ASTM F791-96
(Test Method)Standard Test Method for Stress Crazing of Transparent Plastics
Standard Test Method for Stress Crazing of Transparent Plastics
SCOPE
1.1 This practice covers the determination of the critical crazing stress for a transparent-plastic material when exposed to a specific solvent, chemical, or compound at a specific temperature.
1.2 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 and health practices and determine the applicability of regulatory limitations prior to use .
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
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Designation: F 791 – 96
Standard Test Method for
Stress Crazing of Transparent Plastics
This standard is issued under the fixed designation F 791; 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 4. Significance and Use
1.1 This test method covers the determination of the critical 4.1 This test method provides a guide for evaluating a
crazing stress for a transparent plastic material when exposed specific solvent, chemical, or compound that may be detrimen-
to a specific solvent, chemical, or compound at a specific tal to a transparent plastic as a result of a manufacturing
temperature. process, a fabrication operation, or the operational environ-
1.2 This standard does not purport to address all of the ment. All transparent plastics are susceptible to crazing, though
safety concerns, if any, associated with its use. It is the in widely varying degree and from a variety of causes. This test
responsibility of the user of this standard to establish appro- method is intended to allow establishment of the crazing stress
priate safety and health practices and determine the applica- when the simultaneous action of both load and a material that
bility of regulatory limitations prior to use. would cause crazing is applied producing non-reversible dam-
age that might limit the usage of that transparent plastic in a
2. Referenced Documents
specific application.
2.1 ASTM Standards:
5. Apparatus
D 618 Methods of Conditioning Plastics for Testing
E 691 Practice for Conducting an Interlaboratory Study to 5.1 Test Fixture, with fluorescent light source illustrated and
Determine the Precision of a Test Method constructed as shown in Figs. 1 and 2.
2.2 Other Method: 5.2 Drill Fixture constructed as shown in Fig. 3.
ARTC (Aircraft Research and Testing Committee of the 5.3 Marking Fixture, constructed as shown in Fig. 3.
Aircraft Industries Association of America, Inc.) Condi- 5.4 Portable Specimen Rack, constructed in the manner as
tioning Method shown in Fig. 4 for handling and conditioning test specimens.
5.5 Weights—A container and shot for the application of
3. Terminology
weight on the rack as shown in Fig. 1.
3.1 Definitions of Terms Specific to This Standard: 5.6 Filter Paper, quantity of 0.50 by 1.0-in. (12.7 by
3.1.1 crazing—a group of surface fissures that appear to be
25.4-mm) pieces of filter, medium-retention filter paper.
small cracks in the material, although they are not.
6. Test Specimens
3.1.1.1 Discussion—Crazing is a form of yielding in poly-
mers characterized by a spongy void filled fibrillar structure. 6.1 The test specimen shall be machined from the transpar-
The density in the craze changes resulting in a change in the ent plastic material to be evaluated. A minimum of six
index of refraction, which causes light to be reflected off of the specimens for each solvent, chemical, or compound is re-
crazes. This light reflection causes the crazes to sparkle when quired. It is preferred that the transparent plastic sheet material
viewed from certain angles. The crazes are sometimes random thickness be 6.35 6 0.64 mm (0.250 6 0.025 in.), but any
and scattered with varied lengths and depths but usually are thickness material may be used. Orientation of each test
oriented perpendicular to a tensile stress. Crazing may be specimen within the test sheet or part should be recorded.
difficult to detect. It becomes more pronounced when viewed 6.2 The test specimens shall be 25.4 6 0.8 mm (1.00 6 0.03
with a light source that is at an oblique angle. in.) wide by 177.8 6 1.27 mm (7.00 6 0.05 in.) long by
thickness.
6.3 The edges shall be smooth machined surfaces without
This test method is under the jurisdiction of ASTM Committee F-7 on cracks, and the test specimen surface shall be free of defects or
Aerospace and Aircraft and is the direct responsibility of Subcommittee F07.08 on
irregularities. If the test specimen has been machined to
Transparent Materials and Enclosures.
thickness, the nonmachined surface shall be the test surface.
Current edition approved Oct. 10, 1996. Published December 1996. Originally
published as F 791 – 82. Last previous edition F 791 – 82 (1988).
2 7. Preparation of Apparatus
Annual Book of ASTM Standards, Vol 08.01.
Annual Book of ASTM Standards, Vol 14.02.
