ASTM D4508-98

Standard Test Method for Chip Impact Strength of Plastics

SCOPE
1.1 The purpose of this test method is to provide an impact test that can be performed on small specimens of plastics of different thicknesses. This test method is especially suited for observing the effects of microcracks caused by weathering, or by exposure to solvents or other hostile environments, on the surface of plastic materials. It is not meant to be used as a replacement for any existing impact test, but can be used to measure impact on coupons machined from finished parts that cannot be tested by the drop-weight, Izod, or Charpy method because of shape or thickness limitations.  
1.2 The chip-impact test is run on small, flat, unnotched specimens using a standard pendulum-impact device. The test places the impacted surface in tension and, for notch- sensitive materials, is extremely sensitive to the presence of surface microcracks. Thus, for plastics that develop surface cracks when exposed outdoors, the chip-impact test is a severe test of the weathered impact strength.  
1.3 Round-robin testing has indicated that materials that break at total energy values of less than 0.17 joules (1.5 in.-lbf) have within-laboratory coefficients of variation of approximately 30%. Therefore, such values are considered out of the normal testing range for this test.  
1.4 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.  
1.5 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.

General Information

• Status: Historical
• Publication Date: 09-Jul-1998
• ICS: 83.080.01 - Plastics in general
• Technical Committee: D20 - Plastics
• Drafting Committee: D20.10 - Mechanical Properties

Relations

• Replaced By: ASTM D4508-04 - Standard Test Method for Chip Impact Strength of Plastics
• Effective Date: 01-Feb-2004
• Referred By: ASTM G178-16(2023) - Standard Practice for Determining the Activation Spectrum of a Material (Wavelength Sensitivity to an Exposure Source) Using the Sharp Cut-On Filter or Spectrographic Technique
• Effective Date: 10-Jul-1998

