ASTM_F_791_-_18.pdf

Designation:F79118Standard Test Method forStress Crazing of Transparent Plastics1This standard is issued under the fixed designation F791;the number immediately following the designation indicates the year of originaladoption or,in the case of revision,the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon()indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S.Department of Defense.1.Scope1.1 This test method covers the determination of the criticalcrazing stress for a transparent plastic material when exposedto a specific solvent,chemical,or compound at a specifictemperature.1.2 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 deter-mine the applicability of regulatory limitations prior to use.1.3 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:2D618 Practice for Conditioning Plastics for TestingE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method2.2 Other Method:ARTC(Aircraft Research and Testing Committee of theAircraft Industries Association of America,Inc.)Condi-tioning Method33.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 crazinga group of surface fissures that appear to besmall cracks in the material,although they are not.3.1.1.1 DiscussionCrazing is a form of yielding in poly-mers characterized by a spongy void filled fibrillar structure.The density in the craze changes resulting in a change in theindex of refraction,which causes light to be reflected off of thecrazes.This light reflection causes the crazes to sparkle whenviewed from certain angles.The crazes are sometimes randomand scattered with varied lengths and depths but usually areoriented perpendicular to a tensile stress.Crazing is difficult todetect.It becomes more pronounced when viewed with a lightsource that is at an oblique angle.4.Significance and Use4.1 This test method provides a guide for evaluatingwhether a specific solvent,chemical,or compound is detrimen-tal to a transparent plastic as a result of a manufacturingprocess,a fabrication operation,or the operational environ-ment.All transparent plastics are susceptible to crazing,thoughin widely varying degree and from a variety of causes.This testmethod is intended to allow establishment of the crazing stresswhen the simultaneous action of both load and a material thatwill cause crazing is applied,producing non-reversible damagethat limits the usage of that transparent plastic in a specificapplication.5.Apparatus5.1 Test Fixture,with fluorescent light source illustrated andconstructed as shown in Figs.1 and 2.5.2 Drill Fixture constructed as shown in Fig.3.5.3 Marking Fixture,constructed as shown in Fig.3.5.4 Portable Specimen Rack,constructed in the manner asshown in Fig.4 for handling and conditioning test specimens.5.5 WeightsA container and shot for the application ofweight on the rack as shown in Fig.1.5.6 Filter Paper,quantity of 0.50 by 1.0-in.(12.7 by25.4-mm)pieces of filter,medium-retention filter paper.6.Test Specimens6.1 The test specimen shall be machined from the transpar-ent plastic material to be evaluated.A minimum of six1This test method is under the jurisdiction of ASTM Committee F07 onAerospace and Aircraft and is the direct responsibility of Subcommittee F07.08 onTransparent Enclosures and Materials.Current edition approved June 1,2018.Published June 2018.Originallyapproved in 1982.Last previous edition approved in 2013 as F791 96(2013).DOI:10.1520/F0791-18.2For 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.3Available from Aircraft Industries Association,1725 DeSales St.NW,Washington,DC 20034.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 specimens for each solvent,chemical,or compound is re-quired.The preferred transparent plastic sheet material thick-ness is 6.35 6 0.64 mm(0.250 6 0.025 in.).Other thicknessmaterial is acceptable,but the actual