ASTM F791-96(2013)
(Test Method)Standard Test Method for Stress Crazing of Transparent Plastics
Standard Test Method for Stress Crazing of Transparent Plastics
SIGNIFICANCE AND USE
4.1 This test method provides a guide for evaluating a specific solvent, chemical, or compound that may be detrimental to a transparent plastic as a result of a manufacturing process, a fabrication operation, or the operational environment. All transparent plastics are susceptible to crazing, though in widely varying degree and from a variety of causes. This test method is intended to allow establishment of the crazing stress when the simultaneous action of both load and a material that would cause crazing is applied producing non-reversible damage that might limit the usage of that transparent plastic in a specific application.
SCOPE
1.1 This test method 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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Designation: F791 − 96 (Reapproved 2013)
Standard Test Method for
Stress Crazing of Transparent Plastics
ThisstandardisissuedunderthefixeddesignationF791;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscript
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.
1. Scope and scattered with varied lengths and depths but usually are
oriented perpendicular to a tensile stress. Crazing may be
1.1 This test method covers the determination of the critical
difficult to detect. It becomes more pronounced when viewed
crazing stress for a transparent plastic material when exposed
with a light source that is at an oblique angle.
to a specific solvent, chemical, or compound at a specific
temperature.
4. Significance and Use
1.2 This standard does not purport to address all of the
4.1 This test method provides a guide for evaluating a
safety concerns, if any, associated with its use. It is the
specific solvent, chemical, or compound that may be detrimen-
responsibility of the user of this standard to establish appro-
tal to a transparent plastic as a result of a manufacturing
priate safety and health practices and determine the applica-
process, a fabrication operation, or the operational environ-
bility of regulatory limitations prior to use.
ment.Alltransparentplasticsaresusceptibletocrazing,though
inwidelyvaryingdegreeandfromavarietyofcauses.Thistest
2. Referenced Documents
method is intended to allow establishment of the crazing stress
2.1 ASTM Standards:
when the simultaneous action of both load and a material that
D618 Practice for Conditioning Plastics for Testing
would cause crazing is applied producing non-reversible dam-
E691 Practice for Conducting an Interlaboratory Study to
age that might limit the usage of that transparent plastic in a
Determine the Precision of a Test Method
specific application.
2.2 Other Method:
5. Apparatus
ARTC (Aircraft Research and Testing Committee of the
Aircraft Industries Association of America, Inc.) Condi-
5.1 Test Fixture, with fluorescent light source illustrated and
tioning Method
constructed as shown in Figs. 1 and 2.
5.2 Drill Fixture constructed as shown in Fig. 3.
3. Terminology
5.3 Marking Fixture, constructed as shown in Fig. 3.
3.1 Definitions of Terms Specific to This Standard:
3.1.1 crazing—a group of surface fissures that appear to be
5.4 Portable Specimen Rack, constructed in the manner as
small cracks in the material, although they are not.
shown in Fig. 4 for handling and conditioning test specimens.
3.1.1.1 Discussion—Crazing is a form of yielding in poly-
5.5 Weights—A container and shot for the application of
mers characterized by a spongy void filled fibrillar structure.
weight on the rack as shown in Fig. 1.
The density in the craze changes resulting in a change in the
5.6 Filter Paper, quantity of 0.50 by 1.0-in. (12.7 by
index of refraction, which causes light to be reflected off of the
25.4-mm) pieces of filter, medium-retention filter paper.
crazes. This light reflection causes the crazes to sparkle when
viewed from certain angles. The crazes are sometimes random
6. Test Specimens
6.1 The test specimen shall be machined from the transpar-
This test method is under the jurisdiction of ASTM Committee F07 on
ent plastic material to be evaluated. A minimum of six
Aerospace and Aircraft and is the direct responsibility of Subcommittee F07.08 on
specimens for each solvent, chemical, or compound is re-
Transparent Enclosures and Materials.
quired. It is preferred that the transparent plastic sheet material
Current edition approved Dec. 1, 2013. Published December 2013. Originally
approvedin1982.Lastpreviouseditionapprovedin2008asF791 – 96(2008).DOI:
thickness be 6.35 6 0.64 mm (0.250 6 0.025 in.), but any
10.1520/F0791-96R13.
thickness material may be used. Orientation of each test
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
specimen within the test sheet or part should be recorded.