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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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: D 4508 – 98
Standard Test Method for
Chip Impact Strength of Plastics
This standard is issued under the fixed designation D 4508; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope Insulating Materials for Testing
D 883 Terminology Relating to Plastics
1.1 The purpose of this test method is to provide an impact
D 1600 Terminology for Abbreviated Terms Relating to
test that can be performed on small specimens of plastics of
Plastics
different thicknesses. This test method is especially suited for
D 4000 Classification System for Specifying Plastic Mate-
observing the effects of microcracks caused by weathering, or
rials
by exposure to solvents or other hostile environments, on the
D 4066 Specification for Nylon Injection and Extrusion
surface of plastic materials. It is not meant to be used as a
Materials
replacement for any existing impact test, but can be used to
E 380 Practice for Use of the International System of Units
measure impact on coupons machined from finished parts that
(SI) (the Modernized Metric System)
cannot be tested by the drop-weight, Izod, or Charpy method
E 691 Practice for Conducting an Interlaboratory Study to
because of shape or thickness limitations.
Determine the Precision of a Test Method
1.2 The chip-impact test is run on small, flat, unnotched
specimens using a standard pendulum-impact device. The test
3. Terminology
places the impacted surface in tension and, for notch-sensitive
3.1 Definitions—For definitions of plastic terms see Termi-
materials, is extremely sensitive to the presence of surface
nology D 883 and for abbreviations see Terminology D 1600.
microcracks. Thus, for plastics that develop surface cracks
There are no terms in this test method that require new or
when exposed outdoors, the chip-impact test is a severe test of
other-than-dictionary definitions.
the weathered impact strength.
1.3 Round-robin testing has indicated that materials that
4. Significance and Use
break at total energy values of less than 0.17 joules (1.5 in.-lbf)
4.1 The chip-impact test is a variation of the Izod impact
have within-laboratory coefficients of variation of approxi-
test described in Test Methods D 256.
mately 30 %. Therefore, such values are considered out of the
4.2 The specimen geometry has been chosen to fit three
normal testing range for this test.
basic criteria as follows:
1.4 The values stated in SI units are to be regarded as the
4.2.1 The specimen is relatively thin and is struck on the
standard. The values given in parentheses are for information
broad surface so that the test result is sensitive to the condition
only.
of the surface,
1.5 There is no ISO equivalent to this test method.
4.2.2 The specimen is relatively small for efficient utiliza-
1.6 This standard does not purport to address all of the
tion of space in accelerated testing media or devices and to
safety concerns, if any, associated with its use. It is the
minimize amounts of material needed for testing, and
responsibility of the user of this standard to establish appro-
4.2.3 The specimen can be tested using a standard Izod
priate safety and health practices and determine the applica-
pendulum tester.
bility of regulatory limitations prior to use.
4.3 It has been found that a 12.7-mm (0.500-in.) wide strip
2. Referenced Documents with a thickness in the range from 1.02 to 3.18 mm (0.040 to
0.125 in.) meets the above criteria. Much experimental work
2.1 ASTM Standards:
on 1.78-mm (0.070-in.) strips has demonstrated the utility of
D 256 Test Method for Determining the Pendulum Impact
2 the chip-impact test to track weather aging of a variety of
Resistance of Notched Specimens of Plastics
materials.
D 618 Practice for Conditioning Plastics and Electrical
4.4 The distance (L) between clamping and impact points
(striker height) will affect test results. Extensive experimental
work has established that a ratio of L = 2.182 h (where L is the
This test method is under the jurisdiction of ASTM Committee D-20 on Plastics
and is the direct responsibility of Subcommittee D20.10 on Mechanical Properties.
Current edition approved July 10, 1998. Published September 1998. Originally
published as D 4508 – 85. Last previous edition D 4508 – 93. Annual Book of ASTM Standards, Vol 08.02.
2 4
Annual Book of ASTM Standards, Vol 08.01. Annual Book of ASTM Standards, Vol 14.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 4508
distance between clamping and impact points and h is the 5. Apparatus
thickness of the specimen) will provide accurate and sensitive
5.1 The apparatus shall be a cantilever beam (Izod-type)
chip-impact values. Increasing this ratio (that is, raising the
impact machine as described in the Annex and Test Methods
striker height for a given thickness) lowers chip-impact values
D 256, Method A. The following modifications must be made
and reduces sensitivity of the test. Decreasing the above ratio
to the specimen holder and impacting hammer (see Fig. 1). The
(that is, lowering the striker height for a given thickness)
specimen holder shall be constructed from a 12.7 by 12.7-mm
results in a shearing of the specimen rather than the desired
(0.5 by 0.5-in.) steel bar, the front face of which shall be
bending and breaking.
recessed 1.9 mm (0.075 in.) deep and 7.94 mm (0.312 in.) long
4.5 In general, the chip-impact value during weathering from the top surface to accept the chip-impact specimen.
varies according to specimen thickness, even after adjusting
Corresponding to this recessed area is an adjustable clamp to
striker heights for constant deflection, as given in Table 1. The hold the specimen in place. This specimen holder is clamped
thickness of the specimen should always be reported, along into the standard Izod vise and adjusted to proper height based
on specimen thickness. This adjustment is made by positioning
with the test values, and comparisons should only be made
the adjustment screw in the vertical portion of the specimen
among samples of similar thickness.
holder.
4.6 The standard Izod Methods A, C, D, and E require that
5.2 The chip-impact striker (see Fig. 2) has a flat face and
the type of failure for each specimen be recorded as one of the
bevelled bottom edge to facilitate clearance of specimens that
four coded categories defined as follows:
do not completely break-off on impact (hinge or partial
C= complete break—a break in which the specimen separates into two or
breaks). The standard Izod striker may also be used with no
more pieces,
H= hinge break—an incomplete break such that one part of the specimen
significant change in impact strength.
cannot support itself above the horizontal when the other part is held
5.3 Calibration of the cantilever beam impact machine may
vertically (less than 90° included angle),
be carried out as described in Test Methods D 256.
P= partial break—an incomplete break that does not meet the definition
for a hinge break, but has fractured at least 90 % of the distance be-
6. Test Specimen
tween the surface of the impact side and the opposite side.
NB = non-break—an incomplete break where the fracture extends less than
