OPERATION REDWING. Project 8.4. Thermal Effects on Strength of Aircraft Structural Sandwich-Type Panels,
COOK RESEARCH LABS SKOKIE IL
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In this test, panels of varied construction materials and facing thickness were subject to transient heat pulses in unloaded and prestressed conditions to determine if any change in structural integrity could be noted. Initial specimens were instrumented for measurement of temperature-time history at the core-to-facing bond and exposed to thermal radiation. Results of comparative post-exposure mechanical tests on field-exposed, aluminum facing samples showed no noteworthy change in strength characteristics as a result of the radiant exposure. However, tests conducted on similiar specimens pulse-heated in a restrained and prestressed condition showed that failure will occur at temperatures well within the range of that developed in the field-exposed specimens. Initial results of the loads program, showed that 0.020-inch aluminum facing on balsa-core specimens will fail at temperature rises of approximately 200 F when subjected to relatively low stresses during the heating cycle. As the result of a complete study of the heat-transfer characteristics of sandwich construction, a mathematical formulation was derived. When these formulas were programmed for digital computer use, accurate results were obtained. The program could be used with confidence to predict thermal response to heat pulses from nuclear weapons or laboratory heat sources, and could also be used in establishing material criteria for sandwich structures having superior thermal tolerance.