ASTM D256-23e1

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: Published
• Publication Date: 14-Mar-2023
• ICS: 29.035.20 - Plastics and rubber insulating materials
• Technical Committee: D20 - Plastics
• Drafting Committee: D20.10 - Mechanical Properties

Relations

• Refers: ASTM D883-24 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2024
• Refers: ASTM D883-23 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2023
• Refers: ASTM D883-20 - Standard Terminology Relating to Plastics
• Effective Date: 01-Jan-2020
• Refers: ASTM D4066-13(2019) - Standard Classification System for Nylon Injection and Extrusion Materials (PA)
• Effective Date: 01-Nov-2019
• Refers: ASTM D883-19c - Standard Terminology Relating to Plastics
• Effective Date: 01-Aug-2019
• Refers: ASTM D883-19a - Standard Terminology Relating to Plastics
• Effective Date: 15-Apr-2019
• Refers: ASTM D883-19 - Standard Terminology Relating to Plastics
• Effective Date: 01-Feb-2019
• Refers: ASTM D883-18a - Standard Terminology Relating to Plastics
• Effective Date: 01-Dec-2018
• Refers: ASTM D883-18 - Standard Terminology Relating to Plastics
• Effective Date: 01-Nov-2018
• Refers: ASTM D6110-17 - Standard Test Method for Determining the Charpy Impact Resistance of Notched Specimens of Plastics
• Effective Date: 01-Dec-2017
• Refers: ASTM D883-17 - Standard Terminology Relating to Plastics
• Effective Date: 15-Aug-2017
• Refers: ASTM D3641-14 - Standard Practice for Injection Molding Test Specimens of Thermoplastic Molding and Extrusion Materials
• Effective Date: 01-Mar-2014
• Refers: ASTM D4066-13 - Standard Classification System for Nylon Injection and Extrusion Materials (PA)
• Effective Date: 01-Jul-2013
• Refers: ASTM E691-13 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-May-2013
• Refers: ASTM D883-12e1 - Standard Terminology Relating to Plastics
• Effective Date: 15-Nov-2012

Overview

ASTM D256-23e1 – Standard Test Methods for Determining the Izod Pendulum Impact Resistance of Plastics is a widely accepted international standard published by ASTM International. It outlines procedures for assessing the impact resistance of plastic materials using the Izod pendulum impact test. This standardized method measures the energy a material specimen absorbs when fractured by a swinging pendulum. Its primary purpose is to evaluate the toughness and notch sensitivity of plastics, providing valuable quality control and material comparison data for manufacturers, suppliers, and end-users.

Key Topics

• Standardized Testing Equipment and Specimens:
  The method requires the use of “standardized” pendulum-type hammers and machines, ensuring consistent specimen mounting, notching, and velocity-at-impact. Specimens must have fixed dimensions and a specifically milled notch to create a stress concentration and promote brittle fracture.

• Impact Resistance Measurement:
  Tests are performed by striking the notched, vertically clamped specimen with the pendulum hammer. The energy absorbed, calculated from the pendulum’s loss of energy, is reported per unit width or cross-sectional area. Multiple factors influence the total energy, including energy needed to initiate and propagate fracture, energy lost to vibration, friction, toss correction, and plastic deformation at impact.

• Failure Categorization:
  Test results are classified based on specimen break type: Complete Break (C), Hinge Break (H), Partial Break (P), or Non-Break (NB). This classification supports precise reporting and data analysis.

• Test Method Variants:
  The standard describes several test methods (A, C, D, E), addressing different material characteristics, such as toughness and notch sensitivity. Selection of the appropriate method depends on the material’s Izod impact resistance and desired information.

• Significance in Material Specification:
  ASTM D256 is critical for material specifications, quality control, and comparative studies. It helps detect variations in material composition, processing, or conditioning based on significant differences in energy absorption, break type, or critical dimensions.

Applications

• Material Selection and Development:
  The Izod impact test helps engineers, product designers, and researchers compare the toughness and brittleness of various plastics, influencing material selection for specific applications.

• Quality Control:
  Manufacturers utilize this standardized method to ensure material lot consistency and adherence to customer specifications, helping to detect processing or compounding issues in production.

• Product Performance Evaluation:
  By providing consistent impact resistance values, ASTM D256 supports predictions of plastic component durability under impact or shock loading, which is pivotal in the automotive, electrical, packaging, and consumer goods industries.

• Comparison of Processing Effects:
  The methodology reveals the influence of molding conditions, specimen geometry, and notching quality on impact resistance, guiding process optimization and troubleshooting.