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
6.2 Thetestspecimensshallbe25.4 60.8mm(1.00 60.03
the ASTM website.
in.) wide by 177.8 6 1.27 mm (7.00 6 0.05 in.) long by
Available from Aircraft Industries Association, 1725 DeSales St. NW,
Washington, DC 20034. thickness.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F791 − 96 (2013)
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
Surface of Test Specimen
installed so it slides up and down on the rod, can serve as a
receptacle for the lead shot to attain required weight.
8. Conditioning
6.3 The edges shall be smooth machined surfaces without
cracks, and the test specimen surface shall be free of defects or
8.1 Precondition the test specimens in accordance with one
irregularities. If the test specimen has been machined to
of the following procedures:
thickness, the nonmachined surface shall be the test surface.
8.1.1 Practice D618 Procedure B—Forty-eight hours at
50°C (122°F) followed by cooling to room temperature in
7. Preparation of Apparatus
desiccator over anhydrous calcium chloride for at least 5 h.
7.1 Once the load for a particular stress is calculated, that Designate as Condition 1 and test within 15 min.
load will be the sum of the individual weights of the weight 8.1.2 Two hours at 90°C (194°F), ambient cooled, and
rack, rod, lead weights, container, shot, and the radiused nut. followed by 7 days at 23 6 1.1°C (73.5 6 2°F) and 50 65%
For convenience of assembly, the weight rack pan may be relative humidity. Designate as Condition 2 and test within 1 h.
stamped with the total weight of the pan, rod, and nuts as a 8.1.3 ARTC Method—Sixteen hours at 14°C (25°F) below
unit. A container, such as a ⁄2-pt (0.24-L) paint can with a the average heat deflection temperature, cool at a rate not
6.4-mm ( ⁄4-in.) hole drilled in the center of the bottom and exceeding 28°C (50°F)/h and follow by 96 h at 23 6 1.1°C
F791 − 96 (2013)
10.2 Place each specimen in the marking fixture and draw a
pencil line on the edge of the specimen 101.6 mm (4.0 in.)
from the center of the 7.94-mm (0.3125-in.) diameter hole and
perpendicular to the length of the specimen (see mark in Fig.
2).
10.3 Measure the width and thickness of each specimen to
the nearest 0.03 mm (0.001 in.) at the pencil line. Handle each
specimen only by its edges. Do not clean test specimens in any
manner during the time period between conditioning and
testing.
10.4 Inserttheconditionedspecimenimmediatelyinthetest
fixture with the pencil mark on the specimen in line with the
center of the fulcrum. Raise the weights and insert the 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
FIG. 4 Specimen Rack
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
(73.5 6 2°F) and 50 6 5 % relative humidity. Designate as
accepts the load.
Condition 3 and test within 1 h.
8.1.4 As received, no preconditioning. Designate as Condi-
10.5 Test the first specimen at 27.58 MPa (4000 psi) outer
tion 4.
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
NOTE 1—The conditions listed above may not result in uniform
moisture content for certain plastics. Moisture content reportedly may
1 in.) filter paper directly over the fulcrum in the middle of the
have a strong effect on craze results for certain plastics. If other
specimen so there is a clear area along each edge to avoid
preconditionings are required to ensure uniform or desired moisture
inducing edge crazing. Apply the test chemical to the filter
content, the use of these should be reported in the test report.
paper only. Use care so that the test material does not extend
beyond this area and defeat the purpose of the test. Keep the
9. Calculation of Loads
filter paper moist with test chemical for the duration of the test,
9.1 The width and thickness of each specimen shall be
15 min, 30 min, or any duration desired. Remove the filter
measured to the nearest 0.03 mm (0.001 in.). Enter this data
paper after the test period and inspect for craze. Turn on the
along with the identification of the specimen in the required
fluorescent lamps for inspection only to avoid undesired
records.
heating of the test specimen. Terminate the testing of that
9.2 Calculate the load to be used with each specimen in specimen.
accordance with the following equation:
NOTE 3—It is recommended that a control test be run with each set of
P 5 S 3B 3D / 6L (1)
~ ! ~ ! craze tests. This control test is conducted exactly the same as the other
craze tests, except that no chemicals should be applied to this control
where:
specimen during the craze test. This provides a baseline and allows a
determination of whether the crazing observed in the tests with the
P = load, N (lb.),
chemical applied is due to the chemical/stress combination, or is a
S = 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 Ifthefirstspecimeniscrazed,testthesecondspecimen
L = length of specimen from fulcrum to center of applied
load, mm (in.), at13.79MPa(2000psi).Ifthefirstspecimendidnotcraze,test
B = width of specimen, mm (in.), and the second specimen at 20.68 MPa (6000 psi).
