1、Designation: C 1256 93 (Reapproved 2008)Standard Practice forInterpreting Glass Fracture Surface Features1This standard is issued under the fixed designation C 1256; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、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 Fracture features on the surface of a crack reflect thenature and course of the fracture event associated with thebreakage
3、of a glass object. This practice is a guide to theidentification and interpretation of these fracture surface fea-tures.1.2 The practice describes the various fracture surfacefeatures as to their appearance, the process of formation andtheir significance.1.3 The practice does not provide the procedu
4、ral informa-tion necessary for a complete fractographic analysis. Suchinformation is available in the general literature. (See Glossaryfor suggested literature).2. Referenced Documents2.1 ASTM Standards:2C 162 Terminology of Glass and Glass Products3. Terminology3.1 Definitions:3.1.1 bending stressa
5、 continuously and linearly changingstress across the thickness of a glass body, varying fromcompression on one surface to tension on the opposite surface.3.1.2 forkinga mechanism whereby a propagating frac-ture branches into two fractures, separated from each other byan acute angle.3.1.3 forking ang
6、lethe angle subtended by two immedi-ately adjacent fractures which have just branched or forked.3.1.4 fracture mirror constanta constant, characteristic ofa given glass composition, which, when divided by the squareroot of the fracture mirror radius, will yield the fracture stress.3.1.5 fracture mir
7、ror radiusa dimension of the fracturemirror as measured along the original specimen surface. It isdefined as the distance from the origin to the first detectablemist.3.1.6 fracture surface markingsfeatures of the fracturesurface produced during the fracture event which are useful indetermining the o
8、rigin and the nature of the local stresses thatproduced the fracture.3.1.7 fracture systemthe fracture surfaces that have acommon cause or origin.3.1.8 terminal velocitythe uppermost limiting velocity atwhich a crack can propagate in a material, the approach towhich is marked on the fracture generat
9、ed surface by thepresence of mist. The terminal velocity is approximately onehalf the velocity of sound in the material.3.1.9 uniform stressa state of stress that does not changewithin the region of concern.4. Summary4.1 This practice is intended to aid in the identification offracture surface marki
10、ngs as well as to assist in the understand-ing of their formation and significance.5. Significance and Use5.1 Fractography is often used to help identify the eventsthat have resulted in the fracture of a glass object. This practicedefines the appearance of various fracture surface features, aswell a
11、s their method of formation. Thus, there can be acommon understanding of their relationship to the fractureprocess as well as a common terminology.6. Fracture Surface Markings6.1 Origin:6.1.1 IdentificationThe origin is almost always found atthe junction where the fracture-generated surface meets a
12、freesurface or a dissimilar material. Commonly, the origin issymmetrically located near the apex of the mirror and it isusually small compared to the mirror. Fig. 1 shows typicalorigins and mirrors bounded by mist.6.1.2 FormationThe origin represents the single, uniquelocation at which every fractur
13、e system begins to form.1This practice is under the jurisdiction of ASTM Committee C14 Glass andGlass Products and is the direct responsibility of Subcommittee C14.04 on Physicaland Mechanical PropertiesCurrent edition approved April 1, 2008. Published December 2008. Originallyapproved in 1993. Last
14、 previous edition approved in 2003 as C1256 93 (2003)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.1Copyrig
15、ht ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.6.1.3 SignificanceThe origin defines the location wherethe fracture began. It may contain the stress concentrator or itmay be the stress concentrator.6.2 Mist Region:6.2.1 IdentificationUnder l
16、ow power (5 50 3 ) magni-fication, it has a misty appearance. Proceeding away from theorigin, it becomes more fibrous in appearance and elongated inthe direction of crack spread. (See Fig. 2.)6.2.2 FormationIt is produced as the crack front breaksinto numerous segments, which then round into one ano
17、ther.Their propagation aborts as the crack front approaches terminalvelocity.6.2.3 SignificanceIt defines the limit of the mirror regionand indicates that the crack has nearly reached terminalvelocity, or both.6.3 Mirror:6.3.1 IdentificationThe mirror is a smooth portion of thefracture surface surro
18、unding the origin (see Fig. 2). It iscommonly bounded by mist, but mist may not form when thelocal stress at the fracture front diminishes as the crackextends.6.3.2 FormationIt represents the initial portion of thepropagating crack where the velocity is accelerating from theorigin to a value suffici
