1、Designation: D6068 10Standard Test Method forDetermining J-R Curves of Plastic Materials1This standard is issued under the fixed designation D6068; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number
2、 in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of theJ-integral versus crack growth resistance (J-R) curves forpolymeric materials.1.2 This test m
3、ethod is intended to characterize the slow,stable crack growth resistance of bend-type specimens in sucha manner that it is geometry insensitive within limits set forthin this test method.1.3 The recommended specimens are the three-point bend(SE (B) and pin-loaded compact tension (C (T) specimens.Bo
4、th specimens have in-plane dimensions of constant propor-tionality for all sizes. Specimen configurations other than thoserecommended in this test method may require different proce-dures and validity requirements.1.4 This test method describes a multiple specimen methodthat requires optical measure
5、ment of crack extension fromfracture surfaces. It is not recommended for use with materialsin which the crack front cannot be distinguished from addi-tional deformation processes in advance of the crack tip.1.5 The values stated in SI units are to be regarded as thestandard.1.6 This standard does no
6、t 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 no equivalent ISO standar
7、d.2. Referenced Documents2.1 ASTM Standards:2D618 Practice for Conditioning Plastics for TestingD4066 Classification System for Nylon Injection and Ex-trusion Materials (PA)D5045 Test Methods for Plane-Strain Fracture Toughnessand Strain Energy Release Rate of Plastic MaterialsE399 Test Method for L
8、inear-Elastic Plane-Strain FractureToughness KIcof Metallic MaterialsE616 Terminology Relating to Fracture Testing (Discontin-ued 1996)3E1152 Test Method for Determining-J-R-CurvesE1737 Test Method for J-Integral Characterization of Frac-ture Toughness (Discontinued 1998)3F1473 Test Method for Notch
9、 Tensile Test to Measure theResistance to Slow Crack Growth of Polyethylene Pipesand Resins3. Terminology3.1 DefinitionsTerminology related to fracture testingcontained in Terminology E616 is applicable to this testmethod.3.2 Definitions of Terms Specific to This Standard:3.2.1 J-integral, J (FL1)a
10、mathematical expression, aline or surface integral over a path that encloses the crack frontfrom one crack surface to the other, used to characterize thelocal stress-strain field around the crack front. See TerminologyE616 for additional discussion.3.2.2 J-R curvea plot of resistance to stable physi
11、cal crackextension, Dap.3.2.3 net thickness, BN(L)the distance between the rootsof the side grooves in side grooved specimens.3.2.4 original crack size, a0(L)the physical crack size atthe start of testing.3.2.5 original uncracked ligament, b0(L)the distancefrom the original crack front to the back e
12、dge of the specimen(b0= Wa80).3.2.6 physical crack extension, Dap(L)an increase inphysical crack size (Dap=apa0).3.2.7 physical crack size, ap(L)the distance from areference line to the observed crack front. The distance may bea calculated average of several measurements along the crackfront. The re
13、ference line depends on the specimen geometryand is normally defined as in 3.2.10. The reference line isdefined prior to specimen deformation.3.2.8 specimen span, S(L)the distance between specimensupports for the SE (B) specimen.3.2.9 specimen thickness, B(L)the side-to-side dimensionof the test spe
14、cimen (shown in Fig. 2).1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.10 on Mechanical Properties.Current edition approved July 1, 2010. Published July 2010. Originally approvedin 1996. Last previous edition approved
15、 in 2002 as D6068 - 96(2002)1. DOI:10.1520/D6068-10.2For 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 ASTM website.3Withdraw
16、n. The last approved version of this historical standard is referencedon www.astm.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.10 specimen width, W(L)a physical dimension on atest specimen measured from the rear surface of
17、 the specimento a reference line (for example, the front edge of a bendspecimen or the load line of a compact specimen).4. Summary of Test Method4.1 This test method describes a multiple specimen tech-nique for determining the J-R curve for polymeric materials.The J-R curve consists of a plot of J v
18、ersus crack extension inthe region of J-controlled growth as determined by the dataqualification requirement of 9.2.4.2 This test method uses optical measurements of cracklength and crack extension on the fracture surfaces after eachtest.5. Significance and Use5.1 A J-R curve produced in accordance
