In situ stress gauge calibration

The accuracy of 'in situ' stress measurements is dependent upon the presence of strain within the active gauge element. In gauge records of dynamic stress fields, the onset of strain response of the gauge is not able to be defined. Development of a gauge that responds only to the applied pressure, independent of the strain field, is usable in that the deviance of a stress transducer from its calibration in a dynamic field can be observed by comparison to the pressure indicated by the calibration gauge. Through the use of variations in resistance or dielectric constant that accompany phase transitions, calibration gauges can be constructed for use in 'in situ' calibration of stress transducers. The program conducted investigated various materials as candidates for phase transition gauges, including bismuth metal, bismuth/lead alloy (75:25% by weight), thallium/indium alloy, (77:23%). Gas-gun experiments and explosive plane wave lens experiments were conducted during the program with confirmation of the dynamic response of the phase transition; however, accurate determination of the pressure associated with the phase transition and the duration required for the transition to take place was not accomplished.