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Title: Double lap shear testing of coating modified ice adhesion to liquid oxygen feed line bracket, space shuttle external tank
Authors: Ferrick, M. G.
Mulherin, Nathan D.
Haehnel, Robert B.
Coutermarsh, Barry A.
Durell, Glenn D.
Tantillo, Thomas J.
St. Clair, T.
Weiser, E.
Cano, R.
Smith, T.
Martinez, E.
Keywords: Space shuttles
Issue Date: May-2006
Publisher: Cold Regions Research and Engineering Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Series/Report no.: ERDC/CRREL ; TR-06-11.
Abstract: The brackets that secure the liquid oxygen feed line to the external tank are known locations of frost and ice growth during the period following fuel loading. This experiment quantified the reduced adhesion when ice phobic coatings were applied to test coupons simulating the bracket surface. Double lap shear testing of coated and uncoated coupons provided robust test specimens and consistent load response patterns with exceptional resolution. For these tests ice was grown as strong and consistently as possible, subjected to temperature decreases comparable to those of the prototype bracket, and tested at a controlled temperature of –112ºC. The tests evolved in three phases, with uncoated controls included in each group of tested samples. The first phase of testing evaluated a wide range of coatings, and showed that Rain-X mixed with MP-55 powdered Teflon (RXM) was an outstanding coating to reduce ice adhesion to Koropon coated aluminum. However, significant amounts of coating were retained on the ice surface following each test, indicating failure in the coating and potential loss of effectiveness with repeated ice formation and release. Phase 2 evaluated potential modifications to RXM that might maintain effectiveness and enhance durability. However, the modified RXM mixtures did not improve the ice adhesion performance or coating durability. Phase 3 evaluated the effects of handling, application, resistance to weathering by water, and durability of the RXM coating. Coating material was again progressively lost through the repeat test cycles, but performance generally improved. Results also indicated that cure times longer than 1.5 hr prior to coating disturbance are needed for optimal performance. The MP55 remaining on the surface of three coupons after three cycles of testing, and on one untested coupon from the same group, was measured with XPS. The tested coupons retained slightly less MP55 than the untested coupon, indicating a minor loss of coating. Contact angle analysis of these same coupons showed that the hydrophobic performance of the tested surfaces was largely preserved. Scanning electron microscopy with an energy dispersive spectroscopy elemental map indicated that the MP-55 was evenly dispersed throughout the coated surface, and abrasive wiping did not remove a significant portion of the Teflon. Follow-up studies to refine the optimal coating formulation, mixing, and application procedures, including cure time, are necessary. Phase 1 testing indicated superiority of UF-8TA powdered Teflon over MP-55 when mixed with Braycote. As UF-8TA was not mixed with Rain-X, this change in Teflon powder might offer performance and consistency improvements to the coating. Also, reaction processes and environmental durability of the final coating must be better understood. Double lap shear testing and XPS analysis can quantify ice adhesion and coating profile thickness changes with cycling, and is a proven approach to resolve these remaining issues.
Description: Technical Report
Appears in Collections:Technical Report

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