6.1 The standard test specimen shall be 12.7 mm (0.5 in.)
90 % of the distance between the impacted surface and the opposite
wide by 19.05 mm (0.750 in.) long by 1.02 to 3.175 mm (0.040
side. Non-break data shall not be reported as a standard result, but
may be used to establish a relative sensitivity to aging on a time basis.
to 0.125 in.) in depth. The preferred depth is (1.778 mm (0.070
in.)). These may be cut from molded plaques, extruded sheets,
or finished products and should be cut or milled to the proper
4.6.1 Impact values cannot be directly compared for any
12.7-mm (0.5-in.) width. Smooth edges are necessary to
two materials that experience different types of failure as
minimize edge effects.
defined in the method for this code.
6.2 For determining the effect of aging or environmental
4.7 Before proceeding with this test method, reference
exposure, cut the material to be tested into a convenient size for
should be made to the specification of the material being tested.
the exposure apparatus. Expose these sections for the required
Any test specimen preparation, conditioning, dimensions, or
time in the desired environment. After exposure, cut each
testing parameters, or a combination thereof, covered in the
section into 12.7 by 19.05-mm (0.5 by 0.75-in.) chips for
material specification shall take precedence over those men-
impacting testing. Test each chip by striking it on the exposed
tioned in this test method. If there are no material specifica-
side.
tions, then the default conditions apply.
7. Conditioning
7.1 Condition the test specimens at 23 6 2°C
(73.4 6 3.6°F) and 50 6 5 % relative humidity for not less
TABLE 1 Striker Height Adjustment for Constant Deflection
A B than 40 h prior to test, in accordance with Method A of Practice
h L
D 618, unless otherwise specified.
mm in. mm in.
7.2 Conduct tests in the standard laboratory atmosphere of
1.016 (0.040) 2.21 (0.09)
23 6 2°C (73.4 6 3.6°F) and 50 6 5 % relative humidity,
1.143 (0.045) 2.49 (0.10)
unless otherwise specified.
1.270 (0.050) 2.77 (0.11)
1.397 (0.055) 3.05 (0.12)
7.3 Note that for some hygroscopic materials, such as
1.524 (0.060) 3.33 (0.13)
nylons, the material specifications (for example, Specification
1.651 (0.065) 3.61 (0.14)
1.778 (0.070) 3.89 (0.15) D 4066) call for testing “dry as molded specimens.” Such
1.905 (0.075) 4.17 (0.16)
requirements take precedence over routine preconditioning to
2.032 (0.080) 4.45 (0.18)
50 % relative humidity and require sealing specimens in water
2.159 (0.085) 4.72 (0.19)
2.286 (0.090) 5.00 (0.20) vapor-impermeable containers as soon as molded or extruded,
2.413 (0.095) 5.28 (0.21)
and not removing them until ready for testing.
2.540 (0.100) 5.56 (0.22)
7.4 Post-Conditioning of Specimens After Exposure to Hos-
2.667 (0.105) 5.84 (0.23)
2.794 (0.110) 6.10 (0.24) tile Environment:
2.921 (0.115) 6.38 (0.25)
7.4.1 Specimens shall be conditioned in accordance with
3.048 (0.120) 6.66 (0.26)
section 7.1 or 7.3 prior to subjecting the specimens to the
3.175 (0.125) 6.93 (0.27)
hostile environment, unless otherwise specified.
D 4508
NOTE—Dimensions, mm (in):
A = 4.7625 (0.1875)
B = 7.9375 (0.3125)
C = 12.700 (0.500)
D = 10.795 (0.425)
E = 4.7625 (0.1875)
F = 7.9375 (0.3125)
G = 50.8 (2.0)
H = 25.4 (1.0)
I = 12.7 (0.5)
FIG. 1 Specimen Holder
FIG. 2 Striker
7.4.2 The post-conditioning of specimens which have been purpose of referee testing. One cannot expect comparable
exposed to hostile environments requires careful consideration. results unless all details of sampling, specimen preparation,
The ultimate purpose of the exposure and test must be specimen conditioning, and exposures as well as testing
considered. The post-conditioning requirements for the speci- conditions are identical in all laboratories trying to make a
men shall be agreed upon by seller and purchaser for the comparison or settle a disagreement. Specimens subjected to
D 4508
high temperatures, accelerated weathering, outdoor weather- 8.3.1 With the excess energy-indicating pointer in its nor-
ing, radiation, or other exposure not involving submersion in mal starting position, but without a specimen in the vise,
release the pendulum from its normal starting position and note
liquid shall be allowed to return to the standard laboratory
the position the pointer attains after the swing as one reading of
atmosphere before testing. If the original unexposed specimens
Factor A.
used as references were tested at a temperature other than the
8.3.2 Without resetting the pointer, raise the pendulum and
standard laboratory temperature then the specimens subjected
release again. The pointer should move up the scale an
to the hostile environment must be allowed to reach thermal
additional amount. Repeat until a swing causes no additional
equilibrium at the test temperature before testing.
movement of the pointer and note the final reading as one
NOTE 1—For hygroscopic materials such as nylons that have data based reading of Factor B.
on “dry as molded” conditioning, returning the exposed specimens to the
8.3.3 Repeat the above two operations several times and
same conditions as the original specimen may introduce new (negative)
calculate and record the average A and B readings.
effects on the test specimen, for example, by drying in oven (heat/
NOTE 3—Factor B is an indication of the energy lost by the pendulum
crystallinity) or over chemical desiccant. For these materials, condition the
to friction in the pendulum bearings and to windage. The difference,
exposed sample and a “control” sample at the standard laboratory
A − B, is an indication of the energy lost to friction and inertia in the
atmosphere prior to testing.
excess energy-indicating mechanism. However, the actual corrections will
be smaller than these factors, since in an actual test the energy absorbed
7.4.3 Specimens that have been immersed in a hostile liquid
by the specimen prevents the pendulum from making a full swing.
environment require special handling. The liquid may evapo-
Therefore, the indicated breaking strength of the specimen must be
rate from the specimen while exposed to the standard labora-
included in the calculation of the machine correction before using it in 8.6.
tory atmosphere so all specimens must remain in the liquid
These A and B values also provide an indication of the condition of the
until ready to test. The liquid temperature and specimen must
machine. If they indicate excessive friction, the machine shall be adjusted
before starting a test.
both be at standard laboratory temperature. If the original
unexposed specimens used as references were tested at a
8.4 Check the specimens for conformity with the require-
temperature other than the standard laboratory temperature the
ments of Section 6. Measure the thickness of each specimen
liquid and specimens subjected to the hostile environment must
with a micrometer caliper to the nearest 0.025 mm (0.001 in.)
then be allowed to reach thermal equilibrium at the test
and record its average width, along with its identifying
temperature prior to testing.
markings.
8.4.1 Set the clearance height of the striker (L) above the
8. Procedure clamping device based on the specimen thickness (see Tab
...