1、Designation: D 7474 08Standard Practice forDetermining Residual Stresses in Extruded or MoldedSulfone Plastic (SP) Parts by Immersion in VariousChemical Reagents1This standard is issued under the fixed designation D 7474; the number immediately following the designation indicates the year oforiginal
2、 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 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)
4、techniques 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 m
5、in, max.Lower molecular weight (higher melt flow) materials will crazeat lower stress levels than indicated in Tables 1-3. (SeeSpecification D 6394 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 informationo
6、nly.NOTE 1There is no equivalent ISO 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-bility of regul
7、atory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 543 Practices for Evaluating the Resistance of Plastics toChemical ReagentsD 883 Terminology Relating to PlasticsD 4000 Classification System for Specifying Plastic Mate-rialsD 6394 Specification for Sulfone Plastics (SP)2.2
8、 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 D 883.4. Summary of Practice4.1 The practice inv
9、olves 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 finished part
10、s 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 of residu
11、al 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 contain resid
12、ual 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 in a pa
13、rt. Residual stresses causeshrinkage, warpage, and a decrease in environmental stresscrack resistance. This practice estimates the relative magnitudeof residual stresses in parts produced from the series of sulfoneplastics (SP), namely polysulfone (PSU), polyethersulfone(PESU), and polyphenylsulfone
14、 (PPSU) materials.1This practice is under the jurisdiction ofASTM Committee D20 on Plastics andis the direct responsibility of Subcommittee D20.15 on Thermoplastic Materials.Current edition approved Aug. 1, 2008. Published September 2008.2For referenced ASTM standards, visit the ASTM website, www.as
15、tm.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 American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.
16、org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.2 No direct correlation has been established between theresults of the determination of residual stresses by this practiceand part performance properties. For this reason, this pr
17、acticeis not recommended as a substitute for other tests, nor is itintended for use in purchasing specifications for parts. Despitethis limitation, this practice does yield information of value inindicating the presence of residual stresses and the relativequality of plastic parts.5.3 Residual stres
18、ses cannot be easily calculated, hence it isimportant to have an experimental method, such as thispractice, to estimate residual 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 immer
19、sion in one ormore chemical reagents to evaluate whether or not crackingoccurs. Stresses will relax after molding or extrusion. 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
20、to note thedifferences in part history. Thus, this technique may be used asan indication for quality of plastic processing.5.5 The 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).
21、6.2 Cotton swaps, patches or similar means to apply reagentto a localized area if immersion is impractical.7. Reagents7.1 Ethanol, 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 cloth
22、ing must be utilized toavoid contact of chemical reagents with the skin or eyes. Useadequate ventilation to remove noxious or toxic 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
23、 the stresses being observed. Twisting andbreaking must be avoided in separating cut pieces since theslightest amount of such forces 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 conditi
24、oning 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 % 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 %r
25、elative humidity, unless otherwise specified by the contract orrelevant ASTM material specification.10.3 Residual stresses from 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
26、.11. Procedure11.1 Choose the appropriate table from Tables 1-3, whichlist the series of chemical reagents that shall be used for SPTABLE 1 Liquid Reagents for Residual Stress Test for PSUMixtureMixture CompositionCritical Stress, MPa (psi)% by volume Ethanol % by volume MEK1 50 50 15.2 (2200)2 43 5
27、7 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 0 100 5.9 (850)TABLE 3 Liquid Reagents for Residua
28、l 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)D7474082parts made from PSU, PESU and PPSU, respectively. Ensurethat the required reagents are available.11.2 Rinse t
29、he specimen with isopropyl alcohol and air dry.Starting at the highest critical stress level (1), immerse thespecimen 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 compres
30、sed air on the surface as needed.11.3 Inspect the part for cracked or crazed regions.NOTE 2Hairline fractures are difficult 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
31、residual stress is less than thecritical stress value indicated, and the test is continued with thenext liquid reagent 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
32、crazing doesnot occur, the residual stress is less than the threshold for thisliquid reagent, and the test is continued 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 reag
33、ent, then the residual stress value isbelow the last value in the table and shall be reported as beingbelow that value. 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 bef
34、resh. Over time, the reagents have been known to absorb water,evaporate, degrade when exposed to light, or become contaminated, whichcan lead to erroneous stress indications.NOTE 4Determining stress levels through the use of reagent exposureis approximate in nature. Residual stress levels depend on
35、numerousmolding parameters which at times have been found to be unstable duringmolding. For this reason, individual specimens 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
36、-in stress level for an individual part be made from its end useapplication, in particular, the chemical environment 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 min
37、ute producescracking at stress levels lower than those observed for one minuteexposure.12. Report12.1 Report the following 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
38、Time between molding or extrusion of parts andinitial immersion,12.1.4 Liquid reagents used,12.1.5 Estimated range of residual stress for the specimentested,12.1.6 Date of test, and12.1.7 Test practice number and published/revision date.13. Keywords13.1 liquid reagent; PESU; PPSU; PSU; residual stre
39、ss; SP;stress crackingAPPENDIX(Nonmandatory Information)X1. CALIBRATION OF STRESS LEVELS ASSOCIATED 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
40、in Tables 1-3 in the main body of this practice, whichapply to SP parts produced from PSU, PESU, 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. ASTMflexur
41、al bar specimens were annealed for 1 hour at tempera-tures specified for HDT specimens in Specification D 6394 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 humid
42、ity for aminimum of 40 hours prior to testing.X1.4 Several methods have been found useful for applyingthe 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 com
43、bination. In all applications the exposure time wasone minute. After the time requirement was met 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
44、modulus of the material being testedthe critical stress was calculated for inclusion in Tables 1-3.X1.6 The tabulated information in Tables 1-3 was gener-ated at room temperature with a one-minute exposure timeusing annealed flexural bars.D7474083ASTM International takes no position respecting the v
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47、uarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This stan
48、dard 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).D7474084
