Standard Test Method for Measurements of Internal Stresses in Organic Coatings by Cantilever (Beam) Method
Standard Test Method for Measurements of Internal Stresses in Organic Coatings by Cantilever (Beam) Method
SIGNIFICANCE AND USE 5.1 Stresses in coatings arise as a result of their shrinkage or expansion if expected movements are prevented by coating adhesion to its substrate. 5.2 There are several causes leading to arrival of stresses in the coatings: film formation (cross-linking, solvent evaporation, etc.); differences in thermal expansion coefficients between coating and substrate; humidity and water absorption; environmental effects (ultraviolet radiation, temperature and humidity), and others. 5.3 Knowledge of the internal stresses in coatings is very important because they may effect coating performance and service life. If the internal stress exceeds the tensile strength of the film, cracks are formed. If stress exceeds adhesion between coating and substrate, it will reduce adhesion and can lead to delamination of coatings. Quantitative information about stresses in coatings can be useful in coating formulation and recommendations for their application and use. 5.4 This method has been found useful for air-dry industrial organic coatings but the applicability has not yet been assessed for thin coatings (thickness SCOPE 1.1 This test method covers the procedure for measurements of internal stresses in organic coatings by using the cantilever (beam) method. 1.2 This method is appropriate for the coatings for which the modulus of elasticity of substrate (Es) is significantly greater than the modulus of elasticity of coating (Ec) and for which the thickness of substrate is significantly greater than thickness of coating (see Note 7 and Note 8). 1.3 The stress values are limited by the adhesion values of coating to the substrate and by the tensile strength of the coating, or both. 1.4 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only. 1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and to determine the applicability of regulatory limitations prior to use. 1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
ASTM D6991-17(2022), "Standard Test Method for Measurements of Internal Stresses in Organic Coatings by Cantilever (Beam) Method," provides a reliable procedure for evaluating internal stresses within organic coatings. The standard is maintained by ASTM International and aligns with internationally recognized standardization principles. This test method is especially valuable for industries involved in the development, application, and evaluation of industrial organic coatings, offering a quantitative approach to understanding how internal stress can affect coating performance and durability.
Internal Stress in Coatings Stresses can develop in coatings during film formation (such as cross-linking and solvent evaporation), changes in temperature or humidity, and due to mismatched thermal expansion coefficients between the coating and its substrate. Such internal stresses are key factors influencing coating integrity and long-term performance.
Cantilever (Beam) Test Method The standard describes the use of a cantilever beam – typically a stainless steel strip – with a coating applied on one side. As the coating cures and develops internal stress, it induces deflection in the free end of the beam. The magnitude of this deflection, measured precisely under an optical microscope, is directly related to the internal stress acting within the coating.
Applicability and Limitations The method is primarily intended for coatings where the substrate's modulus of elasticity and thickness is significantly greater than those of the coating itself. It is established as effective for air-dry industrial organic coatings, though applicability to thin films, powder coatings, or thermally cured coatings requires further assessment.
Significance of Stress Measurements Determining internal stresses is critical:
ASTM D6991-17(2022) is widely applied in:
Другие стандарты ASTM
By following ASTM D6991-17(2022), organizations enhance the reliability and performance of organic coatings, reduce risk of coating failures, and comply with leading quality and standardization practices in materials engineering and protective finishes. This makes it an essential resource for labs, manufacturers, and quality professionals focused on coating technology.