Engineering topics
Publications and source records attributed to Platt, R. J., Jr..
Holographic detection of unbonded or delaminated surfaces of materials and structures is improved by using helium instead of air in vacuum test chamber. Helium has index of refraction closer to vacuum (unity) than air. Therefore changes in chamber pressure during test do not alter index of refraction as much as they do with air. With air, much of detail is lost, particularly in curved areas.
An experimental investigation was made of the application of holographic interferometry to the nondestructive detection of unbonded areas (flaws) in bonded panels. Flaw detection results were compared with results obtained with an ultrasonic flaw detector. Holography, with panel deformation accomplished by a reduction in ambient pressure, is less sensitive for flaws beneath 5 and 10 plies of boron-epoxy than the ultrasonic method, though it does have its operational advantages. A process for the manufacture of bonded panels which incorporate known unbonded areas was also developed. The unbonded areas were formed without the use of foreign materials, which makes the method suitable for the construction of reference standards for bonded panels whenever needed for the proper setup of ultrasonic flaw-detection instruments.
With optical holography or ultrasonic equipment, process prepares standards for use in detection of flaws in bonded panels. Metal-to-metal, composite-to-metal, and composite-to-composite flaw standards have been produced by this process, and all have been used and tested successfully.
The effects of aging, vacuum exposure, and thermal cycling on the dimensional stability of mirror-substrate materials, fused silica, Cer-Vit, Kanigen-coated beryllium, polycrystalline silicon, and U.L.E. fused silica were investigated. A multiple-beam interferometer was used to determine nonrecoverable surface-shape changes of the 12.7-cm-diameter mirrors with substrates of these materials. Thermal cycling and aging in vacuum produced the largest changes, but only a few were as large as 1/30 wavelength, where the wavelength was 632.8 nm.
Deformations of paraboloidal shell subjected to axisymmetric thermal loads
Parametric analysis of surface temperatures and distortions of paraboloidal solar concentrators
Ground-based exploratory investigation of jet condenser with water as working fluid for space power systems
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