ASTM C1256-93(2013)
(Practice)Standard Practice for Interpreting Glass Fracture Surface Features
Standard Practice for Interpreting Glass Fracture Surface Features
SIGNIFICANCE AND USE
5.1 Fractography is often used to help identify the events that have resulted in the fracture of a glass object. This practice defines the appearance of various fracture surface features, as well as their method of formation. Thus, there can be a common understanding of their relationship to the fracture process as well as a common terminology.
SCOPE
1.1 Fracture features on the surface of a crack reflect the nature and course of the fracture event associated with the breakage of a glass object. This practice is a guide to the identification and interpretation of these fracture surface features.
1.2 The practice describes the various fracture surface features as to their appearance, the process of formation and their significance.
1.3 The practice does not provide the procedural information necessary for a complete fractographic analysis. Such information is available in the general literature. (See Glossary for suggested literature).
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: C1256 − 93 (Reapproved 2013)
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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.5 fracture mirror radius—a dimension of the fracture
mirror as measured along the original specimen surface. It is
1.1 Fracture features on the surface of a crack reflect the
defined as the distance from the origin to the first detectable
nature and course of the fracture event associated with the
mist.
breakage of a glass object. This practice is a guide to the
identification and interpretation of these fracture surface fea- 3.1.6 fracture surface markings—features of the fracture
tures. surface produced during the fracture event which are useful in
determining the origin and the nature of the local stresses that
1.2 The practice describes the various fracture surface
produced the fracture.
features as to their appearance, the process of formation and
their significance. 3.1.7 fracture system—the fracture surfaces that have a
common cause or origin.
1.3 The practice does not provide the procedural informa-
tion necessary for a complete fractographic analysis. Such 3.1.8 terminal velocity—the uppermost limiting velocity at
information is available in the general literature. (See Glossary which a crack can propagate in a material, the approach to
for suggested literature). which is marked on the fracture generated surface by the
presence of mist. The terminal velocity is approximately one
2. Referenced Documents half the velocity of sound in the material.
2.1 ASTM Standards: 3.1.9 uniform stress—a state of stress that does not change
within the region of concern.
C162Terminology of Glass and Glass Products
3. Terminology 4. Summary
3.1 Definitions: 4.1 This practice is intended to aid in the identification of
3.1.1 bending stress—a continuously and linearly changing
fracturesurfacemarkingsaswellastoassistintheunderstand-
stress across the thickness of a glass body, varying from ing of their formation and significance.
compression on one surface to tension on the opposite surface.
5. Significance and Use
3.1.2 forking—amechanismwherebyapropagatingfracture
branches into two fractures, separated from each other by an
5.1 Fractography is often used to help identify the events
acute angle.
thathaveresultedinthefractureofaglassobject.Thispractice
3.1.3 forking angle—the angle subtended by two immedi- defines the appearance of various fracture surface features, as
well as their method of formation. Thus, there can be a
ately adjacent fractures which have just branched or forked.
common understanding of their relationship to the fracture
3.1.4 fracture mirror constant—a constant, characteristic of
process as well as a common terminology.
a given glass composition, which, when divided by the square
root of the fracture mirror radius, will yield the fracture stress.
6. Fracture Surface Markings
6.1 Origin:
6.1.1 Identification—The origin is almost always found at
ThispracticeisunderthejurisdictionofASTMCommitteeC14GlassandGlass
Products and is the direct responsibility of Subcommittee C14.04 on Physical and
the junction where the fracture-generated surface meets a free
Mechanical Properties
surface or a dissimilar material. Commonly, the origin is
Current edition approved Oct. 1, 2013. Published October 2013. Originally
symmetrically located near the apex of the mirror and it is
approved in 1993. Last previous edition approved in 2008 as C1256–93 (2008)
DOI: 10.1520/C1256-93R13. usually small compared to the mirror. Fig. 1 shows typical
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
origins and mirrors bounded by mist.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
6.1.2 Formation—The origin represents the single, unique
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. location at which every fracture system begins to form.
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C1256 − 93 (2013)
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;
anopenmirror,definedbymistonlyalongtheoriginalsurface,
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
FIG. 1 Origin Areas Produced Under Various Stress Functions
inverselyproportionaltothesquareofthestressatthetimethe
and Their Typical Fracture Features
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
6.1.3 Significance—The origin defines the location where
determined by dividing the mirror diameter by two. A more
the fracture began. It may contain the stress concentrator or it
detailed description of the relationship between the mirror and
may be the stress concentrator.
the breaking strength for various glasses is found on p. 364 of
6.2 Mist Region:
(1) and in (2) and (3). Further discussion on quantitative
6.2.1 Identification—Under low power (5 − 50 × )
fracture analysis techniques is well summarized in (4).
magnification, it has a misty appearance. Proceeding away
6.4 Wallner Lines:
from the origin, it becomes more fibrous in appearance and
6.4.1 Identification—Wallnerlines,alsocalledripplemarks,
elongated in the direction of crack spread. (See Fig. 2.)
are rib-shaped marks, frequently appearing as a series of
6.2.2 Formation—It is produced as the crack front breaks
curved lines resembling ripples created when an object is
into numerous segments, which then round into one another.
dropped into still water. (See Figs. 3-8.)
Theirpropagationabortsasthecrackfrontapproachesterminal
6.4.2 Formation—They are produced when the plane of the
velocity.
propagating crack front is temporarily altered by an elastic
6.2.3 Significance—It defines the limit of the mirror region
pulse.
and indicates that the crack has nearly reached terminal
6.4.3 Significance—The direction of local propagation is
velocity, or both.
perpendicular to the Wallner lines; it proceeds from the
6.3 Mirror:
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:
FIG. 3 Primary Wallner Lines Generated From a Surface Noncon-
FIG. 2 An Origin Area, with Mirror and Mist formity and an Inclusion
C1256 − 93 (2013)
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
6.5.1 Identification—PrimaryWallnerlinesareusuallyquite 6.5.2 Formation—They result from the interaction of a
distinct and always have their source associated with some propagating crack with an elastic pulse coming from the
discontinuity which was present before fracture. Examples encounter of the crack front with a preexisting discontinuity.
would include bubbles or other inclusions, surface damage or 6.5.3 Significance—The convex side is toward the direction
an abrupt change in surface contour. (See Fig. 3 and Fig. 4.) of crack propagation. Primary Wallner lines can be used to
C1256 − 93 (2013)
FIG. 6 Secondary Wallner Lines Generated From Mist Formation
FIG. 8 Tertiary Wallner Lines
within the pattern.They are neither hook-shaped nor trace to a
discontinuity as the source of an elastic pulse. (See Fig. 7 and
Fig. 8.)
6.7.2 Formation—They result from an interaction at the
crack front with sonic waves from an external shock or from
stress release at the onset of cracking.
6.7.3 Significance—They indicate that the failure resulted
fromamechanicalshock,whereanelasticpulsewasgenerated
outside the plane of crack propagation.
6.8 Dwell Mark:
6.8.1 Identification—Dwell marks, also called arrest lines,
have a similar rib-shaped contour to that of Wallner lines but
are distinctly sharper, often exhibiting a noticeable change in
FIG. 7 Tertiary Wallner Lines Created by Sonic Pulses Produced
fracture plane after the mark and may have twist hackle
from Mechanical Shock Which Broke the Material
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 re
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