Related Standards

• ASTM D6110: Standard Test Method for Determining the Charpy Impact Resistance of Notched Specimens of Plastics.
• ASTM D5947: Test Methods for Physical Dimensions of Solid Plastics Specimens.
• ASTM D883: Terminology Relating to Plastics.
• ASTM D618: Practice for Conditioning Plastics for Testing.
• ISO 180: Plastics – Determination of Izod Impact Strength of Rigid Materials.
• ASTM D3641: Practice for Injection Molding Test Specimens of Thermoplastic Molding and Extrusion Materials.

Practical Value

ASTM D256-23e1 provides a robust, internationally recognized framework ensuring reliable measurement of plastic impact resistance. Implementation of this standard improves material specification accuracy, supports engineering design decisions, and ensures compliance with both regulatory and industry-specific requirements for plastic materials.

By following ASTM D256, organizations gain confidence in the mechanical performance data of plastic materials, supporting product safety, durability, and market competitiveness. For laboratories, manufacturers, and buyers in the plastics industry, this standard is essential for maintaining high-quality materials and products.

Standards Content (Sample)

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.
´1
Designation: D256 − 23
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—Summary of Changes section was editorially added in April 2023.
of a plastic’s “notch sensitivity” may be obtained with Test Method D by
1. Scope*
comparing the energies to break specimens having different radii at the
1.1 These test methods cover the determination of the
base of the notch.
resistance of plastics to “standardized” (see Note 1) pendulum- NOTE 4—Caution must be exercised in interpreting the results of these
standard test methods. The following testing parameters may affect test
type hammers, mounted in “standardized” machines, in break-
results significantly:
ing standard specimens with one pendulum swing (see Note 2).
Method of fabrication, including but not limited to processing
The standard tests for these test methods require specimens
technology, molding conditions, mold design, and thermal
made with a milled notch (see Note 3). In Test Methods A, C,
treatments;
and D, the notch produces a stress concentration that increases Method of notching;
Speed of notching tool;
the probability of a brittle, rather than a ductile, fracture. In
Design of notching apparatus;
Test Method E, the impact resistance is obtained by reversing
Quality of the notch;
the notched specimen 180° in the clamping vise. The results of Time between notching and test;
Test specimen thickness,
all test methods are reported in terms of energy absorbed per
Test specimen width under notch, and
unit of specimen width or per unit of cross-sectional area under
Environmental conditioning.
the notch. (See Note 4.)
1.2 The values stated in SI units are to be regarded as
NOTE 1—The machines with their pendulum-type hammers have been standard. The values given in parentheses are for information
“standardized” in that they must comply with certain requirements,
only.
including a fixed height of hammer fall that results in a substantially fixed
1.3 This standard does not purport to address all of the
velocity of the hammer at the moment of impact. However, hammers of
different initial energies (produced by varying their effective weights) are safety concerns, if any, associated with its use. It is the
recommended for use with specimens of different impact resistance.
responsibility of the user of this standard to establish appro-
Moreover, manufacturers of the equipment are permitted to use different
priate safety, health, and environmental practices and deter-
lengths and constructions of pendulums with possible differences in
mine the applicability of regulatory limitations prior to use.
pendulum rigidities resulting. (See Section 5.) Be aware that other
differences in machine design may exist. The specimens are “standard-
NOTE 5—These test methods resemble ISO 180:1993 in regard to title
ized” in that they are required to have one fixed length, one fixed depth,
only. The contents are significantly different.
and one particular design of milled notch. The width of the specimens is
1.4 This international standard was developed in accor-
permitted to vary between limits.
dance with internationally recognized principles on standard-
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
ization established in the Decision on Principles for the
results that are generated using manually or digitally encoded testers that
Development of International Standards, Guides and Recom-
measure the energy remaining in the pendulum after impact.
mendations issued by the World Trade Organization Technical
NOTE 3—The notch in the Izod specimen serves to concentrate the
Barriers to Trade (TBT) Committee.
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
2. Referenced Documents
of plastics, response to a given notch varies among materials. A measure
2.1 ASTM Standards:
D618 Practice for Conditioning Plastics for Testing
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 March 15, 2023. Published March 2023. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1926. Last previous edition approved in 2018 as D256 -10(2018). DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D0256-23E01. 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
´1
D256 − 23
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 Extru-
sion 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 Ter-
