1、Designation: F791 96 (Reapproved 2013)Standard 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 revisio
2、n. A number in parentheses indicates the year of last reapproval. A superscriptepsilon () 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
3、 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 stand
4、ard 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 TestingE691 Practice for Conducting an Interlaboratory Study toDetermine the Precis
5、ion 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 t
6、he 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
7、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 may bedifficult to detect. It becomes more pronounced when viewedwith a light source
8、that is at an oblique angle.4. Significance and Use4.1 This test method provides a guide for evaluating aspecific solvent, chemical, or compound that may be detrimen-tal to a transparent plastic as a result of a manufacturingprocess, a fabrication operation, or the operational environ-ment.All trans
9、parent 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 thatwould cause crazing is applied producing non-reversible dam-ag
10、e that might limit the usage of that transparent plastic in aspecific application.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
11、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-retenti
12、on filter paper.6. Test Specimens6.1 The test specimen shall be machined from the transpar-ent plastic material to be evaluated. A minimum of sixspecimens for each solvent, chemical, or compound is re-quired. It is preferred that the transparent plastic sheet materialthickness be 6.35 6 0.64 mm (0.2
13、50 6 0.025 in.), but anythickness material may be used. Orientation of each testspecimen within the test sheet or part should be recorded.6.2 The test specimens shall be 25.4 6 0.8 mm (1.00 6 0.03in.) wide by 177.8 6 1.27 mm (7.00 6 0.05 in.) long bythickness.1This test method is under the jurisdict
14、ion of ASTM Committee F07 onAerospace and Aircraft and is the direct responsibility of Subcommittee F07.08 onTransparent Enclosures and Materials.Current edition approved Dec. 1, 2013. Published December 2013. Originallyapproved in 1982. Last previous edition approved in 2008 as F791 96(2008). DOI:1
15、0.1520/F0791-96R13.2For 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 Associ
16、ation, 1725 DeSales St. NW,Washington, DC 20034.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States16.3 The edges shall be smooth machined surfaces withoutcracks, and the test specimen surface shall be free of defects orirregularities. If
17、 the test specimen has been machined tothickness, the nonmachined surface shall be the test surface.7. Preparation of Apparatus7.1 Once the load for a particular stress is calculated, thatload will be the sum of the individual weights of the weightrack, rod, lead weights, container, shot, and the ra
18、diused nut.For convenience of assembly, the weight rack pan may bestamped with the total weight of the pan, rod, and nuts as aunit. A container, such as a12-pt (0.24-L) paint can with a6.4-mm (14-in.) hole drilled in the center of the bottom andinstalled so it slides up and down on the rod, can serv
19、e as areceptacle for the lead shot to attain required weight.8. Conditioning8.1 Precondition the test specimens in accordance with oneof the following procedures:8.1.1 Practice D618 Procedure BForty-eight hours at50C (122F) followed by cooling to room temperature indesiccator over anhydrous calcium
20、chloride for at least 5 h.Designate as Condition 1 and test within 15 min.8.1.2 Two hours at 90C (194F), ambient cooled, andfollowed by 7 days at 23 6 1.1C (73.5 6 2F) and 50 6 5%relative humidity. Designate as Condition 2 and test within 1 h.8.1.3 ARTC MethodSixteen hours at 14C (25F) belowthe aver
21、age heat deflection temperature, cool at a rate notexceeding 28C (50F)/h and follow by 96 h at 23 6 1.1CFIG. 1 Accelerated Crazing Test FixtureFIG. 2 Application of Test Liquid to Piece of Filter Paper on TopSurface of Test SpecimenFIG. 3 Fixtures for Specimen PreparationF791 96 (2013)2(73.5 6 2F) a
22、nd 50 6 5 % relative humidity. Designate asCondition 3 and test within 1 h.8.1.4 As received, no preconditioning. Designate as Condi-tion 4.NOTE 1The conditions listed above may not result in uniformmoisture content for certain plastics. Moisture content reportedly mayhave a strong effect on craze r
