ASTM E338-91(1997)
(Test Method)Standard Test Method of Sharp-Notch Tension Testing of High-Strength Sheet Materials
Standard Test Method of Sharp-Notch Tension Testing of High-Strength Sheet Materials
SCOPE
1.1 This test method covers the determination of a comparative measure of the resistance of sheet materials to unstable fracture originating from a very sharp stress-concentrator or crack. It relates specifically to fracture under continuously increasing load and excludes conditions of loading that produce creep or fatigue. The quantity determined is the sharp-notch strength of a specimen of particular dimensions, and this value depends upon these dimensions as well as the characteristics of the material. The sharp-notch strength:yield strength ratio is also determined.
1.2 This test method is restricted to one specimen width which is generally suitable for evaluation of high-strength materials (yield strength-to-density ratio above ? 700 000 psi/lb[dot]in. or (18 kgf/mm )/(g/cm )). The test will discriminate differences in resistance to unstable fracture when the sharp-notch strength is less than the tensile yield strength. The discrimination increases as the ratio of the notch strength to the yield strength decreases.
1.3 This test method is restricted to sheet materials not less than 0.64 mm (0.025 in.) and not exceeding 6 mm (0.25 in.) in thickness. Since the notch strength may depend on the sheet thickness, comparison of various material conditions must be based on tests of specimens having the same nominal thickness.
1.4 The sharp-notch strength may depend strongly upon temperature within a certain range depending upon the characteristics of the material. The test method is suitable for tests at any appropriate temperature. However, comparisons of various material conditions must be based on tests conducted at the same temperature. Note 1-Further information on background and need for this type of test is given in the first report by the ASTM Committee on Fracture Testing of High-Strength Sheet Materials. Note 2-The values stated in SI (metric) units are to be regarded as the standard.
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.
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Designation: E 338 – 91 (Reapproved 1997)
Standard Test Method of
Sharp-Notch Tension Testing of High-Strength Sheet
Materials
This standard is issued under the fixed designation E 338; 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.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope 1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This test method covers the determination of a compara-
responsibility of the user of this standard to establish appro-
tive measure of the resistance of sheet materials to unstable
priate safety and health practices and determine the applica-
fracture originating from a very sharp stress-concentrator or
bility of regulatory limitations prior to use.
crack. It relates specifically to fracture under continuously
increasing load and excludes conditions of loading that pro-
2. Referenced Documents
duce creep or fatigue. The quantity determined is the sharp-
2.1 ASTM Standards:
notch strength of a specimen of particular dimensions, and this
E 4 Practices for Force Verification of Testing Machines
value depends upon these dimensions as well as the character-
E 8 Test Methods for Tension Test of Metallic Materials
istics of the material. The sharp-notch strength:yield strength
E 602 Test Method for Sharp-Notch Tension Testing with
ratio is also determined.
Cylindrical Specimens
1.2 This test method is restricted to one specimen width
E 616 Terminology Relating to Fracture Testing
which is generally suitable for evaluation of high-strength
materials (yield strength-to-density ratio above 700 000 psi/
3. Terminology
−3 2 3
lb·in. or (18 kgf/mm )/(g/cm )). The test will discriminate
3.1 Definitions:
differences in resistance to unstable fracture when the sharp-
−2
3.1.1 crack strength, s [FL ]—the maximum value of the
c
notch strength is less than the tensile yield strength. The
nominal (net-section) stress that a cracked specimen is capable
discrimination increases as the ratio of the notch strength to the
of sustaining.
yield strength decreases.
3.1.1.1 Discussion—See definition of nominal (net-
1.3 This test method is restricted to sheet materials not less
section) stress in Terminology E 616.
than 0.64 mm (0.025 in.) and not exceeding 6 mm (0.25 in.) in
3.1.1.2 Discussion—Crack strength is calculated on the
thickness. Since the notch strength may depend on the sheet
basis of the maximum load and the original minimum cross-
thickness, comparison of various material conditions must be
sectional area (net cross section or ligament). Thus, it takes into
based on tests of specimens having the same nominal thick-
account the original size of the crack, but ignores any crack
ness.
extension that may occur during the test.
