Advanced Hardened Antenna Window Materials Study
Final rept. 7 Dec 1970-7 Nov 1971
GENERAL ELECTRIC CO PHILADELPHIA PA RE-ENTRY SYSTEMS DEPT
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A hardened composite antenna window material designated ADL-10 has been developed, based on Omniweave multidirectional fiber reinforcement woven construction using pure silica fibers and GE SR-350 methyl silicone resin as the matrix. Process studies included the use of Teflon-coated silica fibers to achieve an increase in woven Omniweave density to 1.0 gmcc as compared to earlier values ranging from 0.4 to 0.7 gm cc. Also studied were the effects of hydrofluoric acid etching of the silica fibers, the use of a silicone coupling agent and a range of molding pressures. Based on an optimum fiber volume fraction of 68 percent, predicted minimum directional strength levels of 10,000 to 20,000 psi have been achieved with hardening capability as measured by flyer plate testing in excess of 4000 taps for nominal thickness of 14 to 3 8 inch. The material was verified to completely retain RF transparency up to heat flux levels of 100 Btusq ft sec. An inorganic silicasilica composite designated Markite and derived from multiple pyrolyses and reimpregnation of ADL-10 was studied for antenna window use at heat flux levels above 100 Btusq ft sec. Complete RF TRANSPARENCY WAS MAINTAINED UP TO THE MAXIMUM TEST LEVEL OF 457 Btu sq ft sec. Only marginal improvements were achieved above earlier strength levels for Markite, to 2000-3000 psi, attributable to the improved Omniweave reinforcement fabric density. The effects of multiple reimpregnation and the fibermatrix interaction mechanism are analyzed and recommendations made for new formulations.
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- Laminates and Composite Materials
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