ASTM D6272-00
(Test Method)Standard Test Method for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials by Four-Point Bending
Standard Test Method for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials by Four-Point Bending
SCOPE
1.1 This test method covers the determination of flexural properties of unreinforced and reinforced plastics, including high-modulus composites and electrical insulating materials in the form of rectangular bars molded directly or cut from sheets, plates, or molded shapes. These test methods are generally applicable to rigid and semirigid materials. However, flexural strength cannot be determined for those materials that do not break or that do not fail in the outer fibers. This test method utilizes a four point loading system applied to a simply supported beam.
1.2 This test method may be used with two procedures:
1.2.1 Procedure A, designed principally for materials that break at comparatively small deflections.
1.2.2 Procedure B, designed particularly for those materials that undergo large deflections during testing.
1.2.3 Procedure A shall be used for measurement of flexural properties, particularly flexural modulus, unless the material specification states otherwise. Procedure B may be used for measurement of flexural strength.
1.3 Comparative tests may be run according to either procedure, provided that the procedure is found satisfactory for the material being tested.
1.4 The values stated in SI units are to be regarded as the standard. The values provided in parentheses are for information only.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
Note 1—This test method is equivalent to, but not identical to ISO 14125 (Method B).
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Designation: D 6272 – 00
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 D 6272; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope * Insulating Materials for Testing
D 638 Test Method for Tensile Properties of Plastics
1.1 This test method covers the determination of flexural
D 790 Test Method for Flexural Properties of Unreinforced
properties of unreinforced and reinforced plastics, including
and Reinforced Plastics and Electrical Insulating Materi-
high-modulus composites and electrical insulating materials in
als
the form of rectangular bars molded directly or cut from sheets,
D 883 Terminology Relating to Plastics
plates, or molded shapes. These test methods are generally
D 4000 Classification System for Specifying Plastic Mate-
applicable to rigid and semirigid materials. However, flexural
rials
strength cannot be determined for those materials that do not
D 4066 Classification System for Nylon Injection and Ex-
break or that do not fail in the outer fibers. This test method
trusion Materials (PA)
utilizes a four point loading system applied to a simply
D 5947 Methods for Physical Dimensions of Solid Plastic
supported beam.
Specimens
1.2 This test method may be used with two procedures:
E 4 Practices for Load Verification of Testing Machines
1.2.1 Procedure A, designed principally for materials that
E 83 Practice for Verification and Classification of Exten-
break at comparatively small deflections.
someters
1.2.2 Procedure B, designed particularly for those materials
E 691 Practice for Conducting an Interlaboratory Test Pro-
that undergo large deflections during testing.
gram to Determine the Precision of Test Methods
1.2.3 Procedure A shall be used for measurement of flexural
2.2 ISO Standard:
properties, particularly flexural modulus, unless the material
ISO 14125 (Method B)
specification states otherwise. Procedure B may be used for
measurement of flexural strength.
3. Terminology
1.3 Comparative tests may be run according to either
3.1 Definitions:
procedure, provided that the procedure is found satisfactory for
3.1.1 Definitions of terms applying to these test methods
the material being tested.
appear in Terminology D 883 and Annex A2 of Test Method
1.4 The values stated in SI units are to be regarded as the
D 638.
standard. The values provided in parentheses are for informa-
tion only.
4. Summary of Test Method
1.5 This standard does not purport to address all of the
4.1 A bar of rectangular cross section rests on two supports
safety concerns, if any, associated with its use. It is the
and is loaded at two points (by means of two loading noses),
responsibility of the user of this standard to establish appro-
each an equal distance from the adjacent support point. The
priate safety and health practices and determine the applica-
distance between the loading noses (the load span) is either one
bility of regulatory limitations prior to use.
third or one half of the support span (see Fig. 1). A support
NOTE 1—This test method is equivalent to, but not identical to ISO
span-to-depth ratio of 16:1 shall be used unless there is reason
14125 (Method B).
to suspect that a larger span-to-depth ratio may be required, as
may be the case for certain laminated materials (see Section 7
2. Referenced Documents
and Note 8 for guidance).
2.1 ASTM Standards:
4.2 The specimen is deflected until rupture occurs in the
D 618 Practice for Conditioning Plastics and Electrical
Annual Book of ASTM Standards, Vol 08.01.
Annual Book of ASTM Standards, Vol 08.02.
This test method is under the jurisdiction of ASTM Committee D20 on Plastics
Annual Book of ASTM Standards, Vol 03.01.
and is the direct responsibility of Subcommittee D20.10 on Mechanical Properties.
