Mechanical Behavior of Polymeric Materials for Mounting Systems of Solar-thermal Collectors

Abstract

Three unreinforced and two glass fiber reinforced polymeric materials were tested with regard to their mechanical and fatigue crack growth (FCG) behavior. In the group of the unreinforced plastics, one elastomer modified copolymer (acrylic ester-styrene-acrylonitrile; ASA), one polymer blend of ASA and polycarbonate (PC) as well as one polymer blend of polybutylene terephthalate (PBT) and PC were investigated. As to the reinforced plastics, two glass fiber reinforced polyamide (PA) grades, differing in glass fiber length and glass fiber content, were characterized. Monotonic tensile tests and cyclic fracture mechanics tests were conducted at service relevant temperatures (0°C, 23°C, 60°C). For the three unreinforced plastics, significantly lower values for Young’s modulus and strength were obtained. Conversely, these materials revealed much higher strain-at-break values. Furthermore, glass fiber content dependent mechanical properties were determined for the reinforced plastics. With increasing temperatures, the Young’s moduli and strengths of all polymeric materials decreased distinctly. In terms of fatigue crack growth (FCG), the unreinforced plastics revealed an inferior FCG resistance at all temperatures. The FCG behavior of the reinforced plastics was influenced by the fiber orientation. Tests with the initial crack in mold direction exhibited a superior FCG resistance for the PA grade with the higher fiber content. In contrast, with the initial crack in cross direction, both glass fiber reinforced PA grades showed a similar FCG behavior. These effects are related to differences in the layer thicknesses of equally oriented fibers, which were obtained via microscopic investigation of the fatigue fracture surfaces.