1.1 本规程涵盖了材料直接暴露于环境时应遵循的程序。通常，该测试在以常用的水平倾斜角度（例如5度或45度）倾斜并面向赤道的曝光架上进行。可以使用其他曝光方向。 1.2 本规程不适用于裸金属的腐蚀测试或玻璃后的测试。 1.2.1 关于腐蚀测试，请参考实践 G50 1.2.2 关于玻璃后面的曝光，请参阅实践 G24集团 1.3 单位- 以国际单位制或英寸-磅单位表示的数值应单独视为标准值。每个系统中规定的值不一定是精确的等价物；因此，为确保符合本标准，每个系统应独立使用，且两个系统的值不得组合。 1.4 本规程在技术上等同于ISO 877-1和-2中描述试样直接暴露于环境的部分。 1.5 本标准并非旨在解决与其使用相关的所有安全问题（如有）。 本标准的用户有责任在使用前制定适当的安全、健康和环境实践，并确定监管限制的适用性。 1.6 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认标准化原则制定的。 ====意义和用途====== 4.1 由于紫外线（UV）辐射、相对湿度、湿润时间、温度、干湿循环、冻融循环、污染物和其他因素的差异，材料在自然暴露中的相对耐久性可能因暴露位置而异。因此，不能假设单个位置的一次暴露结果将有助于确定不同位置的相对耐久性。建议在不同气候的多个位置进行暴露，这代表了广泛的预期使用条件。 4.2 由于年复一年的气候变化，单次暴露试验的结果不能用于预测材料降解的绝对速率。为了获得给定位置的代表性测试结果，需要多次暴露，重复几年。 4.3 太阳紫外线辐射随时间变化很大。这可能导致许多材料的表观降解速率存在很大差异。除非材料同时暴露在同一位置，否则不建议比较短期（少于一年）暴露材料的结果。 4.4 自然风化试验的持续时间通常基于时间（例如24个月）。通过使用基于总太阳辐射或太阳紫外线辐射暴露的持续时间，可以减少不同暴露之间的可变性。太阳紫外线测量通常使用记录宽带紫外线（例如295至385 nm）的仪器进行，如中所述 7.2.4 . 仅基于太阳辐射测量的风化试验计时的固有限制是，温度和湿度也可能影响降解的速率或类型。 4.5 曝光架的设计、试样在曝光架上的位置以及相邻试样的类型、颜色和发射率都会影响试样的温度和湿润时间。为了最大限度地减少这些因素引起的可变性，暴露期间，对照和风化标准物质样品应放置在试样附近。 4.6 建议至少有一个对照样品作为任何暴露评估的一部分。使用时，对照样品应符合术语要求 G113页 ，并且与试样具有相似的成分和结构。最好使用两个对照试样，一个具有相对良好的耐久性，另一个具有相对较差的耐久性。除非另有规定，否则每个暴露的测试和对照样品至少使用两个复制样品。作为试验一部分的对照试样应用于比较试样相对于对照的性能。

1.1 This practice covers procedures to be followed for direct exposure of materials to the environment. Typically, this testing is performed on exposure racks tilted at a commonly-used tilt angle from the horizontal (such as 5 or 45 degrees) and facing the equator. Other exposure orientations can be used. 1.2 This practice is not intended for the corrosion testing of bare metals, or for testing behind glass. 1.2.1 For corrosion testing, refer to Practice G50 1.2.2 For exposures behind glass, refer to Practice G24 1.3 Units— The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined. 1.4 This practice is technically equivalent to the parts of ISO 877-1 and -2 that describe direct exposures of specimens to the environment. 1.5 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. 1.6 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. ====== Significance And Use ====== 4.1 The relative durability of materials in natural exposures can be very different depending on the location of the exposure because of differences in ultraviolet (UV) radiation, relative humidity, time of wetness, temperature, wet-dry cycling, freeze-thaw cycling, pollutants, and other factors. Therefore, it cannot be assumed that results from one exposure in a single location will be useful for determining relative durability in a different location. Exposures in several locations with different climates which represent a broad range of anticipated service conditions are recommended. 4.2 Because of year-to-year climatological variations, results from a single exposure test cannot be used to predict the absolute rate at which a material degrades. Several exposures, repeated over several years are needed to get a representative test result for a given location. 4.3 Solar UV radiation varies considerably as a function of time of year. This can cause large differences in the apparent rate of degradation in many materials. Comparing results for materials exposed for short periods (less than one year) is not recommended unless materials are exposed at the same time in the same location. 4.4 The duration of natural weathering tests is often based on time (24 months for example). The variability between different exposures can be reduced by using a duration based on total solar or solar UV radiant exposure. Solar UV measurements are typically made using instruments which record broadband UV (for example, 295 to 385 nm), as described in 7.2.4 . An inherent limitation in timing a weathering test based solely on solar-radiation measurements is that temperature and moisture may also influence the rate or type of degradation. 4.5 The design of the exposure rack, the location of the specimen on the exposure rack, and the type, color, and emissivity of adjacent specimens can affect specimen temperature and time of wetness. In order to minimize variability caused by these factors, control and weathering reference material specimens should be placed adjacent to test specimens during exposure. 4.6 It is recommended that at least one control specimen be part of any exposure evaluation. When used, the control specimen shall meet the requirements of Terminology G113 , and be of similar composition and construction compared to test specimens. It is preferable to use two control specimens, one with relatively good durability and one with relatively poor durability. Unless otherwise specified, use at least two replicate specimens of each test and control specimen being exposed. Control specimens included as part of a test shall be used for the purpose of comparing the performance of test specimens relative to the controls.