Chapter 4.7 - Outdoor Exposure Testing

Abstract

The purposes of outdoor exposure testing (OET) include: (1) obtaining data on material durability and lifetimes at a number of representative locations; (2) understanding why materials degrade at different rates at different test sites; (3) correlating in-service measurements with accelerated life testing results and subsequently making quantitative predictions of material service lifetimes; and (4) validating damage function models derived from accelerated exposure tests. To allow validation, the detailed exposure conditions that candidate sample materials experience must be monitored. For this, test sites must be fully instrumented in terms of monitoring meteorological conditions and solar irradiance. Candidate materials are optically characterized before being subjected to exposure at OET sites. Optical durability is quantified by periodically remeasuring an appropriate response variable as a function of exposure time. By closely monitoring the site- and time-dependent environmental stress conditions experienced by the samples, the actual site dependent loss of performance is obtained. In addition, parallel accelerated exposure testing of these materials in laboratory-controlled conditions permits correlations to be made with in-service results and subsequent prediction of service lifetimes.