ASTM D5045-2014 Standard Test Methods for Plane-Strain Fracture Toughness and Strain Energy Release Rate of Plastic Materials《塑料平面应变裂缝强度和应变能量释放速率的标准试验方法》.pdf

《ASTM D5045-2014 Standard Test Methods for Plane-Strain Fracture Toughness and Strain Energy Release Rate of Plastic Materials《塑料平面应变裂缝强度和应变能量释放速率的标准试验方法》.pdf》由会员分享，可在线阅读，更多相关《ASTM D5045-2014 Standard Test Methods for Plane-Strain Fracture Toughness and Strain Energy Release Rate of Plastic Materials《塑料平面应变裂缝强度和应变能量释放速率的标准试验方法》.pdf（10页珍藏版）》请在麦多课文档分享上搜索。

1、Designation: D5045 14Standard Test Methods forPlane-Strain Fracture Toughness and Strain Energy ReleaseRate of Plastic Materials1This standard is issued under the fixed designation D5045; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revis

2、ion, 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 These test methods are designed to characterize thetoughness of plastics in terms of the critical-st

3、ress-intensityfactor, KIc, and the energy per unit area of crack surface orcritical strain energy release rate, GIc, at fracture initiation.1.2 Two testing geometries are covered by these testmethods, single-edge-notch bending (SENB) and compacttension (CT).1.3 The scheme used assumes linear elastic

4、 behavior of thecracked specimen, so certain restrictions on linearity of theload-displacement diagram are imposed.1.4 A state-of-plane strain at the crack tip is required.Specimen thickness must be sufficient to ensure this stressstate.1.5 The crack must be sufficiently sharp to ensure that aminimu

5、m value of toughness is obtained.1.6 The significance of these test methods and many con-ditions of testing are identical to those of Test Method E399,and, therefore, in most cases, appear here with many similari-ties to the metals standard. However, certain conditions andspecifications not covered

6、in Test Method E399, but importantfor plastics, are included.1.7 This protocol covers the determination of GIcas well,which is of particular importance for plastics.1.8 These test methods give general information concerningthe requirements for KIcand GIctesting. As with Test MethodE399, two annexes

7、are provided which give the specificrequirements for testing of the SENB and CT geometries.1.9 Test data obtained by these test methods are relevant andappropriate for use in engineering design.1.10 This standard does not purport to address all of thesafety concerns, if any, associated with its use.

8、 It is 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.NOTE 1This standard and ISO 13586 address the same subject matter,but differ in technical content.2. Referenced Document

9、s2.1 ASTM Standards:2D638 Test Method for Tensile Properties of PlasticsD4000 Classification System for Specifying Plastic Materi-alsE399 Test Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic MaterialsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precis

10、ion of a Test Method3. Terminology3.1 Definitions:3.1.1 compact tension, nspecimen geometry consisting ofsingle-edge notched plate loaded in tension. See 3.1.5 forreference to additional definition.3.1.2 critical strain energy release rate, GIc,ntoughnessparameter based on energy required to fractur

11、e. See 3.1.5 forreference to additional definition.3.1.3 plane-strain fracture toughness, KIc,ntoughnessparameter indicative of the resistance of a material to fracture.See 3.1.5 for reference to additional definition.3.1.4 single-edge notched bend, nspecimen geometryconsisting of center-notched bea

12、m loaded in three-point bend-ing. See 3.1.5 for reference to additional definition.3.1.5 Reference is made to Test Method E399 for additionalexplanation of definitions.3.2 Definitions of Terms Specific to This Standard:3.2.1 yield stress, nstress at fracture is used. The slope ofthe stress-strain cu

13、rve is not required to be zero. See 7.2 forreference to additional definition.1These test methods are under the jurisdiction of ASTM Committee D20 onPlastics and is the direct responsibility of Subcommittee D20.10 on MechanicalProperties.Current edition approved Dec. 1, 2014. Published December 2014

14、. Originallyapproved in 1990. Last previous edition approved in 1999 as D5045 - 99(2007)1.DOI: 10.1520/D5045-14.2For 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

15、standards Document Summary page onthe ASTM website.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14. Summary of Test Methods4.1 These test methods involve loading a not

16、ched specimenthat has been pre-cracked, in either tension or three-pointbending. The load corresponding to a 2.5 % apparent incre-ment of crack extension is established by a specified deviationfrom the linear portion of the record. The KIcvalue iscalculated from this load by equations that have been

17、 estab-lished on the basis of elastic stress analysis on specimens of thetype described in the test methods. The validity of thedetermination of the KIcvalue by these test methods dependsupon the establishment of a sharp-crack condition at the tip ofthe crack, in a specimen of adequate size to give

