A reusable biaxial strain transducer

This paper describles a transducer which is, in effect, a reusable strain-gage rosette. The sensitive member of the instrument is a flat element shaped in the form of a hollow equilateral triangle. At the corners of the triangle are styli mounted perpendicular to the plane of the triangular element. On each side of each arm, an electric-resistance strain gage is centrally mounted parallel to the edges of the arm. The two gages on an arm form a temperature-compensated pair. In operation, the styli are pressed into the test surface, and subsequent straining of the surface induces bending and twisting strains in the arms of the element. The bending strain in an arm is detected by the strain gages mounted thereon and is proportional to the strain in the test surface in the direction parallel to the arm. The bending strain in a particular arm is unaffected by the forces in the other two arms. The theory of the transducer is discussed and experimental evidence which supports the theory is provided.     

A stiff and compact impact-force transducer based on strain measurement

A stiff and compact transducer for both static and impact compressive forces has been developed. The principle of the transducer is based on measurement of tangential strain around the periphery of an axially loaded short and axixymmetric body. It is shown that for an appropriate choice of transducer geometry the output is nearly insensitive to the distribution of the force over the loaded surface. In an experimental investigation, a prototype of the transducer was subjected to both static and impact loads of different distributions. The results show only a few percent variation in transducer sensitivity for the load distributions used. The transducer consists essentially of a homogeneous body and is simple to male. The size and material can be chosen to fit special applications.     

Bearing Load Measurement in a Hydropower Unit Using Strain Gauges Installed Inside Pivot Pin

To determine a machine’s mechanical condition it is of importance to know the radial bearing forces in the machine. Radial forces are caused by magnetic pull forces in the generator, clamped shafts, mass unbalance and flow properties around the turbine. Measuring the shaft displacement in the bearing or the bearing housing acceleration is not sufficient for status determination of a vertical hydropower unit. It is the magnitude and frequencies of the radial forces in combination with structure properties which give information as to whether a measured value is harmful or not. This paper presents an alternative method for measurement of radial bearing load in a hydropower unit. The method presented in this paper is based on strain measurements on pivot pins. The pivot pins are placed behind the bearing pad and the radial loads acting on the pad propagate through the pivot pin. New pivot pins were purchased and equipped with strain gauges. The new pivot pins were calibrated and a transfer function between applied load and measured output voltage was identified for each pivot pin. After calibration the pivot pins were installed in a vertical hydropower unit. Measurements were performed for several different operating modes of the hydropower unit. To verify that the measured load levels were of right order of magnitude, the radial bearing loads were calculated from numerical simulations of bearing properties and shaft eccentricity measurements. The two methods for determining bearing load showed almost the same results. This indicates that either method can be used to determine bearing load.     

Concepts of the photoelastic stress gage

With the photoelastic stress gage birefringence readings are made with light that traverses a path parallel to the surface of the workpiece. Individual stresses are determined in the elastic range of deformation, rather than stress or strain differences. The theory of a circular and linear stress gage is developed, including the influence of Poisson's ratio, and stress gradients. Stresses in the surface of the workpiece are expressed in terms of measured birefringence. Instrumentation is extremely simple. High sensitivity is derived from the relatively long optical-path length through the transducer. Applications should include stress analysis, load analysis and transducer design.     

Investigation on convective heat transfer over a rotating disk with discrete pins

A three-dimensional numerical study on the flow and heat transfer characteristics over a rotating disk surface with discrete pins was conducted by the use of RNG k–ε turbulent model. And some experiments were also made for validation. The effects of rotating angular speed and pin configuration on the temperature maps and convective heat transfer characteristics on the rotating surface were analyzed. As the increase of rotating velocity, the impingement of pumping jet on the centre of rotating disk becomes stronger and the transition from laminar to turbulent occurs at the outer radius of rotating disk, which resulting in heat transfer enhancement. The pins on the disk make the pumping action of a rotating disk weaker. Simultaneously, they also act as perturbing elements to the cyclone flow near the rotating disk surface, making the overall heat transfer to be enhanced. The needle pins have higher convective heat transfer capacity than the discrete ring pins with the same extend pin areas.     