minology D883.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 cantilever—a projecting beam clamped at only one
FIG. 1 Relationship of Vise, Specimen, and Striking Edge to
end.
Each Other for Izod Test Methods A and C
3.2.2 notch sensitivity—a measure of the variation of impact
energy as a function of notch radius. different notch radii. In the Izod-type test it has been demon-
strated that the function, energy-to-break versus notch radius,
4. Types of Tests
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
4.1 Four similar methods are presented in these test meth-
break. (See 5.8 and 22.1.)
ods. (See Note 6.) All test methods use the same testing
4.1.3.2 For the purpose of this test, the slope, b (see 22.1),
machine and specimen dimensions. There is no known means
of the line between radii of 0.25 and 1.0 mm (0.010 and 0.040
for correlating the results from the different test methods.
in.) is used, unless tests with the 1.0-mm radius give “non-
NOTE 6—Previous versions of this test method contained Test Method
break” results. In that case, 0.25 and 0.50-mm (0.010 and
B for Charpy. It has been removed from this test method and has been
0.020-in.) radii may be used. The effect of notch radius on the
published as D6110.
impact energy to break a specimen under the conditions of this
4.1.1 In Test Method A, the specimen is held as a vertical
test is measured by the value b. Materials with low values of b,
cantilever beam and is broken by a single swing of the
whether high or low energy-to-break with the standard notch,
pendulum. The line of initial contact is at a fixed distance from
are relatively insensitive to differences in notch radius; while
the specimen clamp and from the centerline of the notch and on
the energy-to-break materials with high values of b is highly
the same face as the notch.
dependent on notch radius. The parameter b cannot be used in
4.1.2 Test Method C is similar to Test Method A, except for
design calculations but may serve as a guide to the designer
the addition of a procedure for determining the energy ex-
and in selection of materials.
pended in tossing a portion of the specimen. The value reported
4.2 Test Method E is similar to Test Method A, except that
is called the “estimated net Izod impact resistance.” Test
the specimen is reversed in the vise of the machine 180° to the
Method C is preferred over Test Method A for materials that
usual striking position, such that the striker of the apparatus
have an Izod impact resistance of less than 27 J/m (0.5
impacts the specimen on the face opposite the notch. (See Fig.
ft·lbf/in.) under notch. (See Appendix X4 for optional units.)
1, Fig. 2.) Test Method E is used to give an indication of the
The differences between Test Methods A and C become
unnotched impact resistance of plastics; however, results ob-
unimportant for materials that have an Izod impact resistance
tained by the reversed notch method may not always agree with
higher than this value.
those obtained on a completely unnotched specimen. (See
4.1.3 Test Method D provides a measure of the notch
4,5
28.1.)
sensitivity of a material. The stress-concentration at the notch
increases with decreasing notch radius.
5. Significance and Use
4.1.3.1 For a given system, greater stress concentration
5.1 Before proceeding with these test methods, reference
results in higher localized rates-of-strain. Since the effect of
should be made to the specification of the material being tested.
strain-rate on energy-to-break varies among materials, a mea-
sure of this effect may be obtained by testing specimens with
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.
´1
D256 − 23
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
FIG. 2 Relationship of Vise, Specimen, and Striking Edge to
precisely at the center of percussion reduces vibration of the pendulum
Each Other for Test Method E
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.
Any test specimen preparation, conditioning, dimensions, and
testing parameters covered in the materials specification shall
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 the opposite side.
practical purposes, the sum of factors 5.3.1 and 5.3.3. The toss
NB = Non-Break—An incomplete break where the
correction (see 5.3.3) may represent a very large fraction of the
fracture extends less than 90 % of the distance
total energy absorbed when testing relatively dense and brittle between the vertex of the notch and the opposite
side.
materials. Test Method C shall be used for materials that have
´1
D256 − 23
For tough materials, the pendulum may not have the energy
necessary to complete the breaking of the extreme fibers and
toss the broken piece or pieces. Results obtained from “non-
break” specimens shall be considered a departure from stan-
dard and shall not be reported as a standard result. Impact
resistance cannot be directly compared for any two materials
that experience different types of failure as defined in the test
method by this code. Averages reported must likewise be
derived from specimens contained within a single failure
category. This letter code shall suffix the reported impact
identifying the types of failure associated with the reported
value. If more than one type of failure is observed for a sample
material, then the report will indicate the average impact
resistance for each type of failure, followed by the percent of
the specimens failing in that manner and suffixed by the letter
code.
5.9 The value of the impact methods lies mainly in the areas
of quality control and materials specification. If two groups of
specimens of supposedly the same material show significantly