1.4 The sharp-notch strength may depend strongly upon
3.1.1.3 Discussion—Crack strength is analogous to the
temperature within a certain range depending upon the char-
ultimate tensile strength, as it is based on the ratio of the
acteristics of the material. The test method is suitable for tests
maximum load to the minimum cross-sectional area of the
at any appropriate temperature. However, comparisons of
specimen at the start of the test.
various material conditions must be based on tests conducted at
−2
3.1.2 sharp-notch strength, s [FL ]—the maximum nomi-
s
the same temperature.
nal (net-section) stress that a sharply notched specimen is
NOTE 1—Further information on background and need for this type of
capable of sustaining.
test is given in the first report by the ASTM Committee on Fracture
3.1.2.1 Discussion—See definition of nominal (net-
Testing of High-Strength Sheet Materials.
section) stress in Terminology E 616.
NOTE 2—The values stated in SI (metric) units are to be regarded as the
3.1.2.2 Discussion—Values of sharp-notch strength may
standard.
depend on notch and specimen configuration as these affect the
net cross section and the elastic stress concentration.
This method is under the jurisdiction of ASTM Committee E-8 on Fatigue and
3.1.2.3 Discussion—The tension specimens used in Test
Fracture and is the direct responsibility of Subcommittee E08.02 on Standards and
Method E 602 and this test method have notch root radii that
Terminology.
Current edition approved Aug. 15, 1991. Published October 1991. Originally
e1
published as E 338 – 67. Last previous edition E 338 – 81(86) .
“Fracture Testing of High-Strength Sheet Materials,” ASTM Bulletin, ASTBA,
No. 243, 1960, pp. 29–40; ibid., No. 244, 1960, pp. 18–28. Annual Book of ASTM Standards, Vol 03.01.
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E 338
approach the limit of machining capability. For these speci- 5. Apparatus
mens, the radius is believed to be small enough that any
5.1 The test shall be conducted with a tension testing
smaller radius that is obtainable by standard machining meth-
machine that conforms to the requirements of Practices E 4.
ods would not produce changes, in notch strength, that are
5.2 The devices for transmitting load to the specimen shall
significant from an engineering viewpoint.
be such that the major axis of the specimen coincides with the
3.1.2.4 Discussion—In these test methods, the notch root
load axis. A satisfactory arrangement incorporates clevises
radii are very small (approaching the limit for machining
carrying hardened pins which pass through holes in the ends of
capability), and values of sharp-notch strength may depend on the specimen, the diameter of the pins being only slightly
notch root radius. See definition of notch tensile strength in
smaller than that of the holes. Spacing washers of the necessary
Terminology E 616. thickness shall be used to center the specimen in the clevises.
A typical arrangement is shown in Fig. 1.
4. Significance and Use
4.1 The test method provides a comparative measure of the
resistance of sheet materials to unstable fracture originating
from the presence of cracks or crack-like stress concentrators.
It is not intended to provide an absolute measure of resistance
to crack propagation which might be used in calculations of the
strength of structures. However, it can serve the following
purposes:
4.1.1 In research and development of materials, to study the
effects of the variables of composition, processing, heat-
treatment, etc.;
4.1.2 In service evaluation, to compare the relative crack-
propagation resistance of a number of materials which are
otherwise equally suitable for an application, or to eliminate
materials when an arbitrary minimum acceptable sharp-notch
strength can be established on the basis of service performance
correlation, or some other adequate basis;
4.1.3 For specifications of acceptance and manufacturing
quality control when there is a sound basis for establishing a
FIG. 1 Specimen Loading Clevis with Hardened Pin
minimum acceptable sharp-notch strength. Detailed discussion
of the basis for setting a minimum in a particular case is
5.3 Temperature Control—For the tests at other than room
beyond the scope of this method.
