ASTM G141-09(R2021) pdf free download

ASTM G141-09(R2021) pdf free download.Standard Guide for Addressing Variability in Exposure Testing of Nonmetallic Materials
4. Significance and Use
4.1 Many standards and specifications reference exposure tests performed according to standards that are the responsi- bility of Committee G03 on Durability of Nonmetallic Mate- rials. In many cases, use of the data generated in these tests fails to consider the ramifications of variability in the exposure test practices. This variability can have a profound effect on the interpretation of results from the exposure tests, and if not taken into consideration in test design and data analysis, can lead to erroneous or misleading conclusions. This guide lists some of the sources for test variability and recommends strategies for executing successful weathering studies. Not all sources ofvariability in weathering testing are addressed in this guide. Specific materials, sampling procedures, specimen preparation, specimen conditioning, and material property measurements can contribute significantly to variability in weathering test results. Many of these concerns are addressed in Guide G147. To reduce the contribution of an instrumental method to test variability, it is essential to follow appropriate calibration procedures and ASTM standards associated with the particular property measurement. Additional sources of variability in test results are listed in Guide D4853, along with methods for identifying probable causes.
5. Variability in Outdoor Exposure Tests
5.1 Variability Due to Climate—Climate at the test site location can significantly affect the material failure rates and modes. Typical climatological categories are; arctic, temperate, subtropical, and tropical (that are primarily functions of lati- tude). Subcategories may be of more importance as being dictated by geographic, meteorological, terrain, ecological, and land-use factors, and include such categories as desert, forested, (numerous classifications), open, marine, industrial, and so forth. Because different climates, or even different locations or orientation in the same climate, produce different rates of degradation or different degradation mechanisms, it is extremely important to know the characteristics of the expo- sure sites used and to evaluate materials at sites that produce intensification of important climate stresses. Typically, expo- sures are conducted in “hot/wet” and “hot/dry” climates to provide intensification of important factors such as solar radiation and temperature, and to determine possible effects of moisture. Different exposure sites in one climate (even those in close proximity) can cause significantly different results, de- pending on material. N OTE 1—Exposures in a tropical summer rain climate (for example, Miami, Florida) and in a hot desert climate (for example, Phoenix, AZ) are recognized as benchmarks for evaluating the durability of many different materials.5.2 Variability Due to Time of Year—Solar-ultraviolet radiation, temperature, and time of wetness vary considerably with time of year. This can cause significant differences in the rate of degradation in many materials. Therefore, comparison of results between short-term exposure studies (less than one full year) will be subject to greater variability. If exposures of less than a full year are required, consider using times when climatological stress is maximized so a worst case test result is obtained. It may also be valuable to make several exposure tests with varying start dates in order to provide more repre- sentative data. This is especially true when the material’s response to the environment cannot be predetermined, or when materials with different environmental responses are to be compared. Often exposure periods are timed by total solar or solar-ultraviolet dose, or both. This approach may reduce variability in certain instances. However, an inherent limitation in solar-radiation measurements is that they do not reflect the effects of variation in temperature and moisture, which are often as important as solar radiation.