different energy absorptions, types of breaks, critical widths, or
critical temperatures, it may be assumed that they were made
of different materials or were exposed to different processing or
conditioning environments. The fact that a material shows
FIG. 3 Cantilever Beam (Izod-Type) Impact Machine
twice the energy absorption of another under these conditions
of test does not indicate that this same relationship will exist
under another set of test conditions. The order of toughness
may even be reversed under different testing conditions.
NOTE 8—A documented discrepancy exists between manual and digital
impact testers, primarily with thermoset materials, including phenolics,
having an impact value of less than 54 J/m (1 ft-lb/in.). Comparing data
on the same material, tested on both manual and digital impact testers,
may show the data from the digital tester to be significantly lower than
data from a manual tester. In such cases a correlation study may be
necessary to properly define the true relationship between the instruments.
TEST METHOD A—CANTILEVER BEAM TEST
6. Apparatus
6.1 The machine shall consist of a massive base on which is
mounted a vise for holding the specimen and to which is
connected, through a rigid frame and bearings, a pendulum-
type hammer. (See 6.2.) The machine must also have a
pendulum holding and releasing mechanism and a mechanism
for indicating the breaking energy of the specimen.
6.2 A jig for positioning the specimen in the vise and graphs
or tables to aid in the calculation of the correction for friction
and windage also should be included. One type of machine is
FIG. 4 Jig for Positioning Specimen for Clamping
shown in Fig. 3. One design of specimen-positioning jig is
illustrated in Fig. 4. Detailed requirements are given in
subsequent paragraphs. General test methods for checking and in the measured impact resistance. Both simple and compound
calibrating the machine are given in Appendix X2. Additional pendulum designs may comply with this test method.
instructions for adjusting a particular machine should be
6.4 The striker of the pendulum shall be hardened steel and
supplied by the manufacturer.
shall be a cylindrical surface having a radius of curvature of
6.3 The pendulum shall consist of a single or multi- 0.80 6 0.20 mm (0.031 6 0.008 in.) with its axis horizontal
membered arm with a bearing on one end and a head, and perpendicular to the plane of swing of the pendulum. The
containing the striker, on the other. The arm must be suffi- line of contact of the striker shall be located at the center of
ciently rigid to maintain the proper clearances and geometric percussion of the pendulum within 62.54 mm (60.100 in.)
relationships between the machine parts and the specimen and (See Note 9.) Those portions of the pendulum adjacent to the
to minimize vibrational energy losses that are always included cylindrical striking edge shall be recessed or inclined at a
´1
D256 − 23
suitable angle so that there will be no chance for other than this tolerance of 0.12 mm (0.005 in.). Correct positioning of the
cylindrical surface coming in contact with the specimen during specimen is generally done with a jig furnished with the
the break. machine. The top edges of the fixed and moveable jaws shall
have a radius of 0.25 6 0.12 mm (0.010 6 0.005 in.). For
NOTE 9—The distance from the axis of support to the center of
specimens whose thickness approaches the lower limiting
percussion may be determined experimentally from the period of small
value of 3.00 mm (0.118 in.), means shall be provided to
amplitude oscillations of the pendulum by means of the following
equation:
prevent the lower half of the specimen from moving during the
2 2 clamping or testing operations (see Fig. 4 and Note 11.)
L 5 g/4π p
~ !
NOTE 11—Some plastics are sensitive to clamping pressure; therefore,
where:
cooperating laboratories should agree upon some means of standardizing
L = distance from the axis of support to the center of percussion, m or
the clamping force. One method is using a torque wrench on the screw of
(ft),
the specimen vise. If the faces of the vise or specimen are not flat and
g = local gravitational acceleration (known to an accuracy of one part
parallel, a greater sensitivity to clamping pressure may be evident. See the
2 2
in one thousand), m/s or (ft/s ),
calibration procedure in Appendix X2 for adjustment and correction
π = 3.1416 (4π = 39.48), and
instructions for faulty instruments.
p = period, s, of a single complete swing (to and fro) determined by
averaging at least 20 consecutive and uninterrupted swings. The 6.9 When the pendulum is free hanging, the striking surface
angle of swing shall be less than 5° each side of center.
shall come within 0.2 % of scale of touching the front face of
a standard specimen. During an actual swing this element shall
6.5 The position of the pendulum holding and releasing
make initial contact with the specimen on a line 22.00 6 0.05
mechanism shall be such that the vertical height of fall of the
mm (0.87 6 0.002 in.) above the top surface of the vise.
striker shall be 610 6 2 mm (24.0 6 0.1 in.). This will produce
a velocity of the striker at the moment of impact of approxi-
6.10 Means shall be provided for determining the energy
mately 3.5 m (11.4 ft)/s. (See Note 10.) The mechanism shall
expended by the pendulum in breaking the specimen. This is
be so constructed and operated that it will release the pendulum
accomplished using either a pointer and dial mechanism or an
without imparting acceleration or vibration to it.