19、with this testmethod characterizes the crack growth resistances of a widerange of tough polymers and polymer blends (1-5)4that cannotbe obtained in sufficient size and thickness for valid character-ization by linear elastic fracture mechanics in Test MethodsD5045.5.2 The J-R curve characterizes, wit
20、hin the limits set forth inthis test method, the resistance of a polymeric material to slowstable crack growth after initiation from a preexisting sharpflaw.5.3 A J-R curve can be used as an index of materialtoughness for blend or alloy design, material selection, mate-rials processing, and quality
21、assurance (6).5.4 The J-R curves from bend specimens represent lowerbound estimates of J capacity as a function of crack extension,and have been observed to be conservative relative to thoseobtained from specimen configurations under tensile loading.5.5 The J-R curves for a given material of constan
22、t micro-structure tend to exhibit lower slope (flatter) with increasingthickness. Thus, it is recommended that the largest possiblespecimen with representative microstructure be used.5.6 The J-R curve can be used to assess the stability ofcracks in structures in the presence of ductile tearing, with
23、awareness of the differences that may exist between laboratorytest and field conditions.5.7 A J-R curve may depend on the orientation and propa-gation of the crack in relation to the anisotropy of the materialwhich may be induced by specimen fabrication methods.5.8 Because of the possibility of rate
24、 dependence of crackgrowth resistance, J-R curves can be determined at displace-ment rates other than that specified in this test method (7).6. Apparatus6.1 Measurements of applied load and load-line displace-ment are needed to obtain the total energy absorbed by thespecimen. Load versus load-line d
25、isplacement may be recordeddigitally or autographically.6.2 Testing MachineThe J-integral tests are to be con-ducted under displacement control to maximize the attainableamount of stable crack extension in the test specimens.NOTE 2The extent to which the crack grows in a stable manner isdependent on
26、 the machine stiffness (8) and the mode of control of loading(9).6.3 Bend Test FixtureA suggested fixture for SE (B)specimens is shown in Fig. 2. The fixture may have eitherstationary or moving rollers of sufficiently large diameter tominimize excessive plastic indentation.4The boldface numbers give
27、n in parentheses refer to a list of references at theend of the text.FIG. 1 Specimen ConfigurationsFIG. 2 Bending RigD6068 1026.4 Grips for C (T) SpecimensAsuggested clevis and pinarrangement for gripping compact specimens is given in TestMethod E399. This arrangement accommodates specimenswith B =
28、0.5 W.6.5 Displacement Measurement:6.5.1 Load-line displacement measurements are needed tocalculate J from the area under the load-displacement record.6.5.2 The remote displacement measurement can be per-formed using the stroke or position transducer on the testingmachine. Data obtained in this mann
29、er must be corrected forextraneous displacements (such as indentation effects, pinpenetration, or machine compliance) by conducting a separateindentation measurement described in 8.7.6.5.3 A direct displacement measurement can be performedusing a separate displacement transducer. This arrangement is
30、shown in Fig. 2 for SE (B) specimens. For C (T) specimens, thedisplacement gage should be placed in the notch on the loadline.7. Specimen Configuration, Size, and Preparation7.1 Specimen Size:7.1.1 The initial selection of specimen size and dimensionscan only be based on J results estimated from pre
31、viousexperience. Generally, the largest available specimens arerecommended for testing in order to obtain a larger portion ofthe J-R curve and to obtain the most conservative estimate ofcrack growth resistance.7.1.2 Any thickness may be used with the understandingthat the J-R curve will be limited b
32、y the maximum crackextension considerations of 9.2 and that the J-R curve is onlyappropriate for the thickness that is being evaluated.7.2 Specimen Configurations:7.2.1 The recommended SE (B) and C (T) specimens aresimilar to the configurations in Test Methods D5045 and areshown in Fig. 1. The speci
33、mens can be modified to permitload-line displacement measurement. Suggested modificationsare given in Test Method E1152.7.2.2 All in-plane dimensions are proportional to the speci-men width, W. The thickness is nominally B = 0.5 W.7.2.3 The original crack length, a0, shall be greater than 0.5W, but
34、less than 0.65 W.7.2.4 The span, S, to width, W, ratio in SE (B) specimensshall be 4.7.2.5 Side GroovesSpecimens may need side grooves topromote straighter crack fronts during testing. The sidegrooves should be equal in depth and have an included angle of45 6 5 with a root radius of 0.25 m 6 0.05 mm
