Investigation of Long Term Weathering Characteristics on High Strength and Light Weight Envelope Material Zylon

Abstract

Long term weathering characteristics of a high strength but light weight envelope material is investigated. A two year long outdoor exposure test was conducted on a PBO or Zylon ® based material developed for a 150 m long stratospheric platform (SPF) airship technology demonstrator. Test panels for tensile strength testing every two months were mounted on a 45 degrees inclined rack facing the south 1.8 m wide by 1.2 m long. On each test panel of a 240 mm wide by 430 mm long backboard was a sheet of 220 mm wide by 340 mm long envelope material with its outer (or protection layer side) surface facing outside and with its edge adhered via a rectangular frame/spacer for a 10 mm clearance to the backboard. Tensile strength of the material after exposed to outdoor decreased significantly during hot and humid season of the second year as well as the first year, whereas decreased little in other seasons. A six month long supplemental outdoor exposure test was also conducted to separate humidity effect from temperature effect and vice versa. Test results suggested that the high humidity was the primary factor causing the decrease in tensile strength. With humidity between the inner surface of the envelope material and the backboard controlled, the decreases in tensile strength were negligible for months. The material with an additional protection layer of aluminum evaporated Tedlar on the outer surface showed as small decreases in tensile strength for months as that with humidity controlled.