electronic system consisting of a digital indicator and sensor
(typically an encoder or resolver). In either case, the indicated
NOTE 10—
breaking energy is determined by detecting the height of rise of
0.5
V 5 2gh
~ !
the pendulum beyond the point of impact in terms of energy
where: removed from that specific pendulum. Since the indicated
V = velocity of the striker at the moment of impact (m/s), energy must be corrected for pendulum-bearing friction,
g = local gravitational acceleration (m/s ), and
pointer friction, pointer inertia, and pendulum windage, in-
h = vertical height of fall of the striker (m).
structions for making these corrections are included in 10.3 and
This assumes no windage or friction.
Annex A1 and Annex A2. If the electronic display does not
6.6 The effective length of the pendulum shall be between
automatically correct for windage and friction, it shall be
0.33 and 0.40 m (12.8 and 16.0 in.) so that the required
incumbent for the operator to determine the energy loss
elevation of the striker may be obtained by raising the
manually. (See Note 12.)
pendulum to an angle between 60 and 30° above the horizontal.
NOTE 12—Many digital indicating systems automatically correct for
6.7 The machine shall be provided with a basic pendulum
windage and friction. The equipment manufacturer may be consulted for
capable of delivering an energy of 2.7 6 0.14 J (2.00 6 0.10 details concerning how this is performed, or if it is necessary to determine
the means for manually calculating the energy loss due to windage and
ft·lbf). This pendulum shall be used with all specimens that
friction.
extract less than 85 % of this energy. Heavier pendulums shall
6.11 The vise, pendulum, and frame shall be sufficiently
be provided for specimens that require more energy to break.
rigid to maintain correct alignment of the hammer and
These may be separate interchangeable pendulums or one basic
specimen, both at the moment of impact and during the
pendulum to which extra pairs of equal calibrated weights may
propagation of the fracture, and to minimize energy losses due
be rigidly attached to opposite sides of the pendulum. It is
to vibration. The base shall be sufficiently massive that the
imperative that the extra weights shall not significantly change
impact will not cause it to move. The machine shall be so
the position of the center of percussion or the free-hanging rest
designed, constructed, and maintained that energy losses due to
point of the pendulum (that would consequently take the
pendulum air drag (windage), friction in the pendulum
machine outside of the allowable calibration tolerances). A
bearings, and friction and inertia in the indicating mechanism
range of pendulums having energies from 2.7 to 21.7 J (2 to 16
are held to a minimum.
ft·lbf) has been found to be sufficient for use with most plastic
specimens and may be used with most machines. A series of
6.12 A check of the calibration of an impact machine is
pendulums such that each has twice the energy of the next will
difficult to make under dynamic conditions. The basic param-
be found convenient. Each pendulum shall have an energy
eters are normally checked under static conditions; if the
within 60.5 % of its nominal capacity.
machine passes the static tests, then it is assumed to be
6.8 A vise shall be provided for clamping the specimen accurate. The calibration procedure in Appendix X2 should be
rigidly in position so that the long axis of the specimen is used to establish the accuracy of the equipment. However, for
vertical and at right angles to the top plane of the vise. (See Fig. some machine designs it might be necessary to change the
1.) This top plane shall bisect the angle of the notch with a recommended method of obtaining the required calibration
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NOTE 1—These views not to scale.
NOTE 2—Micrometer to be satin-chrome finished with friction thimble.
NOTE 3—Special anvil for micrometer caliper 0 to 25.4 mm range (50.8 mm frame) (0 to 1 in. range (2-in. frame)).
NOTE 4—Anvil to be oriented with respect to frame as shown.
NOTE 5—Anvil and spindle to have hardened surfaces.
NOTE 6—Range: 0 to 25.4 mm (0 to 1 in. in thousandths of an inch).
NOTE 7—Adjustment must be at zero when spindle and anvil are in contact.
FIG. 5 Early (ca. 1970) Version of a Notch-Depth Micrometer
measurements. Other methods of performing the required shall comply with requirements of Test Methods D5947,
checks may be substituted, provided that they can be shown to provided however that the one anvil or presser foot shall be a
result in an equivalent accuracy. Appendix X1 also describes a tapered blade conforming to the dimensions given in Fig. 5.
dynamic test for checking certain features of the machine and The opposing anvil or presser foot shall be flat and conforming
specimen. to Test Methods D5947.
6.13 Micrometers—Apparatus for measurement of the width
7. Test Specimens
of the specimen shall comply with the requirements of Test
Methods D5947. Apparatus for the measurement of the depth 7.1 The test specimens shall conform to the dimensions and
of plastic material remaining in the specimen under the notch geometry of Fig. 6, except as modified in accordance with 7.2,
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D256 − 23
mm in.
A 10.16 ± 0.05 0.400 ± 0.002
B 31.8 ± 1.0 1.25 ± 0.04
C 63.5 ± 2.0 2.50 ± 0.08
D 0.25R ± 0.05 0.010R ± 0.002
E 12.70 ± 0.20 0.500 ± 0.008
FIG. 6 Dimensions of Izod-Type Test Specimen
sons must clearly spell out the specimen preparation conditions.
7.3, 7.4, and 7.5. To ensure the correct contour and conditions
