ASTM D747-99

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An American National Standard
Designation: D 747 – 99
Standard Test Method for
Apparent Bending Modulus of Plastics by Means of a
Cantilever Beam
This standard is issued under the fixed designation D 747; 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 * Determine the Precision of a Test Method
1.1 This test method covers the determination of the appar-
3. Terminology
ent bending modulus of plastics by means of a cantilever
3.1 Definitions of Terms Specific to This Standard:
beam. It is well suited for determining relative flexibility of
3.1.1 apparent bending modulus—an apparent modulus of
materials over a wide range. It is particularly useful for
elasticity obtained in flexure, using a cantilever beam testing
materials too flexible to be tested by Test Methods D 790.
apparatus, where the deformation involved is not purely elastic
1.2 The values stated in SI units are to be regarded as the
but contains both elastic and plastic components.
standard. The values given in parentheses are for information
only.
4. Significance and Use
1.3 This standard does not purport to address all of the
4.1 This test method provides a means of deriving the
safety concerns, if any, associated with its use. It is the
apparent bending modulus of a material by measuring force
responsibility of the user of this standard to establish appro-
and angle of bend of a cantilever beam. The mathematical
priate safety and health practices and determine the applica-
derivation assumes small deflections and purely elastic behav-
bility of regulatory limitations prior to use.
ior. Under actual test conditions, the deformation has both
NOTE 1—There is no known ISO equivalent for this standard.
elastic and plastic components. This test method does not
distinguish or separate these, and hence a true elastic modulus
2. Referenced Documents
is not calculable. Instead, an apparent value is obtained and is
2.1 ASTM Standards:
defined as the apparent bending modulus of the material. The
D 374 Test Methods for Thickness of Solid Electrical Insu-
tangent modulus obtained by Test Methods D 790 is preferred,
lation
when the material can be tested by the Test Methods D 790 test
D 618 Practice for Conditioning Plastics and Electrical
procedure.
Insulating Materials for Testing
4.2 Because of deviations from purely elastic behavior,
D 790 Test Methods for Flexural Properties of Unreinforced
changes in span length, width, and depth of the specimen will
and Reinforced Plastics and Electrical Insulating Materi-
affect the value of the apparent bending modulus obtained;
als
therefore, values obtained from specimens of different dimen-
D 4000 Classification System for Specifying Plastic Mate-
sions may not necessarily be comparable.
rials
4.3 Rate of loading is controlled only to the extent that the
D 4066 Specification for Nylon Injection and Extrusion
rate of angular change of the rotating jaw is fixed at 58 to
Materials
66°/min. Actual rate of stressing will be affected by span
E 177 Practice for Use of the Terms Precision and Bias in
length, width, depth of the specimen, and weight of the
ASTM Test Methods
pendulum.
E 691 Practice for Conducting an Interlaboratory Study to
4.4 For many materials, there may be a specification that
requires the use of this test method, but with some procedural
modifications that take precedence when adhering to the
This test method is under the jurisdiction of ASTM Committee D-20 on Plastics
specification. Therefore, it is advisable to refer to that material
and is the direct responsibility of Subcommittee D20.10 on Mechanical Properties.
specification before using this test method. Table 1 of Classi-
Current edition approved March 10, 1999. Published June 1999. Originally
published as D 747 – 43 T. Last previous edition D 747 – 93.
fication System D 4000 lists the ASTM materials standards that
This property was designated stiffness in versions of this test method issued
currently exist.
prior to 1984.
Annual Book of ASTM Standards, Vol 10.01.
NOTE 2—A discussion of the theory of obtaining a purely elastic
Annual Book of ASTM Standards, Vol 08.01.
bending modulus, using a cantilever beam testing apparatus, can be found
Annual Book of ASTM Standards, Vol 08.02.
in Appendix X1. The results obtained under actual test conditions will be
Annual Book of ASTM Standards, Vol 14.02.
*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 747
the apparent bending modulus.
5.1.3 Load Scale—A fixed scale that measures the load as a
function of the deflection, u, of the load pendulum system. It
5. Apparatus
shall be calibrated such that:
5.1 The apparatus for the apparent bending modulus test, as
Load scale reading 5 100 WL sin u/ M (2)
shown in Fig. 1, shall be the cantilever beam bending type,
consisting essentially of the following:
where:
5.1.1 Vise—A specimen vise, V, to which the pointer M = bending moment at a load scale reading of 100.
indicator I is attached, and which is capable of uniform
Thus,
clockwise rotation about the point O at a nominal rate of 60° of
M 5 ~M 3 load scale reading!/100 (3)
w
arc/min.
