ASTM E1304-1997(2008) 374 Standard Test Method for Plane-Strain (Chevron-Notch) Fracture Toughness of Metallic Materials.pdf

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1、Designation: E 1304 97 (Reapproved 2008)Standard Test Method forPlane-Strain (Chevron-Notch) Fracture Toughness ofMetallic Materials1This standard is issued under the fixed designation E 1304; the number immediately following the designation indicates the year oforiginal adoption or, in the case of

2、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. Scope1.1 This test method covers the determination of plane-strain (chevron-notch) fracture toughnesses,

3、KIvor KIvM,ofmetallic materials. Fracture toughness by this method isrelative to a slowly advancing steady state crack initiated at achevron-shaped notch, and propagating in a chevron-shapedligament (Fig. 1). Some metallic materials, when tested by thismethod, exhibit a sporadic crack growth in whic

4、h the crackfront remains nearly stationary until a critical load is reached.The crack then becomes unstable and suddenly advances athigh speed to the next arrest point. For these materials, this testmethod covers the determination of the plane-strain fracturetoughness, KIvjor KIvM, relative to the c

5、rack at the points ofinstability.NOTE 1One difference between this test method and Test MethodE 399 (which measures KIc) is that Test Method E 399 centers attention onthe start of crack extension from a fatigue precrack. This test methodmakes use of either a steady state slowly propagating crack, or

6、 a crack atthe initiation of a crack jump. Although both methods are based on theprinciples of linear elastic fracture mechanics, this difference, plus otherdifferences in test procedure, may cause the values from this test methodto be larger than KIcvalues in some materials. Therefore, toughness va

7、luesdetermined by this test method cannot be used interchangeably with KIc.1.2 This test method uses either chevron-notched rod speci-mens of circular cross section, or chevron-notched bar speci-mens of square or rectangular cross section (Figs. 1-10). Theterms “short rod” and “short bar” are used c

8、ommonly for thesetypes of chevron-notched specimens.1.3 The values stated in inch-pound units are to be regardedas standard. The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.4 This standard does not purpor

9、t 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.2. Referenced Documents2.1 ASTM Standards:2E4 Pr

10、actices for Force Verification of Testing MachinesE 8/E 8M Test Methods for Tension Testing of MetallicMaterialsE 399 Test Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic MaterialsE 1823 Terminology Relating to Fatigue and Fracture Test-ing3. Terminology3.1 Definitions:3.1.1

11、The terms described in Terminology E 1823 are ap-plicable to this test method.3.1.2 stress-intensity factor, KI(dimensional units FL3/2)the magnitude of the ideal crack-tip stress field singularity formode I in a homogeneous linear-elastic body.3.1.2.1 DiscussionValues of K for mode I are given by:K

12、I5 limit sy2prx#rx0where:rx= a distance directly forward from the crack tip to alocation where the significant stress is calculated andsy= the principal stress rxnormal to the crack plane.3.2 Definitions of Terms Specific to This Standard:3.2.1 plane-strain (chevron-notch) fracture toughness, KIvor

13、KIvjFL3/2under conditions of crack-tip plane strain in achevron-notched specimen: KIvrelates to extension resistancewith respect to a slowly advancing steady-state crack. KIvjrelates to crack extension resistance with respect to a crackwhich advances sporadically.3.2.1.1 DiscussionFor slow rates of

14、loading the fracturetoughness, KIvor KIvj, is the value of stress-intensity factor asmeasured using the operational procedure (and satisfying all ofthe validity requirements) specified in this test method.1This test method is under the jurisdiction of ASTM Committee E08 on Fatigueand Fracture and is

15、 the direct responsibility of Subcommittee E08.02 on Standardsand Terminology.Current edition approved Nov. 1, 2008. Published March 2009. Originallyapproved in 1989. Last previous edition approved in 2002 as E 1304 97(2002).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcon

16、tact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.2 plane-strain (c

17、hevron-notch) fracture toughness, KIvMFL3/2determined similarly to KIvor KIvj(see 3.2.1) usingthe same specimen, or specimen geometries, but using asimpler analysis based on the maximum test force. Theanalysis is described in Annex A1. Unloading-reloading cyclesas described in 3.2.6 are not required

18、 in a test to determineKIvM.3.2.3 smooth crack growth behaviorgenerally, that type ofcrack extension behavior in chevron-notch specimens that ischaracterized primarily by slow, continuously advancing crackgrowth, and a relatively smooth force displacement record(Fig. 4). However, any test behavior n