23、esults for certain plastics. If otherpreconditionings are required to ensure uniform or desired moisturecontent, the use of these should be reported in the test report.9. Calculation of Loads9.1 The width and thickness of each specimen shall bemeasured to the nearest 0.03 mm (0.001 in.). Enter this
24、dataalong with the identification of the specimen in the requiredrecords.9.2 Calculate the load to be used with each specimen inaccordance with the following equation:P 5 S 3 B 3 D2!/6L! (1)where:P = load, N (lb.),S = maximum outer fiber stress, MPa (psi), determined bytest sequence in 10.5 10.8,or1
25、1.5 11.8,L = length of specimen from fulcrum to center of appliedload, mm (in.),B = width of specimen, mm (in.), andD = thickness of specimen, mm (in.).NOTE 2This equation is valid only for relatively small deflections. Forlarge deflections, the dimension L should be replaced by the actualhorizontal
26、 distance from the point of load application to the fulcrum in thedisplaced condition. A deflection of 25.4 mm (1 in.) at the point of loadapplication will result in an actual stress at the fulcrum which isapproximately 5 % less than the expected stress, and a 38.1 mm (1.5 in.)deflection will result
27、 in an actual stress at the fulcrum which is approxi-mately 10 % less than the expected stress.10. Procedure ACraze Stress Iteration10.1 Place each specimen in the drill fixture and drill a 7.94mm (0.3125 in.) diameter hole at a distance of 12.7 6 1.27 mm(0.50 6 0.050 in.) from one end and on the lo
28、ngitudinalcenterline of the specimen.10.2 Place each specimen in the marking fixture and draw apencil line on the edge of the specimen 101.6 mm (4.0 in.)from the center of the 7.94-mm (0.3125-in.) diameter hole andperpendicular to the length of the specimen (see mark in Fig.2).10.3 Measure the width
29、 and thickness of each specimen tothe nearest 0.03 mm (0.001 in.) at the pencil line. Handle eachspecimen only by its edges. Do not clean test specimens in anymanner during the time period between conditioning andtesting.10.4 Insert the conditioned specimen immediately in the testfixture with the pe
30、ncil mark on the specimen in line with thecenter of the fulcrum. Raise the weights and insert the end ofthe rod through the 7.94-mm (0.3125-in.) hole in the testspecimen. Carefully center the load supporting nut (with a7.94-mm (0.3125-in.) machined radius on the surface contact-ing the plastic) in t
31、he hole and tighten the nut. Align thespecimen edges so they are exactly perpendicular to thefulcrum and slowly lower the weights until the specimenaccepts the load.10.5 Test the first specimen at 27.58 MPa (4000 psi) outerfiber stress. Apply the load for 10 6 0.5 min and observe to besure no crazin
32、g has occurred. Place the 12.5 by 25-mm (12 by1 in.) filter paper directly over the fulcrum in the middle of thespecimen so there is a clear area along each edge to avoidinducing edge crazing. Apply the test chemical to the filterpaper only. Use care so that the test material does not extendbeyond t
33、his area and defeat the purpose of the test. Keep thefilter paper moist with test chemical for the duration of the test,15 min, 30 min, or any duration desired. Remove the filterpaper after the test period and inspect for craze. Turn on thefluorescent lamps for inspection only to avoid undesiredheat
34、ing of the test specimen. Terminate the testing of thatspecimen.NOTE 3It is recommended that a control test be run with each set ofcraze tests. This control test is conducted exactly the same as the othercraze tests, except that no chemicals should be applied to this controlspecimen during the craze
35、 test. This provides a baseline and allows adetermination of whether the crazing observed in the tests with thechemical applied is due to the chemical/stress combination, or is afunction of stress alone.10.6 If the first specimen is crazed, test the second specimenat 13.79 MPa (2000 psi). If the fir
36、st specimen did not craze, testthe second specimen at 20.68 MPa (6000 psi).10.7 If the second specimen does not craze at 2000 psi, testthe third specimen at 20.68 MPa (3000 psi). Test the fourth ata lower or higher stress depending on whether the thirdspecimen did or did not craze. Continue this pro
