No abstract

We have investigated the difference between adiabatic and isothermal compression of liquids by an impacting weight, as observed in the resulting change to the index of refraction. The liquids examined were sebacate, glycerol, and water. For practical reasons, sebacate is best suited for the use of a drop-weight apparatus as a metrologically traceable calibration facility for dynamic pressure. We find that its optical properties under adiabatic and isothermal compression can be converted into each other using literature values of its thermodynamic properties. Care has to be taken to avoid cavitation-like effects, an observation that might need to be taken into account for other methods of generating short pressure pulses in the hundreds-of-MPa range.

To ensure the safety of users like hunters and sports shooters, the dynamic pressure inside an ammunition cartridge must not exceed a maximum value. We have investigated the reproducibility of the dynamic measurement of the gas pressure inside civilian ammunition cartridges during firing, when following the rules formulated by the Permanent International Commission for the Proof of Small Arms (C. I. P.). We find an in-house spread of 0.8 % between maximum and minimum pressure for runs with the same barrel and of 1.8 % among a set of three barrels. This sets a baseline for the expected agreement in measurement comparisons between different laboratories. Furthermore, a difference of more than 3 % is found in a preliminary study of the influence of ammunition storage conditions.

We have characterized the measurement uncertainty of a setup for the dynamic measurement of pressure pulses with amplitudes in the low kbar range and with millisecond duration. The uncertainty is closely proportional to pressure, with a magnitude of 0.34% (coverage factor k = 1). In particular, we treat the safety-critical application of measuring the pressure inside an ammunition cartridge during firing, where a target uncertainty of 3% has been set by the Permanent International Commission for the Proof of Small Arms.