35、. The totalthickness reduction may not exceed 0.20 B. Side grooves mustbe used when the crack front requirements of 9.2.3 cannot bemet with plane sided specimens.7.2.6 Alternative specimens may have 2 # W/B # 4.7.3 Indentation Correction SpecimensSeparately pre-pared unnotched test specimens are use
36、d for indentationdisplacement and energy corrections. The specimens are shownin Fig. 3.7.4 Conditioning:7.4.1 Condition the test specimens at 23 6 2C and 50 610 % relative humidity for not less than 40 h prior to test inaccordance with Procedure A of Practice D618, for those testswhere conditioning
37、is required. In cases of disagreement, thetolerances shall be 61C and 65 % relative humidity.7.4.2 Note that for some hygroscopic materials, such asnylons, the material specifications (for example, SpecificationD4066) call for testing “dry as molded specimens.” Suchrequirements take precedence over
38、the above routine precon-ditioning to 50 % relative humidity and require sealing thespecimens in water vapor-impermeable containers as soon asmolded and not removing them until ready for testing.7.5 Notching:7.5.1 The objective of the notching procedure is to obtainthe sharpest possible crack with m
39、inimal damage to thematerial in advance of the crack tip.7.5.2 Machine a pre-notch into the specimen to a depth of0.5 W using either a saw or a single-point flycutter.7.5.3 Create a natural crack by inserting a razor blade intothe pre-notch and tapping it into the specimen and forcing thecrack to gr
40、ow in advance of the razor blade tip.7.5.4 If a natural crack cannot be successfully generated bytapping the razor blade, slide a fresh, unused razor blade acrossthe root of the machined pre-notch.7.5.5 The length of the razor crack shall not be less than 5 %of the total original crack length, a0.7.
41、5.6 Alternative Notching Techniques:7.5.6.1 Fatigue pre-notching is permissible. Suggestednotching conditions are given in Test Method E1152. Becauseof the possibility of hysteretic heating leading to subsequentdamage, frequencies less than 4 Hz are recommended.FIG. 3 Arrangements for Finding Indent
42、ation DisplacementD6068 1037.5.6.2 Pressing a fresh razor blade into the notch is alsopermissible provided that damage to the material is minimized.Suggested notching conditions and equipment are given in TestMethod F1473.8. Procedure8.1 Testing ProcedureThe objective of this procedure is todevelop
43、a J-R curve consisting of J-integral values at spacedcrack extensions, Dap, as described in 9.3.2. In the multi-specimen method, each test specimen is to develop a singlepoint on the J-R curve. A series of specimens are loaded todifferent displacements using crosshead or displacement con-trol. The r
44、esulting crack fronts are marked (as described inAppendix X1) and the crack extensions are measured from thefracture surface. An independent indentation measurement isalso conducted to correct for non-fracture related energydissipation. The J value is then calculated from the indentationcorrected en
45、ergy for fracture. Each specimen has thus provideda set of J, Dapvalues to describe the J-R curve.8.2 Measure specimen dimensions B, BN, and W to thenearest 0.050 mm or 0.5 % accuracy, whichever is larger.8.3 Because of the viscoelastic nature of polymers, the J-Rcurve may be dependent on test tempe
46、rature and displacementrate. Therefore, record these conditions with the results.8.3.1 Provided that stable, well-defined crack growth can beachieved, any test temperature may be used.8.3.2 Similarly, any test speed that leads to stable, well-defined crack growth may be used. However, test speeds th
47、atlead to loading times (time to maximum load) that are less than1 ms are not recommended for this procedure due to dynamiceffects on the loading signal that can lead to erroneous results.8.3.3 For general characterization, the suggested test condi-tions in the standard laboratory atmosphere are 23
48、6 2C and50 6 5 % relative humidity. The suggested test speed is 1mm/min.8.4 Number of SpecimensAminimum of seven specimensare used to generate the power law fit to the data. All shall bemachined to the same dimensions. The initial precrack lengthsshould be as consistent as possible. The objective is
49、 to replicatethe initial portion of the load versus load-line displacementtraces as much as possible.8.5 Take each specimen through the following steps:8.5.1 Load to a selected displacement level that is judged toproduce a crack extension in a desired position on the J-Rcurve in accordance with 9.3.2. Use displacement or clip gagecontrol in order to control the amount of crack growth andminimize crack growth instability. Record the load versusload-line displacement curve.8.5.2 Unload the specimen, mark the crack front (seeAppendix X1), and break the spe
