Main characteristics of metal resistance strain gauges

Metal resistanceDuring the use of strain gauges, it is important to have a correct understanding of their characteristics and parameters in order to avoid errors. Without understanding these, significant measurement errors may occur, and even the required measurement results may not be obtained.

Strain gaugesGenerally made into a wire grid shape, when measuring strain, strain gauges are attached to the surface of the specimen, with only a thin layer of adhesive between the metal wire and the specimen surface. The deformation of the specimen is easily transmitted to the wire grid. Moreover, the diameter of the metal wire is very small, and its surface area is many times larger than its cross-sectional area. The surrounding area of the metal wire grid is completely covered by adhesive. It will not fall off under tension and will not bend under compression. But its strain effect is different from that of a single wire, that is, the sensitivity coefficient h of the resistance strain gauge and the sensitivity coefficient h of the metal wire. It's different. There are two reasons: firstly, the deformation of the component is transmitted to the metal wire through shear force. According to the experiment, the shear force at both ends of the metal wire is the highest, the axial stress is zero, and the shear force in the middle part is zero. The axial stress is the highest, starting from zero at both ends and then increasing exponentially to the maximum value in the middle. Therefore, the stress distribution at both ends of the metal wire is uneven, equivalent to a reduction in the length of the grid wire participating in deformation. After the metal wire is made into a strain gauge, due to its grid like structure, the number of ends increases and the sensitivity coefficient decreases. Secondly, the metal wire is subjected to strain along its length direction, ε_xWhen, the bending angle of the strain gauge bears the strain ε_yAs the cross-sectional area increases, the resistance of the straight part of the strain gauge increases, while the resistance value of the curved part decreases, which also reduces the sensitivity of the change. Due to the above two reasons, the sensitivity coefficient k of the strain gauge is higher than that of the metal wire₀Low.

Strain gaugesThe sensitivity coefficient is generally obtained by experimental methods. Because strain gauges cannot be removed and reused after being attached to the specimen, the sensitivity coefficient of each strain gauge cannot be calibrated. Only a certain percentage (such as 5%) of the products in each batch can be extracted for calibration, and the average value can be taken as the sensitivity coefficient of this batch of products. Experimental results have shown that the sensitivity coefficient can remain constant over a wide range of measured strains.