Annual Book of ASTM Standards, Vol 14.02.
Current edition approved July 10, 2000. Published October 2000. Originally
Available from American National Standards Institute, 11 W. 42nd St., 13th
published as D 6272 – 98. Last previous edition D 6272 – 98.
Floor, New York, NY 10036.
*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.
D 6272
measuring system shall not exceed 6 1 % of maximum load
expected to be measured. It shall be equipped with a deflection
measuring device. The stiffness of the testing machine shall be
such that the total elastic deformation of the system does not
exceed 1 % of the total deflection of the test specimen during
testing, or appropriate corrections shall be made. The load
indicating mechanism shall be essentially free from inertial lag
at the crosshead rate used. The accuracy of the testing machine
shall be verified in accordance with Practices E 4.
6.2 Loading Noses and Supports—The loading noses and
supports shall have cylindrical surfaces. In order to avoid
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 may
be up to 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-
FIG. 1 Loading Diagram
sions of loading noses and supports must be specified for material
specifications.
outer fibers or until the maximum fiber strain (see 12.7) of 5 %
6.3 Deflection Measuring Device—A properly calibrated
is reached, whichever occurs first.
device to measure the deflection of the beam at the common
center of the loading span, that meets or exceeds Practice E 83,
5. Significance and Use
Class C, shall be used. The device shall automatically and
5.1 Flexural properties determined by this test method are
continuously record the deflection during the test.
especially useful for quality control and specification purposes.
6.4 Micrometers—Suitable micrometers for measuring the
5.2 This test method may be more suited for those materials
width and thickness of the test specimen to an incremental
that do not fail within the strain limits imposed by Test Method
discrimination of at least 0.025 m (0.001 in.) should be used.
D 790. The major difference between four point and three point
All width and thickness measurements of rigid and semi-rigid
bending modes is the location of the maximum bending
plastics may be measured with a hand micrometer with ratchet.
moment and maximum axial fiber stress. In four point bending
A suitable instrument for measuring the thickness of non-rigid
the maximum axial fiber stress is uniformly distributed be-
test specimens shall have: a contact measuring pressure of 25
tween the loading noses. In three point bending the maximum
6 2.5 kPa (3.6 6 0.036 psi), a movable circular contact foot
axial fiber stress is located immediately under the loading nose.
6.35 6 0,025 mm (0.250 6 0.001 in.) in diameter and a fixed
5.3 Flexural properties may vary with specimen depth,
anvil 6.35 6 0,025 mm (0.250 6 0.001 in.) in diameter and
temperature, atmospheric conditions, and the difference in rate
being parallel to the contact foot within 0.005 mm (0.0002 in.)
of straining specified in Procedures A and B.
over the entire foot area. Flatness of foot and anvil shall
5.4 Before proceeding with this test method, reference
should be made to the specification of the material being tested.
Any test specimen preparation, conditioning, dimensions, or
testing parameters covered in the material specification, or
both, shall take precedence over those mentioned in this test
method. If there are no material specifications, then these
default conditions apply. Table 1 in Classification D 4000 lists
the ASTM materials standards that currently exist.
6. Apparatus
6.1 Testing Machine—A properly calibrated testing ma-
NOTE 1—Default radii 5.0 mm; see 6.2.
chine that can be operated at constant rates of crosshead motion
FIG. 2 Loading Noses and Supports (Example of One Third
over the range indicated, and in which the error in the load Support Span)
D 6272
conform to the portion of the calibration section of Test specimens over 12.7 mm ( ⁄2 in.) in nominal depth shall be
Method D 5947. machined on both surfaces to a depth of 12.7 mm. The support
span-to-depth ratio shall be chosen such that failures occur in
7. Test Specimen
the outer fibers of the specimens, due only to the bending
moment (see Note 8). Three recommended support span-to-
7.1 The specimens may be cut from sheets, plates, or
depth ratios are 16, 32, and 40 to 1. When laminated materials
molded shapes, or may be molded to the desired finished
exhibit low compressive strength perpendicular to the lamina-
dimensions. The actual dimensions used in Section 12 (Calcu-
tions, they shall be loaded with a large radius loading noses (up
lation) shall be measured in accordance with Test Method
to 1.5 times the specimen depth) to prevent premature damage
D 5947.
to the outer fibers.