Soil displacement beneath an agricultural tractor drive tire

Soil strain transducers were used to determine strain in an initially loose sandy loam soil in a soil bin beneath the centerline of an 18.4R38 radial-ply tractor drive tire operating at 10% travel reduction. The initial depth of the midpoints of the strain transducers beneath the undisturbed soil surface was 220 mm. Strain was determined in the vertical, longitudinal, and lateral directions. Initial lengths of strain transducers were approximately 118 mm for the longitudinal and lateral transducers and 136 mm for the vertical transducer. The tire dynamic load was 25 kN and the inflation pressure was 110 kPa, which was a recommended pressure corresponding to the load. In each of four replications, as the tire approached and passed over the strain transducers, the soil first compressed in the longitudinal direction, then elongated, and then compressed again. The soil was compressed in the vertical direction and elongated in the lateral direction. Mean natural strains of the soil following the tire pass were −0.200 in the vertical direction, +0.127 in the lateral direction, and −0.027 in the longitudinal direction. The mean final volumetric natural strain from the strain transducer data was −0.099, which was only 35% of the mean change in natural volumetric strain calculated from soil core samples, −0.286. This difference likely resulted from the greater length of the lateral strain transducer relative to the 69 mm lateral dimension of the soil cores. The strain transducer data indicated the occurrence of plastic flow in the soil during one of the four replications. These results indicate the complex nature of soil movement beneath a tire during traffic and emphasize a shortcoming of soil bulk density data because soil deformation can occur during plastic flow while soil bulk density remains constant.     

The delta-element reusable strain transducer

The paper describes a reusable biaxial-strain transducer consisting of a delta-shaped element in the form of a hollow equilateral traingle, with legs mounted perpendicular to its plane at the apices. The legs terminate in hard styli which are impressed into a test surface by axial forces acting on the legs. When the surface is strained, the displacements of the styli induce bending and torsional strains in the arms of the delta element. Strain gages mounted longitudinally on the arms detect the bending strains. It is shown that the strain in any arm is proportional to the strain in the test surface in the direction parallel to the arm. An instrument with a gage length of one inch is described and experimental results show that it has an accuracy of better than one percent.Paper was presented at the 1983 SESA Spring Meeting held in Cleveland, OH on May 15–19, 1983.     

Pool boiling heat transfer of tandem tubes provided with the novel microstructures

The paper presents experimental data on pool boiling heat transfer of tandem tubes, arranged one above the other in the same vertical plane. The outer surface of the tubes is provided with the novel microstructures. The structure elements are micropins created by electrolytic deposition of copper upon the tube, using a specially treated polycarbonate foil. By this technique the pins diameter can be varied from 0.1 μm up to 25 μm, the pins height goes up to 100 μm at densities up to 1 × 10⁹ pins/cm² and pins inclination almost up to 180° regarding the base surface. Micropins with several different inclinations can be created simultaneously on the same surface.Experiments were conducted with two different microstructures using the refrigerant R134a and the highly wetting Fluorinert liquid FC-3284 at pressures of 5-9 bar and 0.5-1.5 bar, respectively. The advantages of the novel microstructure regarding the boiling heat transfer for tandem tubes turned out to be practically the same as for a single tube arrangement. Microstructured tubes have the superheat independent on the heat flux, they show a very low boiling inception superheats (below 2 K), are highly effective in comparison with a technically smooth tubes, and operate stable over the long periods of time.     

Base strain effects on force measurements

Force transducers directly interact with their environment. In this study, a force transducer is attached to the midpoint of a free-free beam and is used to measure the force on a rigid mass that vibrates with the beam. The ratio of force to mass times acceleration is measured for several different masses over a frequency range that includes the first four odd natural frequencies of the beam. Then the force transducer is mounted so that the beam's strain is isolated from the transducer. The tests are repeated. The results dramatically illustrate the effects of base strain on the force measurements. A simple theoretical model is developed that explains the vertical axis shift in the calibration curve. Paper was presented at SEM 1994 Spring Conference and Exhibits.     

简易弓形位移传感器及其在工程岩体研究中的应用

本文介绍了一种用于岩体力学物理模拟试验的位移传感器及其结构，力学原理和制造方法建立了传感器位移量与基本身应变的关系，并进行了标定和验证，同时，介绿了该位移传感器在某双曲拱坝坝肩软岩带变形特征的地质力学模拟试验的应用情况，结果表明，该传感器用模型内部的变形量测，具有独特的优点。     

An experimental method for evaluating the heat transfer coefficient of liquid-cooled short pin fins using infrared thermography

The aim of this research is to evaluate the convective heat transfer coefficient of liquid cooled short pin fins by means of the infrared thermography. An experimental apparatus was set-up to analyze single, in-line and staggered array configurations of short pin fins. In this work the attention is focused on single pins having different shapes: circular, square, triangular and rhomboidal. The infrared thermography is used to indirectly measure the lateral pin temperature by observing the upper surface temperature of radially heated pins; these are placed in a test section chamber equipped with a Zinc Selenide infrared window. Flow visualizations by means of ink tracers are also carried out to relate the thermal behavior with the flow field. Regressions by the Zukauskas correlation were performed for each shape and new coefficients were carried out; a comparison among the different pin geometries underlines a better thermal exchange for the triangular and rhomboidal pins.     

