【国外标准】 Standard Test Method for Evaluation of Transparent Plastics Exposed to Accelerated Weathering Combined with Biaxial Stress

4.1 The degradation of optical properties of transparent plastics is the single greatest cause for in-service removal and replacement. Some optical qualities are inherent in the geometry, manufacturing process, and materials, and remain relatively unchanged after manufacture, while others are subject to gradual change during exposure to the service environment. Factors having an influence on the crazing of transparent plastics include stress, ultraviolet (UV), moisture, and temperature. Sufficient data has been generated to make it evident that real-world conditioning must be experienced by developmental test specimens, as opposed to testing new unexposed material to determine durability, prior to in-service usage. However, the laboratory simulation of natural weathering, and especially accelerated simulation, is imprecise and correlation of results obtained for different plastics or from using different exposure apparatus must not be attempted until a valid database has been generated for such cross-correlation.1.1 This test method covers the resistance of transparent plastics exposed to environmental conditioning (accelerated weathering) under a biaxial stress state induced by a pressure cell/test fixture.1.2 Units—The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.