ASTM C1256-93(2003)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:C1256–93 (Reapproved 2003)
Standard Practice for
Interpreting Glass Fracture Surface Features
This standard is issued under the fixed designation C1256; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.7 fracture system—the fracture surfaces that have a
common cause or origin.
1.1 Fracture features on the surface of a crack reflect the
3.1.8 terminal velocity—the uppermost limiting velocity at
nature and course of the fracture event associated with the
which a crack can propagate in a material, the approach to
breakage of a glass object. This practice is a guide to the
which is marked on the fracture generated surface by the
identification and interpretation of these fracture surface fea-
presence of mist. The terminal velocity is approximately one
tures.
half the velocity of sound in the material.
1.2 The practice describes the various fracture surface
3.1.9 uniform stress—a state of stress that does not change
features as to their appearance, the process of formation and
within the region of concern.
their significance.
1.3 The practice does not provide the procedural informa-
4. Summary
tion necessary for a complete fractographic analysis. Such
4.1 This practice is intended to aid in the identification of
informationisavailableinthegeneralliterature.(SeeGlossary
fracturesurfacemarkingsaswellastoassistintheunderstand-
for suggested literature).
ing of their formation and significance.
2. Referenced Documents
5. Significance and Use
2.1 ASTM Standards:
2 5.1 Fractography is often used to help identify the events
C162 Standard Terminology of Glass and Glass Products
thathaveresultedinthefractureofaglassobject.Thispractice
3. Terminology defines the appearance of various fracture surface features, as
well as their method of formation. Thus, there can be a
3.1 Definitions:
common understanding of their relationship to the fracture
3.1.1 bending stress—a continuously and linearly changing
process as well as a common terminology.
stress across the thickness of a glass body, varying from
compression on one surface to tension on the opposite surface.
6. Fracture Surface Markings
3.1.2 forking—a mechanism whereby a propagating frac-
6.1 Origin:
ture branches into two fractures, separated from each other by
6.1.1 Identification—The origin is almost always found at
an acute angle.
the junction where the fracture-generated surface meets a free
3.1.3 forking angle—the angle subtended by two immedi-
surface or a dissimilar material. Commonly, the origin is
ately adjacent fractures which have just branched or forked.
symmetrically located near the apex of the mirror and it is
3.1.4 fracture mirror constant—a constant, characteristic of
usually small compared to the mirror. Fig. 1 shows typical
a given glass composition, which, when divided by the square
origins and mirrors bounded by mist.
root of the fracture mirror radius, will yield the fracture stress.
6.1.2 Formation—The origin represents the single, unique
3.1.5 fracture mirror radius—a dimension of the fracture
location at which every fracture system begins to form.
mirror as measured along the original specimen surface. It is
6.1.3 Significance—The origin defines the location where
defined as the distance from the origin to the first detectable
the fracture began. It may contain the stress concentrator or it
mist.
may be the stress concentrator.
3.1.6 fracture surface markings—features of the fracture
6.2 Mist Region:
surface produced during the fracture event which are useful in
6.2.1 Identification—Under low power (5−50 3) magni-
determining the origin and the nature of the local stresses that
fication, it has a misty appearance. Proceeding away from the
produced the fracture.
origin,itbecomesmorefibrousinappearanceandelongatedin
the direction of crack spread. (See Fig. 2.)
This practice is under the jurisdiction of ASTM Committee C14 Glass and
6.2.2 Formation—It is produced as the crack front breaks
Glass Products and is the direct responsibility of Subcommittee C14.04 on Physical
into numerous segments, which then round into one another.
and Mechanical Properties.
Theirpropagationabortsasthecrackfrontapproachesterminal
Current edition approved April 10, 2003. Published February 1994.