18、linear elasticbehavior.4.2 A method for the determination of GIcis provided. Themethod requires determination of the energy derived fromintegration of the load versus load-point displacement diagram,while making a correction for indentation at the loading pointsas well as specimen compression and sy

19、stem compliance.5. Significance and Use5.1 The property KIc(GIc) determined by these test methodscharacterizes the resistance of a material to fracture in a neutralenvironment in the presence of a sharp crack under severetensile constraint, such that the state of stress near the crackfront approache

20、s plane strain, and the crack-tip plastic (ornon-linear viscoelastic) region is small compared with thecrack size and specimen dimensions in the constraint direction.A KIcvalue is believed to represent a lower limiting value offracture toughness. This value has been used to estimate therelation betw

21、een failure stress and defect size for a material inservice wherein the conditions of high constraint describedabove would be expected. Background information concerningthe basis for development of these test methods in terms oflinear elastic fracture mechanics can be found in Refs (1-5).35.1.1 The

22、KIc(GIc) value of a given material is a function oftesting speed and temperature. Furthermore, cyclic loads havebeen found to cause crack extension at K values less than KIc(GIc). Crack extension under cyclic or sustained load will beincreased by the presence of an aggressive environment.Therefore,

23、application of KIc(GIc) in the design of servicecomponents should be made considering differences that mayexist between laboratory tests and field conditions.5.1.2 Plane-strain fracture toughness testing is unusual inthat sometimes there is no advance assurance that a valid KIc(GIc) will be determin

24、ed in a particular test. Therefore it isessential that all of the criteria concerning validity of results becarefully considered as described herein.5.1.3 Clearly, it will not be possible to determine KIc(GIc)ifany dimension of the available stock of a material is insuffi-cient to provide a specimen

25、 of the required size.5.2 Inasmuch as the fracture toughness of plastics is oftendependent on specimen process history, that is, injectionmolded, extruded, compression molded, etc., the specimencrack orientation (parallel or perpendicular) relative to anyprocessing direction shall be noted on the re

26、port form dis-cussed in 10.1.5.3 Before proceeding with this test method, referenceshould be made to the specification of the material being tested.Any test specimen preparation, conditioning, dimensions, ortesting parameters, or combination thereof, covered in therelevant ASTM materials specificati

27、on shall take precedenceover those mentioned in this test method. If there are norelevant ASTM material specifications, then the default condi-tions apply.6. Apparatus6.1 Testing MachineA constant displacement-rate deviceshall be used such as an electromechanical, screw-drivenmachine, or a closed lo

28、op, feedback-controlled servohydraulicload frame. For SENB, a rig with either stationary or movingrollers of sufficiently large diameter to avoid excessive plasticindentation is required. A suitable arrangement for loading theSENB specimen is shown in Fig. 1. A loading clevis suitablefor loading com

29、pact tension specimens is shown in Fig. 2.Loading is by means of pins in the specimen holes (Fig. 3(b).6.2 Displacement MeasurementAn accurate displacementmeasurement must be obtained to assure accuracy of the GIcvalue.6.2.1 Internal Displacement TransducerFor either SENBor CT specimen configuration

30、s, the displacement measurementshall be performed using the machines stroke (position)transducer. The fracture-test-displacement data must be cor-rected for system compliance, loading-pin penetration (brinel-ling) and specimen compression by performing a calibration ofthe testing system as described

31、 in 9.2.6.2.2 External Displacement TransducerIf an internal dis-placement transducer is not available, or has insufficientprecision, then an externally applied displacement-measuringdevice shall be used as illustrated in Fig. 1 for the SENBconfiguration. For CT specimens, a clip gauge shall bemount

32、ed across the loading pins. For both the SENB and CTspecimens measure the displacement at the load point.3The boldface numbers in parentheses refer to the list of references at the end ofthese test methods. FIG. 1 Bending Rig with Transducer for SENBD5045 1427. Specimen Size, Configurations, and Pre

33、paration7.1 Specimen Size:7.1.1 SENB and CT geometries are recommended overother configurations because these have predominantly bend-ing stress states which allow smaller specimen sizes to achieveplane strain. Specimen dimensions are shown in Fig. 3 (a, b).If the material is supplied in the form of

34、 a sheet, the specimenthickness, B, is identical with the sheet thickness, in order tomaximize this dimension. The specimen width, W,isW =2B.In both geometries the crack length, a, shall be selected suchthat 0.45 1.1, the test is invalid.9.1.2 Calculate KQin accordance with the procedure givenin A1.

