ASTM_D_3929_-_03_2015.pdf

Designation:D392903(Reapproved 2015)Standard Test Method forEvaluating Stress Cracking of Plastics by Adhesives Usingthe Bent-Beam Method1This standard is issued under the fixed designation D3929;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 procedure for determiningthe compatibility of adhesives with plastics based on whetherthe adhesive causes cracking of stressed samples.1.2 Specimen configurations and test fixture designs aregiven.1.3 This test method is suitable for products in the form ofsheet or strip.It can also be used on injection molded tensilespecimens or flexural bars.1.4 The values stated in SI units are to be regarded as thestandard.The inch-pound units given in parentheses are forinformation only.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 and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D638 Test Method for Tensile Properties of PlasticsD790 Test Methods for Flexural Properties of Unreinforcedand Reinforced Plastics and Electrical Insulating Materi-alsD907 Terminology of Adhesives3.Terminology3.1 DefinitionsMany of the terms in this test method aredefined in Terminology D907.3.2 Definitions of Terms Specific to This Standard:3.2.1 cracking,na continuous localized failure of theplastic,leading to loss of structural integrity.3.2.2 crazing,napparent fine cracks at or under thesurface of a plastic.3.2.2.1 DiscussionThis is a form of localized yielding ofthe plastic due to the combined action of stress and an attackingmedium.Initial crazing may be detectable only by inspectionunder magnification.3.2.3 failure,nan arbitrary point defined by the initialdetection of cracks or crazes.4.Summary of Test Method4.1 This test method involves the qualitative determinationof the compatibility of adhesives with plastics by observing theeffect of adhesives applied in the liquid state on stressed plasticspecimens.Bars of plastic are bent in a three-point loadingfixture to cause a predetermined initial tensile stress on thesurface of the bar.The liquid adhesive is then applied to thearea of maximum stress which is checked periodically forcrazing or cracking.4.1.1 Due to the stress relaxation behavior of certainplastics,initial stress only can be determined and the stresslevel may decrease significantly during the course of the test.5.Significance and Use5.1 This test method is designed for obtaining a qualitativeestimate of the compatibility of plastics and adhesives.Due tothe many process variables associated with the fabrication ofplastic parts,it is not possible to use this test as a substitute forcompatibility tests on actual parts.5.2 The detection of cracks or crazes may be determinedwith or without optical aid.Make comparisons only amongtests employing crack detection methods of equivalent sensi-tivity.6.Apparatus6.1 Test FixturesBent beam test fixtures(see Fig.1)3aredesigned to place the specimen in three-point bending.The1This test method is under the jurisdiction of ASTM Committee D14 onAdhesives and is the direct responsibility of Subcommittee D14.40 on Adhesives forPlastics.Current edition approved Sept.1,2015.Published September 2015.Originallyapproved in 1980.Last previous edition approved in 2010 as D3929 03(2010)1.DOI:10.1520/D3929-03R15.2For 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.3Detailed drawings are shown in Figs.35.Also necessary to complete the testfixture are the following parts:2 pieces at 6 by 38 mm(14by 112-in.)dowel pinsand 2 pieces of M40.7(832 unc)by 32 mm(114-in.)socket head cap screws.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 amount of deflection is adjustable as well as the loading span.Other fixtures may be used as long as specimen deflection isknown.6.2 The amount of deflection on the specimen is measuredby use of a dial gage indicator or a vernier caliper having adepth indicator(see Fig.2).Use a measuring device capable ofreading to 0.025 mm(0.001 in.).7.Test Specimen7.1 The preferred specimen is a flexural bar designed inaccordance with Test Methods D790.Depth6.4 mm(14in.)Width13 mm(12in.)Length130 mm(5 in.)Loading Span100 mm(4 in.)L/d16/1Tensile bars,such as Type I in Test Method D638,can alsobe used.Specimens of rectangular section may also be cut fromsheets or molded plastic articles.7.2 Mold specimens in a lo