Today I would like to introduce you to accelerated weathering testing simulating extreme desert-like conditions. While deserts are commonly associated with cacti and lizards, you should know that numerous industrial products undergo rigorous testing to make sure they endure such challenging environments. Examples are wind and solar parks, personal protection gear, defense, and transportation products.
Desert Conditions
The major questions for realistic simulation of desert climates are:
• How much solar radiation hits a surface?
• How high can the temperature be on a surface?
Peak conditions are given in the US military standard MIL-STD-810H:
• Solar irradiance: 1120 W/m2 (280-3000 nm)
• Air temperature: 49 °C
• Surface temperature: not specified
A quote from the standard:”It represents the hottest conditions exceeded not more than one percent of the hours in the most extreme month at the most severe locations that experience very high temperatures accompanied by high levels of solar radiation.”
Surface temperatures are measured in a daily routine at the Atlas Desert Sun Exposure Testing site (DSET) in Phoenix, Arizona. For a specific client we took measurements at several different locations on a black car. The surface temperature was typically between 70 and 75°C, with very little variation between different locations. However, during extreme summer days with 52°C hot air, the black coating could heat up to 90°C.
Black car on a sun-tracking carousel at Atlas’ Arizona desert test site
Standard Weathering Testing
Part 505.7 Solar Radiation, Procedure II of MIL-STD-810H describes a static hot durability test, using the accelerating effect of maximum natural values for irradiance and air temperature. 1 24-hour cycle is:
20 hours:
• Irradiance: 1120 W/m2 (280-3000 nm)
• Chamber air temperature: 49°C
4 hours:
• Dark
Cycling between light and dark (hot and cold) phases add some degree of mechanical stress to the test. A typical total test time is 8 weeks (56 days).
The practice of testing under consistently high irradiance and desert-like temperatures is a well-established standard across global automotive OEM’s. A good example is Volkswagen’s accelerated weathering test PV 3929 - also known as “Kalahari test”. This test applies 75 W/m2 (300-400 nm), which is slightly higher than the natural maximum 65-67 W/m2. Testing with black a standard temperature (BST) of 90°C matches exactly the above mentioned highest measured surface temperature of a black car in Phoenix.
To simulate 1 year of extreme desert exposure, VW tests for about 1500 hours reflecting an acceleration factor of about 6 compared to real time.
More Information
Do you want to discuss your desert testing needs together with us? Do not hesitate to contact us. The Atlas team is always here to answer your testing questions.
Lear more from recorded online seminars on MIL-STD-810H testing and test methods used by the automotive industry.