37、cedure insuitable increments until the critical crazing stress for specificsolvent, chemical, or compound is determined to the desiredaccuracy.10.8 Report the critical crazing stress as the stress midwaybetween the stress at which crazing was and was not observedon duplicate specimens. For example:
38、Crazing was observed at27.58 MPa (4000 psi) and none at 24.13 MPa (3500 psi). Thecritical crazing stress would be 25.86 6 1.72 MPa (3750 6 250psi).FIG. 4 Specimen RackF791 96 (2013)310.9 In the examination of the crazing, note all cracks at theedge of the specimen as “edge crazing.” Disregard thisco
39、ndition when ascertaining the end point unless the edge ofcrazing grows and extends across the entire width of thespecimen.10.10 Testing shall be at the specified temperature 63C(65F).11. Procedure BCraze Stress Tracking11.1 Place each specimen in the drill fixture and drill a7.94-mm (0.3125-in.) di
40、ameter hole at a distance of 12.7 61.27 mm (0.50 6 0.050 in.) from one end and on thelongitudinal centerline of the specimen.11.2 Place each specimen in the marking fixture and draw apencil line on the edge of the specimen 101.6 mm (4.0 in.)from the center of the 7.94-mm (0.3125-in.) diameter hole a
41、ndperpendicular to the length of the specimen (see the mark inFig. 2). On the side opposite the test surface, using an inksuitable for marking plastic, mark lines across the specimensurface perpendicular to the edge, from edge to edge, at 6.4mm (0.25 in.) intervals, starting at the hole and progress
42、ing101.6 mm (4.0 in.) to the point at which the beam will rest onthe fulcrum.11.3 Measure the width and thickness of each specimen tothe nearest 0.03 mm (0.001 in.) at the pencil line. Handle eachspecimen only by its edges. Do not clean test specimens in anymanner during the time period between cond
43、itioning andtesting.11.4 Firmly press a 3.18 mm (0.125 in.) wide ribbon ofnon-compressible black butyl glazing tape sealant on the testsurface of the specimen along each edge to create a dam whichprevents the test chemical from coming in contact with thespecimen edges. Insert the conditioned specime
44、n immediatelyin the test fixture with the pencil mark on the specimen in linewith the center of the fulcrum. Raise the weights and insert theend of the rod through the 7.94-mm (0.3125-in.) hole in the testspecimen. Carefully center the load supporting nut (with a 7.94mm (0.3125 in.) machined radius
45、on the surface contacting theplastic) in the hole and tighten the nut. Align the specimenedges so they are exactly perpendicular to the fulcrum andslowly lower the weights until the specimen accepts the load.NOTE 4It is important that the butyl sealant does not itself causecrazing of the plastic mat
46、erial: KPTI-303 glazing tape butyl sealant fromProtective Treatments Inc. 3345 Stop-Eight Rd. Dayton, Ohio 45413(phone number 513-890-3150) has been utilized for craze testing ofacrylics and polycarbonates with no adverse effects. To evaluate crazingwith butyl or other substituted dam material, cond
47、uct craze testing asdescribed in this test method using the sealant material as the craze agent.11.5 Test the first specimen at 27.58 MPa (4000 psi) outerfiber stress. Use the equation of 9.2 to calculate the requiredload. Apply the load for 10 6 0.5 min and observe to be sureno crazing has occurred
48、. At the completion of the 10 minutestabilization period, activate a stop watch or timer for referenceduring the test. Using an eye dropper, apply test chemical to thesurface of the specimen allowing it to run down the specimenbetween the butyl dams placed at each top surface edge of thespecimens as
49、 described in 10.4. Apply chemical as neededthroughout the test to maintain a wetted condition on the entiretest surface of the specimen, from the fulcrum down to thepoint of load application. Place a pan under the point of loadapplication to catch the chemical which drips off of thespecimen. Continue the test for 15 minutes, 30 minutes, or anyduration desired. During the test, monitor the specimen con-tinuously for craze development. Record the time and locationof the craze front as crazing progresses down the beam.11.6 Calculate the craze stress
