ASTM D6272-17e1

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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Designation: D6272 − 17
Standard Test Method for
Flexural Properties of Unreinforced and Reinforced Plastics
and Electrical Insulating Materials by Four-Point Bending
This standard is issued under the fixed designation D6272; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Editorially corrected 7.2.2 in July 2020.
However, ISO 14125, Method B specifies only a load span of ⁄3 the
1. Scope*
support span whereas D6272 also permits a load span of ⁄2 the support
1.1 This test method covers the determination of flexural
span. For this reason and other differences in technical content, exercise
properties of unreinforced and reinforced plastics, including extreme care if attempting to compare results between the two test
methods.
high-modulus composites and electrical insulating materials in
theformofrectangularbarsmoldeddirectlyorcutfromsheets, 1.6 This international standard was developed in accor-
plates, or molded shapes. These test methods are generally
dance with internationally recognized principles on standard-
applicable to rigid and semirigid materials. However, flexural ization established in the Decision on Principles for the
strength cannot be determined for those materials that do not
Development of International Standards, Guides and Recom-
break or that do not fail in the outer fibers. This test method mendations issued by the World Trade Organization Technical
utilizes a four point loading system applied to a simply
Barriers to Trade (TBT) Committee.
supported beam.
2. Referenced Documents
1.2 This test method describes two procedures (ProcedureA
2.1 ASTM Standards:
and Procedure B), the selection of which depends on the
D618 Practice for Conditioning Plastics for Testing
behavior of the sample to be tested as explained below:
D638 Test Method for Tensile Properties of Plastics
1.2.1 Procedure A, designed principally for materials that
D790 Test Methods for Flexural Properties of Unreinforced
break at comparatively small deflections. It shall be used for
and Reinforced Plastics and Electrical Insulating Materi-
measurement of flexural properties, particularly flexural
als
modulus, unless the material specification states otherwise.
D883 Terminology Relating to Plastics
1.2.2 Procedure B, designed particularly for those materials
D4000 Classification System for Specifying Plastic Materi-
that undergo large deflections during testing. It is suitable for
als
measurement of flexural strength.
D5947 Test Methods for Physical Dimensions of Solid
1.3 Comparative tests are permitted to be run according to
Plastics Specimens
either procedure, provided that the procedure is found satisfac-
E4 Practices for Force Verification of Testing Machines
tory for the material being tested.
E83 Practice for Verification and Classification of Exten-
1.4 The values stated in SI units are to be regarded as the
someter Systems
standard. The values provided in parentheses are for informa-
E691 Practice for Conducting an Interlaboratory Study to
tion only.
Determine the Precision of a Test Method
2.2 ISO Standard:
1.5 This standard does not purport to address all of the
ISO 14125 (Method B) Fibre-Reinforced Plastic
safety concerns, if any, associated with its use. It is the
Composites—Determination of Flexural Properties
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
3. Terminology
mine the applicability of regulatory limitations prior to use.
3.1 Definitions:
NOTE 1—This test method is similar to ISO 14125, Method B.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
This test method is under the jurisdiction ofASTM Committee D20 on Plastics contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
and is the direct responsibility of Subcommittee D20.10 on Mechanical Properties. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved March 1, 2017. Published March 2017. Originally the ASTM website.
approved in 1998. Last previous edition approved in 2010 as D6272 - 10. DOI: Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
10.1520/D6272-17E01. 4th Floor, New York, NY 10036, http://www.ansi.org.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D6272 − 17
3.1.1 Definitions of terms applying to these test methods 5.3 Flexural properties vary with specimen depth,
appear in Terminology D883 and Annex A2 of Test Method temperature, atmospheric conditions, and the difference in rate
D638. of straining specified in Procedures A and B.
