ASTM D256-10(2018)

Standard Test Methods for Determining the Izod Pendulum Impact Resistance of Plastics

SIGNIFICANCE AND USE
5.1 Before proceeding with these test methods, reference should be made to the specification of the material being tested. Any test specimen preparation, conditioning, dimensions, and testing parameters covered in the materials specification shall take precedence over those mentioned in these test methods. If there is no material specification, then the default conditions apply.  
5.2 The pendulum impact test indicates the energy to break standard test specimens of specified size under stipulated parameters of specimen mounting, notching, and pendulum velocity-at-impact.  
5.3 The energy lost by the pendulum during the breakage of the specimen is the sum of the following:  
5.3.1 Energy to initiate fracture of the specimen;  
5.3.2 Energy to propagate the fracture across the specimen;  
5.3.3 Energy to throw the free end (or ends) of the broken specimen (“toss correction”);  
5.3.4 Energy to bend the specimen;  
5.3.5 Energy to produce vibration in the pendulum arm;  
5.3.6 Energy to produce vibration or horizontal movement of the machine frame or base;  
5.3.7 Energy to overcome friction in the pendulum bearing and in the indicating mechanism, and to overcome windage (pendulum air drag);  
5.3.8 Energy to indent or deform plastically the specimen at the line of impact; and  
5.3.9 Energy to overcome the friction caused by the rubbing of the striker (or other part of the pendulum) over the face of the bent specimen.  
5.4 For relatively brittle materials, for which fracture propagation energy is small in comparison with the fracture initiation energy, the indicated impact energy absorbed is, for all practical purposes, the sum of factors 5.3.1 and 5.3.3. The toss correction (see 5.3.3) may represent a very large fraction of the total energy absorbed when testing relatively dense and brittle materials. Test Method C shall be used for materials that have an Izod impact resistance of less than 27 J/m (0.5 ft·lbf/in.). (See Appendix X4 for optional units.) T...
SCOPE
1.1 These test methods cover the determination of the resistance of plastics to “standardized” (see Note 1) pendulum-type hammers, mounted in “standardized” machines, in breaking standard specimens with one pendulum swing (see Note 2). The standard tests for these test methods require specimens made with a milled notch (see Note 3). In Test Methods A, C, and D, the notch produces a stress concentration that increases the probability of a brittle, rather than a ductile, fracture. In Test Method E, the impact resistance is obtained by reversing the notched specimen 180° in the clamping vise. The results of all test methods are reported in terms of energy absorbed per unit of specimen width or per unit of cross-sectional area under the notch. (See Note 4.)
Note 1: The machines with their pendulum-type hammers have been “standardized” in that they must comply with certain requirements, including a fixed height of hammer fall that results in a substantially fixed velocity of the hammer at the moment of impact. However, hammers of different initial energies (produced by varying their effective weights) are recommended for use with specimens of different impact resistance. Moreover, manufacturers of the equipment are permitted to use different lengths and constructions of pendulums with possible differences in pendulum rigidities resulting. (See Section 5.) Be aware that other differences in machine design may exist. The specimens are “standardized” in that they are required to have one fixed length, one fixed depth, and one particular design of milled notch. The width of the specimens is permitted to vary between limits.
Note 2: Results generated using pendulums that utilize a load cell to record the impact force and thus impact energy, may not be equivalent to results that are generated using manually or digitally encoded testers that measure the energy remaining in the pendulum after impact.
Note 3: The notch in the Iz...

General Information

• Status: Historical
• Publication Date: 31-Oct-2018
• ICS: 29.035.20 - Plastics and rubber insulating materials
• Technical Committee: D20 - Plastics
• Drafting Committee: D20.10 - Mechanical Properties

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D256 − 10 (Reapproved 2018)
Standard Test Methods for
Determining the Izod Pendulum Impact Resistance of
Plastics
This standard is issued under the fixed designation D256; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
NOTE 4—Caution must be exercised in interpreting the results of these
1. Scope
standard test methods. The following testing parameters may affect test
1.1 These test methods cover the determination of the
results significantly:
resistance of plastics to “standardized” (see Note 1) pendulum-
Method of fabrication, including but not limited to processing
type hammers, mounted in “standardized” machines, in break- technology, molding conditions, mold design, and thermal
treatments;
ing standard specimens with one pendulum swing (see Note 2).
