1、Designation: D7474 12Standard Practice forDetermining Residual Stresses in Extruded or MoldedSulfone Plastic (SP) Parts by Immersion in VariousChemical Reagents1This standard is issued under the fixed designation D7474; the number immediately following the designation indicates the year oforiginal a
2、doption 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. Scope*1.1 This practice covers the evaluation of residual stressesin extruded
3、profile or molded SP parts. The presence andrelative magnitude of residual stresses are indicated by thecrazing of the specimen part upon immersion in one or more ofa series of chemical reagents. The specified chemical reagentswere previously calibrated by use of Environmental StressCracking (ESC) t
4、echniques to cause crazing in sulfone plastics(SP) at specified stress levels.1.2 This practice applies only to unfilled injection moldingand extrusion grade materials of high molecular weight asindicated by the following melt flow rates: PSU 9 g/10 min,max., PESU 30 g/10 m, max, and PPSU 25 g/10 mi
5、n, max.Lower molecular weight (higher melt flow) materials will crazeat lower stress levels than indicated in Tables 1-3. (SeeSpecification D6394 for melt flow rate conditions.)1.3 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonl
6、y.NOTE 1There is no known ISO equivalent for this standard.1.4 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-bi
7、lity of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D543 Practices for Evaluating the Resistance of Plastics toChemical ReagentsD883 Terminology Relating to PlasticsD4000 Classification System for Specifying Plastic Materi-alsD6394 Specification for Sulfone Plastic
8、s (SP)2.2 ISO Standard:3ISO 220883 PlasticsDetermination of Resistance to En-vironmental Stress Cracking (ESC)Part 3: Bent StripMethod3. Terminology3.1 DefinitionsFor definitions of technical terms pertain-ing to plastics used in this practice, see Terminology D883.4. Summary of Practice4.1 The prac
9、tice involves the exposure of finished plasticparts to a specified series of chemical reagents which areknown to produce cracking or crazing of Sulfone Plastic (SP)materials at specific stress levels, under otherwise constantconditions including a fixed time of one minute. Thus, theexposure of finis
10、hed parts to one or more chemical reagentsunder no load conditions allows the quantification of theresidual stress levels in the finished parts. Since the evaluationis based on the subjective criteria of presence or absence ofcrazing, this practice only yields an approximate indication ofthe level o
11、f residual stresses in the parts. This practiceestimates the relative magnitude of residual stresses in partsproduced from the series of sulfone plastics, namely polysul-fone (PSU), polyethersulfone (PESU), and polyphenylsulfone(PPSU) materials.5. Significance and Use5.1 Thermoplastic moldings conta
12、in residual stresses due todifferential cooling rates through the thickness of the molding.Changes in residual stress have been found to occur with timeafter molding due to stress relaxation. Many part performanceparameters as well as part failures are affected by the level ofresidual stress present
13、 in a part. Residual stresses causeshrinkage, warpage, and a decrease in environmental stresscrack resistance. This practice estimates the relative magnitude1This practice is under the jurisdiction ofASTM Committee D20 on Plastics andis the direct responsibility of Subcommittee D20.15 on Thermoplast
14、ic Materials.Current edition approved April 1, 2012. Published May 2012. Originallyapproved in 2008. Last previous edition approved in 2008 as D7474 - 08.DOI:10.1520/D7474-12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For
15、 Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.1*A Summary of Changes section appears at the end of this s
16、tandard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.of residual stresses in parts produced from the series of sulfoneplastics (SP), namely polysulfone (PSU), polyethersulfone(PESU), and polyphenylsulfone (PPSU) materials.5.2 No di
17、rect correlation has been established between theresults of the determination of residual stresses by this practiceand part performance properties. For this reason, this practiceis not recommended as a substitute for other tests, nor is itintended for use in purchasing specifications for parts. Desp
18、itethis limitation, this practice does yield information of value inindicating the presence of residual stresses and the relativequality of plastic parts.5.3 Residual stresses cannot be easily calculated, hence it isimportant to have an experimental method, such as thispractice, to estimate residual
19、 stresses.5.4 This practice is useful for extruders and molders whowish to evaluate residual stresses in SP parts. This can beaccomplished by visual examination after immersion in one ormore chemical reagents to evaluate whether or not crackingoccurs. Stresses will relax after molding or extrusion.
