Standard Practice for Natural Weathering of Materials

Importancia y uso:

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.

Subcomité:

G03.02

Referida por:

D4956-19, D4364-13R22E01, E0782-95R22, D5970_D5970M-16R21, E0881-92R22, D8514_D8514M-23, D5272-08R21

Volúmen:

14.04

Número ICS:

19.040 (Environmental testing)

Palabras clave:

durability; exposure; weathering;