Method of notching;
The standard tests for these test methods require specimens
Speed of notching tool;
made with a milled notch (see Note 3). In Test Methods A, C,
Design of notching apparatus;
Quality of the notch;
and D, the notch produces a stress concentration that increases
Time between notching and test;
the probability of a brittle, rather than a ductile, fracture. In
Test specimen thickness,
Test Method E, the impact resistance is obtained by reversing Test specimen width under notch, and
Environmental conditioning.
the notched specimen 180° in the clamping vise. The results of
1.2 The values stated in SI units are to be regarded as
all test methods are reported in terms of energy absorbed per
unit of specimen width or per unit of cross-sectional area under standard. The values given in parentheses are for information
only.
the notch. (See Note 4.)
1.3 This standard does not purport to address all of the
NOTE 1—The machines with their pendulum-type hammers have been
safety concerns, if any, associated with its use. It is the
“standardized” in that they must comply with certain requirements,
including a fixed height of hammer fall that results in a substantially fixed
responsibility of the user of this standard to establish appro-
velocity of the hammer at the moment of impact. However, hammers of
priate safety, health, and environmental practices and deter-
different initial energies (produced by varying their effective weights) are
mine the applicability of regulatory limitations prior to use.
recommended for use with specimens of different impact resistance.
Moreover, manufacturers of the equipment are permitted to use different
NOTE 5—These test methods resemble ISO 180:1993 in regard to title
lengths and constructions of pendulums with possible differences in
only. The contents are significantly different.
pendulum rigidities resulting. (See Section 5.) Be aware that other
1.4 This international standard was developed in accor-
differences in machine design may exist. The specimens are “standard-
dance with internationally recognized principles on standard-
ized” in that they are required to have one fixed length, one fixed depth,
and one particular design of milled notch. The width of the specimens is
ization established in the Decision on Principles for the
permitted to vary between limits.
Development of International Standards, Guides and Recom-
NOTE 2—Results generated using pendulums that utilize a load cell to
mendations issued by the World Trade Organization Technical
record the impact force and thus impact energy, may not be equivalent to
Barriers to Trade (TBT) Committee.
results that are generated using manually or digitally encoded testers that
measure the energy remaining in the pendulum after impact.
2. Referenced Documents
NOTE 3—The notch in the Izod specimen serves to concentrate the
stress, minimize plastic deformation, and direct the fracture to the part of 2
2.1 ASTM Standards:
the specimen behind the notch. Scatter in energy-to-break is thus reduced.
D618 Practice for Conditioning Plastics for Testing
However, because of differences in the elastic and viscoelastic properties
D883 Terminology Relating to Plastics
of plastics, response to a given notch varies among materials. A measure
of a plastic’s “notch sensitivity” may be obtained with Test Method D by D3641 Practice for Injection Molding Test Specimens of
comparing the energies to break specimens having different radii at the
Thermoplastic Molding and Extrusion Materials
base of the notch.
D4066 Classification System for Nylon Injection and Extru-
sion Materials (PA)
These test methods are under the jurisdiction of ASTM Committee D20 on
Plastics and are the direct responsibility of Subcommittee D20.10 on Mechanical
Properties. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Nov. 1, 2018. Published November 2018. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
ɛ1
approved in 1926. Last previous edition approved in 2010 as D256 -10 . DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D0256-10R18. the ASTM website.
*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
D256 − 10 (2018)
D5947 Test Methods for Physical Dimensions of Solid
Plastics Specimens
D6110 Test Method for Determining the Charpy Impact
Resistance of Notched Specimens of Plastics
E691 Practice for Conducting an Interlaboratory Study to
Determine the Precision of a Test Method
2.2 ISO Standard:
ISO 180:1993 Plastics—Determination of Izod Impact
Strength of Rigid Materials
3. Terminology
3.1 Definitions—For definitions related to plastics see Ter-
minology D883.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 cantilever—a projecting beam clamped at only one
end.
3.2.2 notch sensitivity—a measure of the variation of impact
energy as a function of notch radius.
4. Types of Tests
FIG. 1 Relationship of Vise, Specimen, and Striking Edge to
Each Other for Izod Test Methods A and C
4.1 Four similar methods are presented in these test meth-
ods. (See Note 6.) All test methods use the same testing
machine and specimen dimensions. There is no known means
for correlating the results from the different test methods.
