ASTM D4812-99
(Test Method)Standard Test Method for Unnotched Cantilever Beam Impact Strength of Plastics
Standard Test Method for Unnotched Cantilever Beam Impact Strength of Plastics
SCOPE
1.1 This test method covers the determination of the resistance to breakage by flexural shock of plastics, as indicated by the energy extracted from standardized (Note 1) pendulum-type hammers, mounted in standardized machines, in breaking standard specimens with one pendulum swing. The result of this test is reported in terms of impact strength per unit of specimen width. 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. Hammers of different initial energies (produced by varying their effective weights) are recommended for use with specimens of different impact strengths. Moreover, manufacturers of the equipment are permitted to use different lengths and constructions of pendulums (with resulting possible differences in pendulum rigidities (see Section 4), and other differences in machine design).
1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.3 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:D4812–99
Standard Test Method for
Unnotched Cantilever Beam Impact Resistance of Plastics
This standard is issued under the fixed designation D4812; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope E691 Practice for Conducting an Interlaboratory Study to
Determine the Precision of a Test Method
1.1 This test method covers the determination of the resis-
tance of plastics to breakage by flexural shock, as indicated by
3. Terminology
the energy extracted from standardized pendulum-type ham-
3.1 Definitions—Definitions used in this test method are in
mers, mounted in standardized machines, in breaking standard
accordance with Terminology D883.
specimens with one pendulum swing. The result of this test
method is reported as energy absorbed per unit of specimen
4. Summary of Test Method
width.
4.1 This test method differs from others of similar character
NOTE 1—The pendulum-type test instruments have been standardized
in that unnotched test specimens are used (see Test Methods
in that they must comply with certain requirements, including a fixed
D256 for procedures using notched test specimens). The lack
height of hammer fall that results in a substantially fixed velocity of the
of a notch makes this test method especially useful for
hammer at the moment of impact. Pendulums of different initial energies
reinforced materials where a notch may mask the effects of
(produced by varying their effective weights) are recommended for use
orientation. It may also be used with other filled or unrein-
with specimens of different impact strengths. Moreover, manufacturers of
the equipment are permitted to use different lengths and constructions of forced materials where a stress-concentrating notch is not
pendulums (with resulting possible differences in pendulum rigidities (see
desired. It is not valid for materials that twist when subjected
Section 5), and other differences in machine design).
to this test.
1.2 The values stated in SI units are to be regarded as the
5. Significance and Use
standard. The values given in parentheses are for information
5.1 The excess-energy pendulum-impact test indicates the
only.
energy to break standard test specimens of specified size under
1.3 This standard does not purport to address all of the
stipulated conditions of specimen mounting and pendulum
safety concerns, if any, associated with its use. It is the
velocity at impact.
responsibility of the user of this standard to establish appro-
5.2 The energy lost by the pendulum during the breakage of
priate safety and health practices and determine the applica-
thespecimenisthesumoftheenergiesrequiredtoproducethe
bility of regulatory limitations prior to use.
following results:
NOTE 2—ThisstandardandISO180,Method1U,aresimilarincontent
5.2.1 To initiate fracture of the specimen,
but are not technically equivalent.
5.2.2 To propagate the fracture across the specimen,
2. Referenced Documents 5.2.3 To throw the free end (or pieces) of the broken
2 specimen (toss correction),
2.1 ASTM Standards:
5.2.4 To bend the specimen,
D256 Test Methods for Impact Resistance of Plastics and
5.2.5 To produce vibration in the pendulum arm,
Electrical Insulating Materials
5.2.6 To produce vibration or horizontal movement of the
D618 Practice for Conditioning Plastics for Testing
machine frame or base,
D883 Terminology Relating to Plastics
5.2.7 To overcome friction in the pendulum bearing and in
D5947 Test Methods for Physical Dimensions of Solid
the excess-energy-indicating mechanism, and to overcome
Plastic Specimens
windage (pendulum air drag),
5.2.8 To indent or deform plastically the specimen at the
This test method is under the jurisdiction ofASTM Committee D20 on Plastics line of impact, and
and is the direct responsibility of Subcommittee D20.10 on Mechanical Properties.
