The effects of high pressure on foil strain gages

The purpose of this investigation was to determine whether a linear pressure-strain response was possible for gages subjected to hydrostatic pressures to 140 ksi. This was motivated by the desire to use this information to measure the elastic-plastic behavior of material at the inside surface of thick-walled cylinders subjected to high internal pressure. This paper shows the effects of fluid pressure to 140 ksi on four different types of foil strain gage. Linear pressure-strain curves were obtained for these gages mounted on flat surfaces of tungsten, steel and aluminum specimens. The linear strains of several materials due to pressure are compared with the compressibility constant (1–2ν)/E as calculated from experimentally determined values ofE and ν, whereE is defined as the modulus of elasticity and ν is Poisson's ratio. Experimental results show the percent deviation between the constants to be a function of the material, being greatest for tungsten and least for aluminum. The fact that a linear pressure-strain response was obtained makes it possible to correct the readings for strain gages mounted on flat surfaces of materials subjected to direct hydrostatic pressure. Temperature effects as a function of pressurization rate were investigated. Various gage failures encountered along with photomicrographs showing probable causes are presented.