Annual Book of ASTM Standards, Vol 15.02. velocity.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C1256–93 (2003)
implies bending; a semicircular mirror implies uniform ten-
sion: (See Fig. 1) The mirror dimensions may be used to
calculate the stress at breakage, because the mirror radius is
inverselyproportionaltothesquareofthestressatthetimethe
mirror was formed. If the mirror is symmetrical, then use the
radius to the mist boundary.To calculate the stress at breakage
when the mirror is not symmetrical, the mirror radius is best
determined by dividing the mirror diameter by two. A more
detailed description of the relationship between the mirror and
the breaking strength for various glasses is found on p. 364 of
(1) and in (2) and (3). Further discussion on quantitative
fracture analysis techniques is well summarized in (4).
6.4 Wallner Lines:
6.4.1 Identification—Wallnerlines,alsocalledripplemarks,
are rib-shaped marks, frequently appearing as a series of
curved lines resembling ripples created when an object is
dropped into still water. (See Figs. 3-8.)
FIG. 1 Origin Areas Produced Under Various Stress Functions
6.4.2 Formation—They are produced when the plane of the
and Their Typical Fracture Features
propagating crack front is temporarily altered by an elastic
pulse.
6.4.3 Significance—The direction of local propagation is
perpendicular to the Wallner lines; it proceeds from the
concave to the convex side of the line. The shape of the line
indicatesthedirectionofstressesatvariouspointsonthecrack
front. The more advanced portions of the line generally
correspond to regions of higher tension.
6.5 Wallner Lines, Primary:
6.5.1 Identification—Primary Wallner lines are usually
quite distinct and always have their source associated with
some discontinuity which was present before fracture. Ex-
amples would include bubbles or other inclusions, surface
damageoranabruptchangeinsurfacecontour.(SeeFig.3and
Fig. 4.)
6.5.2 Formation—They result from the interaction of a
propagating crack with an elastic pulse coming from the
encounter of the crack front with a preexisting discontinuity.
6.5.3 Significance—The convex side is toward the direction
of crack propagation. Primary Wallner lines can be used to
determine whether a discontinuity was present before or after
FIG. 2 An Origin Area, with Mirror and Mist
the breakage occured. In thin glassware, the crack breaking
throughtotheoppositesurfacewillgenerateaprimaryWallner
6.2.3 Significance—It defines the limit of the mirror region
linewhichindicatesthestressdistributionatthetimeoffailure.
and indicates that the crack has nearly reached terminal
velocity, or both.
6.3 Mirror:
6.3.1 Identification—The mirror is a smooth portion of the
fracture surface surrounding the origin (see Fig. 2). It is
commonly bounded by mist, but mist may not form when the
local stress at the fracture front diminishes as the crack
extends.
6.3.2 Formation—It represents the initial portion of the
propagating crack where the velocity is accelerating from the
origin to a value sufficient to induce turbulence at the crack
front, that is, approaching terminal velocity, where mist and
forking may appear.
6.3.3 Significance—It is often helpful in locating the origin.
The shape defined by the mist boundary is indicative of the
uniformityofthestressfieldatthetimeoffailure,forexample;
FIG. 3 Primary Wallner Lines Generated From a Surface
anopenmirror,definedbymistonlyalongtheoriginalsurface, Nonconformity and an Inclusion
C1256–93 (2003)
FIG. 4 Primary Wallner Lines Generated; (a) From Surface
Scratches, (b) A Bubble Generating Gull Wings
FIG. 5 Secondary Wallner Lines Generated From Mist Formation
6.6 Wallner Lines, Secondary: 6.6.2 Formation—They result from perturbations of the
6.6.1 Identification—Secondary Wallner lines are fish-hook crackfrontasitpassesthroughthemisthacklethatisproduced
shaped, numerous and closely spaced. (See Fig. 5 and Fig. 6.) when the crack approaches terminal velocity.
C1256–93 (2003)
FIG. 6 Secondary Wallner Lines Generated From Mist Formation
FIG. 8 Tertiary Wallner Lines
fracture plane after the mark and may have twist hackle
associated. (See Fig. 9 and Fig. 10.)
6.8.2 Formation—They are formed when there is an abrupt
change in the direction of the stress field such as when the
crack stops and then is restarted by a different stress field.
6.8.3 Significance—They indicate that the crack stopped
propagation along a given plane and was restarted by a
different stress field, along a new plane. In conjunction with
other information, they may indicate a p
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