1、Designation: D 6746 03Standard Test Method forRaw Rubber or Unvulcanized CompoundsDeterminationof Tensile Green Strength1This standard is issued under the fixed designation D 6746; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, th
2、e 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 method to evaluate acharacteristic of raw rubber or unvulcanized rubber com-po
3、unds, or both, that is designated as tensile green strength.This special strength property for uncured rubbers is animportant processing performance attribute in rubber productmanufacturing.1.2 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It i
4、s theresponsibility of the user of this standard 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:2D 412 Test Methods for Vulcanized Rubber and Thermo-plastic ElastomersTensionD 134
5、9 Practice for RubberStandard Temperatures forTestingD 3182 Practice for RubberMaterials, Equipment, andProcedures for Mixing Standard Compounds and Prepar-ing Standard Vulcanized Sheets3. Terminology3.1 Definitions:3.1.1 green strength, na characteristic property of a rawor unvulcanized rubber comp
6、ound that indicates the capabilityof retaining mechanical or structural integrity when the rubberis subjected to deformation of any type.3.1.1.1 DiscussionThe word “green” is a synonym foruncured or unvulcanized.3.1.2 tensile green strength, ngreen strength of a raw orunvulcanized rubber compound th
7、at is evaluated by the appli-cation of tensile stress or strain.4. Summary of Test Method4.1 The tensile stress-strain characteristics of a dumbbell oranother recommended test piece of raw or unvulcanizedcompounded rubber are determined on a tensile testing ma-chine capable of maintaining a constant
8、 rate of separation ofthe moving jaws.4.2 In evaluating tensile green strength, several types ofstress-strain behavior may be observed, depending on therubber and the composition of the unvulcanized compound.(See Section 5.) Fig. 1 indicates three typical stress-straincurves. Type 1 has a yield poin
9、t and exhibits elongational flowbeyond the yield point, culminating in rupture at a higher stressand elongation compared to the initial yield stress. Type 2 alsohas a yield point, but beyond this point follows a decreasingstress behavior as the maximum rupture elongation is attained.Type 3 has a str
10、ess-strain curve that is similar to cured rubbers,with no yield or elongation beyond the point of rupture atmaximum stress.5. Significance and Use5.1 The stress-strain properties of unvulcanized rubber (ei-ther a prepared mix or in the raw state) are important to certainprocessing operations in the
11、rubber industry. These unvulca-nized rubber properties are frequently referred to as “tensilegreen strength,” denoting that the final vulcanization cycle hasnot yet been achieved.5.2 Tensile green strength is determined primarily by thephysical and chemical characteristics of polymers, such asmolecu
12、lar weight, tendency to crystallize, degree of branching,and so forth. It is also related to the compound formulation,particularly filler and plasticizer content, and the presence ofpeptizers. Tensile green strength can be a good indication ofprocessing behavior. It is a particularly important chara
13、cteristicfor all processing operations in which elongation predomi-nates.1This test method is under the jurisdiction of ASTM Committee D11 on Rubberand is the direct responsibility of Subcommittee D11.12 on Processability Tests.Current edition approved Dec. 1, 2003. Published January 2004. Originall
14、yapproved in 2002. Last previous edition approved in 2002 as D 674602a.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 AST
15、M website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.FIG. 1 Typical Tensile Stress-Strain CurvesD67460325.3 Tensile green strength is dependent on the test piecepreparation, rate of extension, and test temperature. Therefore,a s
16、ingle-point method cannot be expected to give correlationbetween tensile green strength and processing behavior overthe whole range of processing conditions.6. Interferences6.1 For reliable test results, it is important that test speci-mens are of accurate dimensions and are free of air inclusions,b
17、listers, and contaminants.6.2 A defective cutting die or slippage of the test specimenin the clamps may cause incorrect results.6.3 Exposure to excessive ultraviolet radiation or chemicalvapors may also affect the results.7. Apparatus7.1 Tensile Testing MachineThe tensile testing machineshall be in
18、accordance with the requirements of Test MethodsD 412. It shall be capable of maintaining a constant rate ofseparation of the jaws at 100 6 10 mm/min or, for specialcases, at a value within the range of 20 to 1000 mm/min. Itshould have means to test the force on the test piece and theelongation by t