4.1.3.2 For the purpose of this test, the slope, b (see 22.1),
NOTE 6—Previous versions of this test method contained Test Method
of the line between radii of 0.25 and 1.0 mm (0.010 and 0.040
B for Charpy. It has been removed from this test method and has been
in.) is used, unless tests with the 1.0-mm radius give “non-
published as D6110.
break” results. In that case, 0.25 and 0.50-mm (0.010 and
4.1.1 In Test Method A, the specimen is held as a vertical
0.020-in.) radii may be used. The effect of notch radius on the
cantilever beam and is broken by a single swing of the
impact energy to break a specimen under the conditions of this
pendulum. The line of initial contact is at a fixed distance from
test is measured by the value b. Materials with low values of b,
the specimen clamp and from the centerline of the notch and on
whether high or low energy-to-break with the standard notch,
the same face as the notch.
are relatively insensitive to differences in notch radius; while
4.1.2 Test Method C is similar to Test Method A, except for
the energy-to-break materials with high values of b is highly
the addition of a procedure for determining the energy ex-
dependent on notch radius. The parameter b cannot be used in
pended in tossing a portion of the specimen. The value reported
design calculations but may serve as a guide to the designer
is called the “estimated net Izod impact resistance.” Test
and in selection of materials.
Method C is preferred over Test Method A for materials that
4.2 Test Method E is similar to Test Method A, except that
have an Izod impact resistance of less than 27 J/m (0.5
the specimen is reversed in the vise of the machine 180° to the
ft·lbf/in.) under notch. (See Appendix X4 for optional units.)
usual striking position, such that the striker of the apparatus
The differences between Test Methods A and C become
impacts the specimen on the face opposite the notch. (See Fig.
unimportant for materials that have an Izod impact resistance
1, Fig. 2.) Test Method E is used to give an indication of the
higher than this value.
unnotched impact resistance of plastics; however, results ob-
4.1.3 Test Method D provides a measure of the notch
tained by the reversed notch method may not always agree with
sensitivity of a material. The stress-concentration at the notch
those obtained on a completely unnotched specimen. (See
increases with decreasing notch radius.
4,5
28.1.)
4.1.3.1 For a given system, greater stress concentration
results in higher localized rates-of-strain. Since the effect of
5. Significance and Use
strain-rate on energy-to-break varies among materials, a mea-
5.1 Before proceeding with these test methods, reference
sure of this effect may be obtained by testing specimens with
should be made to the specification of the material being tested.
different notch radii. In the Izod-type test it has been demon-
Any test specimen preparation, conditioning, dimensions, and
strated that the function, energy-to-break versus notch radius,
testing parameters covered in the materials specification shall
is reasonably linear from a radius of 0.03 to 2.5 mm (0.001 to
0.100 in.), provided that all specimens have the same type of
break. (See 5.8 and 22.1.)
Supporting data giving results of the interlaboratory tests are available from
ASTM Headquarters. Request RR:D20-1021.
3 5
Available from American National Standards Institute (ANSI), 25 W. 43rd St., Supporting data giving results of the interlaboratory tests are available from
4th Floor, New York, NY 10036, http://www.ansi.org. ASTM Headquarters. Request RR:D20-1026.
D256 − 10 (2018)
obtained in Test Method C is only an approximation of the toss
error, since the rotational and rectilinear velocities may not be
the same during the re-toss of the specimen as for the original
toss, and because stored stresses in the specimen may have
been released as kinetic energy during the specimen fracture.
5.5 For tough, ductile, fiber filled, or cloth-laminated
materials, the fracture propagation energy (see 5.3.2) may be
large compared to the fracture initiation energy (see 5.3.1).
When testing these materials, factors (see 5.3.2, 5.3.5, and
5.3.9) can become quite significant, even when the specimen is
accurately machined and positioned and the machine is in good
condition with adequate capacity. (See Note 7.) Bending (see
5.3.4) and indentation losses (see 5.3.8) may be appreciable
when testing soft materials.
NOTE 7—Although the frame and base of the machine should be
sufficiently rigid and massive to handle the energies of tough specimens
without motion or excessive vibration, the design must ensure that the
center of percussion be at the center of strike. Locating the striker
precisely at the center of percussion reduces vibration of the pendulum
arm when used with brittle specimens. However, some losses due to
FIG. 2 Relationship of Vise, Specimen, and Striking Edge to
pendulum arm vibration, the amount varying with the design of the
Each Other for Test Method E pendulum, will occur with tough specimens, even when the striker is
properly positioned.
5.6 In a well-designed machine of sufficient rigidity and
take precedence over those mentioned in these test methods. If
mass, the losses due to factors 5.3.6 and 5.3.7 should be very
there is no material specification, then the default conditions
small. Vibrational losses (see 5.3.6) can be quite large when
apply.
wide specimens of tough materials are tested in machines of
insufficient mass, not securely fastened to a heavy base.