35、4 for SENB and A2.5 for CT. For this calculation, avalue of a, which is the total crack length after both notchingand pre-cracking, but before fracture, is best determined fromthe fracture surface after testing. An average value is used, butthe difference between the shortest and longest length shou

36、ldnot exceed 10 %. Take care that it is the original crack whichis being observed, since slow growth can occur prior tocatastrophic fast fracture.9.1.3 Check the validity of KQvia the size criteria. Calculate2.5 (KQ/y)2where yis the yield stress discussed in 7.2.1.Ifthis quantity is less than the sp

37、ecimen thickness, B, the cracklength, a, and the ligament (Wa), KQis equal to KIc.Otherwise the test is not a valid KIctest.NOTE 4Note that use of a specimen with too small a thickness, B, willresult in KQbeing higher than the true KIcvalue while a small (Wa)will result in a KQvalue that is lower th

38、an the true KIcvalue. The net effectmay be close to the correct KIcbut unfortunately in an unpredictable way,since the dependence on B cannot be quantified.9.1.4 For the recommended specimen dimensions of W=2B and a/W = 0.5, all the relationships of 9.1.3 are satisfiedsimultaneously. In fact, the cr

39、iterion covers two limitations inthat B must be sufficient to ensure plane strain, but (Wa) hasto be sufficient to avoid excessive plasticity in the ligament. If(Wa) is too small the test will often violate the linearitycriteria. If the linearity criterion is violated, a possible option isto increas

40、e W for the same a/W and S/W ratios. Values of W/Bof up to 4 are permitted.9.1.5 If the test result fails to meet the requirements in either9.1.1 or 9.1.3, or both, it will be necessary to use a largerspecimen to determine KQ. The dimensions of the largerspecimen can be estimated on the basis of KQ,

41、 but generallymust be increased to 1.5 times those of the specimen that failedto produce a valid KIcvalue.9.2 Displacement Correction for Calculation of GQMakea displacement correction for system compliance, loading-pinpenetration, and specimen compression, then calculate GIcfrom the energy derived

42、from integration of the load versusload-point displacement curve.9.2.1 The procedure for obtaining the correcteddisplacement, uc(P), at load P from the measureddisplacement, uQ(P), is as follows: Use an un-cracked dis-placement correction specimen prepared from the same mate-rial as that being teste

43、d (refer to 7.3.3). Using the same testingparameters as the actual test, load the specimen to a point at orabove the fracture loads observed during actual testing. Fromthe load-displacement curve, determine ui(P). The correcteddisplacement is then calculated using uc(P)=uQ(P)ui(P) forboth the SENB a

44、nd CT geometries.9.2.2 In practice, it is common to obtain a linear displace-ment correction curve (up to the fracture loads observed duringactual testing). This simplifies the displacement correction tobe applied to the fracture test. Initial non-linearity due topenetration of the loading pins into

45、 the specimen should occurduring both the calibration test and the actual fracture test.Linearization of the near-zero correction data and the fracturetest data can compensate for this initial non-linearity.9.2.3 The displacement correction must be performed foreach material and at each test tempera

46、ture or rate. Polymers aregenerally temperature- and rate-sensitive and the degree ofloading-pin penetration and sample compression have beenfound to vary with changes in these variables.9.2.4 Perform indentation tests in such a way that theloading times are the same as the fracture tests. Since the

47、indentations are stiffer, this will involve lower rates to reach thesame loads.9.3 Calculation of GQIn principle, GIccan be obtainedfrom the following:GIc51 2 2!KIc2E(2)but for plastics, E must be obtained at the same time andtemperature conditions as the fracture test because of vis-coelastic effec

48、ts. Many uncertainties are introduced by thisprocedure and it is considered preferable to determine GIcdirectly from the energy derived from integration of the loadversus displacement curve up to the same load point as used forKIcand shown in Fig. 6(a, b).9.3.1 The energy must be corrected for syste

49、m compliance,loading-pin penetration, and specimen compression. This isdone by correcting the measured displacement values, asshown in Fig. 6(a, b). Accordingly, if complete linearity isobtained, one form of the integration for energy is as U =12PQuQ ui, where PQis defined in 9.1.1.NOTE 1C is the inverse slope of line AB.FIG. 5 Determination of C and PQD5045 1459.3.2 Alternatively, it is possible to use the integrated areasfrom the measured curve, UQ,ofFig. 6(a) and indentationcurves, Ui,ofFig. 6(b) in accordance with the following:U 5 UQ2 Ui(3)9.3.3 Ca