19、ot satisfying the condi-tions for crack jump behavior is automatically characterized assmooth crack growth behavior.3.2.4 crack jump behaviorin tests of chevron-notch speci-mens, that type of sporadic crack growth which is character-ized primarily by periods during which the crack front is nearlysta

20、tionary until a critical force is reached, whereupon the crackbecomes unstable and suddenly advances at high speed to thenext arrest point, where it remains nearly stationary until theforce again reaches a critical value, etc. (see Fig. 5).3.2.4.1 DiscussionA chevron-notch specimen is said tohave a

21、crack jump behavior when crack jumps account formore than one half of the change in unloading slope ratio (see3.2.6) as the unloading slope ratio passes through the rangefrom 0.8rcto 1.2rc(see 3.2.6 and 3.2.7, and 8.3.5.2). Only thosesudden crack advances that result in more than a 5 % decreasein fo

22、rce during the advance are counted as crack jumps (Fig. 5).3.2.5 steady-state cracka crack that has advanced slowlyuntil the crack-tip plastic zone size and crack-tip sharpness nolonger change with further crack extension.Although crack-tipconditions can be a function of crack velocity, the steady-s

23、tatecrack-tip conditions for metals have appeared to be indepen-dent of the crack velocity within the range attained by theloading rates specified in this test method.3.2.6 effective unloading slope ratio, rthe ratio of aneffective unloading slope to that of the initial elastic loadingslope on a tes

24、t record of force versus specimen mouth openingdisplacement.3.2.6.1 DiscussionThis unloading slope ratio provides amethod of determining the crack length at various points on thetest record and therefore allows evaluation of stress intensitycoefficient Y* (see 3.2.11). The effective unloading slope

25、ratiois measured by performing unloading-reloading cycles duringthe test as indicated schematically in Fig. 4 and Fig. 5. For eachunloading-reloading trace, the effective unloading slope ratio,r, is defined in terms of the tangents of two angles:r 5 tan u/tan uowhere:tan uo= the slope of the initial

26、 elastic line, andtan u = the slope of an effective unloading line.The effective unloading line is defined as having an origin atthe high point where the displacement reverses direction onunloading (slot mouth begins to close) and joining the lowpoint on the reloading line where the force is one hal

27、f that atthe high point.3.2.6.2 DiscussionFor a brittle material with linear elasticbehavior the unloading-reloading lines of an unloading-reloading cycle would be linear and coincident. For manyengineering materials, deviations from linear elastic behaviorand hysteresis are commonly observed to a v

28、arying degree.These effects require an unambiguous method of obtaining aneffective unloading slope from the test record (1-4).33.2.6.3 DiscussionAlthough r is measured only at thosecrack positions where unloading-reloading cycles are per-formed, r is nevertheless defined at all points during achevro

29、n-notch specimen test. For any particular point it is thevalue that would be measured for r if an unloading-reloadingcycle were performed at that point.3.2.7 critical slope ratio, rcthe unloading slope ratio atthe critical crack length.3.2.8 critical crack lengththe crack length in a chevron-notch s

30、pecimen at which the specimens stress-intensity factorcoefficient, Y* (see 3.2.11 and Table 3), is a minimum, orequivalently, the crack length at which the maximum forcewould occur in a purely linear elastic fracture mechanics test.At the critical crack length, the width of the crack front isapproxi

31、mately one third the dimension B (Figs. 2 and 3).3.2.9 high point, Highthe point on a force-displacementplot, at the start of an unloading-reloading cycle, at which thedisplacement reverses direction, that is, the point at which thespecimen mouth begins closing due to unloading (see pointslabeled Hi

32、gh in Figs. 4 and 5).3.2.10 low point, Lowthe point on the reloading portion ofan unloading-reloading cycle where the force is one half thehigh point force (see points labeled Low in Figs. 4 and 5).3.2.11 stress-intensity factor coeffcient, Y*a dimension-less parameter that relates the applied force

33、 and specimengeometry to the resulting crack-tip stress-intensity factor in achevron-notch specimen test (see 9.6.3).3.2.11.1 DiscussionValues of Y* can be found from thegraphs in Fig. 10, or from the tabulations in Table 4 or from thepolynominal expressions in Table 5.3.2.12 minimum stress-intensit

34、y factor coeffcient, Y*mthe minimum value of Y*(Table 3).3The boldface numbers in parentheses refer to the list of references at the endof this standard.NOTE 1The crack commences at the tip of the chevron-shapedligament and propagates (shaded area) along the ligament, and has thelength “a” shown. (N