5.2 The pendulum impact test indicates the energy to break
standard test specimens of specified size under stipulated
5.7 With some materials, a critical width of specimen may
parameters of specimen mounting, notching, and pendulum
be found below which specimens will appear ductile, as
velocity-at-impact.
evidenced by considerable drawing or necking down in the
region behind the notch and by a relatively high-energy
5.3 The energy lost by the pendulum during the breakage of
absorption, and above which they will appear brittle as
the specimen is the sum of the following:
evidenced by little or no drawing down or necking and by a
5.3.1 Energy to initiate fracture of the specimen;
relatively low-energy absorption. Since these methods permit a
5.3.2 Energy to propagate the fracture across the specimen;
variation in the width of the specimens, and since the width
5.3.3 Energy to throw the free end (or ends) of the broken
dictates, for many materials, whether a brittle, low-energy
specimen (“toss correction”);
break or a ductile, high energy break will occur, it is necessary
5.3.4 Energy to bend the specimen;
that the width be stated in the specification covering that
5.3.5 Energy to produce vibration in the pendulum arm;
material and that the width be reported along with the impact
5.3.6 Energy to produce vibration or horizontal movement
resistance. In view of the preceding, one should not make
of the machine frame or base;
comparisons between data from specimens having widths that
5.3.7 Energy to overcome friction in the pendulum bearing
differ by more than a few mils.
and in the indicating mechanism, and to overcome windage
(pendulum air drag);
5.8 The type of failure for each specimen shall be recorded
5.3.8 Energy to indent or deform plastically the specimen at
as one of the four categories listed as follows:
the line of impact; and
C = Complete Break—A break where the specimen
5.3.9 Energy to overcome the friction caused by the rubbing
separates into two or more pieces.
of the striker (or other part of the pendulum) over the face of H = Hinge Break—An incomplete break, such that one
part of the specimen cannot support itself above
the bent specimen.
the horizontal when the other part is held vertically
(less than 90° included angle).
5.4 For relatively brittle materials, for which fracture propa-
P = Partial Break—An incomplete break that does not
gation energy is small in comparison with the fracture initiation
meet the definition for a hinge break but has
energy, the indicated impact energy absorbed is, for all
fractured at least 90 % of the distance between
the vertex of the notch and
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
´1
Designation: D256 − 10 D256 − 10 (Reapproved 2018)
Standard Test Methods for
Determining the Izod Pendulum Impact Resistance of
Plastics
This standard is issued under the fixed designation D256; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
ε NOTE—Editorially corrected Figure 2 in October 2015.
1. Scope*Scope
1.1 These test methods cover the determination of the resistance of plastics to “standardized” (see Note 1) pendulum-type
hammers, mounted in “standardized” machines, in breaking standard specimens with one pendulum swing (see Note 2). The
standard tests for these test methods require specimens made with a milled notch (see Note 3). In Test Methods A, C, and D, the
notch produces a stress concentration that increases the probability of a brittle, rather than a ductile, fracture. In Test Method E,
the impact resistance is obtained by reversing the notched specimen 180° in the clamping vise. The results of all test methods are
reported in terms of energy absorbed per unit of specimen width or per unit of cross-sectional area under the notch. (See Note 4.)
NOTE 1—The machines with their pendulum-type hammers have been “standardized” in that they must comply with certain requirements, including
a fixed height of hammer fall that results in a substantially fixed velocity of the hammer at the moment of impact. However, hammers of different initial
energies (produced by varying their effective weights) are recommended for use with specimens of different impact resistance. Moreover, manufacturers
of the equipment are permitted to use different lengths and constructions of pendulums with possible differences in pendulum rigidities resulting. (See
Section 5.) Be aware that other differences in machine design may exist. The specimens are “standardized” in that they are required to have one fixed
length, one fixed depth, and one particular design of milled notch. The width of the specimens is permitted to vary between limits.
NOTE 2—Results generated using pendulums that utilize a load cell to record the impact force and thus impact energy, may not be equivalent to results
that are generated using manually or digitally encoded testers that measure the energy remaining in the pendulum after impact.
NOTE 3—The notch in the Izod specimen serves to concentrate the stress, minimize plastic deformation, and direct the fracture to the part of the
specimen behind the notch. Scatter in energy-to-break is thus reduced. However, because of differences in the elastic and viscoelastic properties of
plastics, response to a given notch varies among materials. A measure of a plastic’s “notch sensitivity” may be obtained with Test Method D by comparing
the energies to break specimens having different radii at the base of the notch.
