A study on the elastic modulus of silicone duplex or bi-layer coatings using micro-indentation

A Fischerscope continuous microindenter with a spherical indenter was used to obtain maximum indentation load and depth data for a 2.2 mm sheet of RTV11 (a silicone elastomer), a 1.6 mm sheet of J501 tan elastomer containing 60% silicone and 30% butyl acrylate styrene) as well as six duplex elastomeric coatings. The duplex coatings consisted of RTV11 top coat and J501 bond coat. The Waters's empirical relationship was used to determine the modulus of elasticity E for the RTV11 and J501 sheets. The Waters's relationship was then used to determine the equivalent modulus, E-c, for duplex coatings from maximum indentation load versus elastic indentation depth data. The values of E-c as determined from the Waters's model land experimental data) were in good agreement with the values obtained by an equivalent stiffness method. By being able to determine E-c from the equivalent stiffness method and using this value in the Waters's model, one may determine the load versus elastic depth of indentation for duplex coatings. (C) 2001 Elsevier Science B.V. All rights reserved.