1、Designation: E1304 97 (Reapproved 2014)Standard Test Method forPlane-Strain (Chevron-Notch) Fracture Toughness ofMetallic Materials1This standard is issued under the fixed designation E1304; the number immediately following the designation indicates the year oforiginal adoption or, in the case of re
2、vision, 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, KI
3、vor 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 which
4、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 cra
5、ck at the points ofinstability.NOTE 1One difference between this test method and Test MethodE399 (which measures KIc) is that Test Method E399 centers attention onthe start of crack extension from a fatigue precrack. This test methodmakes use of either a steady state slowly propagating crack, or a c
6、rack 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 values
7、determined 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 commo
8、nly 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 purport to
9、 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 Practi
10、ces for Force Verification of Testing MachinesE8/E8M Test Methods for Tension Testing of Metallic Ma-terialsE399 Test Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic MaterialsE1823 Terminology Relating to Fatigue and Fracture Testing3. Terminology3.1 Definitions:3.1.1 The ter
11、ms described in Terminology E1823 are appli-cable to this test method.3.1.2 stress-intensity factor, KIFL3/2the magnitude ofthe mathematically ideal crack-tip stress field (stress-fieldsingularity) for mode I in a homogeneous linear-elastic body.3.1.2.1 DiscussionValues of K for mode I are given by
12、thefollowing equation:KI5 limit y2rx#rx0where:rx= distance from the crack tip to a location where thestress is calculated andy= 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 KIvjFL3/2un
13、der 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 loading the
14、 fracturetoughness, KIvor KIvj, is the value of stress-intensity factor as1This test method is under the jurisdiction of ASTM Committee E08 on Fatigueand Fracture and is the direct responsibility of Subcommittee E08.02 on Standardsand Terminology.Current edition approved July 1, 2014. Published Sept
15、ember 2014. Originallyapproved in 1989. Last previous edition approved in 2009 as E1304 97(2009)1.DOI: 10.1520/E1304-97R14.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, re
16、fer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1measured using the operational procedure (and satisfying all ofthe validity requirements) specified in this test method.3.2.
17、2 plane-strain (chevron-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 AnnexA1. Unloading-reloading cyclesas described in 3.2.6
18、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 force displacement record(Fig. 4). However, any
19、 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-notchspecimens, that type of sporadic crack growth which ischaracterized primarily by periods during which the crack fronti
20、s nearly stationary until a critical force is reached, whereuponthe crack becomes unstable and suddenly advances at highspeed to the next arrest point, where it remains nearly station-ary until the force again reaches a critical value, etc. (see Fig.5).3.2.4.1 DiscussionA chevron-notch specimen is s
21、aid 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). Onlythose sudden crack advances that result in more than a 5 %d
22、ecrease in force during the advance are counted as crackjumps (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,
23、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 unloading slope to that of the initial elastic loadingsl
24、ope 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 intensitycoefficient Y* (see 3.2.11). The effective unlo
25、ading 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 angles:r 5 tan /tanowhere:tan o= the slope of the
26、 initial elastic line, andtan = 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 o
27、ne 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 elastic behaviorand hysteresis are commonly observed
28、to a varying degree.These effects require an unambiguous method of obtaining aneffective unloading slope from the test record (6-5).33.2.6.3 DiscussionAlthough r is measured only at thosecrack positions where unloading-reloading cycles areperformed, r is nevertheless defined at all points during ach
29、evron-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-not
30、ch 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 critical crack length, the width of the crack front isapp
31、roximately 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 pointslabele
32、d 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, Y*a dimension-less parameter that relates the applied f
33、orce and specimen3The 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. (Not to scale.)FIG. 1 Schematic Diagrams o
34、f Chevron-Notched Short Rod (a)and Short Bar (b) SpecimensE1304 97 (2014)2geometry 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 thepoly
35、nominal expressions in Table 5.3.2.12 minimum stress-intensity factor coeffcient, Y*mtheminimum value of Y*(Table 3).4. 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 a
36、utographic 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
37、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 versus displacementtraces are recognized, namely, smooth
38、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-sponds to an increase in crack front width and requires f
39、urtherincrease 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 t
40、he loadingNOTE 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 ProportionsE1304 97 (2014)3system is sufficiently stiff, the crack can be made to continue itssmooth crack growth und
41、er 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 toughness is calculated fromthe force required to advance the crack when the crack is at thecritical 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 for
43、ce. 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 t
44、he 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.FIG. 4 Schematic of a Load-Displacement Test Record forSmooth Crack Growth Behavior, with Unloading/ReloadingCycles, Data Reduct
45、ion Constructions, and Definitions of TermsFIG. 5 Schematic of a Load-Displacement Test Record for CrackJump Behavior, with Unloading/Reloading Cycles, Data Reduc-tion Constructions, and Definitions of TermsR # 0.010Bs# 60t # 0.03BNOTE 1These requirements are satisfied by slots with a round bottomwh
46、enever 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 DesignE1304 97 (2014)44.1.3 The equations for calc
47、ulating the toughness have beenestablished 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 yieldstrength of the material (see 6.1), therefore
48、proportionalspecimen configurations are provided.NOTE 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 1C
49、ompiled from Refs (1), (2), (3), and (4).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 the chevron ligament have curved profiles,provided that the blade diameter exceeds 5.0B. In this case, is the anglebetween the chords spanning the plunge cut arcs, and it is necessary to usedifferent