Using strain gages to measure both strain and temperature

A transducer is proposed that measures both temperature and strain by using two different strain gages. The theoretical basis for designing such a transducer is developed. Experimental results indicate that the temperature signal can be measured satisfactorily. Paper was presented at the 1991 SEM Spring Conference on Experimental Mechanics held in Milwaukee, WI on June 10–13.     

Surface structuring of case hardened chain pins by cold-sprayed microparticles to modify friction and wear properties

This paper presents the results of the application of a cold spray technique for structuring metallic surfaces with microparticles. The resulting changes in surface properties were characterized to observe their influences on the tribological behavior of the structured surface. The spray technique was applied to a technical component, a 16MnCr5 steel chain pin, designed to be mounted in a linear reciprocating tribometer. TiO₂ microparticles were used to structure the surface with a homogeneous distribution of singly dispersed particles, rather than a homogeneous closed coating on the surface. Tribometer tests were performed to directly compare structured and unstructured chain pins, and a significantly reduced sliding friction coefficient was observed for the structured pin. The pins were characterized in detail by surface analysis prior to and after application of the tribological load to set the surface parameters and surface chemistry, even on the microscale. It was confirmed that the particle structuring induced changes in the surface properties, and the durability of the changes after tribological loading was evaluated.     

Surface structuring of case hardened chain pins by cold-sprayed microparticles to modify friction and wear properties

This paper presents the results of the application of a cold spray technique for structuring metallic surfaces with microparticles.The resulting changes in surface properties were characterized to observe their influences on the tribological behavior of the structured surface.The spray technique was applied to a technical component,a 16MnCr5 steel chain pin,designed to be mounted in a linear reciprocating tribometer.TiO_2 microparticles were used to structure the surface with a homogeneous distribution of singly dispersed particles,rather than a homogeneous closed coating on the surface.Tribometer tests were performed to directly compare structured and unstructured chain pins,and a significantly reduced sliding friction coefficient was observed for the structured pin.The pins were characterized in detail by surface analysis prior to and after application of the tribological load to set the surface parameters and surface chemistry,even on the microscale.It was confirmed that the particle structuring induced changes in the surface properties,and the durability of the changes after tribological loading was evaluated.     

Shear measurement using strain gages under large deformation and rotation

The measurement of shear strain under finite deformation and large rotation by using electrical-resistance metallic foil strain gages is studied both analytically and experimentally. Equations for calculating shear strain and axial and circumferential stretches are derived based on the kinematics of general tension-torsion deformation mode. These equations are applied to analyzing pure torsion experimental data. Comparison is made between results obtained with strain gages and a rotary transducer. It is shown that, in case of large rotation, one simple equation can be used to calculate the shear strain up to 30 percent with adequate accuracy.     

膨胀柱壳恒定应变率的本构关系

考虑到金属柱壳膨胀过程中随机裂纹萌生对测试结果的可能干扰,设计了预置有中心穿透圆孔的柱壳样品,采用多普勒光纤探针测量系统获得了柱壳外壁更优的径向速度历史。基于膨胀柱壳实验中固有的非恒定应变率现象,研究了获得恒定应变率下本构方程的方法,并采用改进后的本构方程确定方法,获得了20钢恒定应变率下的应力应变关系。     

A biaxial stress transducer for fabrics

A transducer^* is developed for measurement of biaxial stresses in fabrics and other flexible sheet materials. The stress transducer responds directly to the far-field stresses by means of strains induced in an elastic inclusion which are monitored by strain gages. Design of the transducer is based on the analytical solution for such inclusions in linear-anisotropic materials, but the concept is applied and tested in nonlinear-orthotropic structural fabrics. Calibration and verification tests are conducted for principal far-field stresses in the yarn directions in vinyl-coated polyester and tefloncoated fiberglass.     

销-盘摩擦磨损试验中聚醚醚酮试销的温度场测定

销－盘摩擦磨损试验中聚醚醚酮（ＰＥＥＫ）试销的摩擦温度场测量结果表明,摩擦时其圆截面内的同一圆周上温度近似均匀,当ＰＶ值增大时,所测截面上的平均温度升高,当进行强迫降温时,温度始终维持在一定值上而不继续不高,表明摩擦磨损在恒定温度下进行。     

双杠三维测力系统的研制及应用

双柑三维测力系统由三维测力传感器、动态电阻应变仪，７Ｔ１７Ｓ数字信号处理机组成，可提供各种实时处理的测量数据及图形。经运动员实际测试，取得了比较满意的结果，可用于双杠运动员的实际训练中。