1、Designation: D 5045 99 (Reapproved 2007)e1Standard Test Methods forPlane-Strain Fracture Toughness and Strain Energy ReleaseRate of Plastic Materials1This standard is issued under the fixed designation D 5045; the number immediately following the designation indicates the year oforiginal adoption or
2、, in the case of revision, the 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.e1NOTEReapproved with editorial changes in March 20071. Scope*1.1 These test methods are d
3、esigned to characterize thetoughness of plastics in terms of the critical-stress-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 test meth-ods, single-edge-notch ben
4、ding (SENB) and compact tension(CT).1.3 The scheme used assumes linear elastic 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 th
5、is stressstate.1.5 The crack must be sufficiently sharp to ensure that aminimum 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 E 399,and, therefore, in most cases, appear here with many similari-ties to
6、the metals standard. However, certain conditions andspecifications not covered in Test Method E 399, 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 concern
7、ingthe requirements for KIcand GIctesting. As with Test MethodE 399, two annexes 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 n
8、ot 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 regulatory limitations prior to use.NOTE 1There is currently no ISO standar
9、d that duplicates these testmethods. Pending ISO/CD 13586 covers similar testing and referencesthis test method for testing conditions.2. Referenced Documents2.1 ASTM Standards:2D 638 Test Method for Tensile Properties of PlasticsD 4000 Classification System for Specifying Plastic Mate-rialsE 399 Te
10、st Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic MaterialsE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 Definitions:3.1.1 compact tension, nspecimen geometry consisting ofsingle-edge notched plate loaded i
11、n tension. See 3.1.5 forreference to additional definition.3.1.2 critical strain energy release rate, GIc, ntoughnessparameter based on energy required to fracture. See 3.1.5 forreference to additional definition.3.1.3 plane-strain fracture toughness, KIc, ntoughnessparameter indicative of the resis
12、tance 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 beam loaded in three-point bend-ing. See 3.1.5 for reference to additional definition.3.1.5 Reference is made to Test Method E 399 for addit
13、ionalexplanation of definitions.3.2 Definitions of Terms Specific to This Standard: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 March 1, 2007. Published June 20
14、07. Originallyapproved in 1990. Last previous edition approved in 1999 as D 5045 - 99.2For 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
15、 page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.1 yield stress, nstress at fracture is used. The slope ofthe stress-strain curve is not re
16、quired to be zero. See 7.2 forreference to additional definition.4. Summary of Test Methods4.1 These test methods involve loading a notched 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 establis
17、hed by a specified deviationfrom the linear portion of the record. The KIcvalue iscalculated from this load by equations that have been 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 thes
18、e test methods dependsupon the establishment of a sharp-crack condition at the tip ofthe crack, in a specimen of adequate size to give linear elasticbehavior.4.2 A method for the determination of GIcis provided. Themethod requires determination of the energy derived fromintegration of the load versu
19、s load-point displacement diagram,while making a correction for indentation at the loading pointsas well as specimen compression and system compliance.5. Significance and Use5.1 The property KIc(GIc) determined by these test methodscharacterizes the resistance of a material to fracture in a neutrale
20、nvironment in the presence of a sharp crack under severetensile constraint, such that the state of stress near the crackfront approaches plane strain, and the crack-tip plastic (ornon-linear viscoelastic) region is small compared with thecrack size and specimen dimensions in the constraint direction
21、.A KIcvalue is believed to represent a lower limiting value offracture toughness. This value may be used to estimate therelation between failure stress and defect size for a material inservice wherein the conditions of high constraint describedabove would be expected. Background information concerni
22、ngthe basis for development of these test methods in terms oflinear elastic fracture mechanics can be found in Refs (1-5).35.1.1 The KIc(GIc) value of a given material is a function oftesting speed and temperature. Furthermore, cyclic loads cancause crack extension at K values less than KIc(GIc). Cr
23、ackextension under cyclic or sustained load will be increased bythe presence of an aggressive environment. Therefore, appli-cation of KIc(GIc) in the design of service components shouldbe made considering differences that may exist betweenlaboratory tests and field conditions.5.1.2 Plane-strain frac
24、ture toughness testing is unusual inthat there can be no advance assurance that a valid KIc(GIc)will be determined in a particular test. Therefore it is essentialthat all of the criteria concerning validity of results be carefullyconsidered as described herein.5.1.3 Clearly, it will not be possible
25、to determine KIc(GIc)ifany dimension of the available stock of a material is insuffi-cient to provide a specimen 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 sp
26、ecimencrack orientation (parallel or perpendicular) relative to anyprocessing direction should be noted on the report formdiscussed in 10.1.5.3 For many materials, there may be a specification thatrequires the use of these test methods, but with some proce-dural modifications that take precedence wh
27、en adhering to thespecification. Therefore, it is advisable to refer to that materialspecification before using these test methods. Table 1 ofClassification System D 4000 lists the ASTM materials stan-dards that currently exist.6. Apparatus6.1 Testing MachineA constant displacement-rate deviceshall
28、be used such as an electromechanical, screw-drivenmachine, or a closed loop, 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 theS
29、ENB specimen is that shown in Fig. 1. A loading clevissuitable for loading compact tension specimens is shown inFig. 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.
