ASTM C158-02(2012)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: C158 − 02 (Reapproved 2012)
Standard Test Methods for
Strength of Glass by Flexure (Determination of Modulus of
Rupture)
This standard is issued under the fixed designation C158; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope SI10-02 IEEE/ASTM SI 10American National Standard for
UseoftheInternationalSystemofUnits(SI):TheModern
1.1 These test methods cover the determination of the
Metric System
modulus of rupture in bending of glass and glass-ceramics.
1.2 These test methods are applicable to annealed and
3. Terminology
prestressed glasses and glass-ceramics available in varied
3.1 Definitions:
forms.Alternative test methods are described; the test method
3.1.1 glass-ceramics—solid materials, predominantly crys-
used shall be determined by the purpose of the test and
talline in nature, formed by the controlled crystallization of
geometric characteristics of specimens representative of the
glasses.
material.
3.1.2 modulus of rupture in bending—the value of maxi-
1.2.1 Test Method A is a test for modulus of rupture of flat
mum tensile or compressive stress (whichever causes failure)
glass.
in the extreme fiber of a beam loaded to failure in bending
1.2.2 Test Method B is a comparative test for modulus of
computed from the flexure formula:
rupture of glass and glass-ceramics.
Mc
1.3 The test methods appear in the following order:
S 5 (1)
b
I
Sections
Test Method A 6 to 9
where:
Test Method B 10 to 15
M = maximum bending moment, computed from the maxi-
1.4 This standard does not purport to address all of the
mum load and the original moment arm,
safety concerns, if any, associated with its use. It is the
c = initialdistancefromtheneutralaxistotheextremefiber
responsibility of the user of this standard to establish appro-
where failure occurs, and
priate safety and health practices and determine the applica-
I = initial moment of inertia of the cross section about the
bility of regulatory limitations prior to use. Specific hazard
neutral axis.
statements are given in Section 10 and A1.5, A2.3.3, A2.4.3
3.1.3 prestressed—material in which a significant and con-
and A2.5.3.
trolled degree of compressive stress has been deliberately
produced in the surfaces.
2. Referenced Documents
3.1.4 standard laboratory atmosphere—an atmosphere hav-
2.1 ASTM Standards:
ingatemperatureof23 62°Candarelativehumidityof40 6
C148Test Methods for Polariscopic Examination of Glass
10%.
Containers
E4Practices for Force Verification of Testing Machines 3.2 Definitions of Terms Specific to This Standard:
3.2.1 abraded—describes a test specimen that has at least a
portionoftheareaofmaximumsurfacetensilestresssubjected
to an operationally defined procedure for mechanical abrasion.
These test methods are under the jurisdiction of ASTM Committee C14 on
The severity and uniformity of abrasion should be sufficient to
Glass and Glass Products and are the direct responsibility of Subcommittee C14.04
on Physical and Mechanical Properties.
ensureoriginoffailuresubstantiallyintheregionofmaximum
Current edition approved Oct. 1, 2012. Published October 2012. Originally
stress.
approvedin1940.Lastpreviouseditionapprovedin2002asC158–02(2007).DOI:
10.1520/C0158-02R12.
3.2.2 annealed glass—describes a specimen that shall not
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
have a temper or degree of residual stress resulting from prior
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
thermal treatment in excess of the following limits when
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. measured polarimetrically (see Annex A1):
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C158 − 02 (2012)
3.2.2.1 Specimens of rectangular section shall not have a The use of a controlled abrasion of the specimen as a final
tensile stress at the midplane of more than 1.38-MPa (200-psi) normalizing procedure is recommended for such comparative
nor more than 2.76-MPa (400-psi) compression at the surface. tests.
3.2.2.2 Specimensinrodformmaybeexaminedbyviewing
4.6 A comparative abraded strength, determined as sug-
through a diameter at least four diameters from an end. The
gestedinTestMethodB,isnottobeconsideredasaminimum
apparent central axial tension shall not exceed 0.92 MPa (133
valuecharacteristicofthematerialtestednorasdirectlyrelated
psi).Surfacecompression,ifmeasuredonsectionscutfromthe
to a maximum attainable strength value through test of
rods,shallnotexceed2.76MPa(400psi)whenviewedaxially.
specimens with identical flaws. The operationally defined
abrasion procedure undoubtedly produces flaws of differing
4. Significance and Use
severity when applied to varied materials, and the measured
comparative strengths describe the relative ability to withstand
4.1 For the purpose of this test, glasses and glass-ceramics
are considered brittle (perfectly elastic) and to have the externally induced stress as affected by the specific abrasion
procedure.
property that fracture normally occurs at the surface of the test
specimen from the principal tensile stress. The modulus of
5. Apparatus
rupture is considered a valid measure of the tensile strength
subject to the considerations discussed below.
