ASTM_D_6991_-_17e1.pdf

Designation:D6991171Standard Test Method forMeasurements of Internal Stresses in Organic Coatings byCantilever(Beam)Method1This standard is issued under the fixed designation D6991;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1NOTEEditorial corrections were made in Note 2 and Note 3 in October 2017.1.Scope1.1 This test method covers the procedure for measurementsof internal stresses in organic coatings by using the cantilever(beam)method.1.2 This method is appropriate for the coatings for whichthe modulus of elasticity of substrate(Es)is significantlygreater than the modulus of elasticity of coating(Ec)and forwhich the thickness of substrate is significantly greater thanthickness of coating(see Note 7 and Note 8).1.3 The stress values are limited by the adhesion values ofcoating to the substrate and by the tensile strength of thecoating,or both.1.4 The values stated in SI units are to be regarded as thestandard.The values given in parentheses are for informationonly.1.5 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety,health,and environmental practices and todetermine the applicability of regulatory limitations prior touse.1.6 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade(TBT)Committee.2.Referenced Documents2.1 ASTM Standards:2D823 Practices for Producing Films of Uniform Thicknessof Paint,Varnish,and Related Products on Test PanelsD7091 Practice for Nondestructive Measurement of DryFilm Thickness of Nonmagnetic Coatings Applied toFerrous Metals and Nonmagnetic,Nonconductive Coat-ings Applied to Non-Ferrous Metals3.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 cantilever,na beam or member securely fixed at oneend and hanging free at the other end.3.1.2 deflection,nthe displacement of a beam from itsoriginal position by an applied force.3.1.2.1 DiscussionThe deflection of the beam is used tomeasure that force acting on the tip.3.1.3 internal stress,na stress system within a solid that isnot dependent on external forces.4.Test Method4.1 Internal stresses in coatings are determined by thecantilever method(Fig.1).Substrate A in the shape of arectangular cantilever beam is clamped by its end B in a specialfixture E.Coating(F)is applied to one side of the beam.Internal stresses occur in the film when it is being cured(drying,cross-linking,etc.).When there is sufficient adhesionbetween the coating and the substrate,the stresses bend thecantilever beam,forcing its free end D to be deflected from itsoriginal position by a distance of h.The deflection of the beamis measured under an optical microscope and internal stress iscalculated using the equation for the cantilever method.See Eq1 in Section 9,(Formula 1).5.Significance and Use5.1 Stresses in coatings arise as a result of their shrinkage orexpansion if expected movements are prevented by coatingadhesion to its substrate.5.2 There are several causes leading to arrival of stresses inthecoatings:filmformation(cross-linking,solventevaporation,etc.);differences in thermal expansion coefficientsbetween coating and substrate;humidity and water absorption;1This test method is under the jurisdiction of ASTM Committee D01 on Paintand Related Coatings,Materials,and Applications and is the direct responsibility ofSubcommittee D01.23 on Physical Properties of Applied Paint Films.Current edition approved May 1,2017.Published August 2017.Originallyapproved in 2005.Last previous edition approved in 2010 as D6991 05(2100).DOI:10.1520/D6991-17E01.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade(TBT)Committee.1 environmental effects(ultraviolet radiation,temperature andhumidity),and others.5.3 Knowledge of the internal stresses in coatings is veryimportant because they may effect coating performance andservice life.If the internal stress exceeds the