D = thickness of specimen, mm (in.).
10.7 If the second specimen does not craze at 2000 psi, test
NOTE2—Thisequationisvalidonlyforrelativelysmalldeflections.For
the third specimen at 20.68 MPa (3000 psi). Test the fourth at
large deflections, the dimension L should be replaced by the actual
horizontal distance from the point of load application to the fulcrum in the a lower or higher stress depending on whether the third
displaced condition. A deflection of 25.4 mm (1 in.) at the point of load
specimen did or did not craze. Continue this procedure in
application will result in an actual stress at the fulcrum which is
suitable increments until the critical crazing stress for specific
approximately 5 % less than the expected stress, and a 38.1 mm (1.5 in.)
solvent, chemical, or compound is determined to the desired
deflection will result in an actual stress at the fulcrum which is approxi-
accuracy.
mately 10 % less than the expected stress.
10.8 Report the critical crazing stress as the stress midway
10. Procedure A—Craze Stress Iteration
between the stress at which crazing was and was not observed
10.1 Place each specimen in the drill fixture and drill a 7.94 on duplicate specimens. For example: Crazing was observed at
mm (0.3125 in.) diameter hole at a distance of 12.7 6 1.27 mm 27.58 MPa (4000 psi) and none at 24.13 MPa (3500 psi). The
(0.50 6 0.050 in.) from one end and on the longitudinal criticalcrazingstresswouldbe25.86 61.72MPa(3750 6250
centerline of the specimen. psi).
F791 − 96 (2013)
10.9 In the examination of the crazing, note all cracks at the throughout the test to maintain a wetted condition on the entire
edge of the specimen as “edge crazing.” Disregard this test surface of the specimen, from the fulcrum down to the
condition when ascertaining the end point unless the edge of point of load application. Place a pan under the point of load
crazing grows and extends across the entire width of the application to catch the chemical which drips off of the
specimen. specimen. Continue the test for 15 minutes, 30 minutes, or any
duration desired. During the test, monitor the specimen con-
10.10 Testing shall be at the specified temperature 63°C
tinuously for craze development. Record the time and location
(65°F).
of the craze front as crazing progresses down the beam.
11. Procedure B—Craze Stress Tracking 11.6 Calculate the craze stress for each recorded time with
the following equation:
11.1 Place each specimen in the drill fixture and drill a
S 5 ~6 3P 3Z!/~B 3D ! (2)
7.94-mm (0.3125-in.) diameter hole at a distance of 12.7 6
1.27 mm (0.50 6 0.050 in.) from one end and on the
where:
longitudinal centerline of the specimen.
S = maximum outer fiber stress, MPa (psi),
11.2 Place each specimen in the marking fixture and draw a
P = load, N (lb.),
pencil line on the edge of the specimen 101.6 mm (4.0 in.)
Z = the distance from the point of load application to the
from the center of the 7.94-mm (0.3125-in.) diameter hole and craze front, mm (in.),
perpendicular to the length of the specimen (see the mark in B = width of specimen, mm (in.), and
D = thickness of specimen, mm (in.)
Fig. 2). On the side opposite the test surface, using an ink
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.
thetest,testtheremainingspecimensatastresslevelbelowthe
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-
11.4 Firmly press a 3.18 mm (0.125 in.) wide ribbon of
curs. This stress may be calculated from the equation in 11.6.
non-compressible black butyl glazing tape sealant on the test
surface of the specimen along each edge to create a dam which
11.11 In the examination of the crazing, note all cracks at
prevents the test chemical from coming in contact with the
the edge of the specimen as edge crazing. Disregard this
specimen edges. Insert the conditioned specimen immediately
condition when ascer
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