NOTE 4—Caution must be exercised in interpreting the results of these standard test methods. The following testing parameters may affect test results
significantly:
Method of fabrication, including but not limited to processing
technology, molding conditions, mold design, and thermal
treatments;
Method of notching;
Speed of notching tool;
Design of notching apparatus;
Quality of the notch;
Time between notching and test;
Test specimen thickness,
Test specimen width under notch, and
Environmental conditioning.
1.2 The values stated in SI units are to be regarded as standard. The values given in parentheses are for information only.
1.3 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
NOTE 5—These test methods resemble ISO 180:1993 in regard to title only. The contents are significantly different.
1.4 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.
These test methods are under the jurisdiction of ASTM Committee D20 on Plastics and are the direct responsibility of Subcommittee D20.10 on Mechanical Properties.
Current edition approved May 1, 2010Nov. 1, 2018. Published June 2010November 2018. Originally approved in 1926. Last previous edition approved in 20062010 as
ε1ɛ1
D256 - 06aD256 -10 . DOI: 10.1520/D0256-10.10.1520/D0256-10R18.
*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
D256 − 10 (2018)
2. Referenced Documents
2.1 ASTM Standards:
D618 Practice for Conditioning Plastics for Testing
D883 Terminology Relating to Plastics
D3641 Practice for Injection Molding Test Specimens of Thermoplastic Molding and Extrusion Materials
D4066 Classification System for Nylon Injection and Extrusion Materials (PA)
D5947 Test Methods for Physical Dimensions of Solid Plastics Specimens
D6110 Test Method for Determining the Charpy Impact Resistance of Notched Specimens of Plastics
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
2.2 ISO Standard:
ISO 180:1993 Plastics—Determination of Izod Impact Strength of Rigid Materials
3. Terminology
3.1 Definitions—For definitions related to plastics see Terminology D883.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 cantilever—a projecting beam clamped at only one end.
3.2.2 notch sensitivity—a measure of the variation of impact energy as a function of notch radius.
4. Types of Tests
4.1 Four similar methods are presented in these test methods. (See Note 6.) All test methods use the same testing machine and
specimen dimensions. There is no known means for correlating the results from the different test methods.
NOTE 6—Previous versions of this test method contained Test Method B for Charpy. It has been removed from this test method and has been published
as D6110.
4.1.1 In Test Method A, the specimen is held as a vertical cantilever beam and is broken by a single swing of the pendulum.
The line of initial contact is at a fixed distance from the specimen clamp and from the centerline of the notch and on the same face
as the notch.
4.1.2 Test Method C is similar to Test Method A, except for the addition of a procedure for determining the energy expended
in tossing a portion of the specimen. The value reported is called the “estimated net Izod impact resistance.” Test Method C is
preferred over Test Method A for materials that have an Izod impact resistance of less than 27 J/m (0.5 ft·lbf/in.) under notch. (See
Appendix X4 for optional units.) The differences between Test Methods A and C become unimportant for materials that have an
Izod impact resistance higher than this value.
4.1.3 Test Method D provides a measure of the notch sensitivity of a material. The stress-concentration at the notch increases
with decreasing notch radius.
4.1.3.1 For a given system, greater stress concentration results in higher localized rates-of-strain. Since the effect of strain-rate
on energy-to-break varies among materials, a measure of this effect may be obtained by testing specimens with different notch
radii. In the Izod-type test it has been demonstrated that the function, energy-to-break versus notch radius, is reasonably linear from
a radius of 0.03 to 2.5 mm (0.001 to 0.100 in.), provided that all specimens have the same type of break. (See 5.8 and 22.1.)
4.1.3.2 For the purpose of this test, the slope, b (see 22.1), of the line between radii of 0.25 and 1.0 mm (0.010 and 0.040 in.)
is used, unless tests with the 1.0-mm radius give “non-break” results. In that case, 0.25 and 0.50-mm (0.010 and 0.020-in.) radii
may be used. The effect of notch radius on the impact energy to break a specimen under the conditions of this test is measured
by the value b. Materials with low values of b, whether high or low energy-to-break with the standard notch, are relatively
insensitive to differences in notch radius; while the energy-to-break materials with high values of b is highly dependent on notch
radius. The parameter b cannot be used in design calculations but may serve as a guide to the designer and in selection of materials.