5.1.2 Weighing System—A pendulum weighing system, in- where:
M = actual bending moment.
cluding an angular deflection scale, pointer indicator I , bend-
1 w
5.1.4 Angular Deflection Scale—The angular deflection
ing plate Q for contacting the free end of the specimen, and a
scale shall be calibrated in degrees of arc and shall indicate the
series of detachable weights. This system shall be pivoted for
angle through which the rotating vise has been turned relative
nearly frictionless rotation about the point O. The total applied
to the pendulum system. This is the difference between the
bending moment, M , consists of the effective moment of the
W
angle through which the vise has been turned and the angle
pendulum and the bending plate, A , plus the moments of the
through which the load pendulum has been deflected, and is
added calibrated weights, A . Thus,
designated as angle f.
M 5 WL sin u (1)
W
5.1.5 Depth Measuring Devices—Suitable micrometers, or
where:
thickness gages, reading to 0.0025 mm (0.0001 in.) or less,
M = actual bending moment at the angle u,
shall be used for measuring the depth of the test specimens.
w
W = total applied load, N (or lbf),
The pressure exerted by the gage on the specimen being
L = length of the pendulum arm, m (or in.), and
measured shall be between 159 and 186 kPa (23 and 27 psi).
u = angle through which the pendulum rotates.
Method A of Test Methods D 374 may be used. Alternatively,
the apparatus and procedure of Method C of Test Methods
NOTE 3—Auxiliary weights for the test apparatus are calibrated and
marked directly with the values for M, the bending moment at a load D 374 may be used provided the load on the spindle is
reading of 100. Since M depends on the geometry of the testing machine,
increased so that the exerted pressure is between 159 and 186
w
these weights are not interchangeable between machines of different
kPa (23 and 27 psi).
capacities.
5.1.6 Width-Measuring Devices—Suitable scales or other
width measuring devices reading to 0.025 mm (0.001 in.) or
less shall be used for measuring the width of the test specimen.
This apparatus can be obtained from Tinius Olsen Testing Machine Co., Inc.,
Easton Road., Willow Grove, PA 19090.
6. Test Specimens
6.1 Test specimens may be molded or cut from molded,
calendered, or cast sheets of the material to be tested. They
shall have a rectangular cross section and shall be cut with their
longitudinal axes parallel to the direction of the principal axis
of anisotropy, unless anisotropy effects are specifically to be
evaluated. The width and depth of the specimen to be tested, as
well as the span length, will depend upon the apparent bending
modulus of the material and the capacity of the testing
machine. Specimens shall have an even surface. If they exhibit
a surface tackiness, they shall be dusted lightly with talc before
being tested.
6.2 Specimen width shall be between 5.0 and 25.4 mm (0.25
and 1.00 in.), provided the material does not extend over the
width of the anvil. Width shall be measured to the nearest 0.025
mm (0.001 in.).
6.3 The minimum specimen depth shall be 0.5 mm (0.020
in.) and shall be measured to the nearest 0.0025 cm (0.0001
in.).
NOTE 4—A minimum specimen depth requirement is included since a
large percentage error can result in the final apparent bending modulus
value because of small errors in the depth measurement. The reason for
this large dependence of apparent bending modulus on depth errors is
because the depth is to the third power in the formula.
6.4 The span-to-depth ratio shall be greater than 15 to 1.
FIG. 1 Mechanical System of Test Apparatus Large span-to-depth ratios may be limited by the sensitivity of
D 747
the load-measuring and deflectometer equipment.
6.5 The number of specimens tested shall be at least five.
7. Conditioning
7.1 Conditioning—Condition the test specimens at 23 6
2°C (73.4 6 3.6°F) and 50 6 5 % relative humidity for not less
than 40 h prior to test in accordance with Procedure A of
Practice D 618, for those tests where conditioning is required.
In cases of disagreement, the tolerances shall be 61°C
(61.8°F) and 62 % relative humidity.
7.1.1 Note that for some hygroscopic materials, such as
nylons, the material specifications (for example, Specification
D 4066) call for testing “dry as-molded specimens.” Such
requirements take precedence over the above routine precon-
ditioning to 50 % relative humidity and require sealing the
specimens in water vapor-impermeable containers as soon as
molded and not removing them until ready for testing. FIG. 2 Ideal Curve
7.2 Test Conditions—Conduct tests in the standard labora-
tory atmosphere of 23 6 2°C (73.4 6 3.6°F) and 50 6 5%
relative humidity, unless otherwise specified in the test meth-
ods or in this test method. In cases of disagreement, the
tolerances shall be 61°C (61.8°F) and 62 % relative humid-
ity.
7.3 Spec
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