Title page for ETD etd-06062008-171727

Type of Document Dissertation
Author Kang, Chiun-Chia
URN etd-06062008-171727
Title Moisture and stress effects on fretting between steel and polyimide coatings
Degree PhD
Department Materials Engineering Science
Advisory Committee
Advisor Name Title
Eiss, Norman S. Jr. Committee Chair
Furey, Michael J. Committee Member
Ward, Thomas C. Committee Member
Wightman, James P. Committee Member
Wilkes, Garth L. Committee Member
  • Polyimides
Date of Defense 1993-07-15
Availability restricted

Fretting of solvent cast polyimide coatings was investigated in a ball-on-flat geometry as a function of relative humidity. Polyimides were synthesized from benzophenone tetracarboxylic dianhydride (BTDA) and bisanline (Bis P), 6-fluoro bis dian hydride (6FDA) and Bis P, and pyromellitic dianhydride (PMDA) and bis A phenyl phosphine oxide (BAPPO). Coating life - the time for the steel ball to wear through the coating - shortened with increasing humidity. Iron oxides or other reaction products from 52100 ball generated at high humidity acted as abrasives and accelerated the wear of the coatings. Variation of coating life among the three polyimides was attributed to the residual stress, which developed upon cooling from the annealing temperature due to the mismatch of thermal expansion coefficients between the polymer and the metal substrate. Calculated from elasticity theory, the normal stress dropped shortly after the start of the test, remained relatively constant, and increased toward the end. This variation correlated with the wear rate and accounted for the non-linear increase of coating life with coating thickness. Sub-surface shear stress and surface tensile stress predicted well, respectively, the debonded shape and the inter-crack spacing of Hertzian cracks.

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