of the specified notch, all specimens shall be notched as
7.2.1 Extreme care must be used in handling specimens less
directed in Section 8.
than 6.35 mm (0.250 in.) wide. Such specimens must be
7.1.1 Studies have shown that, for some materials, the
accurately positioned and supported to prevent twist or lateral
location of the notch on the specimen and the length of the
buckling during the test. Some materials, furthermore, are very
impacted end may have a slight effect on the measured impact
sensitive to clamping pressure (see Note 11).
resistance. Therefore, unless otherwise specified, care must be
7.2.2 A critical investigation of the mechanics of impact
taken to ensure that the specimen conforms to the dimensions
testing has shown that tests made upon specimens under 6.35
shown in Fig. 6 and that it is positioned as shown in Fig. 1 or
mm (0.250 in.) wide absorb more energy due to crushing,
Fig. 2.
bending, and twisting than do wider specimens. Therefore,
7.2 Molded specimens shall have a width between 3.0 and
specimens 6.35 mm (0.250 in.) or over in width are recom-
12.7 mm (0.118 and 0.500 in.). Use the specimen width as
mended. The responsibility for determining the minimum
specified in the material specification or as agreed upon
specimen width shall be the investigator’s, with due reference
between the supplier and the customer. All specimens having
to the specification for that material.
one dimension less than 12.7 mm (0.500 in.) shall have the
7.2.3 Material specification should be consulted for pre-
notch cut on the shorter side. Otherwise, all compression-
ferred molding conditions. The type of mold and molding
molded specimens shall be notched on the side parallel to the
direction of application of molding pressure. (See Fig. 6.) machine used and the flow behavior in the mold cavity will
influence the impact resistance obtained. A specimen taken
NOTE 13—While subsection 7.5 requires perpendicular pairs of plane
from one end of a molded plaque may give different results
parallel surfaces, the common practice has been to accept the non-parallel
drafted surfaces formed when directly injection molding specimens for than a specimen taken from the other end. Cooperating
Izod testing. Users must be aware that employing a trapezoidal section
laboratories should therefore agree on standard molds con-
rather than a rectangular section may lead to data shifts and scatter.
forming to the material specification. Practice D3641 can be
Unequal stress, created by clamping in the fracture region and dynamic
used as a guide for general molding tolerances, but refer to the
twisting, caused by uneven striking of the specimen are prone to occur
when the faces of the specimen are not parallel. Interlaboratory compari- material specification for specific molding conditions.
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D256 − 23
7.2.4 The impact resistance of a plastic material may be the cutter speed shall be constant throughout the notching
different if the notch is perpendicular to, rather than parallel to, operation (see Note 15). Provision for cooling the specimen
the direction of molding. The same is true for specimens cut with either a liquid or gas coolant is recommended. A single-
with or across the grain of an anisotropic sheet or plate. tooth cutter shall be used for notching the specimen, unless
notches of an equivalent quality can be produced with a
7.3 For sheet materials, the specimens shall be cut from the
multi-tooth cutter. Single-tooth cutters are preferred because of
sheet in both the lengthwise and crosswise directions unless
the ease of grinding the cutter to the specimen contour and
otherwise specified. The width of the specimen shall be the
because of the smoother cut on the specimen. The cutting edge
thickness of the sheet if the sheet thickness is between 3.0 and
shall be carefully ground and honed to ensure sharpness and
12.7 mm (0.118 and 0.500 in.). Sheet material thicker than 12.7
freedom from nicks and burrs. Tools with no rake and a work
mm shall be machined down to 12.7 mm. Specimens with a
relief angle of 15 to 20° have been found satisfactory.
12.7-mm square cross section may be tested either edgewise or
flatwise as cut from the sheet. When specimens are tested
NOTE 15—For some thermoplastics, cutter speeds from 53 to 150
flatwise, the notch shall be made on the machined surface if the m/min (175 to 490 ft/min) at a feed speed of 89 to 160 mm/min (3.5 to 6.3
in./min) without a water coolant or the same cutter speeds at a feed speed
specimen is machined on one face only. When the specimen is
of from 36 to 160 mm/min (1.4 to 6.3 in./min) with water coolant
cut from a thick sheet, notation shall be made of the portion of
produced suitable notches.
the thickness of the sheet from which the specimen was cut, for
8.2 Specimens may be notched separately or in a group.
example, center, top, or bottom surface.
However, in either case an unnotched backup or “dummy bar”
7.4 The practice of cementing, bolting, clamping, or other-
shall be placed behind the last specimen in the sample holder
wise combining specimens of substandard width to form a
to prevent distortion and chipping by the cutter as it exits from
composite test specimen is not recommended and should be
the last test specimen.
avoided since test results may be seriously affected by interface
8.3 The profile of the cutting tooth or teeth shall be such as
effects or effects of solvents and cements on energy absorption
to produce a notch of the contour and depth in the test
of composite test specimens, or both. However, if Izod test data
