果和理论分析结果进行了对比和精度分析,给出了相应的实验标定曲线,并探讨了测量过程中应变片粘接、电桥连接方式、液氮冷却和数据采集对实验结果精度的影响因素等。结果表明：在采用温度补偿和应变片的正确粘贴和良好固化情形下,低温应变片能够在液氮低温区给出较高精度的应变测量;拉线式位移传感器几乎不受低温的影响,测量简单易行。相关技术和结果将为中科院近代物理研究所自主研制的兰州潘宁离子阱7T超导磁体的低温下应变测量提供方法和指导。     

Direct pneumatic pressure in a clamping technique during strain gauge bonding

A technique is described for the clamping of metallic foil strain gauges during epoxy adhesion bonding to non -porous surfaces. Following application of the uncured adhesive, the gauge is conformed to the surface using self-adhesive tape and the workpiece placed in a pressurised environment for the duration of cure. The pnematically derived clamping pressure is transmitted directly to the glue line, and is equal to the pressure within the containment vessel. Since the clamping pressure is both uniform over the strain gauge area, and readily reproducible between installations, it is possible to produce consistent gauge performance. The technique may offer time and cost advantages over classical clamping methods where gauges are installed on small, intricate, or batch components in stress analysis and transducer applications.     

Local stiffening effect of 'double deck' bending strain gauges: part 1

In stress measurement where it is difficult or impossible to access the inside surface of the structure, "double deck" (DD) or "sandwich" bending strain gauges can be used to measure both the membrane and bending strains. A DD gauge consists of a pair of constituent foil gauges which are bonded on the upper and lower surfaces of a plastic base or filling. It is mounted on the external surface of the test specimen to measure the external surface strain, and by extrapolation, the internal surface strain of the specimen. The sensitivity of the DD bending gauge increases when the separation between the pair of constituent foil gauges increases. However, this also increases the stiffness of the whole gauge. If the stiffness of the DD gauge is significant compared with that of the plate to which it is attached, the presence of the gauge may cause significant changes in local stiffness and result in errors of strain interpretation. This study is presented in two papers. Part I presents an approximate, analytical solution for the local stiffening effect of a DD gauge and quantifies the errors in the strain measurement. Part 2, to appear subsequently in Strain, will present the verification of the solution using a three dimensional finite element calculation, a parametric study and a correction method that can be applied easily. The extrapolation errors due to the stiffening effect and random reading noises are also explored.     

Use of commercial metallic strain gauges as low temperature heaters

The heat capacity of a resistive strain gauge has been measured. Such gauges may be used as electrical heaters in low-temperature applications. The units are small, inexpensive, durable and reusable.