Materials

The ASTM round robin utilized four sealants that are typical of commercial materials: a silicone, modified polyester, an acrylic, and polyurethane. Speci­mens were provided to different laboratories. Each laboratory exposed the specimens according to the ASTM C1519-10 protocol and evaluated them after exposure via visual inspection. The specimens were fabricated by curing the sealant between two metal beams in the geometry shown in Fig. 1. This is simi­lar to the geometry specified in ASTM C719 [10]. The specimens were fabricated by one of the primary manufacturers of sealants and were arbitrarily identified by the letters A through D. Specimens of each type of sealant were obtained from one of the participants in the round robin. For each sealant, five replicate specimens were provided: two fresh specimens having no exposure history, and three specimens after exposure according to the round robin protocol.

The specimen geometry used here is a widely accepted industry standard; however, unlike the simple dog-bone geometry, the sealant is constrained where it is attached to the metal bars. Consequently, when stretched, the center region of the sealant can contract laterally, but the sealant adjacent to the metal bars cannot. This means that deformation is not uniform throughout the sample, and an apparent modulus calculated from these tests, Ea, will be different from that obtained in a simple tension test with a dog-bone specimen, E. It is customary to treat this difference by defining a parameter, S, known as the shape factor, where Ea = S x E. As the goal for the test procedure developed in this work is for com­parisons using a single geometry, these results will be presented in terms of Ea.