# ASTM E1304-97 (Reapproved 2014)

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 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, 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 which 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 crack at the points ofinstability.NOTE 1—One 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 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 valuesdetermined 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 commonly 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 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 Practices 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 terms described in Terminology E1823 are appli-cable to this test method.3.1.2 stress-intensity factor, KI[FL−3/2]—the magnitude ofthe mathematically ideal crack-tip stress field (stress-fieldsingularity) for mode I in a homogeneous linear-elastic body.3.1.2.1 Discussion—Values of K for mode I are given by thefollowing equation:KI5 limit σy@2πrx#½rx→0where:rx= distance from the crack tip to a location where thestress is calculated andσy= 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 KIvj[FL−3/2]—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 respect to a crackwhich advances sporadically.3.2.1.1 Discussion—For slow rates of loading the 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 September 2014. Originallyapproved in 1989. Last previous edition approved in 2009 as E1304 – 97(2009)ε1.DOI: 10.1520/E1304-97R14.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at service@astm.org. For Annual Book of ASTMStandards volume information, refer to the standard’s 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.3.2.2 plane-strain (chevron-notch) fracture toughness, KIvM[FL−3/2]—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 AnnexA1. Unloading-reloading cyclesas described in 3.2.6 are not required in a test to determineKIvM.3.2.3 smooth crack growth behavior—generally, 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 not satisfying the condi-tions for crack jump behavior is automatically characterized assmooth crack growth behavior.3.2.4 crack jump behavior—in tests of chevron-notchspecimens, that type of sporadic crack growth which ischaracterized primarily by periods during which the crack frontis 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 Discussion—A 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 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 crack—a 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-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, r—the ratio of aneffective unloading slope to that of the initial elastic loadingslope on a test record of force versus specimen mouth openingdisplacement.3.2.6.1 Discussion—This 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 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 θ/tanθowhere:tan θo= the slope of the initial elastic line, andtan θ = 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 half that atthe high point.3.2.6.2 Discussion—For 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 varying degree.These effects require an unambiguous method of obtaining aneffective unloading slope from the test record (6-5).33.2.6.3 Discussion—Although r is measured only at thosecrack positions where unloading-reloading cycles areperformed, 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, rc—the unloading slope ratio atthe critical crack length.3.2.8 critical crack length—the crack length in a chevron-notch specimen at which the specimen’s 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 isapproximately one third the dimension B (Figs. 2 and 3).3.2.9 high point, High—the 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 High in Figs. 4 and 5).3.2.10 low point, Low—the 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 coeffıcient, Y*—a dimension-less parameter that relates the applied force and specimen3The boldface numbers in parentheses refer to the list of references at the endof this standard.NOTE 1—The 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 of 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 Discussion—Values 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-intensity factor coeffıcient, Y*m—theminimum 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 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 slope 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 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-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 approximatelyone third the specimen diameter or thickness. If the loadingNOTE 1—See Table 1 for tolerances and other details.FIG. 2 Rod Specimens Standard ProportionsNOTE 1—See 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 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 toughness is calculated fromthe force required to advance the crack when the crack is at thecritical 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 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 the 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.FIG. 4 Schematic of a Load-Displacement Test Record forSmooth Crack Growth Behavior, with Unloading/ReloadingCycles, Data Reduction 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 # 0.010Bφs# 60°t # 0.03BNOTE 1—These requirements are satisfied by slots with a round bottomwhenever t ≤ 0.020B.FIG. 6 Slot Bottom ConfigurationNOTE 1—Machine finish all over equal to or better than 64 µin.NOTE 2—Unless otherwise specified, dimensions 60.010B; angles62°.NOTE 3—Grip hardness should be RC = 45 or greater.FIG. 7 Suggested Loading Grip DesignE1304 − 97 (2014)44.1.3 The equations for calculating 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 proportionalspecimen configurations are provided.NOTE 1—To 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 1—Compiled 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 1—All surfaces to be 64-µin. finish or better.NOTE 2—Side 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, φ is the anglebetween the chords spanning the plunge cut arcs, and it is necessary to usedifferen