5.2.9 To overcome the friction caused by the rubbing of the
Current edition approved March 10, 1999. Published June 1999. Originally
striking nose (or other part of the pendulum) over the face of
published as D4812–88. Last previous edition D4812–93.
the bent specimen.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
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D4812–99
5.3 For relatively brittle materials for which fracture propa- relationship will exist under another set of test conditions. The
gationenergyissmallincomparisonwiththefractureinitiation ranking of materials may even be changed under different
energy, the indicated impact energy absorbed is, for all testing conditions.
practical purposes, the sum of items given in 5.2.1 and 5.2.3. 5.8 Before proceeding with this test method, reference
The toss correction (5.2.3) may represent a very large fraction shouldbemadetothespecificationofthematerialbeingtested.
of the total energy absorbed when testing relatively dense and Any test specimen preparation, conditioning, dimensions, or
brittle materials. testing parameters, or combination thereof, covered in the
5.4 For materials for which the fracture propagation energy material specification shall take precedence over those men-
(5.2.2) may be large compared to the fracture initiation energy tionedinthistestmethodexceptincaseswheretodosowould
(5.2.1), factors (5.2.2, 5.2.5, and 5.2.9) can become quite conflict with the purpose for conducting testing. If there are no
significant, even when the specimen is accurately machined material specifications, then the default conditions apply.
and positioned and the machine is in good condition with
6. Apparatus
adequate capacity (Note 3). Bending (5.2.4) and indentation
6.1 Impact Machine, consisting of a massive base on which
losses (5.2.8) may be appreciable when testing soft materials.
is mounted a vise for holding the specimen and to which is
NOTE 3—Although the frame and base of the machine should be
connected, through a rigid frame and antifriction bearings, one
sufficiently rigid and massive to handle the energies of tough specimens
of a number of pendulum-type hammers (or one basic hammer
without motion or excessive vibration, the pendulum arm cannot be made
to which extra weights may be attached) having an initial
very massive because the greater part of its mass must be concentrated
nearitscenterofpercussionatthestrikingnose.Locatingthestrikingnose
energy suitable for use with the particular specimen to be
precisely at the center of percussion reduces vibration of the pendulum
tested, plus a pendulum holding and releasing mechanism and
arm when used with brittle specimens. However, some losses due to
a pointer and dial mechanism for indicating the excess energy
pendulum-arm vibration, the amount varying with the design of the
remaining in the pendulum after breaking the specimen. A jig
pendulum, will occur with tough specimens even when the striking nose
for positioning the specimen in the vise and graphs or tables to
is properly positioned.
aid in the calculation of the correction for frictionandwindage
5.5 In a well-designed machine of sufficient rigidity and
should be included. See Fig. 1 for one type of machine that
massthelossesduetotheitemsgivenin5.2.6and5.2.7should
may be used. The type of machine that is depicted can also be
be very small. Vibrational losses (5.2.6) can be quite large
used for the testing of notched specimens using Test Methods
when specimens of tough materials are tested in machines of
D256. Detailed requirements are given in 6.2-6.5. SeeAppen-
insufficient mass which are not securely fastened to a heavy
dix X1 for general methods for checking and calibrating the
base.
machine. Additional instructions for adjusting a particular
5.6 Thistestmethodrequiresthatthetypeoffailureforeach
machine should be supplied by the manufacturer.
specimen be recorded as one of the three coded categories
6.2 Pendulum,consistingofasingleormultimemberedarm
defined as follows:
with a bearing on one end and a head, containing the striking
5.6.1 C (Complete Break)—Abreak in which the specimen
nose, on the other.Although a large proportion of the mass of
is separated into two or more pieces.
5.6.2 P (Partial Break)—An incomplete break that has
fractured at least 90% of the depth of the specimen.
5.6.3 NB (Non-Break)—An incomplete break where the
fracture extends less than 90% of the depth of the specimen.
5.6.3.1 For tough materials the pendulum may not have the
energy necessary to completely break the extreme outermost
fibers and toss the broken piece or pieces. Results obtained
from “non-break” specimens shall be considered a departure
from standard and shall be reported as “NB” only and a
numerical value shall not be reported. Impact values cannot be
directly compared for any two materials that experience
different types of failure as defined by this code.
5.6.4 Averages reported must likewise be derived from
specimens contained within a single failure category. This
letter code will be included with the reported impact identify-
ing the types of failure associated with the reported value. If
morethanonetypeoffailureisobservedforasamplematerial,
then the report will indicate the average impact value for each
typeoffailure,followedbythepercentofthespecimensfailing
in that manner and identified by the letter code.