5.4 Before proceeding with this test method, reference the
4. Summary of Test Method
specification of the material being tested. Any test specimen
4.1 A bar of rectangular cross section rests on two supports
preparation, conditioning, dimensions, or testing parameters
and is loaded at two points (by means of two loading noses),
covered in the material specification, or both, shall take
each an equal distance from the adjacent support point. The
precedence over those mentioned in this test method. If there
distancebetweentheloadingnoses(theloadspan)iseitherone
are no material specifications, then these default conditions
third or one half of the support span (see Fig. 1). A support
apply. Table 1 in Classification D4000 lists the ASTM materi-
span-to-depth ratio of 16:1 shall be used unless there is reason
als standards that currently exist.
to suspect that a larger span-to-depth ratio is required, such as
with certain laminated materials (see Section 7 for guidance).
6. Apparatus
4.2 The specimen is deflected until rupture occurs in the
6.1 Testing Machine—Aproperly calibrated testing machine
outer fibers or until the maximum fiber strain (see 12.8)of5%
capable of operating at constant rates of crosshead motion over
is reached, whichever occurs first.
the range indicated, and in which the error in the load
measuring system shall not exceed 6 1 % of maximum load
5. Significance and Use
expected to be measured. It shall be equipped with a deflection
5.1 Flexural properties determined by this test method are
measuring device. The stiffness of the testing machine shall be
especially useful for quality control and specification purposes. such that the total elastic deformation of the system does not
exceed 1 % of the total deflection of the test specimen during
5.2 This test method is recommended for those materials
testing, or appropriate corrections shall be made. The load
that do not fail within the strain limits imposed byTest Method
indicating mechanism shall be essentially free from inertial lag
D790. The major difference between four point and three point
at the crosshead rate used. The accuracy of the testing machine
bending modes is the location of the maximum bending
shall be verified in accordance with Practices E4.
moment and maximum axial fiber stress. In four point bending
the maximum axial fiber stress is uniformly distributed be- 6.2 Loading Noses and Supports—The loading noses and
tween the loading noses. In three point bending the maximum supports shall have cylindrical surfaces. In order to avoid
axialfiberstressislocatedimmediatelyundertheloadingnose. excessive indentation, or failure due to stress concentration
directly under the loading noses, the radii of the loading noses
and supports shall be 5.0 6 0.1 mm (0.197 6 0.004 in.) unless
otherwise specified or agreed upon between the interested
parties. When other loading noses and supports are used they
must comply with the following requirements: they shall be at
least 3.2 mm ( ⁄8 in.) for all specimens, and for specimens 3.2
mm ( ⁄8 in.) or greater in depth, the radius of the supports shall
not exceed 1.6 times the specimen depth. They shall be this
large if significant indentation or compressive failure occurs.
The arc of the loading noses in contact with the specimen shall
be sufficiently large to prevent contact of the specimen with the
sides of the noses (see Fig. 2).
NOTE 2—Test data have shown that the loading noses and support
dimensions can influence the flexural modulus and flexural strength
values. The loading noses dimension has the greater influence. Dimen-
sions of loading noses and supports are requirements for the material
specifications.
NOTE 1—Default radii 5.0 mm; see 6.2.
FIG. 2 Loading Noses and Supports (Example of One Third Sup-
FIG. 1 Loading Diagram port Span)
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D6272 − 17
depth exceeds the width, buckling may occur.
6.3 Deflection Measuring Device—A properly calibrated
device to measure the deflection of the beam at the common 1
7.2.2 Materials Less than 1.6 mm ( ⁄16 in.) in Thickness—
center of the loading span, that meets or exceeds Practice E83,
Thespecimenshallbe50.8mm(2in.)longby12.7mm( ⁄2in.)
