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, ɛl and ɛt, and of the stress, σn, 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.

A comparison of three‐dimensional embedded strain transducers, compression tested within the same strain field while offset at an angle with the principal axes

“…However, the difference in error for the Kyowa gauges (Figure 7B) is very significant, and at 3.3 N mm −2 stress level, the error between Gauges 3 and 4 is given as 10.95% compared with theoretical calculation of 3.25%. This result reflects on the work carried out by Ajovalasit [12], indicating that gauges with a transverse sensitivity values lower than 0.4% are not significantly affected by normal pressure.…”

“…Ajovalasit [12] derived a theoretical formula for the percentage strain error between two gauges (Gauge 4 perpendicular to the load and Gauge 3 parallel to load, illustrated in Figure 6). This formula is given in , which calculates the difference in measured strains with reference to the stress normal to the grid of Gauge 4.…”

“…Cristofolini and Viceconti [11] indicated that gauges orientated parallel to the applied load were significantly affected by the pressure perpendicular to the grids (see Gauges 4, 5 and 6 in Figure 6). However, Ajovalasit [12] showed that their results were only problematic with gauges that had a transverse sensitivity >0.4%. To confirm that this effect did not influence the results of tests carried out in the work reported here, the following preliminary testing was undertaken.…”

Advances in Strain Gauge Measurement on Composite Materials

“…Equation (33) shows that the error depends on the fibre and strain gauge orientations, h 1 and u x , and on the following parameters of the material:…”

“…Other procedures are found in the bibliography [8, 28]. On laminates, back‐to‐back rosettes installed on the opposite surfaces of the laminate can be used in order to deduce the state of strain within each subsurface lamina from surface strain measurements [25], in this technique care is necessary when strain measurements are made near a free edge [2, 18] Techniques based on the use of strain gauge embedded between laminae are also used [9, 21, 29–33].…”