1、Designation: E 1304 97 (Reapproved 2002)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 (e) 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 whi
4、ch 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
5、crack 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, o
6、r 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 v
7、aluesdetermined 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
8、commonly for thesetypes of chevron-notched specimens.1.3 This standard does not 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 o
9、f regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E4 Practices for Force Verification of Testing MachinesE8 Test Methods for Tension Testing of Metallic MaterialsE 399 Test Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic MaterialsE 1823 Terminol
10、ogy Relating to Fatigue and Fracture Test-ing3. Terminology3.1 Definitions:3.1.1 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 homoge
11、neous linear-elastic body.3.1.2.1 DiscussionValues of K for mode I are given by:KI5 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 Specif
12、ic to This Standard:3.2.1 plane-strain (chevron-notch) fracture toughness, KIvor KIvj(FL3/2)under 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
13、 respect to a crackwhich advances sporadically.3.2.1.1 DiscussionFor slow rates of 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 m
14、ethod is under the jurisdiction ofASTM Committee E08 on FractureFatigue and is the direct responsibility of Subcommittee E08.02 on Standards andTerminology.Current edition approved Apr. 10, 1997. Published June 1997. Originallypublished as E 1304 89. Last previous edition E 1304 89.2For referenced A
15、STM 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Consho
16、hocken, PA 19428-2959, United States.3.2.2 plane-strain (chevron-notch) fracture toughness, KIvM(FL3/2)determined 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. Unlo
17、ading-reloading cyclesas described in 3.2.6 are not required 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 for
18、ce displacement record(Fig. 4). However, any test behavior not 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 pr
19、imarily by periods during which the crack front is nearlystationary 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).
20、3.2.4.1 DiscussionA chevron-notch specimen is said tohave a 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
21、 crack advances that result in more than a 5 % decreasein force 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-tip
22、conditions can be a function of crack velocity, the steady-statecrack-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 unloadin
23、g slope to that of the initial elastic loadingslope on a test 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 intensit
24、ycoefficient Y* (see 3.2.11). The effective unloading slope 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 a
25、ngles:r 5 tan u/tan uowhere:tan uo= the slope of the initial 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 t
26、he lowpoint on the reloading line where the force is one half 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
27、 elastic behaviorand hysteresis are commonly observed to a varying 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-fo
28、rmed, r is nevertheless defined at all points during achevron-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.
29、8 critical crack lengththe crack length in a chevron-notch specimen 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 c
30、ritical crack length, the width of the crack front isapproximately 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
31、 mouth begins closing due to unloading (see pointslabeled High 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,
32、 Y*a dimension-less parameter that relates the applied force 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 thepolyn
33、ominal expressions in Table 5.3.2.12 minimum stress-intensity 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 (shad
34、ed area) along the ligament, and has thelength “a” shown. (Not to scale.)FIG. 1 Schematic Diagrams of Chevron-Notched Short Rod (a)and Short Bar (b) SpecimensE 1304 97 (2002)24. Summary of Test Method4.1 This test method involves the application of a load to themouth of a chevron-notched specimen to
35、 induce an openingdisplacement of the specimen mouth. An autographic 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 s
36、lope ratios.The characteristics of the force versus mouth opening 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
37、 versus displacementtraces are recognized, namely, smooth behavior (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
38、-sponds to an increase in crack front width and requires furtherincrease 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 appro
39、ximatelyone third the specimen diameter or thickness. If the 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
40、to provide validitychecks on the test. The fracture toughness 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 Sp
41、ecimens Standard ProportionsE 1304 97 (2002)3critical crack 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
42、toughness KIvM, where M signifies theuse of the maximum force. 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 th
43、e next jump will begin. The KIvjvalues arecalculated from the 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 beenestablishe
44、d on the basis of elastic stress analyses of thespecimen types 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, wi
45、th Unloading/ReloadingCycles, Data Reduction Constructions, 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
46、satisfied by slots with a round bottomwhenever t # 0.020B.FIG. 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
47、1304 97 (2002)4strength of the material (see 6.1), therefore 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
48、a neutral environ-ment under severe tensile constraint.The state 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
49、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 Factor Coefficients as aFunction of Slope Ratio (r) for Chevron-Notch SpecimensTABLE 1 Rod DimensionsNOTE 1All surfaces to be 64-in. finish or better.NOTE 2Side grooves may be made with a plunge cut with a circularblade, such that the sides of t
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