Air Blast Pressure Research Articles

Measurements Of Residual Stress Due ToShot-peening Using HolographicInterferometry Technique

Holographic interferometry was used to measure the maximum in-plane residual stress for shot-peened plate specimens. The specimens used for the experiments were of Aluminium Alloy 6061-T651. The residual stress was released by central hole drilling technique. The effects of two main peening parameters, the air-blast preasure and the exposure time on the residual stress of shot-peened plates were investigated and analysed, the experimental data showing that the residual stress is affected by the air-blast pressure as a power law, and that there is an exponential relationship between the residual stress and the exposure time. An emperical equation for the relationship of the residual stress with the pressure and the time has been derived from the data measured. The results are in good agreement with those obtained by 3-element strain gauge measurements.

Physical Model for Airblast Generation by Underwater Explosions

The technique for calculating airblast pressure signatures from deep underwater explosions presented earlier [J. Acoust. Soc. Am. 36, 1033(A) (1964)] requires detailed knowledge of the interface motion. An experimental study recently completed showed disagreement with linear continuous theory—the decay of the interface velocity following its abrupt rise is position-dependent and of the order of 20 times longer than that of the underwater pulse. A physical model that explains these discrepancies is presented. It is based on the existence of one or more delaminated layers of water just below the interface, originated by reflected negative underwater pressure pulses. Quantitative predictions based on this model are in good agreement with interface-velocity data, photographic evidence, and airblast pressures recorded from deep explosions. For shallow explosions, a different mechanism applies; the “bow shock wave” originated by the supersonically rising dome and plume is the dominant feature in airblast generation. [Research supported by the U. S. Naval Ordnance Laboratory.]

Far Transmission of Air Blast Waves

A semiacoustic theory of blast energy propagation, incorporating Sachs' scaling modified for altitude of observation, gives excellent agreement with experiments, providing Hilliar's similarity principle is restricted to similar ambient (weather) conditions. Comparisons between this theory and experiments are made for free air (no reflections) blast pressures; ground-level blast pressures in an isothermal, still atmosphere; and blast pressures under a linear temperature inversion.

Air Shock Wave Velocities over Water

A procedure was devised for determining the air blast pressures of the A-bomb at Bikini. In such a disturbance the air particles move with large and finite amplitudes; hence, the propagated waves do not obey the ordinary laws of acoustics. By measuring the ratio of the air shock wave velocity to normal acoustic velocity, an indication may be obtained as to the peak pressure of the explosion. Blast waves in water, on the other hand, follow substantially the familiar acoustic laws and are propagated at a well-known velocity. Measurements were made of transit times at identical positions for the air and the water blast waves. These yielded immediately the desired air blast velocity in terms of the known velocity of sound in water. This procedure eliminated the need for simultaneous measurement of the continually shifting distances between buoys which carried observational equipments. However, careful positioning of the buoys was necessary in order to avoid their destruction and yet record the maximum possible air blast. These positions were calculated on the basis of an equivalent explosion from 20,000 tons of TNT. Since the measurements had to be made automatically and without human observers, special timing and recording systems were provided. All requirements for gathering the data were successfully met in the assembly of apparatus described herein.