19、he distance between the gauge marks on thedumbbell. It should be capable of recording the force/elongation curve obtained during the test. If using an automaticextensometer, a non-contacting type of extensometer is pre-ferred.7.2 MoldThe mold shall meet the requirements of Prac-tice D 3182.8. Hazard
20、s8.1 There are no hazards inherent to the techniques de-scribed. Caution should be exercised and the user should beaware of any possible pinch points.8.2 Normal safety precautions, including the use of personalprotective equipment and good laboratory practice, should beobserved when using any equipm
21、ent. This is especially truewhen performing tests at elevated temperatures.9. Test Specimen9.1 The preferred test specimen is the dumbbell Die Cspecimen in accordance with Test Methods D 412. Other typesof test specimens may also be used. Since surface conditionscan affect the results, there may be
22、cases where a widerspecimen would be preferred, such as Die A from Test MethodsD 412.9.2 Since different types of test specimens do not necessar-ily give the same values, comparison of results from differentspecimen types should be avoided.10. Preparation10.1 Raw rubber and unvulcanized compounds sh
23、all besheeted out to approximately 2.5-mm thickness and placed inthe mold with the grain direction oriented so as to have thegrain direction parallel with the length of the dumbbells. It isalso permissible to test against the grain, but this must be notedin the report section. (See Section 15.) Only
24、 fresh stock shall beused.10.2 Polyester film (0.05-mm thickness) shall be placedbetween the mold walls and the rubber in order to promotemold release. The sample shall be compressed for 5 6 1 minat 100 6 2C under a minimum of 2.5 MPa platen pressure,allowed to cool to laboratory temperature for 30
25、6 2 min underadequate pressure to keep test specimen flat, then removed.The cooling shall be done out of the press using roomtemperature metal plates.10.3 For some raw rubbers, longer times or higher tempera-tures may be necessary in order to obtain a smooth sheet freefrom porosity. For some compoun
26、ds, a lower temperature maybe necessary when there is a danger of scorch at the preferredtemperature.10.4 A sample may also be acquired during processing bysheeting off a mill, calender, or by extrusion and then cut witha die. Special care should be taken to ensure that the sample isfree of trapped
27、air.10.5 Cut three test specimens from the sheet, using asuitable die. (See 9.1.)11. Calibration and Standardization11.1 The tensile testing machine shall be calibrated accord-ing to the procedure in Test Methods D 412.12. Conditioning12.1 The test specimens shall be conditioned at a tempera-ture of
28、 23 6 2C for at least 16 h and not more than 24 h beforetesting.12.2 Some slow crystallizing polymers, such as polychlo-roprene, may need a longer conditioning period in order toaccurately measure the maximum green strength.13. Procedure13.1 Place the dumbbell in the grips of the testing machinein a
29、ccordance with the procedure in Test Methods D 412.Adjust the rate of displacement of the moving jaw to 100 6 10mm/min and start the tensile test. If the sample breaks at thegrips, that result shall be discarded and a retest carried out.13.1.1 The preferred rate of separation of the jaws is 100 610
30、mm/min. In special cases, other rates may be used, but onlytests carried out at the same rate can be compared. Rollover orself-tightening grips may help prevent slippage.13.2 The test shall be carried out on three test specimens. Ifthe standard deviation is greater than 20 % of the mean value,then f
31、ive specimens should be tested.13.3 Unless otherwise specified, the standard test tempera-ture shall be 23 6 2C.13.4 When it is necessary to test at other temperatures, useone of the standard temperatures listed in Practice D 1349.Specimens shall be conditioned at these test temperatures for15 6 2 m
32、in prior to testing.14. Calculation or Interpretation of Results14.1 Using the typical stress-strain curves given in Fig. 1,determine the yield stress or maximum stress in MPa. Otherparameters may be determined, such as yield elongation (E1)orthe stress at a definite reference elongation correspondi
33、ng tothe deformation entailed by a subsequent processing operation.The median value is the preferred value to report.D674603314.2 Calculate the tensile stress at any specified elongationas follows:Txxx!5 Fxxx!/A (1)where:T(xxx)= tensile stress at (xxx) % elongation, MPa,F(xxx)= force at specified el
34、ongation, MN, andA = cross-sectional area of unstrained specimen, m2.14.3 Calculate the yield stress as follows:Ystress!5 Fy!/A (2)where:Y(stress)= yield stress, that stress level where the yieldpoint occurs, MPa,F(y)= magnitude of force at the yield point, MN, andA = cross-sectional area of unstrai
