The paper describes the development, implementation and testing of two thermally driven outdoor exposure instruments. These devices are unique in their ability to impose thermally driven strain while monitoring the resulting stress and displacement for sealant samples in outdoor weathering conditions. The instruments combine a fixed wood and steel supporting frame with a moving polyvinyl chloride (PVC) frame, and employ differences in the coefficients of thermal expansion between the supporting frame and moving frame to induce thermally driven strain on the sealant specimens. Two different kinds of instruments have been fabricated, winter/tension and winter/compression designs. In the winter/tension design, the thermally induced dimensional change is directly transferred to the specimens; while in the winter compression design, the samples are in parallel with the dimensional change. Both designs are instrumented to monitor forces and extension, and are built so the strain on the specimen does not exceed 25 % over the range of temperatures expected in Gaithersburg, MD. Additionally, a weather station is located at the exposure site to record weather elements on a one minute interval. This combination of weather information with mechanical property data enables a direct link between weather events and the corresponding sealant responses. The reliability and effectiveness of these instruments were demonstrated with a typical sealant material. The results show that the instruments work according to the design criteria, and provide a meaningful quantitative platform to monitor the mechanical response of sealant exposed to outdoor weathering.
Citation: Review of Scientific Instruments
Pub Type: Journals
Stiffness, outdoor testing, outdoor weathering, sealant, weathering