The effects of high pressure on foil strain gages on convex and concave surfaces

Abstract

The present investigation was undertaken to determine whether a linear pressure-strain response could be obtained for gages mounted on convex and concave specimens subjected to hydrostatic pressures to 140 ksi. This is an extension of a previously reported work where flat surfaces only were considered.

Linear pressure-strain curves were obtained for five different types of foil strain gage having gage lengths varying from 1/16 to 1/4 in. These were mounted on steel, aluminum and magnesium specimens having diameters ranging from 1/4 in. convex to 3/8 in. concave.

The inverse slope of the pressure-strain curves was compared with the compressibility constant 1–2v)/E to determine a percent deviation. In this constant,v andE are Poisson's ratio and the modulus of elasticity respectively. Experimental results show the percent deviation to be a function of the compressibility constant of the material and the radius of curvature and that these two parameters are inter-related. The percent deviation was found to be essentially independent of gage length for the range of specimen configurations investigated except where the radius of curvature of the specimen induces problems in mounting the gages.

Since a linear pressure-strain response was obtained, it is possible to correct the strain readings for gages mounted on specimens of varied hydrostatic compressibility and geometrical configuration.