5.1 Testing Machine—The loading mechanism shall be
sufficiently adjustable to give the required uniform rate of
4.2 It is recognized that the modulus of rupture for a group
increase of stress. The load-measuring system shall be essen-
oftestspecimensisinfluencedbyvariablesassociatedwiththe
tially free of inertial lag at the loading rates used and shall be
test procedure. These include the rate of stressing, test
equipped with means for retaining indication of the maximum
environment, and the area of the specimen subjected to stress.
load applied to the specimen. The accuracy of the testing
Suchfactorsarespecifiedinthetestprocedureorrequiredtobe
machine shall conform to the requirements of Practice E4.
stated in the report.
5.2 Bearing Edges—Cylindrical bearing edges of approxi-
4.3 It is also recognized that the variables having the
mately3-mm( ⁄8-in.)radiusshallbeusedforthesupportofthe
greatest effect on the modulus of rupture value for a group of
test specimen and the application of the load. The bearing
test specimens are the condition of the surfaces and glass
edges shall be of steel and sufficiently hardened to prevent
quality near the surfaces in regard to the number and severity
excessive deformation under load. Two-point loading tests
of stress-concentrating discontinuities or flaws, and the degree
shall be performed with the loading member pivoted about a
of prestress existing in the specimens. Each of these can
central transverse axis to ensure equal distribution of load
represent an inherent part of the strength characteristic being
betweenthetwobearingedges.Forthetestingofspecimensof
determined or can be a random interfering factor in the
rectangular section, both loading bearing edges and one sup-
measurement.
port bearing edge also shall be provided laterally to compen-
4.4 Test Method A is designed to include the condition of
sate for irregularities of the test specimen. Fig. 1 shows a
the surface of the specimen as a factor in the measured
suitable arrangement using pinned bearing edges. In test of
strength. It is, therefore, desirable to subject a fixed and
specimens of a circular or elliptical section, the fixed cylindri-
significant area of the surface to the maximum tensile stress.
cal support edges may have a curvature of approximately 76
Since the number and severity of surface flaws in glass are
mm (3 in.) in the plane of the bearing edge to stabilize the
primarily determined by manufacturing and handling
alignment of the specimens. Such support edges are shown in
processes, this test method is limited to products from which
Fig. 2.
specimens of suitable size can be obtained with minimal
dependence of measured strength upon specimen preparation
TEST METHOD A—TEST FOR MODULUS OF
techniques. This test method is therefore designated as a test
RUPTURE OF FLAT GLASS
for modulus of rupture of flat glass.
6. Test Specimens
4.5 Test Method B describes a general procedure for test,
applicable to specimens of rectangular or elliptical cross 6.1 Preparation of Specimens—Test specimens shall be cut
section. This test method is based on the assumption that a from the sheet stock with a diamond or a cutting wheel. Both
comparative measurement of strength on groups of specimens longitudinalcutsshallbeonthesameoriginalsurfaceandnone
is of significance for many purposes, such as determining the of the original edge of the sheet shall be used as a longitudinal
effect of environment or stress duration, or the effectiveness of side of the specimen. End cuts may be on either surface. The
varied prestressing techniques or strengths characteristic of direction of cutting of half of the total number of specimens
glass-ceramics of differing composition or heat treatment. In shall be perpendicular to the direction of cutting of the
this test method the surfaces of the specimens are not assumed remainder. Specimens that must be cut from sheet stock prior
to be characteristic of a product or material, but are considered to the use of a prestressing treatment shall have the corners of
to be determined by the procedures used to prepare the the longitudinal edges rounded to minimize damage to the
specimens. Though the stated procedure permits a wide varia- edges in the prestressing process. All operations shall be
tion in both specimen size and test geometry, it is necessary to performed with the direction of grind or polish parallel to the
use identical test conditions and equivalent procedures for longitudinal axis.The radius of the corner shall not exceed 1.6
specimen preparation to obtain comparable strength values. mm ( ⁄16 in.).
