Meaning and use
4.1 Significance:
4.1.1 When performing exposure in equipment using laboratory light sources, it is important to consider how the accelerated test conditions will reproduce the performance changes and failure modes associated with the final use environment of the material under test. In addition, the effects of the variability of accelerated testing and outdoor exposure need to be considered when setting up exposure experiments and interpreting the results of accelerated exposure tests.

4.1.2 Laboratory exposure tests cannot be specified as a total simulation of actual conditions of use in an outdoor environment. The results obtained from these laboratory accelerated exposures can only be considered representative of actual use exposures if the degree of grade correlation is established for the particular material tested and the type of degradation is the same. Due to differences in UV radiation, humidity time, relative humidity, temperature, contaminants, and other factors, the relative durability of materials under actual conditions of use can vary greatly in different locations. Therefore, even if the results of specific exposure tests conducted under this procedure are found to be useful in comparing the relative durability of exposed materials in a particular external environment, they cannot be assumed to be useful in determining the relative durability of the same material in different environments.

4.1.3 Although this is very tempting, it is not recommended to calculate the acceleration coefficient associated with radiation exposure over y months or years in laboratory acceleration tests. These acceleration factors are ineffective for a variety of reasons.

ASTM G151-2019 “Practice for Exposure Testing of Nonmetallic Materials Using Laboratory Light Sources”

4.1.3.1 The acceleration coefficient depends on the material and may vary significantly for each material and for different formulations of the same material.

4.1.3.2 Changes in degradation rates in both real-world use and laboratory accelerated exposure tests can have a significant impact on the calculated acceleration factor.

4.1.3.3 The acceleration coefficient calculated based on the irradiance ratio between the laboratory light source and the solar radiation, even if the same bandpass is used, does not take into account the effects on the material of irradiance, temperature, humidity and the difference in spectral power distribution between the laboratory light source and the solar radiation.

Note 4: If the use of an acceleration coefficient is required despite the warnings given in this practice, this acceleration coefficient for a particular material is only valid if it is based on a sufficient number of data for individual external and laboratory accelerated exposures in order to use statistical methods to analyze results used to correlate failure times in each exposure. J. A. Simms (1) describes an example of A statistical analysis using multiple laboratory and external exposures to calculate acceleration factors. 9

4.1.4 There are a number of factors that may reduce the correlation between accelerated testing using laboratory light sources and external exposure. More specific information about how each factor changes a material’s stability rating is provided in Appendix X1.

ASTM G151-2019 “Practice for Exposure Testing of Nonmetallic Materials Using Laboratory Light Sources”

4.1.4.1 Differences in spectral distribution between laboratory light sources and solar radiation.

4.1.4.2 The light intensity is higher than the actual light intensity.

4.1.4.3 Test conditions under which the sample is continuously exposed to light when the actual conditions of use provide alternate periods of light and dark.

4.1.4.4 The sample temperature is higher than the actual temperature.

4.1.4.5 Exposure conditions that produce unrealistic temperature differences between light and dark specimens.

4.1.4.6 The absence of any temperature cycle or exposure conditions that produce a temperature cycle or thermal shock, or both, does not represent a condition of use.

4.1.4.7 Unrealistically high or low moisture levels.

4.1.4.8 No biological agents or contaminants.

4.2 Use laboratory light sources for accelerated testing:
4.2.1 The results of accelerated exposure tests conducted in accordance with this standard are suitable for comparing the relative properties of materials. A common application is to conduct tests to determine that the quality level of different batches does not differ from that of control materials with known properties. Comparisons are recommended when materials are tested simultaneously in the same exposure equipment. The result can be expressed by comparing the exposure time or radiation exposure required to change the feature property to a specified level.

4.2.1.1 The reproducibility of test results between laboratories has been shown to be good when evaluating the stability of materials according to performance rankings compared to other materials or controls (2,3); Therefore, it is strongly recommended to expose similar materials with known properties (controls) at the same time as the test material.

ASTM G151-2019 “Practice for Exposure Testing of Nonmetallic Materials Using Laboratory Light Sources”

4.2.2 In some applications, aged reference materials are used to establish consistency of operating conditions in exposure tests.

4.2.3 Reference materials, such as blue wool test fabrics, may also be used for time exposure purposes. In some cases, the reference substance is exposed at the same time as the test material, and the exposure is carried out until a defined change in the properties of the reference material occurs. The test material is then evaluated. In some cases, the results of the test material are compared with the results of the reference material. These are not appropriate when the reference material is not sensitive to exposure stresses that cause the test material to fail, or when the reference material is very sensitive to exposure stresses that have little effect on the test material.

Note 5: Control and reference substances applicable to aging tests are defined in the term G113.

Note 6: Practice G156 describes procedures for the selection and characterization of aging reference substances used to determine the consistency of operating conditions in accelerated laboratory tests.

Note 7: The results of accelerated exposure tests can only be used to determine a material’s pass/fail approval after a specific period of exposure to a set of specified conditions, and a statistically significant pass/fail judgment can be made when the variability of the exposure and performance measurement procedure has been quantified.

ASTM G151-2019 “Practice for Exposure Testing of Nonmetallic Materials Using Laboratory Light Sources”

Radius
1.1 This practice covers general procedures to be used when exposing non-metallic materials in accelerated test equipment using laboratory light sources. For more information about programs for a specific device, see standards that describe the specific device being used. For example, detailed information on the exposure of equipment using open flame carbon arcs, closed carbon arcs, xenon arcs, and fluorescent UV sources is found in practices G152, G153, G154, and G155, respectively.

Note 1: Carbon arc, xenon arc, and fluorescent ultraviolet irradiation are also described in Practice G23, G26, and G53, where very specific device designs are mentioned. Practices G152, G153, G154, and G155 are performance-based standards that replace Practices G23, G26, and G53.

1.2 The practice also describes the general performance requirements for devices used to expose non-metallic materials to laboratory light sources. This information is intended for manufacturers of laboratory accelerated exposure equipment.

1.3 This practice provides information on the use and interpretation of accelerated exposure test data. Specific information on the methods used to determine the properties of non-metallic materials before and after exposure can be found in the standards describing the methods used to measure each property. Information on the reporting of exposure test results for plastic materials is described in Practice D5870.

Note 2: Guideline G141 provides information to address variations in exposure testing for non-metallic materials. Guidance G169 provides information on applying statistics to exposure test results.

Note 3: This standard is technically equivalent to ISO 4892 Part 1.

1.4 This standard is not intended to address all safety concerns, if any, associated with its use. It is the responsibility of users of this standard to establish appropriate safety, health and environmental practices and to determine the applicability of regulatory restrictions prior to use.

1.5 This international standard is based on internationally recognized standardization principles established in the Decision on Principles for the Development of International Standards, Guidelines and Recommendations issued by the WTO Committee on Technical Barriers to Trade.