7.1 Once the load for a particular stress is calculated, that
Available from Aircraft Industries Association, 1725 DeSales St. NW, Wash-
load will be the sum of the individual weights of the weight
ington, DC 20034.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
F 791
FIG. 1 Accelerated Crazing Test Fixture
FIG. 3 Fixtures for Specimen Preparation
FIG. 2 Application of Test Liquid to Piece of Filter Paper on Top
8.1.2 Two hours at 90°C (194°F), ambient cooled, and
Surface of Test Specimen
followed by 7 days at 23 6 1.1°C (73.5 6 2°F) and 50 6 5%
relative humidity. Designate as Condition 2 and test within 1 h.
rack, rod, lead weights, container, shot, and the radiused nut.
8.1.3 ARTC Method. Sixteen hours at 14°C (25°F) below
For convenience of assembly, the weight rack pan may be
the average heat deflection temperature, cool at a rate not
stamped with the total weight of the pan, rod, and nuts as a
exceeding 28°C (50°F)/h and follow by 96 h at 23 6 1.1°C
unit. A container, such as a ⁄2-pt (0.24-L) paint can with a
(73.5 6 2°F) and 50 6 5 % relative humidity. Designate as
6.4-mm ( ⁄4-in.) hole drilled in the center of the bottom and
Condition 3 and test within 1 h.
installed so it slides up and down on the rod, can serve as a
8.1.4 As received, no preconditioning. Designate as Condi-
receptacle for the lead shot to attain required weight.
tion 4.
8. Conditioning
NOTE 1—The conditions listed above may not result in uniform
moisture content for certain plastics. Moisture content reportedly may
8.1 Precondition the test specimens in accordance with one
have a strong effect on craze results for certain plastics. If other
of the following procedures:
preconditionings are required to ensure uniform or desired moisture
8.1.1 Practice D 618 Procedure B. Forty-eight hours at 50°C
content, the use of these should be reported in the test report.
(122°F) followed by cooling to room temperature in desiccator
9. Calculation of Loads
over anhydrous calcium chloride for at least 5 h. Designate as
Condition 1 and test within 15 min. 9.1 The width and thickness of each specimen shall be
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
F 791
specimen. Carefully center the load supporting nut (with a
7.94-mm (0.3125-in.) machined radius on the surface contact-
ing the plastic) in the hole and tighten the nut. Align the
specimen edges so they are exactly perpendicular to the
fulcrum and slowly lower the weights until the specimen
accepts the load.
10.5 Test the first specimen at 27.58 MPa (4000 psi) outer
fiber stress. Apply the load for 10 6 0.5 min and observe to be
sure no crazing has occurred. Place the 12.5 by 25-mm ( ⁄2 by
1 in.) filter paper directly over the fulcrum in the middle of the
specimen so there is a clear area along each edge to avoid
inducing edge crazing. Apply the test chemical to the filter
paper only. Use care so that the test material does not extend
beyond this area and defeat the purpose of the test. Keep the
filter paper moist with test chemical for the duration of the test,
FIG. 4 Specimen Rack
15 minutes, 30 minutes, or any duration desired. Remove the
filter paper after the test period and inspect for craze. Turn on
measured to the nearest 0.03 mm (0.001 in.). Enter this data
the fluorescent lamps for inspection only to avoid undesired
along with the identification of the specimen in the required
heating of the test specimen. Terminate the testing of that
records.
specimen.
9.2 Calculate the load to be used with each specimen in
NOTE 3—It is recommended that a control test be run with each set of
accordance with the following equation:
craze tests. This control test is conducted exactly the same as the other
P 5 ~S 3 B 3 D!/~6L! (1)
craze tests, except that no chemicals should be applied to this control
specimen during the craze test. This provides a baseline and allows a
where:
determination of whether the crazing observed in the tests with the
P 5 load, N (lb.),
chemical applied is due to the chemical/stress combination, or is a
S 5 maximum outer fiber stress, MPa (psi), determined by
function of stress alone.
test sequence in 10.5-10.8, or 11.5-11.8,
10.6 If the first specimen is crazed, test the second specimen
L 5 length of specimen from fulcrum to center of applied
at 13.79 MPa (2000 psi). If the first specimen did not craze, test
load, mm (in.),
the second specimen at 20.68 MPa (6000 psi).
B 5 width of specimen, mm (in.), and
10.7 If the second specimen does not craze at 2000 psi, test
D 5 thickness of specimen, mm (in.).
the third specimen at 20.68 MPa (3000 psi). Test the fourth at
NOTE 2—This equation is valid only for relatively small deflections.
a lower or higher stress depending on whether the third
For large deflections, the dimension L should be replaced by the actual
specimen did or did not craze. Continue this procedure in
horizontal distance from the point of load application to the fulcrum in the
suitable increments until the critical crazing stress for specific
displaced condition. A deflection of 25.4 mm (1 in.) at the point of load
solvent, chemical, or compound is determined to the desired
application will result in an actual stress at the fulcrum which is
accuracy.
approximately 5 % less than the expected stress, and a 38.1 mm (1.5 in.)