specimen as specified in Fig. 6 (see Note 16). The included
on such thin materials are required when no other means of
angle of the notch shall be 45 6 1° with a radius of curvature
preparing specimens are available, and if possible sources of
at the apex of 0.25 6 0.05 mm (0.010 6 0.002 in.). The plane
error are recognized and acceptable, the following technique of
bisecting the notch angle shall be perpendicular to the face of
preparing composites may be utilized.
the test specimen within 2°.
7.4.1 The test specimen shall be a composite of individual
thin specimens totaling 6.35 to 12.7 mm (0.250 to 0.500 in.) in
NOTE 16—There is evidence that notches in materials of widely varying
width. Individual members of the composite shall be accurately
physical dimensions may differ in contour even when using the same
cutter.
aligned with each other and clamped, bolted, or cemented
together. The composite shall be machined to proper dimen-
8.4 The depth of the plastic material remaining in the
sions and then notched. In all such cases the use of composite
specimen under the notch shall be 10.16 6 0.05 mm (0.400 6
specimens shall be noted in the report of test results.
0.002 in.). This dimension shall be measured with apparatus in
7.4.2 Care must be taken to select a solvent or adhesive that
accordance with 6.13. The tapered blade will be fitted to the
will not affect the impact resistance of the material under test.
notch. The specimen will be approximately vertical between
If solvents or solvent-containing adhesives are employed, a
the anvils. For specimens with a draft angle, position edge of
conditioning procedure shall be established to ensure complete
the non-cavity (wider edge) surface centered on the microm-
removal of the solvent prior to test.
eter’s flat circular anvil.
7.5 Each specimen shall be free of twist (see Note 14) and
8.5 Cutter speed and feed speed should be chosen appropri-
shall have mutually perpendicular pairs of plane parallel
ate for the material being tested since the quality of the notch
surfaces and free from scratches, pits, and sink marks. The
may be adversely affected by thermal deformations and
specimens shall be checked for compliance with these require-
stresses induced during the cutting operation if proper condi-
ments by visual observation against straightedges, squares, and
tions are not selected. The notching parameters used shall not
flat plates, and by measuring with micrometer calipers. Any
alter the physical state of the material such as by raising the
specimen showing observable or measurable departure from
temperature of a thermoplastic above its glass transition
one or more of these requirements shall be rejected or
temperature. In general, high cutter speeds, slow feed rates, and
machined to the proper size and shape before testing.
lack of coolant induce more thermal damage than a slow cutter
speed, fast feed speed, and the use of a coolant. Too high a feed
NOTE 14—A specimen that has a slight twist to its notched face of 0.05
mm (0.002 in.) at the point of contact with the pendulum striking edge will
speed/cutter speed ratio, however, may cause impacting and
be likely to have a characteristic fracture surface with considerable greater
cracking of the specimen. The range of cutter speed/feed ratios
fracture area than for a normal break. In this case the energy to break and
possible to produce acceptable notches can be extended by the
toss the broken section may be considerably larger (20 to 30 %) than for
use of a suitable coolant. (See Note 17.) In the case of new
a normal break. A tapered specimen may require more energy to bend it
types of plastics, it is necessary to study the effect of variations
in the vise before fracture.
in the notching conditions. (See Note 18.)
8. Notching Test Specimens
8.1 Notching shall be done on a milling machine, engine
Supporting data are available from ASTM Headquarters. Request RR:D20-
lathe, or other suitable machine tool. Both the feed speed and 1066.
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D256 − 23
NOTE 17—Water or compressed gas is a suitable coolant for many
with a loss of not more than 85 % of its energy (see Note 20).
plastics.
Check the machine with the proper pendulum in place for
NOTE 18—Embedded thermocouples, or another temperature measur-
conformity with the requirements of Section 6 before starting
ing device, can be used to determine the temperature rise in the material
the tests. (See Appendix X1.)
near the apex of the notch during machining. Thermal stresses induced
during the notching operation can be observed in transparent materials by
NOTE 20—Ideally, an impact test would be conducted at a constant test
viewing the specimen at low magnification between crossed polars in
velocity. In a pendulum-type test, the velocity decreases as the fracture
monochromatic light.
progresses. For specimens that have an impact energy approaching the
8.6 A notching operation notches one or more specimens capacity of the pendulum there is insufficient energy to complete the break
and toss. By avoiding the higher 15 % scale energy readings, the velocity
plus the “dummy bar” at a single pass through the notcher. The
of the pendulum will not be reduced below 1.3 m/s (4.4 ft/s). On the other
specimen notch produced by each cutter will be examined after
hand, the use of too heavy a pendulum would reduce the sensitivity of the
every 500 notching operations or less frequently if experience
reading.
shows this to be acceptable. The notch in the specimen, made
10.3 If the machine is equipped with a mechanical pointer
