1、Designation: D6991 05 (Reapproved 2010)Standard 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 th
2、e 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.1. Scope1.1 This test method covers the procedure for measurementsof internal stresses in organic
3、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
4、coating (see Note 4 and Note 5).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
5、 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 and health practices and to determine theapplicability of regulatory limitations prior to use.2. Referenced Document
6、s2.1 ASTM Standards:2D823 Practices for Producing Films of Uniform Thicknessof Paint, Varnish, and Related Products on Test PanelsD1186 Test Methods for Nondestructive Measurement ofDry Film Thickness of Nonmagnetic Coatings Applied toa Ferrous Base3D1400 Test Method for Nondestructive Measurement o
7、fDry Film Thickness of Nonconductive CoatingsApplied toa Nonferrous Metal Base33. 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 itsorigina
8、l 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 me
9、thod (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
10、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 E
11、q1 in Section 9, (Formula 1).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 Dec. 1, 2010. Publish
12、ed December 2010. Originallyapproved in 2005. Last previous edition approved in 2005 as D6991 - 05. DOI:10.1520/D6991-05R10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, r
13、efer to the standards Document Summary page onthe ASTM website.3Withdrawn. The last approved version of this historical standard is referencedon www.astm.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5. Significance and Use5.1
14、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 inthe coatings: film formation (cross-linking, solvent evapora-tion, etc.); differences in thermal
15、 expansion coefficients be-tween coating and substrate; humidity and water absorption;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
16、 the internal stress exceeds the tensile strength ofthe film, cracks are formed. If stress exceeds adhesion betweencoating and substrate, it will reduce adhesion and can lead todelamination of coatings. Quantitative information aboutstresses in coatings can be useful in coating formulation andrecomm
17、endations for their application and use.5.4 This method has been found useful for air-dry industrialorganic coatings but the applicability has not yet been assessedfor thin coatings (thickness Es; the ratio between t and c should becarefully selected. For example, if t=c, the contribution of the sec
18、ond termin formula (2) will be up to 20 %; if t=2c, the contribution will be 5-6 %.10. Report10.1 Report the following information:10.1.1 Complete identification of the test specimen: coatingdescription, coating thickness (minimum, maximum, average,and its distribution along the length and width of
19、the substrate),application conditions.10.1.2 Complete identification of the cantilever substrate(material, length, width, and thickness; modulus of elasticityand Poissons Ratio; length between clamping point anddeflection measured point).10.1.3 Report ratio between thickness of film to substrate.10.
20、1.4 Report if the sample was fixed at all times during thetest or if it was periodically removed and reinstalled.10.1.5 Report the deflection values, their correspondingtime intervals and exposure conditions (temperature, humidity,etc.).10.1.6 Report the calculated stress.11. Precision and Bias11.1
21、Accuracy of this method depends upon the followingvariables: precision of measuring the deflection, the ratio of thethickness of the coating and the substrate, length of theworking part of the substrate, uniformity of applied film,reinstallation of cantilever in the fixture, and environment.11.2 Pre
22、cisionThe pooled repeatability standard devia-tion has been determined to be 0.7 MPa representing a pooledcoefficient of variation of 13 %. These values were obtainedusing 6 different formulations and 2 different film thicknesses.10 readings of each sample were made by one operator in onelaboratory.
23、 See Appendix X2 for the precision data.11.2.1 The reproducibility of this method and bias state-ments are not available at this time. Round robin tests will beperformed at a later date within 5 years after the method isapproved.12. Keywords12.1 cantilever; deflection; internal stress; organic coati
24、ngs.APPENDIXES(Nonmandatory Information)X1. RECOMMENDED DIMENSIONS OF TESTING APPARATUS (see Fig. 1 and Fig. 2):Fig.1A rectangular cantilever beam (substrate): made of 304SSstainless steel; width 12 mm (0.5 in.); length, 102 mm (4 in.);thickness t = 0.254 mm (0.01 in.);Beam is clamped by its end B i
25、n a special fixture E; free endD is deflected under stress from its original position by adistance of h (deflection).Fig.2A (support): 127 by 25.4 by 12.7mm (5 by 1 by12 in.);make small supporting base area 19 by 12.7 mm (34 by12 in.)for sample installation under the pressure shim and thescrew-clamp
26、. This base area should be 1.6 mm (116 in.) higherthan the rest of the support surface; Polish base surface.B (stop): L shape; 45 by 25.4 mm (134 by 1 in.); thickness6.4 mm (14 in.); Stop should be attached to the support by twoscrews;D (screw-clamp): screw with attached 12.7 mm (12 in.)diameter cla
27、mp;L distance between engraved point and clamping point= 80 mm (3 in.).Notes:1. Use rectangular pressure shim 19 by 12.7 by 1.6 mm (34by12 by116 in.) between clamp and sample;2. Use stainless steel for all parts to avoid corrosion;3. Polish support base and clamping surface area to makethem parallel
28、;4. Polish both sides of the pressure shim;5. Make clamping screw perpendicular to the clampingsurface.D6991 05 (2010)4X2. PRECISION DATAASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this sta
29、ndard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years an
30、dif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee,
31、which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-295
32、9,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard
33、 may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).TABLE 1 Repeatability of Stress Measurements Within One Lab by One OperatorStress Readings, psiPanel ID DFT, mils 1st2nd3rd4th5th6th7th8th9th10thaverage stdvcoef.Var, %5A 3.0 708 885 708 708 708 885 708 531 531 885 726 131 185B 2.8
34、 1155 1155 1155 963 963 1155 963 963 963 963 1040 99 109A 3.5 1022 1314 1314 1022 1022 1022 876 876 876 876 1022 169 169B 3.5 584 584 584 584 584 438 584 438 438 438 526 75 1417A 4.2 694 810 694 694 578 578 578 578 578 578 636 82 1317B 3.2 490 490 653 490 490 490 490 490 490 490 506 52 1020A 3.6 846
35、 846 987 846 846 846 846 705 705 705 818 89 1120B 3.0 885 708 531 708 708 531 708 708 708 708 690 100 1524A 3.0 1062 1062 1062 1062 1062 1062 885 1062 1062 1062 1044 56 524B 2.8 963 963 963 963 770 963 770 578 963 770 867 136 1626A 3.6 987 846 846 846 846 846 846 846 987 846 874 59 7Pooled 102 psi 130.7 MPaD6991 05 (2010)5
