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Use of a Rotating-Drum Camera for Recording Impact Loading Deformations
By D. F. MUSTER and E. G. VOLTERRA
The details of a rotating-drum camera are described. The camera is used to record displacement-time data for short cylindrical specimens made of a rubberlike material which are subjected to compressive impact loadings lasting from 5 to 20 milliseconds. The auxiliaries to the camera are discussed in light of the particular needs of a study being conducted on the dynamic properties of plastics and rubberlike materials.
LN INVESTIGATION on the dynamic stress-strain properties of plastics and rubberlike materials is bein£ conducted at Illinois Institute of Technology under the sponsorship of the Mechanics Branch, Office of Naval Research, as part of their basic research program on the properties of materials.
For determining directly the stressstrain curves of plastics and rubberlike materials subjected to impact loads, the duration of which are of the order of milliseconds, a special apparatus has been built which uses mechanical and optical devices. The paper is confined to only a brief description of the optical parts of the apparatus, and particularly of a special rotating-drum camera and its accessories which is used to record displacement-time data for the specimens being tested.
The apparatus employed in the experiments is shown in Figs. 1, 2 and 3. It consists essentially of:
Presented on April 23, 1952, at the Society's Convention at Chicago, 111., by D. F. Muster and E. G. Volterra, Dept. of Mechanics, Illinois Institute of Technology, Chicago 16, 111.
(1) two 3-ft, 1-in. diameter steel bars, of equal mass, suspended as ballistic pendulums;
(2) a rotating-drum camera, the drum of which rotates at a known speed, and the shutter of which is synchronized to operate with the motion of the steel bars;
(3) an optical system which focuses the image of a very thin slit on the knife edges machined on the adjoining ends of the steel bars; and
(4) an electromagnetic device which can release one or both of the bars at the same time.
The cylindrical specimens of plastics or rubberlike materials to be tested are \ in. in diameter and \ in. long. They are placed on the plane end of one of the steel bars such that the longitudinal axes of the bar and of the specimen coincide. The other steel bar is released from a predetermined height by a magnetic release mechanism and is made to impinge upon the free end of the specimen. During the impact a photograph is taken of the interval between the knife edges which lie in the plane of the ends of the steel bars.
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July 1952 Journal of the SMPTE Vol.59