4.2 Test Method E is similar to Test Method A, except that the specimen is reversed in the vise of the machine 180° to the usual
striking position, such that the striker of the apparatus impacts the specimen on the face opposite the notch. (See Fig. 1, Fig. 2.)
Test Method E is used to give an indication of the unnotched impact resistance of plastics; however, results obtained by the
4,5
reversed notch method may not always agree with those obtained on a completely unnotched specimen. (See 28.1.)
5. Significance and Use
5.1 Before proceeding with these test methods, reference should be made to the specification of the material being tested. Any
test specimen preparation, conditioning, dimensions, and testing parameters covered in the materials specification shall take
precedence over those mentioned in these test methods. If there is no material specification, then the default conditions apply.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
Supporting data giving results of the interlaboratory tests are available from ASTM Headquarters. Request RR:D20-1021.
Supporting data giving results of the interlaboratory tests are available from ASTM Headquarters. Request RR:D20-1026.
D256 − 10 (2018)
FIG. 1 Relationship of Vise, Specimen, and Striking Edge to Each Other for Izod Test Methods A and C
FIG. 2 Relationship of Vise, Specimen, and Striking Edge to Each Other for Test Method E
5.2 The pendulum impact test indicates the energy to break standard test specimens of specified size under stipulated parameters
of specimen mounting, notching, and pendulum velocity-at-impact.
5.3 The energy lost by the pendulum during the breakage of the specimen is the sum of the following:
5.3.1 Energy to initiate fracture of the specimen;
5.3.2 Energy to propagate the fracture across the specimen;
5.3.3 Energy to throw the free end (or ends) of the broken specimen (“toss correction”);
5.3.4 Energy to bend the specimen;
5.3.5 Energy to produce vibration in the pendulum arm;
5.3.6 Energy to produce vibration or horizontal movement of the machine frame or base;
5.3.7 Energy to overcome friction in the pendulum bearing and in the indicating mechanism, and to overcome windage
(pendulum air drag);
5.3.8 Energy to indent or deform plastically the specimen at the line of impact; and
5.3.9 Energy to overcome the friction caused by the rubbing of the striker (or other part of the pendulum) over the face of the
bent specimen.
D256 − 10 (2018)
5.4 For relatively brittle materials, for which fracture propagation energy is small in comparison with the fracture initiation
energy, the indicated impact energy absorbed is, for all practical purposes, the sum of factors 5.3.1 and 5.3.3. The toss correction
(see 5.3.3) may represent a very large fraction of the total energy absorbed when testing relatively dense and brittle materials. Test
Method C shall be used for materials that have an Izod impact resistance of less than 27 J/m (0.5 ft·lbf/in.). (See Appendix X4
for optional units.) The toss correction obtained in Test Method C is only an approximation of the toss error, since the rotational
and rectilinear velocities may not be the same during the re-toss of the specimen as for the original toss, and because stored stresses
in the specimen may have been released as kinetic energy during the specimen fracture.
5.5 For tough, ductile, fiber filled, or cloth-laminated materials, the fracture propagation energy (see 5.3.2) may be large
compared to the fracture initiation energy (see 5.3.1). When testing these materials, factors (see 5.3.2, 5.3.5, and 5.3.9) can become
quite significant, even when the specimen is accurately machined and positioned and the machine is in good condition with
adequate capacity. (See Note 7.) Bending (see 5.3.4) and indentation losses (see 5.3.8) may be appreciable when testing soft
materials.
NOTE 7—Although the frame and base of the machine should be sufficiently rigid and massive to handle the energies of tough specimens without
motion or excessive vibration, the design must ensure that the center of percussion be at the center of strike. Locating the striker precisely at the center
of percussion reduces vibration of the pendulum arm when used with brittle specimens. However, some losses due to pendulum arm vibration, the amount
varying with the design of the pendulum, will occur with tough specimens, even when the striker is properly positioned.
5.6 In a well-designed machine of sufficient rigidity and mass, the losses due to factors 5.3.6 and 5.3.7 should be very small.
Vibrational losses (see 5.3.6) can be quite large when wide specimens of tough materials are tested in machines of insufficient mass,
not securely fastened to a heavy base.
5.7 With some materials, a critical width of specimen may be found below which specimens will appear ductile, as evidenced
by considerable drawing or necking down in the region behind the notch and by a relatively high-energy absorption, and above
which they will appear brittle as evidenced by little or no drawing down or necking and by a relatively low-energy absorption.
Since these methods permit a variation in the width of the specimens, and since the width dictates, for many materials, whether
a brittle, low-energy break or a ductile, high energy break will occur, it is necess
...