Effect of moistureproof coatings on the sensitivity of strain gauges to deformations

Conclusions

The rise in the sensitivity factor of strain gauges with a direct application of the moistureproof epoxy-resin compound coating is due mainly to the change in the stiffness of the beam as a result of the firm adhesion of the 2–3 mm thick resin layer and the strain gauges to the beam and the formation of a single monolithic structure. The amount of change in the sensitivity of the strain gauges depends in each specific case on the relationship of the stiffness (strength) of the beam (structure) to that of the applied coating, i.e., to its thickness, strength characteristics, and hardening time.

Therefore, in order to avoid obtaining results which are known to be distorted, it is necessary to limit the application of moistureproof epoxy-resin compounds or other materials which have relatively large strength characteristics when hardened in cases when the coating together with the strain gauges changes considerably the stiffness of the structure and it is impossible to calibrate the glued gauges. As an example of this, it is possible to cite the measurement of stresses in thin-walled articles.

The method of moistureproofing glued strain gauges described in [2] does not lead to a change in their sensitivity factor, this can be explained in the light of the above considerations by the fact that in this case the epoxyresin layer applied to the PKhL film does not contact the beam directly; i.e., it does not change the beam stiffness on the section of the glued strain gauges and, therefore, their sensitivity to deformations remains constant.