Class B-2 for modulus, and Class C for other strain
wide, tested flatwise on a 25.4-mm (1-in.) support span.
measurements, shall be used. The device shall automatically
NOTE 4—Use of the formulas for simple beams cited in these test
and continuously record the deflection during the test.
methods for calculating results presumes that beam width is small in
6.4 Micrometers—Suitable micrometers for measuring the
comparison with the support span. Therefore, the formulas do not apply
rigorously to these dimensions.
width and thickness of the test specimen to an incremental
NOTE 5—Where machine sensitivity is such that specimens of these
discrimination of at least 0.025 mm (0.001 in.) shall be used.
dimensions cannot be measured, wider specimens or shorter support
All width and thickness measurements of rigid and semi-rigid
spans, or both, may be used, provided the support span-to-depth ratio is at
plastics are measurable with a hand micrometer with ratchet as
least 14 to 1. Include all dimensions in the report.
described in Test Method D5947. A similar instrument for
7.3 Laminated Thermosetting Materials and Sheet and
measuring the thickness of non-rigid test specimens shall have
Plate Materials Used for Electrical Insulation, Including
a reduced contact measuring pressure of 25 6 2.5 kPa (3.6 6
Vulcanized Fiber and Glass-Bonded Mica—Forpaper-baseand
0.36 psi). Parallelism and flatness of foot and anvil shall
fabric-base grades over 25.4 mm (1 in.) in nominal thickness,
conform to the portion of the calibration section of Test
the specimens shall be machined on both surfaces to a depth of
Method D5947.
25.4 mm. For glass-base and nylon-base grades, specimens
7. Test Specimen over 12.7 mm ( ⁄2 in.) in nominal depth shall be machined on
bothsurfacestoadepthof12.7mm.Thesupportspan-to-depth
7.1 Methods to produce the specimens include cutting them
ratio shall be chosen such that failures occur in the outer fibers
from sheets, plates, or molded shapes, or molding them to the
of the specimens, due only to the bending moment (see Note
desired finished dimensions. The actual dimensions used in
6). Three recommended support span-to-depth ratios are 16,
Section 12 (Calculation) shall be measured in accordance with
32, and 40 to 1. When laminated materials exhibit low
Test Method D5947.
compressive strength perpendicular to the laminations, they
7.1.1 Any necessary polishing of specimens shall be done
shall be loaded with a large radius loading noses (up to 1.5
only in the lengthwise direction of the specimen.
times the specimen depth) to prevent premature damage to the
7.2 Sheet Materials (Except Laminated Thermosetting Ma-
outer fibers.
terials and Certain Materials Used for Electrical Insulation,
7.4 Molding Materials (Thermoplastics and Thermosets)—
Including Vulcanized Fiber and Glass Bonded Mica):
The recommended specimen for molding materials is 127 by
7.2.1 Materials 1.6 mm ( ⁄16 in.) or Greater in Thickness—
1 1
12.7 by 3.2 mm (5 by ⁄2 by ⁄8 in.) tested flatwise on a support
For flatwise tests, the depth of the specimen shall be the
span, resulting in a support span-to-depth ratio of 16 (tolerance
thickness of the material. For edgewise tests, the width of the
+ 4 or – 2).Avoid thicker specimens if they exhibit significant
specimenshallbethethicknessofthesheet,andthedepthshall
shrink marks or bubbles when molded.
not exceed the width (see Notes 3 and 4). For all tests, the
support span shall be 16 (tolerance 6 1) times the depth of the
7.5 High-Strength Reinforced Composites, Including Highly
beam. Specimen width shall not exceed one fourth of the
Orthotropic Laminates—The support span-to-depth ratio shall
support span for specimens greater than 3.2 mm ( ⁄8 in.) in
be chosen such that failures occur in the outer fibers of the
depth. Specimens 3.2 mm or less in depth shall be 12.7 mm ( ⁄2
specimens, due only to the bending moment (Note 6). Three
in.) in width. The specimen shall be long enough to allow for
recommended support span-to-depth ratios are 16:1, 32:1, and
overhanging on each end of at least 10 % of the support span,
40:1. However, for some highly anisotropic composites, shear
but in no case less than 6.4 mm ( ⁄4 in.) on each end. Overhang
deformation can significantly influence modulus
shall be sufficient to prevent the specimen from slipping
measurements, even at span-to-depth ratios as high as 40:1.
through the supports.
