1、Designation: D7474 17Standard 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, health and environmental practices and deter-min
7、e the applicability of regulatory limitations prior to use.1.5 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
8、issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D543 Practices for Evaluating the Resistance of Plastics toChemical ReagentsD618 Practice for Conditioning Plastics for TestingD883 Terminology Relating to PlasticsD4000 Class
9、ification System for Specifying Plastic Materi-alsD6394 Specification for Sulfone Plastics (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 t
10、o plastics used in this practice, see Terminology D883.4. Summary of Practice4.1 The practice 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 othe
11、rwise constantconditions including a fixed time of one minute. Thus, theexposure of finished 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 presenc
12、e or absence ofcrazing, this practice only yields an approximate indication ofthe level of residual stresses in the parts. This practiceestimates the relative magnitude of residual stresses in parts1This practice is under the jurisdiction ofASTM Committee D20 on Plastics andis the direct responsibil
13、ity of Subcommittee D20.15 on Thermoplastic Materials.Current edition approved Aug. 15, 2017. Published August 2017. Originallyapproved in 2008. Last previous edition approved in 2012 as D7474 - 12.DOI:10.1520/D7474-17.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact A
14、STM 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.org.*A Summary of C
15、hanges section appears at the end of this standardCopyright 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
16、Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1produced from the series of sulfone plastics, namely polysul-fone (PSU), polyethersulfone (PESU), and polyphenylsulfone
17、(PPSU) materials.5. Significance and Use5.1 Thermoplastic moldings contain 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 w
18、ell as part failures are affected by the level ofresidual stress present in a part. 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 sulfoneplasti
19、cs (SP), namely polysulfone (PSU), polyethersulfone(PESU), and polyphenylsulfone (PPSU) materials.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 practiceis not recommen
20、ded 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 stresses cannot be easily
21、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 immersion in one ormore ch
22、emical reagents to evaluate whether or not crackingoccurs. Stresses will relax after molding or extrusion.Accordingly, both immersion in the test medium and visualexamination must be made at identical times and conditionsafter processing, if comparing parts. It is important to note thedifferences in
23、 part history. Thus, this technique is suitable as anindication 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).6.2 Cotton swaps, patches
24、 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 Use protective equipment and clothing to avoid contacto
25、f chemical reagents with the skin or eyes. Use adequateventilation 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 the stresses being observed. Avoidtwi
26、sting and breaking when separating cut pieces because 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 conditioning is utilized for a controlledTABLE 1 Li
27、quid Reagents for Residual Stress Test for PSUMixtureMixture CompositionCritical Stress, MPa (psi)% by volume Ethanol % 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 CompositionC
28、ritical 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 Residual Stress Test for PPSUMixtureMixture CompositionCritical Stress, MPa (psi)% by volume Ethanol % by volume MEK1 50 50 22.8 (3300)2 25
29、 75 13.8 (2000)3 10 90 9.0 (1300)4 0 100 8.0 (1150)D7474 172study in a series of parts, then condition the test specimens inaccordance with Procedure A of Practice D618 for a minimumof 4 h before performing the test.10.2 Test ConditionsConduct tests in the standard labora-tory atmosphere of 23 6 2C
30、(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 molding decrease with timeafter fabrication. For some studies, it is necessary to test assoon as possible after molding. In such cases, allow th
31、e part tocool before testing.11. Procedure11.1 Choose the appropriate table from Tables 1-3, whichlist the series of chemical reagents to be used for SP parts madefrom PSU, PESU and PPSU, respectively. Ensure that therequired reagents are available.11.2 Rinse the specimen with isopropyl alcohol and
32、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 compressed air on the surface as needed.11.3 I
33、nspect the part for cracked or crazed regions.NOTE 2Hairline fractures are often difficult to see.11.4 If the part is crazed, the residual stress is greater thanthe critical stress value indicated for that reagent in the Tableand is reported as being greater than that stress value. If thepart is not
34、 crazed, the residual stress is less than the criticalstress value indicated, and the test is continued with the nextliquid 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
35、 crazing. If 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
36、the last reagent, 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 reag
37、ents must befresh. 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 leve
38、ls depend on 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 acc
39、eptablemolded-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
40、 than one minute 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 com
41、plete,12.1.3 Time between molding or extrusion of parts andinitial immersion,12.1.4 Conditioning,12.1.5 Liquid reagents used,12.1.6 Estimated range of residual stress for the specimentested,12.1.7 Date of test, and12.1.8 Test practice number and published/revision date.13. Keywords13.1 liquid reagen
42、t; PESU; PPSU; PSU; residual stress; 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 descr
43、ibed 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, 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 a
44、t known stress levels. ASTMflexural bar specimens were annealed for 1 hour at tempera-tures specified for HDT specimens in Specification D6394 toremove any stresses other than caused later by flexural strainduring the ISO 22088-3 test.X1.3 The parts being tested were conditioned in accordancewith Pr
45、ocedure A of Practice D618 for a minimum of 40 hoursprior 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 onD7474 173the surface of the specimen and then soak
46、ed with the solventcombination. In all applications the exposure time was oneminute. After the time requirement was met the patches wereremoved 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 cr
47、itical strain and the 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 generatedat room temperature, as defined in 3.1.1 of Practice D618, witha one-minute exposure time using annealed flexural bars.SU
48、MMARY OF CHANGESCommittee D20 has identified the location of selected changes to this standard since the last issue (D7474 - 12)that may impact the use of this standard. (August 15, 2017)(1) Conditioning section (10.1) changed to agree with condi-tioning requirements in D6394, Standard Specifcation
49、forSulfone Plastics (SP).(2) Clarified reporting (11.4) when specimens do not fail at thegreatest stress level.(3) Clarified X1.3 on how specimens were conditioned duringcalibration.(4) Revised X1.6 to define “room temperature”.(5) Editorial changes were made in 8.1, 9.1, 11.1, Note 2, andX1.4.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 of the validity of any such patent rights, and the ris
