ASTM_C_1256_-_93_2013.pdf

Designation:C125693(Reapproved 2013)Standard Practice forInterpreting Glass Fracture Surface Features1This standard is issued under the fixed designation C1256;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 Fracture features on the surface of a crack reflect thenature and course of the fracture event associated with thebreakage 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 procedural 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:2C162 Terminology of Glass and Glass Products3.Terminology3.1 Definitions:3.1.1 bending stressa 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 fracturebranches into two fractures,separated from each other by anacute angle.3.1.3 forking anglethe 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 mirror 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 origin 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 generated 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 markings 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 as 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 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 fracture system begins to form.1This practice is under the jurisdiction ofASTM Committee C14Glass and GlassProducts and is the direct responsibility of Subcommittee C14.04 on Physical andMechanical PropertiesCurrent edition approved Oct.1,2013.Published October 2013.Originallyapproved in 1993.Last previous edition approved in 2008 as C1256 93(2008)DOI:10.1520/C1256-93R13.2For 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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 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 IdentificationUnderlowpower(5 50 )magnification,it has a misty appearance.Proceeding awayfrom the origin,it becomes more fibrous in appearance andelongated in the 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 another.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