19、ent to induce turbulence at the crackfront, that is, approaching terminal velocity, where mist andforking may appear.6.3.3 SignificanceIt is often helpful in locating the origin.The shape defined by the mist boundary is indicative of theuniformity of the stress field at the time of failure, for exam
20、ple;an open mirror, defined by mist only along the original surface,implies bending; a semicircular mirror implies uniform ten-sion: (See Fig. 1) The mirror dimensions may be used tocalculate the stress at breakage, because the mirror radius isinversely proportional to the square of the stress at th
21、e time themirror was formed. If the mirror is symmetrical, then use theradius to the mist boundary. To calculate the stress at breakagewhen the mirror is not symmetrical, the mirror radius is bestdetermined by dividing the mirror diameter by two. A moredetailed description of the relationship betwee
22、n the mirror andthe breaking strength for various glasses is found on p. 364 of(1) and in (2) and (3). Further discussion on quantitativefracture analysis techniques is well summarized in (4).6.4 Wallner Lines:6.4.1 IdentificationWallner lines, also called ripple marks,are rib-shaped marks, frequent
23、ly appearing as a series ofcurved lines resembling ripples created when an object isdropped into still water. (See Figs. 3-8.)6.4.2 FormationThey are produced when the plane of thepropagating crack front is temporarily altered by an elasticpulse.6.4.3 SignificanceThe direction of local propagation i
24、sperpendicular to the Wallner lines; it proceeds from theconcave to the convex side of the line. The shape of the lineindicates the direction of stresses at various points on the crackfront. The more advanced portions of the line generallycorrespond to regions of higher tension.6.5 Wallner Lines, Pr
25、imary:6.5.1 IdentificationPrimary Wallner lines are usuallyquite distinct and always have their source associated withFIG. 1 Origin Areas Produced Under Various Stress Functionsand Their Typical Fracture FeaturesFIG. 2 An Origin Area, with Mirror and MistFIG. 3 Primary Wallner Lines Generated From a
26、 SurfaceNonconformity and an InclusionC 1256 93 (2008)2some discontinuity which was present before fracture. Ex-amples would include bubbles or other inclusions, surfacedamage or an abrupt change in surface contour. (See Fig. 3 andFig. 4.)6.5.2 FormationThey result from the interaction of apropagati
27、ng crack with an elastic pulse coming from theencounter of the crack front with a preexisting discontinuity.FIG. 4 Primary Wallner Lines Generated; (a) From SurfaceScratches, (b) A Bubble Generating Gull WingsFIG. 5 Secondary Wallner Lines Generated From Mist FormationC 1256 93 (2008)36.5.3 Signific
28、anceThe convex side is toward the directionof crack propagation. Primary Wallner lines can be used todetermine whether a discontinuity was present before or afterthe breakage occured. In thin glassware, the crack breakingthrough to the opposite surface will generate a primary Wallnerline which indic
29、ates the stress distribution at the time of failure.6.6 Wallner Lines, Secondary:6.6.1 IdentificationSecondary Wallner lines are fish-hookshaped, numerous and closely spaced. (See Fig. 5 and Fig. 6.)6.6.2 FormationThey result from perturbations of thecrack front as it passes through the mist hackle
30、that is producedwhen the crack approaches terminal velocity.6.6.3 SignificanceThe convex side points toward the di-rection of crack propagation. They are indicative of the stressprofile at the crack front. In instances where the mist hackleband is quite narrow, they verify its presence.6.7 Wallner L
31、ines, Tertiary:6.7.1 IdentificationThese are a complex set of lines,exhibiting a periodicity and an intensity which may diminishwithin the pattern. They are neither hook-shaped nor trace to adiscontinuity as the source of an elastic pulse. (See Fig. 7 andFig. 8.)6.7.2 FormationThey result from an in
32、teraction at thecrack front with sonic waves from an external shock or fromstress release at the onset of cracking.6.7.3 SignificanceThey indicate that the failure resultedfrom a mechanical shock, where an elastic pulse was generatedoutside the plane of crack propagation.6.8 Dwell Mark:6.8.1 Identif
33、icationDwell marks, also called arrest lines,have a similar rib-shaped contour to that of Wallner lines butare distinctly sharper, often exhibiting a noticeable change infracture plane after the mark and may have twist hackleassociated. (See Fig. 9 and Fig. 10.)6.8.2 FormationThey are formed when th
34、ere is an abruptchange in the direction of the stress field such as when thecrack stops and then is restarted by a different stress field.FIG. 6 Secondary Wallner Lines Generated From Mist FormationFIG. 7 Tertiary Wallner Lines Created by Sonic Pulses Producedfrom Mechanical Shock Which Broke the Ma
