Preliminary evaluation of the use of elevated pressure to accelerate thermo-oxidative aging in composites

• Published in: Polymer degradation and stability 1999-01, Vol.64 (2), p.207-212
• Main Authors: Tsotsis, Thomas K., Keller, Scott, Bardis, Jason, Bish, Jack
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Forms of application and semi-finished materials; Laminates; Polymer industry, paints, wood; Technology of polymers
• ISSN: 0141-3910; 1873-2321
• DOI: 10.1016/S0141-3910(98)00190-6

A study was conducted to evaluate the use of elevated pressure to accelerate the rate of thermo-oxidative degradation in polymeric composite materials. The motivation for this work was based on earlier studies by Tsotsis [1, 2], Kerr and Haskins [3]and by Ciutacu, et al. [4]which demonstrated that higher pressures of air or oxygen tended to increase the rate of degradation of polymeric composites. Moreover, accelerated aging methods are needed to evaluate materials which are to be used under long-term exposure to elevated temperature in oxidative environments such as the High-Speed Civil Transport (HSCT). The methodology proposed herein augments elevated temperature aging with elevated pressure to accelerate the rate of thermo-oxidative degradation. Temperatures below those used by previous workers were employed in order to avoid anomalous non-linear effects which can occur near the glass-transition temperature of polymeric materials. In the present work, Hexcel AS4/3501-6 [±45°] 2 s shear and [+45°/0°/−45°/90°] 2 s quasi-isotropic Hexcel IM7/8552 open hole compression specimens were aged at 121°C (250°F) at pressures of 0.101, 0.345, 1.03, and 1.72 MPa (14.7, 50, 150, and 250 psi). Three pressure vessels were designed and built to contain the prescribed pressures. These vessels were placed inside an oven and used an air bleed to recycle the air inside the vessels. For the open hole testing, a test method was derived from Boeing BSS 7260 to reduce the material required for each specimen. Specimens were tested as-made and after 1000 h exposure to each of the pressures. Results show up to a 20% reduction in tensile shear strength for the [±45°] 2 s specimens but show no decrease in open hole compression strength though weight losses and visible discoloration of the specimens are present in both materials. Differences are attributed to the different lay-ups used as well as the different materials systems of the two specimen types.