35、ot to scale.)FIG. 1 Schematic Diagrams of Chevron-Notched Short Rod (a)and Short Bar (b) SpecimensE 1304 97 (2008)24. Summary of Test Method4.1 This test method involves the application of a load to themouth of a chevron-notched specimen to induce an openingdisplacement of the specimen mouth. An aut

36、ographic record ismade of the load versus mouth opening displacement and theslopes of periodic unloading-reloading cycles are used tocalculate the crack length based on compliance techniques.These crack lengths are expressed indirectly as slope ratios.The characteristics of the force versus mouth op

37、ening displace-ment trace depend on the geometry of the specimen, thespecimen plasticity during the test, any residual stresses in thespecimen, and the crack growth characteristics of the materialbeing tested. In general, two types of force versus displacementtraces are recognized, namely, smooth be

38、havior (see 3.2.3) andcrack jump behavior (see 3.2.4).4.1.1 In metals that exhibit smooth crack behavior (3.2.3),the crack initiates at a low force at the tip of a sufficiently sharpchevron, and each incremental increase in its length corre-sponds to an increase in crack front width and requires fur

39、therincrease in force. This force increase continues until a point isreached where further increases in force provide energy inexcess of that required to advance the crack. This maximumforce point corresponds to a width of crack front approximatelyone third the specimen diameter or thickness. If the

40、 loadingsystem is sufficiently stiff, the crack can be made to continue itssmooth crack growth under decreasing force. Two unloading-reloading cycles are performed to determine the location of thecrack, the force used to calculate KIv, and to provide validitychecks on the test. The fracture toughnes

41、s is calculated fromthe force required to advance the crack when the crack is at theNOTE 1See Table 1 for tolerances and other details.FIG. 2 Rod Specimens Standard ProportionsNOTE 1See Table 2 for tolerances and other details.FIG. 3 Bar Specimens Standard ProportionsE 1304 97 (2008)3critical crack

42、length (see 3.2.8). The plane-strain fracturetoughness determined by this procedure is termed KIv.Analternative procedure, described in Annex A1, omits theunloading cycles and uses the maximum test force to calculatea plane-strain fracture toughness KIvM, where M signifies theuse of the maximum forc

43、e. Values of KIvversus KIvMarediscussed in Annex A1.4.1.2 A modified procedure is used to determine KIvjwhencrack jump behavior is encountered. In this procedure,unloading-reloading cycles are used to determine the cracklocation at which the next jump will begin. The KIvjvalues arecalculated from th

44、e forces that produce crack jumps when thecrack front is in a defined region near the center of thespecimen. The KIvjvalues so determined have the samesignificance as KIv.4.1.3 The equations for calculating the toughness have beenestablished on the basis of elastic stress analyses of thespecimen typ

45、es described in this test method.4.2 The specimen size required for testing purposes in-creases as the square of the ratio of fracture toughness to yieldFIG. 4 Schematic of a Load-Displacement Test Record forSmooth Crack Growth Behavior, with Unloading/ReloadingCycles, Data Reduction Constructions,

46、and Definitions of TermsFIG. 5 Schematic of a Load-Displacement Test Record for CrackJump Behavior, with Unloading/Reloading Cycles, DataReduction Constructions, and Definitions of TermsR # 0.010Bfs# 60t # 0.03BNOTE 1These requirements are satisfied by slots with a round bottomwhenever t # 0.020B.FI

47、G. 6 Slot Bottom ConfigurationNOTE 1Machine finish all over equal to or better than 64 in.NOTE 2Unless otherwise specified, dimensions 60.010B; angles62.NOTE 3Grip hardness should be RC = 45 or greater.FIG. 7 Suggested Loading Grip DesignE 1304 97 (2008)4strength of the material (see 6.1), therefore

48、 proportionalspecimen configurations are provided.5. Significance and Use5.1 The fracture toughness determined by this test methodcharacterizes the resistance of a material to fracture by a slowlyadvancing steady-state crack (see 3.2.5) in a neutral environ-ment under severe tensile constraint.The s

49、tate of stress near thecrack front approaches plane strain, and the crack-tip plasticregion is small compared with the crack size and specimendimensions in the constraint direction. A KIvor KIvjvalue mayNOTE 1To assist alignment, shims may be placed at these locationsand removed before the load is applied, as described in 8.3.2.FIG. 8 Recommended Tensile Test Machine Test ConfigurationFIG. 9 Suggested Design for the Specimen Mouth Opening GageNOTE 1Compiled from Refs (8), (10), (11), and (13).FIG. 10 Normalized Stress-Intensity Facto