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Measuring Shock with High-Speed Motion Pictures*
BY J. T. MULLER
BELL TELEPHONE LABORATORIES, WHIPPANY, NEW JERSEY
Summary — The use of high-speed motion pictures has made it possible to analyze extremely rapid motions associated with explosion phenomena and high-impact shock. In order to do this efficiently, certain techniques have been developed in the preparation of the test specimen and the calibration and measurement of the results on the film.
npHE USE OF MOTION PICTURES as a tool for the measuring of JL physical quantities has been a valuable aid in the analysis of vast or explosive motions. It has been particularly helpful in the laboratory study of mechanical shock which is a simulation of an underwater explosion near the hull of a ship.
High-impact shock is the name given to the action which hammer blows produce in a suitable machine to test the mechanical sturdiness of certain types of apparatus. These hammers are of considerable size. The one used in the lightweight machine is 400 pounds with a 5-foot arm and in the medium-weight machine 3000 pounds on a 5-foot arm. A more precise definition is that shock is the physical manifestation of the transfer of mechanical energy at extremely short intervals of time. The order of magnitude of the time interval is milliseconds and quite frequently microseconds. A transient motion is always associated with such a transfer of energy, and since the displacement is a parameter easy to visualize and to work with, it has been chosen as the final indication to be recorded.
Although the analysis of shock phenomena is usually confined to one direction only which is a perfectly plausible method to obtain an insight into the behavior of the apparatus under test, it is never experienced when a shock is produced on our high-impact machines. On the contrary the equipment may bounce around in all directions
* Presented October 12, 1949, at the SMPE Convention in Hollywood.
NOVEMBER, 1949 JOURNAL OF THE SMPE VOLUME 53 579