35、terialFIG. 8 Tertiary Wallner LinesFIG. 9 A Dwell Mark is Created When the Crack StopsPropagating and/or Suddenly Changes PlaneC 1256 93 (2008)46.8.3 SignificanceThey indicate that the crack stoppedpropagation along a given plane and was restarted by adifferent stress field, along a new plane. In co
36、njunction withother information, they may indicate a position of the crackfront which separates two events in time.6.9 Hackle:6.9.1 IdentificationLines parallel to the direction of crackpropagation separating portions of the crack surface which areparallel but not coplanar.6.9.2 FormationThey are cr
37、eated when a propagatingfracture front becomes discontinuous so that it proceeds ondifferent planes which subsequently propagate laterally tointersect one another.6.9.3 SignificanceHackle indicates the direction of crackpropagation. Hackle can be useful in defining the mirror radius.6.10 Hackle, Twi
38、st:6.10.1 IdentificationResembles a staircase as seen fromabove, the stair risers representing the lines; overall it mayresemble the pattern of a river, running from multiple tributar-ies to streams into larger rivers (also known as striations). (SeeFig. 11(a).)6.10.2 FormationA lateral twist of the
39、 stress field be-comes accommodated by breakup of the crack front into manysegments which are parallel but not coplanar. This is followedby a lateral fracture allowing the separate crack segments toconnect, thus forming the“ line” or “step” between them.6.10.3 SignificanceThey verify general and eve
40、n localpropagation direction. The local direction of crack propagationproceeds from the smaller tributary features toward the direc-tion of convergence and larger features.6.11 Hackle, Shear:6.11.1 IdentificationA spray or fan of twist hackle whichcurves or radiates away from a central line toward o
41、ppositesurfaces. (See Fig. 11(b).) Also known as striations or Wood-worths Feathers.6.11.2 FormationIt results from the addition of a shearstress to the principle tensile stress.6.11.3 SignificanceIndicates that there was a shear stresspresent at the time of fracture. The shear stress may beindicati
42、ve of a transition between two types of forces, such asbending force in the sidewall of a vessel which changes touniform tension across the bottom of a vessel, producing shearhackle as the crack rounds the corner.6.12 Hackle, Wake:6.12.1 IdentificationA single hackle step at the trailingedge of an i
43、nclusion. (See Fig. 3 and Fig. 4(b).)6.12.2 FormationAs the crack front passes by an inclu-sion it splits, producing two parallel but non-coplanar crackswhich join after the crack front has passed beyond the trailingedge of the inclusion.6.12.3 SignificanceIt indicates the local direction of crackpr
44、opagation and calls attention to the presence of the inclusion.6.13 Scarp:6.13.1 IdentificationA single line on a fracture surfacewhich is unlike any other fracture feature. Examples of twocommon types of scarps are shown in Fig. 12(a) and (b),Cavitation scarp and Sierra Scarp, respectively.6.13.2 F
45、ormationIt marks the line of confluence betweentwo portions of the crack front which travel in different planesFIG. 10 Dwell Mark, the Crack Was Propagating from Left toRightFIG. 11 Hackle, (a) Twist Hackle, (b) Shear HackleC 1256 93 (2008)5as a result of local direction differences in crack advance
46、ment.These differences are due to unequal access of moisture to thetwo portions of the crack front.6.13.3 SignificanceIt can only be present if there has beenan opportunity for water to access the crack front. Its presencespecifically defines the presence of water at the time of thefracture event. I
47、ts absence, however, is inconclusive. There arevarious types of scarps as discussed in greater detail in (4), (5),and (6).6.14 Cantilever Curl:6.14.1 IdentificationA flat crack surface, more or lessperpendicular to one free surface, which curves as it ap-proaches the other surface so that it interse
48、cts that other surfaceat an oblique angle. (See Fig. 13.)6.14.2 FormationWhen a crack is generated by a bendingstress, it initially propagates perpendicular to the free surfacewhich is in tension and upon which the fracture originated. Asthe crack propagates through the thickness toward the freesurf
49、ace that was originally in compression, the plane of tensionrotates, causing a rotation in the developing crack surface, sothat, by the time it intersects the opposite free surface, a ridge,or lip, has formed. That ridge is strongly tilted with respect tothe general crack plane.6.14.3 SignificanceIts presence opposite the origin indi-cates that breakage occurred from a bending force.7. Precision and Bias7.1 Since for the most part, the results cannot be expressedquantitatively, the precision and bias cannot be so expressede
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