5.7 The value of this impact test method lies mainly in the
areas of quality control and materials specification. The fact
that a material shows twice the energy absorption of another
under these conditions of test does not indicate that this same FIG. 1 Cantilever Beam Impact Test Equipment
D4812–99
thependulumshouldbeconcentratedinthehead,thearmmust energy of the next lighter one will be found convenient. Each
be sufficiently rigid to maintain the proper clearances and pendulum shall have an energy within 60.5% of its nominal
geometric relationships between the machine parts and the capacity.
specimen and to minimize vibrational losses which are always 6.2.5 When the pendulum is free-hanging, the striking
surface shall come within 0.5% of scale of touching the front
included in the measured impact value.
face of a standard specimen. During an actual swing this
6.2.1 Striking Nose (of the Pendulum),ofhardenedsteeland
element shall make initial contact with the specimen on a line
cylindrical surface having a radius of curvature of 0.80 6 0.20
22.00 6 0.05 mm (0.866 6 0.002 in.) above the top surface of
mm (0.031 6 0.008 in.) with its axis horizontal and perpen-
the vise.
dicular to the plane of swing of the pendulum.
6.2.6 Means shall be provided for determining energy re-
6.2.1.1 The line of contact of the striking nose shall be
maining in the pendulum after breaking the specimen. This
located at the center of percussion of the pendulum within
may consist of a pointer and dial mechanism or it may consist
62.54 mm (0.100 in.) (Note 4). Those portions of the pendu-
of an electronic determination provided with a digital display.
lum adjacent to the cylindrical striking edge shall be recessed
The device will indicate the height of rise of the pendulum
orinclinedatasuitableanglesothattherewillbenochancefor
beyond the point of impact in terms of energy removed from
other than this cylindrical surface coming into contact with the
thespecificpendulum.Theindicatedremainingenergymustbe
specimen during the break.
corrected for friction and pendulum windage. Instructions for
6.2.2 Pendulum Holding and Releasing Mechanism,ina
makingthesecorrectionsareincludedin9.3andAppendixX2.
position such that the vertical height of fall of the striking nose
6.3 Vise, for clamping the specimen rigidly in position so
shall be 610 6 2 mm (24.0 6 0.1 in.); this will produce a
thatthelongaxisofthespecimenisverticalandatrightangles
velocity of the striking nose at the moment of impact of
to the top plane of the vise. The top edges of the jaws of the
approximately 3.46 m (11.35 ft)/s. The mechanism shall be so
vise shall have a radius of 0.25 6 0.12 mm (0.0106 0.005 in.)
constructed and operated that it will release the pendulum
(see Fig. 2).
without imparting acceleration or vibration to it.
NOTE 5—Itisespeciallyimportantthatthecorrectradiusbemaintained
6.2.3 The effective length of the pendulum shall be between
on the moveable vise jaw. Any sharp edge, nick, or burr on this jaw will
0.325 and 0.406 m (12.8 and 16.0 in.) so that the above
create a “notch” or stress concentration point when the jaw is clamped
required elevation of the striking nose may be obtained by
against the test specimen. This stress concentration point has lowered
raisingthependulumtoananglebetween60and30°abovethe values of some materials to less than 50% of the value obtained when the
jaw has the correct radius.
horizontal.
6.3.1 It is very important that exactly 31.75 6 0.25 mm
NOTE 4—The distance from the axis of support to the center of
(1.25 6 0.010 in.) of the specimen project above the top
percussion may be determined experimentally from the period of small
surface of the vise (see 9.5).
amplitude oscillations of the pendulum, as follows:
2 2
NOTE 6—Some plastics are sensitive to clamping pressure. For this
L 5 ~g/4p !p (1)
reason, cooperating laboratories should agree upon some means of
standardizing the clamping force, such as with a torque wrench on the
where:
L = distance from the axis of support to the center of percussion, m
(ft),
g = localgravitationalacceleration(knowntoanaccuracyofonepart
2 2
in one thousand), m/s (ft/s ),
p = 3.1416 (4p =39.4786), and
p = period,s,ofasinglecompleteswing(toandfro)determinedfrom
at least 50 consecutive and uninterrupted swings (known to one
part in two thousands). The angle of swing shall be less than 5°
each side of center.
6.2.4 The machine shall be provided with a basic pendulum
capable of delivering an energy of 2.710 6 0.135 J (2.00 6
0.10 ft-lbf). This pendulum shall be used with all specimens
that extract less than 85% of this energy. Heavier pendulums
shall be provided for specimens that require more energy to
break. These may be separate interchangeable pendulums or
one basic pendulum to which extra pairs of equal calibrated
weights may be attached rigidly to opposite sides of the
pendulum at its center of percussion. It is imperative that the
extra weights shall not change the position of the center of
percussion of the free-hang
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