Weathering

Weathering Tests for Material Resistance

Weathering generally refers to the exposure to radiation, temperature, and humidity/water. A distinction is made between natural weathering (outdoor weathering) and artificial weathering (laboratory weathering).

Natural Weathering

Natural weathering represents the most realistic test of material properties, but it depends on the exposure site and, above all, on seasonal variations (the weather is not the same every year). Typical outdoor exposure sites with higher stress due to extreme climates are, for example, in Florida and Arizona. Outdoor weathering also takes into account local influencing factors, such as potential air pollutants from industry or traffic, as well as atmospheric components like salts near the sea. Exceptional weather conditions, such as strong winds or hail, are also included in outdoor weathering.

Artificial Weathering

Artificial weathering takes place in special test chambers under defined and reproducible laboratory conditions. Radiation intensity, temperature, and humidity are modeled after locations on Earth that are to be simulated during storage. For this purpose, extreme climatic conditions with high solar radiation are often chosen, such as those prevalent in Florida (high humidity and temperature) or the Kalahari/Arizona (dry desert climate). Compared to outdoor weathering, periods of lower radiation exposure at night can be omitted, resulting in artificial weathering occurring in a significantly shorter time (time-lapse). However, depending on the weathering program, it is also possible to specifically include dark periods or spray cycles.

At Analytik Service Obernburg, several weathering devices with xenon arc lamps (xenotest devices) are used. These emit the full solar spectrum from the short-wave UV to the long-wave IR range. The lamp is located vertically in the center of the device, while the samples, also vertically oriented, rotate around the lamp in special holders. According to customer-specified weathering cycles, temperature and humidity are adjusted, or the sample surface is sprayed with water. The general procedure for weathering is described in standard ISO 4892-2 (Plastics – Methods of exposure to laboratory light sources – Part 2: Xenon-arc lamps). The conditions and duration of the weathering cycles, as well as the number of repetitions, are specified in the automotive sector in the individual OEM standards and are based on particularly critical parameters for the material/coating to be tested.

Component Evaluation after Weathering

The evaluation of a component after weathering first involves a visual assessment regarding discolorations, blistering, cracks, or other optical changes. Additionally, the adhesion of a coating or paint can be checked using cross-cut tests. Mechanical tests before and after weathering provide indications of material degradation.

Damage Patterns after Weathering

A common damage pattern after weathering is the fading of color pigments or yellowing of the component. However, material degradation can also occur, leading to microcracks in the surface or a significant reduction in the strength of the base material (embrittlement). In the case of unsuitable coatings, the binder matrix can be destroyed, causing fillers from the coating to reach the surface. The result is increased light scattering and thus a lighter appearance. This effect, known as chalking, can be reduced by wiping the surface. Our damage analysis can assist you with any damage cases that may arise.