20、Accord-ingly, both immersion in the test medium and visual examina-tion must be made at identical times and conditions afterprocessing, if comparing parts. It is important to note thedifferences in part history. Thus, this technique may be used asan indication for quality of plastic processing.5.5 T
21、he practice is useful primarily for indicating residualstresses near the surface.6. Apparatus6.1 Container, of sufficient size to ensure complete immer-sion of specimen(s).6.2 Cotton swaps, patches or similar means to apply reagentto a localized area if immersion is impractical.7. Reagents7.1 Ethano
22、l, or Ethyl Alcohol, denatured,7.2 Ethyl acetate (EA),7.3 Methyl Ethyl Ketone (MEK), and7.4 Isopropyl alcohol, 70 %.8. Safety Precaustions8.1 Protective equipment and clothing must be utilized toavoid contact of chemical reagents with the skin or eyes. Useadequate ventilation to remove noxious or to
23、xic fumes, or both.9. Test Specimen9.1 Size of SpecimenThe specimen shall be a completemolding or a cut piece of the extrusion or molding of sufficientsize to not influence the stresses being observed. Twisting andbreaking must be avoided in separating cut pieces since theslightest amount of such fo
24、rces has the potential to changestresses and cause false results.10. Conditioning10.1 It is not necessary to condition the part prior to testingby this practice. If conditioning is utilized for a controlledstudy in a series of parts, recommended conditioning is at 23 62C (73.4 6 3.6F) and 50 6 10 %
25、relative humidity for aminimum of 40 hours prior to testing.10.2 Test ConditionsConduct tests in the standard labora-tory atmosphere of 23 6 2C (73.4 6 3.6F) and 50 6 10 %relative humidity, unless otherwise specified by the contract orrelevant ASTM material specification.10.3 Residual stresses from
26、molding decrease with timeafter fabrication. For some studies, it is necessary to test assoon as possible after molding. In such cases, allow the part tocool before testing.TABLE 1 Liquid Reagents for Residual Stress Test for PSUMixtureMixture CompositionCritical Stress, MPa (psi)% by volume Ethanol
27、 % by volume Ethyl Acetate1 50 50 15.2 (2200)2 43 57 12.1 (1750)3 37 63 9.0 (1300)4 25 75 5.5 (800)TABLE 2 Liquid Reagents for Residual Stress Test for PESUMixtureMixture CompositionCritical Stress, MPa (psi)% by volume Ethanol % by volume MEK1 50 50 17.9 (2600)2 40 60 10.3 (1500)3 20 80 6.9 (1000)4
28、 0 100 5.9 (850)TABLE 3 Liquid Reagents for Residual Stress Test for PPSUMixtureMixture CompositionCritical Stress, MPa (psi)% by volume Ethanol % by volume MEK1 50 50 22.8 (3300)2 25 75 13.8 (2000)3 10 90 9.0 (1300)4 0 100 8.0 (1150)D7474 12211. Procedure11.1 Choose the appropriate table from Table
29、s 1-3, whichlist the series of chemical reagents that shall be used for SPparts made from PSU, PESU and PPSU, respectively. Ensurethat the required reagents are available.11.2 Rinse the specimen with isopropyl alcohol and air dry.Starting at the highest critical stress level (1), immerse thespecimen
30、 for one minute in the liquid reagent listed in theappropriate Table. Immediately after immersion rinse thespecimen with water, wipe dry and dry further by blowinglow-pressure compressed air on the surface as needed.11.3 Inspect the part for cracked or crazed regions.NOTE 2Hairline fractures are dif
31、ficult to see at times.11.4 If the part is crazed, the residual stress is greater thanthe critical stress value indicated for that reagent in the Table.If the part is not crazed, the residual stress is less than thecritical stress value indicated, and the test is continued with thenext liquid reagen
32、t in the Table.11.5 Using the same specimen, immerse the specimen in thenext lower critical stress liquid reagent (2) for one minute,rinse with water, dry and inspect for crazing. If crazing doesnot occur, the residual stress is less than the threshold for thisliquid reagent, and the test is continu
33、ed with the next liquidreagent.11.6 Continue until crazing occurs, or the last liquid reagentin the table is reached and no crazing occurs. If crazing doesnot occur with the last reagent, then the residual stress value isbelow the last value in the table and shall be reported as beingbelow that valu