NOTE 3—Any necessary polishing of specimens shall be done only in
7.4 Molding Materials (Thermoplastics and Thermosets)—
the lengthwise direction of the specimen.
The recommended specimen for molding materials is 127 by
7.2 Sheet Materials (Except Laminated Thermosetting Ma- 1 1
12.7 by 3.2 mm (5 by ⁄2by ⁄8 in.) tested flatwise on a support
terials and Certain Materials Used for Electrical Insulation,
span, resulting in a support span-to-depth ratio of 16 (tolerance
Including Vulcanized Fiber and Glass Bonded Mica):
+ 4 or – 2). Thicker specimens should be avoided if they
7.2.1 Materials 1.6 mm ( ⁄16 in.) or Greater in Thickness—
exhibit significant shrink marks or bubbles when molded.
For flatwise tests, the depth of the specimen shall be the
7.5 High-Strength Reinforced Composites, Including Highly
thickness of the material. For edgewise tests, the width of the
Orthotropic Laminates—The support span-to-depth ratio shall
specimen shall be the thickness of the sheet, and the depth shall
be chosen such that failures occur in the outer fibers of the
not exceed the width (see Notes 5 and 6). For all tests, the
specimens, due only to the bending moment (Note 8). Three
support span shall be 16 (tolerance 6 1) times the depth of the
recommended support span-to-depth ratios are 16:1, 32:1, and
beam. Specimen width shall not exceed one fourth of the
40:1. However, for some highly anisotropic composites, shear
support span for specimens greater than 3.2 mm ( ⁄8 in.) in
deformation can significantly influence modulus measure-
depth. Specimens 3.2 mm or less in depth shall be 12.7 mm ( ⁄2
ments, even at span-to-depth ratios as high as 40:1. Hence, for
in.) in width. The specimen shall be long enough to allow for
these materials, an increase in span-to-depth ratio to 60:1 is
overhanging on each end of at least 10 % of the support span,
recommended to eliminate shear effects when modulus data are
but in no case less than 6.4 mm ( ⁄4in.) on each end. Overhang
required. It should also be noted that the flexural modulus of
shall be sufficient to prevent the specimen from slipping
highly anisotropic laminates is a strong function of ply-
through the supports.
stacking sequence and will not necessarily correlate with
tensile modulus, that is not stacking-sequence dependent.
NOTE 4—Whenever possible, the original surface of the sheet shall be
unaltered. However, where testing machine limitations make it impossible
NOTE 8—As a general rule, support span-to-depth ratios of 16 to 1 are
to follow the above criterion on the unaltered sheet, one or both surfaces
satisfactory when the ratio of the tensile strength to shear strength is less
shall be machined to provide the desired dimensions, and the location of
than 8 to 1, but the support span-to-depth ratio must be increased for
the specimens with reference to the total depth shall be noted. The value
composite laminates having relatively low shear strength in the plane of
obtained on specimens with machined surfaces may differ from those
the laminate and relatively high tensile strength parallel to the support
obtained on specimens with original surfaces. Consequently, any specifi-
span.
cations for flexural properties on the thicker sheets must state whether the
original surfaces are to be retained or not. When only one surface was
8. Number of Test Specimens
machined, it must be stated whether the machined surface was on the
8.1 At least five specimens shall be tested for each sample in
tension or compression side of the beam.
the case of isotropic materials or molded specimens.
NOTE 5—Edgewise tests are not applicable for sheets that are so thin
that specimens meeting these requirements cannot be cut. If specimen
8.2 For each sample of anisotropic material in sheet form, at
depth exceeds the width, buckling may occur.
least five specimens shall be tested for each of the following
conditions. Recommended conditions are flatwise and edge-
7.2.2 Materials Less than 1.6 m ( ⁄16 in.) in Thickness—The
1 wise tests on specimens cut in lengthwise and crosswise
specimen shall be 50.8 mm (2 in.) long by 12.7 mm ( ⁄2 in.)
directions of the sheet. For the purposes of this test, “length-
wide, tested flatwise on a 25.4-mm (1-in.) support span.
wise” shall designate the principal axis of anisotropy and shall
NOTE 6—Use of the formulas for simple beams cited in these test
be interpreted to mean the direction of the sheet known to be
methods for calculating results presumes that beam width is small in
stronger in flexure. “Crosswise” shall be the sheet direction
comparison with the support span. Therefore, the formulas do not apply
known to be the weaker in flexure and shall be at 90° to the
rigorously to these dimensions.
lengthwise direction.
NOTE 7—Where machine sensit
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