Some strain-gage applications to ballistic problems

This paper deals with three ballistic problems in which variable-resistance strain and temperature gages were used. High pressures beyond the range of available piezoelectric pressure transducers were determined from strain-gage measurements on a conventional-propellant gun. During firing, the chamber (a thick-walled tube, OD=2.5 in., wall ratio,w=OD/ID=2) was overstrained and autofrettaged so that elastic behavior was attained at elevated pressures up to about 120 kpsi. Strain gages were used on a light-gas gun to determine chamber pressures, piston velocities and pressures in the central breech (OD=7 in.,w=4.3). The central breech deformed plastically in most rounds, and pressures as high as 800 kpsi were estimated on the basis of the elastic strain recovered during unloading. Transient strains and temperatures were measured on a rifle gas tube (OD=3/16 in.,w=1.5). It was found that surface strains were not a reliable measure of the internal pressure because significant thermal strains were produced by the hot gases flowing through the tube.