ASTM G154 and G155 Explained
The ASTM G154 and G155 tests evaluate sunlight and moisture exposure. When rays of sunlight—particularly UV rays—bombard a surface, they degrade smaller pigment particles, changing the surface color and creating a chalky effect. Cracking, peeling, de-glossing, oxidation, and tensile weakening are additional outcomes of exposure; sometimes such deterioration can even occur through window glass. Moisture takes its own toll on surfaces, and the combination of sunlight and moisture can amplify damage, costing millions of dollars of depreciation each year. The ASTM G154 and G155 tests empower manufacturers to design products that can withstand exposure to sunlight and moisture.
However, it’s important to remember that both tests provide exposure approximations. Ultimately, the most realistic way to test for weathering is to allow the product to degrade in real time, with outdoor testing panels. Such real-time testing facilities are typically situated in hot locales, as sunlight’s damaging effects are magnified under high temperatures. In the U.S., the gold standard locations for outdoor exposure testing facilities are located in Arizona (for simulating hot, dry climates) and south Florida (for simulating hot, humid climates). Due to time constraints, however, many producers employ the G154 and G155 laboratory chamber tests for reliable exposure results in shorter time periods.
Florescent vs. Xenon Arc Testing
Weatherometers used in the G154 and G155 tests approximate performance via intense exposure to the damaging elements in sunlight. UV Rays make up just 5% of sunlight, yet they cause the majority of exposure damage. By blasting a product with UV rays, a weatherometer can simulate exposure results.
In the ASTM G155 test, xenon arc lamps simulate full-spectrum sunlight within a controlled test chamber. The ASTM G154 test is similar, but it utilizes fluorescent bulbs to simulate weathering. Element provides both types of tests at our ISO 17025 accredited testing laboratories. Because xenon arc light is most similar to natural sunlight, we generally use the ASTM G155 test for outdoor weatherization testing. Our team understands that florescent light has lower correlation to sunlight than xenon arc light; therefore, we generally recommend using the ASTM G154 fluorescent test to test for interior exposure (i.e., sunlight through glass).
ASTM G154: Our Most Popular Accelerated Weathering Test
The ASTM G154 test consists of exposing samples to 42 cycles of 8 hours of UVA-340 ultraviolet light at 60°C, followed by 4 hours of condensation (mimicking dew) at 50°C. Overall, this test involves 21 days of exposure.
In ASTM G154 testing, UVA-340 bulbs create the best correlation with outdoor exposure, as they have the closest wavelengths to damaging natural light from 295 to 365 nm. Different UV bulbs are useful for different testing purposes. For instance, UVA-351 lamps recreate the portion of UV light filtered through windowpanes. Therefore, these bulbs are useful for testing interior applications. UV-B light accelerates the brittleness that materials, particularly polymers, may suffer as they age indoors. In contrast, UV-A bulbs have a propensity for accelerating color fading and yellowing. If the aim of testing is to boost color fastness, UV-A bulbs are ideal.
Finally, Element also offers “Cool White” exposure testing to evaluate performance under exposure to indoor fluorescent lighting. Our Engaged Experts can help you select the best UV bulbs for your testing purposes.
Exposure Testing Considerations
It is impossible to recreate nature in the lab. Every location on the globe has its own unique combination of damaging elements, such as pollution, salt spray, and biological attack. Without testing in a specific location over a number of years, it is impossible to perfectly predict product response. As such, the ASTM G154 and G155 tests produce comparative, not absolute data, but these comparative evaluations can still prove extremely valuable to designers. For instance, a slight shift in formula may produce twice as much resistance to weathering. Such outcomes cannot be quickly obtained in outdoor settings; therefore, these weatherization tests are invaluable in timely product development.
Recreate specialized conditions with filters. In xenon arc testing, different optical filters may be applied to shift testing conditions for daylight, window glass, or extended UV spectrum exposure.
Include a control, to act as a weatherization standard. ASTM International recommends that a comparable material of identified performance (a control) be exposed at the same time as the test specimen. This allows for accurate comparison. Additionally, it’s best to include a minimum of three replicates of each specimen material, for optimized statistical evaluation. Remember, these accelerated weatherization tests cannot exactly reproduce outdoor conditions, as they cannot account for altitude, seasonal variations, local geographical features, and other variables. Control samples and multiple material samples produce the best comparative data.
There is no easy exposure formula. As a general guide, 500 hours under UV-B bulbs is equivalent to 1 year of exposure in South Florida, while 1000 hours under UV-A bulbs can create the same exposure effects. However, there is no simple equation for calculating exposure. Instead, each manufacturer must create their own “rule of thumb” for outdoor exposure correlation.
Don’t fall for common weathering myths. It may be tempting to assume that shorter wavelengths, continuous exposure, high temperatures, and other variables can result in more intense acceleration. However, each of these variables brings uniquely inaccurate results. For instance, constant exposure with no temperature cycling fails to recreate the expansion and contraction stress that materials face in outdoor locations.
Element has been helping companies make Certain for over 188 years. We can work with you to ascertain the most cost-effective, accurate testing approach for your material. Costs for weatherization testing will vary according to a number of factors, including moisturization, sample size, number of cycles, and more.
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