Hence, for these materials, an increase in span-to-depth ratio to
7.2.1.1 Whenever possible, the original surface of the sheet
60:1 is recommended to eliminate shear effects when modulus
shall be unaltered. However, where testing machine limitations
data are required. The flexural modulus of highly anisotropic
make it impossible to follow the above criterion on the
laminatesisastrongfunctionofply-stackingsequenceandwill
unaltered sheet, one or both surfaces shall be machined to
not necessarily correlate with tensile modulus, that is not
provide the desired dimensions, and the location of the
stacking-sequence dependent.
specimens with reference to the total depth shall be noted. It is
NOTE 6—As a general rule, support span-to-depth ratios of 16 to 1 are
feasible that the value obtained on specimens with machined
satisfactory when the ratio of the tensile strength to shear strength is less
surfaces will differ from those obtained on specimens with
than 8 to 1, but the support span-to-depth ratio must be increased for
original surfaces. Consequently, any specifications for flexural
composite laminates having relatively low shear strength in the plane of
properties on the thicker sheets must state whether the original the laminate and relatively high tensile strength parallel to the support
span.
surfaces are to be retained or not. When only one surface was
machined, it must be stated whether the machined surface was
8. Number of Test Specimens
on the tension or compression side of the beam.
8.1 Atleastfivespecimensshallbetestedforeachsamplein
NOTE 3—Edgewise tests are not applicable for sheets that are so thin
that specimens meeting these requirements cannot be cut. If specimen the case of isotropic materials or molded specimens.
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D6272 − 17
8.2 For each sample of anisotropic material in sheet form, at 10.1.5 Align the loading noses and supports so that the axes
least five specimens shall be tested for each of the following of the cylindrical surfaces are parallel and the load span is
conditions. Recommended conditions are flatwise and edge- either one third or one half of the support span. A plate
wise tests on specimens cut in lengthwise and crosswise containing parallel grooves into which the loading noses and
directions of the sheet. For the purposes of this test, “length- supports will fit when properly aligned is suitable for checking
wise” shall designate the principal axis of anisotropy and shall parallelism. Center the specimen on the supports, with the long
be interpreted to mean the direction of the sheet known to be axis of the specimen perpendicular to the loading noses and
stronger in flexure. “Crosswise” shall be the sheet direction supports.The loading nose assembly shall be of the type which
known to be the weaker in flexure and shall be at 90° to the will not rotate.
lengthwise direction. 10.1.6 Apply the load to the specimen at the specified
crosshead rate, and take simultaneous load-deflection data.
9. Conditioning Measure deflection by a device under the specimen in contact
with it at the common center of the spans, the device being
9.1 Conditioning—Condition the test specimens in accor-
mounted stationary relative to the specimen supports. Do not
dance with Procedure A of Practice D618, unless otherwise
use the movement of the loading noses relative to the supports.
specified by contract or the relevant ASTM material specifica-
Make appropriate corrections for indentation in the specimens
tion. Temperature and humidity tolerances shall be in accor-
and deflections in the weighing system of the machine. If
dance with Section 7 of Practice D618 unless specified
desired, plot load-deflection curves to determine the flexural
differently by contract or material specification.
yield strength, secant or tangent modulus of elasticity, and the
9.2 Test Conditions—Conduct the tests the same tempera-
total work measured by the area under the load-deflection
ture and humidity used for conditioning with tolerances in
curve.
accordance with Section 7 of Practice D618 unless otherwise
10.1.7 If no break has occurred in a specimen by the time
specified by contract or the relevant ASTM material specifica-
the maximum strain in the outer fibers has reached 0.05
tion.
mm/mm (in./in.), discontinue the test (Note 7). The deflection
at which this
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