Electrical resistance strain gauges

There are different techniques to evaluate the quantitative stress level in prototype and production products. They can predict potential problems. Included is the use of electrical resistance strain gauges bonded on the surface of the product. This popular method identifies external and internal stresses. Their various configurations are made to identify stresses in different directions. This technique has been extensively used for over a half century on very small to very large products such as toys to airplanes. There is the optical strain measurement system that is based on the principles of optical interference. It uses Moire, laser, or holographic interferometry (2,3,20). 

The strain due to bending is measured by an electrical-resistance strain gauge mounted near the region examined by x-rays. The product of this strain and the mechanically measured elastic modulus E of the material is the surface longitudinal stress stress constant K, The best approach is to measure E on the same specimen by direct loading of the same kind as that used, in the x-ray calibration, e.g., by four-point bending.)... 

For example, a delamination in a composite layup produces strain distribution in the surroimding area that is substantially different from that in a pristine zone [20]. Strain monitoring can be done with conventional electrical resistance strain gauges or with fiber optics. The latter offer the capability of having several measuring locations that can be individually addressed on the same fiber. Kesavan et al. [20] used conventional strain gauges to monitor delaminalion in a composite T-joint. The strain gauges were placed on the outside of the joint in zones deemed sensitive to strain redistribution due to delaminations. 

The wall circumferential strains were measured with electric resistance strain gauges (5) glued at the surface of thin steel bands (4) erected inside the wall section near the external surface (as seen in Fig. 3). Temperature indicators were situated at the same points and connected with, the registration system. On each steel band four measurement points were installed and situated at equal distances on the model perimeter. The model was equipped with five measuring levels. The registration System Daq/Book equipped with computer was used for recording and processing of the test results. 

The electrical resistance strain gauge method is the most popular and widely accepted method for strain measurements. The strain gauge consists of a grid of strain-sensitive... 

The deflections if the element were measured by dial gauges at three cross-sections. The strain deformations along the depth of the beam were measured by electrical resistance strain gauges. In each case a loading was applied in 1 kN increments until fracture occurred, A detailed description of the test programme and procedure is given in [3]. 

The principle of the resistance strain gauge 2 0 is that the electrical resistance of a conductor will change when it is stretched or compressed due to the consequent variation in its physical dimensions. There is an additional effect called the piezoresistance which is the relation between the resistivity p of the material and the mechanical strain. The resistance R of a conductor of area of cross-section A and length x is given by ... 

Barometry measures a broad variety of pressures using an equally broad variety of measurement techniques, including liquid column methods, elastic element methods, and electrical sensors. Electrical sensors include resistance strain gauges, capacitances, piezoresistive instruments, and piezoelectric devices. The technologies range from those developed by French mathematician Blaise Pascal, Greek mathematician Archimedes, and Torricelli to early twenty-first century MEMS sensors and those used to conduct nanoscale materials science. 

Strictly, the strain gauges referred to above come into this category, since in such cases the change in the measured quantity causes a corresponding change in the resistance of the element. However, the principle has a much wider application, using changes in either the inductive or capacitive reactance of electrical circuit elements. 

In this chapter we take a careful look at the phenomenon of electrical conductivity of materials, particularly electrolytic solutions. In the first section, the nature of electrical conductivity and its relation to the electrolyte composition and temperature is developed. The first section and the second (which deals with the direct-current contact methods for measuring conductance) introduce the basic considerations and techniques of conductance measurement. This introduction to conductance measurements is useful to the scientist, not only for electrolytic conductance, but also for understanding the applications of common resistive indicator devices such as thermistors for temperature, photoconductors for light, and strain gauges for mechanical distortion. The third section of this chapter describes the special techniques that are used to minimize the effects of electrode phenomena on the measurement of electrolytic conductance. In that section you will encounter the most recent solutions to the problems of conductometric measurements, the solutions that have sparked the resurgent interest in analytical conductometry. 

The aim is to eliminate entrance effects as much as possible and any influence on the flow of the pressure tap holes into the channels. This was achieved by integrating on the same silicon chip the microchannel, the pressure taps and the pressure sensors. The fabrication process and the operating mode are described in [28]. The pressure sensors are constituted cf a membrane which is deformed under the fluid pressure and on which is deposited a thin film strain gauge. This strain gauge forms a Wheatstone bridge whose the membrane deformation modifies the electrical resistances. 

The sensing layer transforms mechanical strain into an electrical parameter. Most often, the dependence of electrical resistance on strain is exploited in strain gauges. The requirements for a suitable strain gauge material can be summarized as follows ... 

---