35、ned specimen,m2.14.4 Evaluate the yield strain as that strain or elongationmagnitude, where the rate of change of stress with respect tostrain goes through a zero value.14.5 Calculate the elongation (at any degree of extension) asfollows:E 5 100L Lo!#/Lo!(3)where:E = the elongation in percent (of or
36、iginal bench markdistance),L = observed distance between bench marks on theextended specimen, andL(o)= original distance between bench marks (use sameunits for L and L(o).14.6 The maximum elongation is evaluated when L is equalto the distance between benchmarks at the point of specimenrupture.15. Re
37、port15.1 Report the following information:15.1.1 Full description of the sample and its origin,15.1.2 Method of preparation of the test specimen, that is,time and temperature of molding, if not at standard conditions,15.1.3 Type and dimensions of test specimen, if not a Die Cdumbbell,15.1.4 Grain di
38、rection, if not at the standard condition oftesting with the grain,15.1.5 Date of test,15.1.6 Rate of extension, if not at standard conditions,15.1.7 Temperature and humidity of test room, if not atstandard conditions,15.1.8 Time of conditioning,15.1.9 Temperature of test if at other than 23 6 2C,15
39、.1.10 Number of test specimens tested if not three, and15.1.11 Median of all results (yield stress, maximum stress,yield elongation, maximum elongation).16. Precision and Bias16.1 IntroductionThe interlaboratory test program (ITP)for precision evaluation for both yield stress and yield strainwas con
40、ducted in 2003 using the precision procedures andguidelines as described in the newly revised version of TestMethod D4483 (scheduled for publication in 2004) whichreplaces the previous version of Test Method D4483. Refer tothe new Test Method D4483 for additional background onprecision terminology.1
41、6.2 The precision results as determined by this ITP maynot be applied to acceptance or rejection testing for any groupof materials or products without documentation that the resultsof this precision evaluation actually apply to the products ormaterials tested.16.3 Four rubbers (compounds) were used
42、in the ITP;EPDM, NR, SBR and NBR. Four laboratories participated inthe testing program. Mixed compounds of each rubber weresent to the participating laboratories and in each laboratoryeach compound was milled, test sheets molded and testspecimens cut for testing. This procedure is essentially equiva
43、-lent to a Type 2 precision where a complete set of operationalsteps are required to generate a test specimen. A full orcomplete Type 2 precision would require that each laboratorymix each compound and conduct the other remaining prepara-tion steps. Thus the precision as evaluated is designated as a
44、modified Type 2 precision. See Test Method D4483, sec 5.1.5for more on Type 1 vs Type 2 precision.16.4 The testing was conducted on a test day 1 vs test day2 basis, one day apart. On each test day milling, molding andspecimen cutting were conducted as well as stress-straintesting. As stipulated in t
45、he method, three specimens weretested on each day and the mean was used as a test result. Allanalysis was conducted using test results. Due to the smallnumber of participating laboratories, Test Method D4483precision analysis Option 2 was used to respond to outliers asdetected by the h and k analysi
46、s operations. Option 2 usesoutlier replacement rather than outlier deletion which reducesthe degrees of freedom for precision evaluation. See Sections 7and 8, 9 and 10 of Test Method D4483 for more details onoutlier detection and on the AOT outlier replacement opera-tions.16.5 Precision ResultsThe p
47、recision results for both yieldstress and yield strain are given in Table 1 on the basis ofascending order of the mean test result value. General state-ments for the use of the precision results are cited below. Theseare given in terms of both the absolute precision, r or R andalso for relative prec
48、ision ( r ) and ( R ).16.5.1 RepeatabilityThe repeatability, or local domainprecision, for each material or rubber for each of the testmethods has been established by the values found in Table 1.Two individual test results (obtained by the proper use of thisstandard) that differ by more than the tab
49、ulated values for r ,inmeasurement units and ( r ), in percent, shall be considered assuspect, for example, to have come from different populations.Such a decision suggests that some appropriate investigativeaction be taken.16.5.2 RepeatabilityThe reproducibility, or global domainprecision, for each material or rubber for each of the testmethods has been established by the values found in Table 1.Two individual test results obtained in different laboratories (by the proper use of this standard) that differ by more than thetabulated values forR,inmeasurement