30、1 Internal Displacement Transducer For either SENBor CT specimen configurations, 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 spec
31、imen compression by performing a calibration ofthe testing system as described in 9.2.6.2.2 External Displacement Transducer If an internaldisplacement transducer is not available, or has insufficientprecision, then an externally applied displacement-measuringdevice shall be used as illustrated in F
32、ig. 1 for the SENBconfiguration. For CT specimens, a clip gauge shall be3The boldface numbers in parentheses refer to the list of references at the end ofthese test methods. FIG. 1 Bending Rig with Transducer for SENBD 5045 99 (2007)e12mounted across the loading pins. For both the SENB and CTspecime
33、ns, the displacement should be taken at the load point.7. Specimen Size, Configurations, and Preparation7.1 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 s
34、train. Specimen dimensions are shown in Fig. 3 (a, b).If the material is supplied in the form of a sheet, the specimenthickness, B, should be identical with the sheet thickness, inorder to maximize this dimension. The specimen width, W,isW =2B. In both geometries the crack length, a, should beselect
35、ed such that 0.45 1.1, the test isinvalid.9.1.2 Calculate KQin accordance with the procedure giveninA1.4 for SENB andA2.5 for CT. For this calculation, a valueof a, which is the total crack length after both notching andpre-cracking, but before fracture, is best determined from thefracture surface a
36、fter testing. An average value is used, but thedifference between the shortest and longest length should notexceed 10 %. Take care that it is the original crack which isbeing observed, since slow growth can occur prior to cata-strophic fast fracture.9.1.3 Check the validity of KQvia the size criteri
37、a. Calculate2.5 ( KQ/sy)2where syis the yield stress discussed in 7.2.1.Ifthis quantity is less than the specimen 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, will
38、result in KQbeing higher than the true KIcvalue while a small (Wa) willresult in a KQvalue that is lower than 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 di
39、mensions of W=2B and a/W = 0.5, all the relationships of 9.1.3 are satisfiedsimultaneously. In fact, the criterion 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
40、often violate the linearitycriteria. If the linearity criterion is violated, a possible option isto increase 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
41、a largerspecimen to determine KQ. The dimensions of the largerspecimen can be estimated on the basis of KQ, 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 syst
42、em compliance, loading-pinpenetration, and specimen compression, then calculate GIcfrom the energy derived from integration of the load versusload-point displacement curve.9.2.1 The procedure for obtaining the corrected displace-ment, uc(P), at load P from the measured displacement, uQ(P),is as foll
43、ows: Use an un-cracked displacement correctionspecimen prepared from the same material as that being tested(refer to 7.3.3). Using the same testing parameters as the actualtest, load the specimen to a point at or above the fracture loadsobserved during actual testing. From the load-displacementcurve
44、, determine ui(P). The corrected displacement is thencalculated using uc(P)=uQ(P)ui(P) for both the SENB andCT 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 corre
45、ction tobe applied to the fracture test. Initial non-linearity due topenetration of the loading pins into 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 no
46、n-linearity.9.2.3 The displacement correction must be performed foreach material and at each test temperature or rate. Polymers aregenerally temperature- and rate-sensitive and the degree ofloading-pin penetration and sample compression can vary withchanges in these variables.9.2.4 The indentation t
47、ests should be performed in such away that the loading times are the same as the fracture tests.Since the indentations are stiffer, this will involve lower ratesto reach the same loads.9.3 Calculation of GQIn principle, GIccan be obtainedfrom the following:GIc51 2n2!KIc2E(2)but for plastics, E must
48、be obtained at the same time andtemperature conditions as the fracture test because of vis-coelastic effects. 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 t
49、o the same load point as used forKIcand shown in Fig. 6(a, b).9.3.1 The energy must be corrected for system 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 9.1.1.9.3.2 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:NOT