34、e. Otherwise, the residual stress is reported tobe between the last level that crazing did occur and the passinglevel.NOTE 3To maintain accurate stress readings, the reagents must befresh. Over time, the reagents have been known to absorb water,evaporate, degrade when exposed to light, or become con
35、taminated, whichcan lead to erroneous stress indications.NOTE 4Determining stress levels through the use of reagent exposureis approximate in nature. Residual stress levels depend on numerousmolding parameters which at times have been found to be unstable duringmolding. For this reason, individual s
36、pecimens have been found to exhibitvariations in stress levels. Therefore, testing multiple parts is recom-mended.NOTE 5It is recommended that the determination of an acceptablemolded-in stress level for an individual part be made from its end useapplication, in particular, the chemical environment
37、to which the part willbe exposed. Parts whose residual stress levels are below 6 to 8 MPa aretypically considered to be well molded.NOTE 6Exposure for time periods longer than one minute producescracking at stress levels lower than those observed for one minuteexposure.12. Report12.1 Report the foll
38、owing information:12.1.1 Identification of the type of material tested,12.1.2 Identification of the specimen, including whetherextruded or molded, and cut specimen or complete,12.1.3 Time between molding or extrusion of parts andinitial immersion,12.1.4 Liquid reagents used,12.1.5 Estimated range of
39、 residual stress for the specimentested,12.1.6 Date of test, and12.1.7 Test practice number and published/revision date.13. Precision and Bias14. Keywords14.1 liquid reagent; PESU; PPSU; PSU; residual stress; SP;stress crackingAPPENDIX(Nonmandatory Information)X1. CALIBRATION OF STRESS LEVELS ASSOCI
40、ATED WITH EACH CHEMICAL REAGENTX1.1 The solvent mixtures and stress levels at which theycause crazing were determined using environmental stresscracking techniques as described in ISO 22088-3 and areshown in Tables 1-3 in the main body of this practice, whichapply to SP parts produced from PSU, PESU
41、, and PPSU,respectively.X1.2 The stress level required for crazing to occur for eachliquid reagent mixture was determined using annealed speci-mens exposed for one minute at known stress levels. ASTMflexural bar specimens were annealed for 1 hour at tempera-tures specified for HDT specimens in Speci
42、fication D6394 toremove any stresses other than caused later by flexural strainduring the ISO 22088-3 test.X1.3 The parts being tested were conditioned at 23 6 2C(73.4 6 3.6F) and 50 6 10 % relative humidity for aminimum of 40 hours prior to testing.X1.4 Several methods have been found useful for ap
43、plyingthe solvents; swiping with a cotton swab, immersion, or cottonpatches laid on top. In most cases, cotton patches were laid onthe surface of the specimen and then soaked the patch with thesolvent combination. In all applications the exposure time wasone minute. After the time requirement was me
44、t the patcheswere removed and any residual solvent wiped off.X1.5 The mounted specimens were examined for crazing.The strain level at which crazing started was noted. Then fromthe critical strain and the modulus of the material being testedthe critical stress was calculated for inclusion in Tables 1
45、-3.X1.6 The tabulated information in Tables 1-3 was gener-ated at room temperature with a one-minute exposure timeusing annealed flexural bars.D7474 123SUMMARY OF CHANGESCommittee D20 has identified the location of selected changes to this standard since the last issue (D7474 - 08)that may impact th
46、e use of this standard. (April 1, 2012)(1) MEK in Table 1 was corrected to Ethyl Acetate.ASTM 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 o
47、f the validity of any such patent rights, and the riskof infringement 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.
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