C158 − 02 (2012)
FIG. 1 Pinned Bearing Edges
FIG. 2 Fixed Cylindrical Support Edges
6.2 Size of Specimens—The specimens shall be approxi- Carefully place each specimen in the test fixture to minimize
mately 250 mm (10 in.) in length and 38.1 6 3.2 mm (1 ⁄2 6 possible damage and to ensure alignment of specimen in the
⁄8 in.) in width. The variation in width or thickness shall not fixture. The permissible maximum fiber stress due to initial
exceed 5% from one end to the other. load on the specimen shall not exceed 25% of the mean
modulus of rupture. Load the specimen at a constant rate to
6.3 Number of Specimens—At least 30 specimens shall be
failure. For annealed glass the rate of loading shall correspond
used for one test and shall preferably be taken from several
to a rate of increase of maximum stress of 1.1 6 0.2 MPa/s
sheets, or regions of a single sheet.
(10000 6 2000 psi/min). Test prestressed glasses with the
6.4 Examination of Specimens—Any specimen may be re-
increase of maximum stress per minute between 80 and 120%
jected prior to test for observable defects considered likely to
of the modulus of rupture.The first six specimens of the group
affect the modulus of rupture. To be considered representative
may be tested at a loading rate based on an estimate of the
of annealed glass the specimens must meet the requirement of
modulus of rupture and the average value for these specimens
3.2.2. At least 30% of the specimens shall be examined for
used to correct this estimate. If range of width and thickness
residual stress. If any of these fail to meet the requirement, the
variation in the specimens is less than 5%, the mean values
remainder of the specimens shall be examined and those
may be used to represent all specimens for the purpose of
exceeding the stated limit shall be rejected.
calculation of rate of loading.
6.5 Float Glass—The surface of float glass in contact with
7.2 Determine the thickness and width of each specimen to
tin has been found to be lower in strength (1) as compared to
61%. To avoid damage from gaging in the critical area, take
the “air” surface. For comparative tests, therefore, surface
measurements prior to testing near each end with a separation
orientation should be kept constant.
equal to the support span, and average the values. Measure-
ments following test shall be in the uniformly stressed region
7. Procedure
of the specimen.
7.1 Space the supporting edges of the test fixture 200 mm
(8.00 in.) apart and centrally position the loading edges with a 7.3 Determine the location of point of failure and note it as
separation of 100 mm (4.00 in.). Break specimens having cut edgeorfaceorigin.Plasticorothertapeoflowelasticmodulus
edges with the cutter marks on the face under compression. may be used on the compressive surface to contain the
C158 − 02 (2012)
fragmentation and allow observation of point of failure for TEST METHOD B—COMPARATIVE TEST FOR
highly prestressed specimens. Report all values, although MODULUS OF RUPTURE OF GLASS AND GLASS-
segregation of edge break values is permitted. CERAMICS
10. Hazards
8. Calculation
10.1 Care should be exercised in all handling of specimens
8.1 Calculate the modulus of rupture, initial maximum fiber
to avoid the introduction of random and severe flaws.
stress, and rate of increase of stress as follows:
10.2 Abrasionofspecimensofrectangularsectionshouldbe
8.1.1 Modulus of rupture:
performed so that corners are not subjected to abrasion.
3 La
Abrasion should be limited to the region of uniform tensile
S 5 (2)
bd
stress between the loading edges, and it should cover a
significant fraction of this area.
8.1.2 Maximum stress due to initial load if present:
10.3 Followinganabrasionprocedure,aminimumtimeof1
3 L a
S 5 (3)
hmustelapsebeforetapingortestingofspecimens(seeA2.2).
0 2
bd
10.4 Deflectometers, if used during testing, should not
8.1.3 Rate of increase of maximum stress:
contact the tension face of the specimen.
3a ∆L
10.5 If tests are performed at temperatures deviating from
R 5 3 (4)
bd ∆t
ambient, it is necessary to allow the specimen to reach thermal
equilibrium to eliminate the presence of thermally induced
S
R 5 S 2
stressesinthespecimen.Thereportshouldindicatethethermal
t
history prior to testing.
where:
11. Test Specimens
S = modulus of rupture, MPa (psi),
S = maximum fiber stress due to initial load if present,
11.1 Preparation of Specimens:
MPa
...