10.8 Report the critical crazing stress as the stress midway
deflection will result in an actual stress at the fulcrum which is approxi-
mately 10 % less than the expected stress. between the stress at which crazing was and was not observed
on duplicate specimens. Example: Crazing was observed at
10. Procedure A—Craze Stress Iteration
27.58 MPa (4000 psi) and none at 24.13 MPa (3500 psi). The
10.1 Place each specimen in the drill fixture and drill a 7.94
critical crazing stress would be 25.86 6 1.72 MPa (3750 6 250
mm (0.3125 in.) diameter hole at a distance of 12.7 6 1.27 mm
psi).
(0.50 6 0.050 in.) from one end and on the longitudinal
10.9 In the examination of the crazing, note all cracks at the
centerline of the specimen.
edge of the specimen as “edge crazing.” Disregard this
10.2 Place each specimen in the marking fixture and draw a
condition when ascertaining the end point unless the edge of
pencil line on the edge of the specimen 101.6 mm (4.0 in.)
crazing grows and extends across the entire width of the
from the center of the 7.94-mm (0.3125-in.) diameter hole and
specimen.
perpendicular to the length of the specimen (see mark in Fig.
10.10 Testing shall be at the specified temperature 63°C
2).
(65°F).
10.3 Measure the width and thickness of each specimen to
11. Procedure B—Craze Stress Tracking
the nearest 0.03 mm (0.001 in.) at the pencil line. Handle each
11.1 Place each specimen in the drill fixture and drill a
specimen only by its edges. Do not clean test specimens in any
manner during the time period between conditioning and 7.94-mm (0.3125-in.) diameter hole at a distance of 12.7 6
testing. 1.27 mm (0.50 6 0.050 in.) from one end and on the
10.4 Insert the conditioned specimen immediately in the test longitudinal centerline of the specimen.
fixture with the pencil mark on the specimen in line with the 11.2 Place each specimen in the marking fixture and draw a
center of the fulcrum. Raise the weights and insert the end of pencil line on the edge of the specimen 101.6 mm (4.0 in.)
the rod through the 7.94-mm (0.3125-in.) hole in the test from the center of the 7.94-mm (0.3125-in.) diameter hole and
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
F 791
perpendicular to the length of the specimen (see the mark in
B 5 width of specimen, mm (in.), and
Fig. 2). On the side opposite the test surface, using an ink
D 5 thickness of specimen, mm (in.)
suitable for marking plastic, mark lines across the specimen
11.7 If the first specimen does not craze, test the second
surface perpendicular to the edge, from edge to edge, at 6.4
specimen at 41.37 MPa (6000 psi). If no crazing is observed at
mm (0.25 in.) intervals, starting at the hole and progressing
41.37 MPa (6000 psi), discontinue testing.
101.6 mm (4.0 in.) to the point at which the beam will rest on
11.8 If the first specimen breaks before the completion of
the fulcrum.
the test, test the remaining specimens at a stress level below the
11.3 Measure the width and thickness of each specimen to stress at which the specimen fractured.
the nearest 0.03 mm (0.001 in.) at the pencil line. Handle each
11.9 If the first specimen crazes below 6.895 MPa (1000
specimen only by its edges. Do not clean test specimens in any psi) (more than ⁄4 of the way down the beam) conduct the
manner during the time period between conditioning and
remaining tests with 13.79 MPa (2000 psi) at the fulcrum.
testing. 11.10 Calculate the minimum stress at which crazing oc-
curs. This stress may be calculated from the equation in 11.6.
11.4 Firmly press a 3.18 mm (0.125 in.) wide ribbon of
11.11 In the examination of the crazing, note all cracks at
non-compressible black butyl glazing tape sealant on the test
the edge of the specimen as edge crazing. Disregard this
surface of the specimen along each edge to create a dam which
condition when ascertaining the end point unless the edge
prevents the test chemical from coming in contact with the
crazing grows and extends across the entire width of the
specimen edges. Insert the conditioned specimen immediately
specimen.
in the test fixture with the pencil mark on the specimen in line
11.12 Testing shall be at the specified temperature 6 3°C
with the center of the fulcrum. Raise the weights and insert the
(6 5°F).
end of the rod through the 7.94-mm (0.3125-in.) hole in the test
specimen. Carefully center the load supporting nut (with a 7.94
NOTE 5—It is recommended that a control test
...
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