ASTM_D_7027_-_13.pdf

Designation:D702713Standard Test Method forEvaluation of Scratch Resistance of Polymeric Coatings andPlastics Using an Instrumented Scratch Machine1This standard is issued under the fixed designation D7027;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.1.Scope1.1 This test method describes a laboratory procedure usingan instrumented scratch machine to produce and quantifysurface damage under controlled conditions.This test methodis able to characterize the scratch resistance of polymers bymeasuring many significant material parameters.The scratch-inducing and data acquisition process is automated to avoiduser-influenced effects that may affect the results.1.2 The values stated in SI units are to be regarded asstandard.The values in parentheses are for information only.1.3 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 and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D618 Practice for Conditioning Plastics for TestingD638 Test Method for Tensile Properties of PlasticsD1894 Test Method for Static and Kinetic Coefficients ofFriction of Plastic Film and SheetingE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsG99 Test Method for Wear Testing with a Pin-on-DiskApparatusG171 Test Method for Scratch Hardness of Materials Usinga Diamond Stylus3.Terminology3.1 Definitions:3.1.1 ASV Software,nAutomatic Scratch Visualization,acomputer program which automates the identification of thepoint of failure in a rising load scratch tests using contrast asthe failure criteria.The software determines failure if acontinuous change in contrast between the scratch groove andthe undamaged material surface reaches+3%,-3%,or 63%.The continuity criterion is defined as a region of length equalto 2 diameters of the scratch stylus with 90%or more of theregion exceeding the contrast criterion.The lowest load pointon the scratch from which there is a continuous contrastingregion is considered the point of failure.This program is usefulfor visual analysis of the test and may be used for otherapplications,such as pass-fail criterion for scratch visibility.Anexample of the application of ASV is shown in Fig.1.3.1.2 critical normal load,nthe normal load at whichfailure(see 3.1.4)of the material within the scratch groove firstoccurs.3.1.3 normal load,na load applied onto the scratch stylusthat is imposed in a vertically downward direction,perpendicu-lar to the surface of the specimen.The normal load is alsoreferred to as the“Z-direction load.”3.1.4 point of failure,nthe point along a rising-loadscratch path at which the damage to the surface is firstconsidered to be unacceptable.The point of failure for a givenstudy shall be defined in a quantifiable manner.For aestheticstudies the recommended criteria is a contrast of 63%between the scratch groove and the undamaged materialsurface.For different studies other criteria for failure may beused.For example,failure may occur when the scratch width ordepth exceeds a predetermined value.Onset of micro-cracking,crazing,fish-scale formation,plowing can also be used asfailure criteria.For a coated specimen the point of failure mightbe defined as the point at which the coating is penetrated,revealing the underlying substrate.An image of styrene acry-lonitrile(SAN)subjected to Test Mode A(4.1.1)under alinearly increasing normal load range of 1-90 N is shown inFig.1 to illustrate several possible points of failure that canoccur during the scratch process.3.1.5 scratch coeffcient of friction,nthe ratio of thetangential force(3.1.10)to the normal load(3.1.3).Thiscoefficient is a measure of the resistance of a material toscratching motion.For tests conducted under constant load,two distinct quantities may be characterized,the static andkinetic coefficients.The static coefficient is related to the1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.10 on Mechanical Properties.Current edition approved Oct.15,2013.Published October 2013.Originallyapproved in 2005.Last previous edition approved in 2005 as D7027051.DOI:10.1520/D7027-13.2For 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 States1 tangential force measured prior to the movement of the scratchstylus while the kine