1、Designation: D 3929 03Standard Test Method forEvaluating Stress Cracking of Plastics by Adhesives Usingthe Bent-Beam Method1This standard is issued under the fixed designation D 3929; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision,
2、 the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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
3、 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
4、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 a
5、nd health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:D 638 Test Method for Tensile Properties of Plastics2D 790 Test Methods for Flexural Properties of Unreinforcedand Reinforced Plastics and Electrical Insulating Mater
6、i-als2D 907 Terminology of Adhesives23. Terminology3.1 DefinitionsMany of the terms in this test method aredefined in Terminology D 907.3.2 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 craz
7、ing, 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
8、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 be
9、nt 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 certain plas-tics, initial
10、 stress only can be determined and the stress levelmay 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
11、 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
12、. Apparatus6.1 Test FixturesBent beam test fixtures (see Fig. 1)3aredesigned to place the specimen in three-point bending. Theamount of deflection is adjustable as well as the loading span.Other fixtures may be used as long as specimen deflection isknown.1This test method is under the jurisdiction o
13、f ASTM Committee D14 onAdhesives and is the direct responsibility of Subcommittee D14.40 on Adhesives forPlastics.Current edition approved April 10, 2003. Published May 2003. Originallyapproved in 1980. Last previous edition approved in 1996 as D 3929 96e1.2Annual Book of ASTM Standards, Vol 08.01.3
14、Detailed drawings are shown in Figs. 3-5. Also necessary to complete the testfixture are the following parts: 2 pieces at 6 by 38 mm (14 by 112-in.) dowel pinsand 2 pieces of M40.7 (832 unc) by 32 mm (114-in.) socket head cap screws.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700,
15、West Conshohocken, PA 19428-2959, United States.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 specim
16、en is a flexural bar designed inaccordance with Test Methods D 790.Depth 6.4 mm (14 in.)Width 13 mm (12 in.)Length 130 mm (5 in.)Loading Span 100 mm (4 in.)L/d 16/1Tensile bars, such as Type I in Test Method D 638, can alsobe used. Specimens of rectangular section may also be cut fromsheets or molde
17、d plastic articles.7.2 Mold specimens in a low-stress condition or anneal sothat molded-in stresses will not have a significant effect.7.3 Carefully cut or machine specimens in accordance withthe plastic manufacturers recommended procedures to avoidintroducing stresses at machined surfaces.8. Proced
18、ure8.1 Place the plastic test specimen in the test fixture at therequired loading (see Fig. 6).8.2 Apply adhesive to be tested to the center point on thelength of the loaded specimen. Cover a specimen length ofapproximately 25 mm (1 in.). In general, apply the adhesiveonly once, as would be the case
19、 in an actual end-use applica-tion.8.2.1 If the adhesive contains a solvent, allow it to evaporateat a normal rate.8.2.2 If the adhesive is a curing type, cure in a normalfashion.FIG. 1 Test Fixture with Plastic Bar in PlaceFIG. 2 Measurement of Test Bar Deflection with Depth Gage of Vernier Caliper
20、D39290328.2.3 If the adhesive is a hot melt, apply at the normalapplication temperature and then allow to cool. This is a lesssevere condition than would occur if the adhesive werecontinually applied, but is more consistent with situations thatoccur in actual adhesive use.8.3 Control SpecimensConcur
21、rently run one controlspecimen with the test specimens in the same location. Exces-sive molded-in stresses or airborne solvent vapors may causestress cracking even without application of adhesive.9. Stress Calculations9.1 The equation given below is valid only for specimens ofrectangular cross secti
22、on at stresses below the elastic limit ofthe material. The deflection is based on initial stress only. Thelevel of stress will normally decrease with time as the plasticundergoes relaxation. Deflection is calculated based on thedesired stress level as follows:FIG. 3 Test Fixture FrameFIG. 4 Test Fix
23、ture Center Loading BarFIG. 5 Test Fixture Top PlateD3929033D 5 SL2/6 dE (1)where:D = deflection, m (in.),S = stress, Pa (psi),L = loading span, m (in.),d = specimen depth, m (in.), andE = modulus of the plastic, Pa (psi).NOTE 1This equation holds for rectangular specimens only.9.2 If it is desired
24、to run tests on the basis of constant strain,the following formula can be used:D 5rL26 d(2)where r = strain, m/m (in./in.).9.3 Tensile stress and strain values represent the maximumlevel at the surface of the specimen in the area to whichadhesive is applied. This is mid-span in the three-point loadi
25、ngarrangement.10. Choice of Test Conditions10.1 Suggested stress levels for testing are 7, 14, and 21MPa (1000, 2000, and 3000 psi). For initial screening, 21 MPa(3000 psi) is recommended since incompatible adhesives willcause rapid crazing or cracking. Lower stress levels may beused for discerning
26、finer differences in materials.10.2 Testing can also be based on constant strain if this ismore meaningful for particular end-use applications.10.3 The test duration is 5 days for adhesives that harden orcure. For adhesives that remain in the liquid state on thespecimens (for example, anaerobic adhe
27、sives), the test shouldbe extended to 10 days.10.4 Maintain environmental conditioning at 23 6 2C (736 3.5F), 50 6 5 % RH. Specify other conditions as agreed toby user and manufacturer.10.5 Since stress cracking is more likely to occur immedi-ately after application of the adhesive, it is desirable
28、to observethe specimens at frequent intervals in the beginning of the test.A suggested observation schedule is as follows: 1 min, 5 min,1 h, 24 h, and daily thereafter.11. Inspection of Specimens11.1 Determine the presence of cracks or crazes by carefulvisual observation.NOTE 2Magnification may be u
29、sed upon agreement by user andmanufacturer.11.2 If adhesives are not transparent, remove sufficientadhesive to determine if cracks or crazes are present.12. Report12.1 Report the results of the test as the absence or presenceof cracks or crazes at a given stress level. If cracks or crazes arepresent
30、, the time required for their occurrence is also reported.Report the following specific items:12.1.1 Specimen identification,12.1.2 Material name or specification code,12.1.3 Adhesive identification,12.1.4 Stress level,12.1.5 Type and orientation of specimen used and method offabrication (injection
31、molded, tensile specimen, annealed, etc.),12.1.6 Detailed description of test environment (for ex-ample, temperature, humidity, exposure time), and12.1.7 Remarks concerning the size and appearance ofcracks or crazes may be included if significant.NOTE 3Indicate magnification techniques used for insp
32、ection, if any.13. Precision and Bias13.1 No information is presented about either the precisionor bias of Test Method D 3929 for evaluating stress cracking ofplastics by adhesives since the test result is nonquantitative.14. Keywords14.1 adhesive compatibility; bent-beam; cracking; crazing;liquid a
33、dhesive; stress crackingASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringe
34、ment 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 andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard o
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36、nown 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 19428-2959,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).FIG. 6 Cut-Away View of Sample Mounted in FixtureD3929034
