Response of foil strain gages to hydraulic pressure

A series of tests to determine the effect that hydraulic pressure has on the output of electrical-resistance foil strain gages is described. Tests were conducted on Micro-Measurements gages, type EA-13-125BT-120 for pressures up to 20.7 MPa and frequencies up to 150 Hz, both for purely dilatational strain as well as various combinations of dilatational and distortional strains. The results showed that gage performance due to the combined effects of hydrostatic pressure and distortion of the structure differed from the condition predicted when pressure and distortion were considered separately. Rate of pressurization (and, hence, strain rate) had no measurable effect within practical limits.