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Increasing Weathering Test Acceleration Through higher Irradiance

While real time outdoor weathering exposures in benchmark climates, such as South Florida, are highly recommended for determining coating performance and service lifetimes, the lengthy test times required are often problematic. Therefore, outdoor and laboratory artificial accelerated weathering testing has become a mainstay in coatings testing, particularly in the product development phase. 

Product Number: 41214-873-SG
Author: Allen F. Zienik
Publication Date: 2014
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While real time outdoor weathering exposures in benchmark climates, such as South Florida, are highly recommended for determining coating performance and service lifetimes, the lengthy test times required are often problematic. Therefore, outdoor and laboratory artificial accelerated weathering testing has become a mainstay in coatings testing, particularly in the product development phase. For long-lived durable coatings, however, most of these tests still do not produce desirable acceleration factors. Testing at higher irradiance levels than that provided by normal solar radiation affords one option for further test acceleration, typically by a factor of several-fold. However, as stress magnitudes deviate from their natural levels, non-linearity of property response with radiant exposure may occur. Therefore, reciprocity validation is a necessary step when testing at high irradiance. This paper will explain irradiance reciprocity, detail some of the reasons for “reciprocity failure”, describe a simplified test validation method, and illustrate examples of higher irradiance testing and their acceptance in standards.

While real time outdoor weathering exposures in benchmark climates, such as South Florida, are highly recommended for determining coating performance and service lifetimes, the lengthy test times required are often problematic. Therefore, outdoor and laboratory artificial accelerated weathering testing has become a mainstay in coatings testing, particularly in the product development phase. For long-lived durable coatings, however, most of these tests still do not produce desirable acceleration factors. Testing at higher irradiance levels than that provided by normal solar radiation affords one option for further test acceleration, typically by a factor of several-fold. However, as stress magnitudes deviate from their natural levels, non-linearity of property response with radiant exposure may occur. Therefore, reciprocity validation is a necessary step when testing at high irradiance. This paper will explain irradiance reciprocity, detail some of the reasons for “reciprocity failure”, describe a simplified test validation method, and illustrate examples of higher irradiance testing and their acceptance in standards.

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