Abstract
IN recent experiments at this laboratory, the photo-elastic method has been successfully applied to the determination of centrifugal stresses in rotating disks. The new technique depends upon the double structure of Bakelite BT-61-8931. Bakelite consists of two phases, one of which (the A phase) fuses at relatively low temperatures. If a sample is heated, the viscosity of the A phase is rapidly lowered until it becomes virtually negligible at about 115°C., whereas the C phase is little affected. At this temperature the modulus of elasticity is reduced to 1/640 of its value at room temperature and the stress-optical coefficient is increased twenty-five times. If the specimen is subjected to external load at this temperature, and allowed to cool slowly to room temperature while still under load, the deformation and photo-elastic optical effect are ‘frozen in’. This is brought about by the solidification of the liquid A phase within the space lattice formed by the C phase. Subsequent removal of load leaves the deformation and optical pattern virtually unaltered.
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References
For a complete account, see Hetenyi, M., "The Fundamentals of Three-Dimensional Photoelasticity", J. App. Mech., (Dec. 1938).
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NEWTON, R. Centrifugal Stresses in Rotating Disks. Nature 143, 981 (1939). https://doi.org/10.1038/143981a0
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DOI: https://doi.org/10.1038/143981a0
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