of the material to be tested, shall be inspected and verified. One
and dial, perform the following operations before testing the
procedure for the inspection and verification of the notch is
specimens. If the machine is equipped with a digital indicating
presented in Appendix X1. Each type of material being
system, follow the manufacturer’s instructions to correct for
notched must be inspected and verified at that time. If the angle
windage and friction. If excessive friction is indicated, the
or radius does not fall within the specified limits for materials
machine shall be adjusted before starting a test.
of satisfactory machining characteristics, then the cutter shall
10.3.1 With the indicating pointer in its normal starting
be replaced with a newly sharpened and honed one. (See Note
position but without a specimen in the vise, release the
19.)
pendulum from its normal starting position and note the
NOTE 19—A carbide-tipped or industrial diamond-tipped notching
position the pointer attains after the swing as one reading of
cutter is recommended for longer service life.
Factor A.
9. Conditioning 10.3.2 Without resetting the pointer, raise the pendulum and
release again. The pointer should move up the scale an
9.1 Conditioning—Condition the test specimens at 23 6
additional amount. Repeat (10.3.2) until a swing causes no
2°C (73 6 3.6°F) and 50 6 10 % relative humidity for not less
additional movement of the pointer and note the final reading
than 40 h after notching and prior to testing in accordance with
as one reading of Factor B (see Note 21).
Procedure A of Practice D618, unless it can be documented
10.3.3 Repeat the preceding two operations several times
(between supplier and customer) that a shorter conditioning
and calculate and record the average A and B readings.
time is sufficient for a given material to reach equilibrium of
impact resistance.
NOTE 21—Factor B is an indication of the energy lost by the pendulum
9.1.1 Note that for some hygroscopic materials, such as to friction in the pendulum bearings and to windage. The difference A – B
is an indication of the energy lost to friction and inertia in the indicating
nylons, the material specifications (for example, Specification
mechanism. However, the actual corrections will be smaller than these
D4066) call for testing “dry as-molded specimens.” Such
factors, since in an actual test the energy absorbed by the specimen
requirements take precedence over the above routine precon-
prevents the pendulum from making a full swing. Therefore, the indicated
ditioning to 50 % relative humidity and require sealing the
breaking energy of the specimen must be included in the calculation of the
specimens in water vapor-impermeable containers as soon as machine correction before determining the breaking energy of the speci-
men (see 10.8). The A and B values also provide an indication of the
molded and not removing them until ready for testing.
condition of the machine.
9.2 Test Conditions—Conduct tests in the standard labora-
10.3.4 If excessive friction is indicated, the machine shall be
tory atmosphere of 23 6 2°C (73 6 3.6°F) and 50 6 10 %
adjusted before starting a test.
relative humidity, unless otherwise specified in the material
specification or by customer requirements. In cases of
10.4 Check the specimens for conformity with the require-
disagreement, the tolerances shall be 61°C (61.8°F) and 6
ments of Sections 7, 8, and 10.1.
5 % relative humidity.
10.5 Measure and record the width of each specimen after
notching to the nearest 0.025 mm (0.001 in.). Measure the
10. Procedure
width in one location adjacent to the notch centered about the
10.1 At least five and preferably ten or more individual
anticipated fracture plane.
determinations of impact resistance must be made on each
10.6 Measure and record the depth of material remaining in
sample to be tested under the conditions prescribed in Section
the specimen under the notch of each specimen to the nearest
9. Each group shall consist of specimens with the same
0.025 mm (0.001 in.). The tapered blade will be fitted to the
nominal width (60.13 mm (60.005 in.)). In the case of
notch. The specimen will be approximately vertical between
specimens cut from sheets that are suspected of being
the anvils. For specimens with a draft angle, position edge of
anisotropic, prepare and test specimens from each principal
the non-cavity (wider edge) surface centered on the microm-
direction (lengthwise and crosswise to the direction of anisot-
eter’s flat circular anvil.
ropy).
10.2 Estimate the breaking energy for the specimen and 10.7 Position the specimen precisely (see 6.7) so that it is
select a pendulum of suitable energy. Use the lightest standard rigidly, but not too tightly (see Note 11), clamped in the vise.
pendulum that is expected to break each specimen in the group Pay special attention to ensure that the “impacted end” of the
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D256 − 23
specimen as shown and dimensioned in Fig. 6 is the end 11.1.9 The number of those specimens that resulted in
projecting above the vise. Release the pendulum and record the failures which conforms to each of the requirement categories
indicated breaking energy of the specimen together with a in 5.8,
description of the appearance of the broken specimen (see 11.1.10 The average impact resistance and standard devia-
failure categories in 5.8). tion (in J/m (ft·lbf/in.)) for those specimens in each failure
category, except non-break as presented in 5.8. Optional uni
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