temperature, any suitable means may be used to heat or cool
4.2 The sharp-notch strength may decrease rapidly through
the specimen and to maintain a uniform temperature over the
a narrow range of decreasing temperature. This temperature
region that includes the notch or crack. The ability of the
range and the rate of decrease depend on the material and its
equipment to provide a region of uniform temperature shall be
thickness. The temperature of the specimen during each test
established by measurements of the temperature at positions on
shall therefore be controlled and recorded. Tests shall be
both faces of a specimen as shown in Fig. 2. The temperature
conducted throughout the range of expected service tempera-
surveys shall be conducted either at each temperature level at
tures to ascertain the relation between notch strength and
which tests are to be made, or at a series of temperature levels
temperature. Care shall be taken that the lowest and highest
at intervals of 30°C (50°F) over the range of test temperatures.
anticipated service temperatures are included.
1 1
The test temperature shall be held within 61 ⁄2°C (62 ⁄2 °F)
4.3 Limited results suggest that the sharp-notch strengths of
during the course of the test. At the test temperature the
stable high-strength steels are not appreciably sensitive to rate
difference between the indicated temperatures at any two of the
of loading within the range of loading rates normally used in
four thermocouple positions shall not exceed 3°C (5°F).
conventional tension tests. Where very low or high rates of
loading are expected in service, the effect of loading rate NOTE 3—A convenient means of heating or cooling flat specimens
consists of a pair of flat copper or brass plates which contact the surfaces
should be investigated using special procedures that are beyond
of the specimen. The plates are fitted with heating or cooling devices
the scope of this method.
designed to maintain uniformity of temperature of the contact surfaces.
4.4 The precision of sharp-notch strength measurement
Thermocouples may be permanently incorporated with their junctions at
should be equivalent to that of the ordinary tensile strength of
the contact surfaces. Such devices have been found convenient and
a sheet specimen since both depend upon measurements of
reliable for temperatures from that of liquid nitrogen to at least 330°C
(600°F). The use of liquid baths for heating specimens shall be avoided
load and of dimensions of comparable magnitude. However,
unless it can be established that the liquid has no effect on the sharp-notch
the sharp-notch strength is more sensitive to local flaws than
strength of the material.
the tensile strength and normally shows more scatter. The
influence of this scatter should be reduced by testing duplicate
specimens and averaging the results. Srawley, J. E., and Beachem, C. D., NRL Report 5127, NRLRA, April 9, 1958.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
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E 338
NOTE 1—Dimensions in inches with millimetre dimensions in paren-
theses.
FIG. 4 Fatigue Center-Crack Specimen M(T)
indicated and pin loading shall be used. It will be noted that the
NOTE 1—Dimensions in inches with millimetre dimensions in paren-
length of the standard specimen is specified as 300 mm (12 in.)
theses.
with the provision that, where unavoidable due to material
FIG. 2 Positions of Thermocouple Junctions for Temperature
Surveys limitations, a substandard length (200 mm, 8 in.) specimen
may be used. However, for identical test conditions on the
same material the 8-in. specimen will give a different strength
5.4 Temperature Measurement—The temperature of the
value than the standard specimen. For this reason comparisons
specimen during any test at other than room temperature shall
of various material conditions must be based on tests con-
be measured at one, or preferably more than one, of the
ducted with the same length specimen. Specimens with parallel
positions shown in Fig. 2. The junctions of the thermocouples
sides are shown, and these will fracture in the notched section
shall be in good thermal contact with the specimen. The
for the great majority of materials. However, for exceptionally
thermocouples and measuring instruments shall be calibrated
tough conditions where the notch strength exceeds the yield
and shall not exceed 3°C (5°F).
strength, fracture may occur at the pin hole unless suitable head
reinforcing plates are provided. A suggested design for such
6. Test Specimens
plates is shown in Fig. 5. One plate is used on each side of the
6.1 Suggested designs for a standard 75-mm (3-in.) wide
specimen heads, and loads are transmitted to the plates by three
machined sharp edge-notch test specimen, DE(T), and a fatigue
center-crack specimen, M(T), are shown in Fig. 3 and Fig. 4.
The dimensions of the notched or cracked regions shall be as
NOTE 1—Dimensions in inches with millimetre dimensions in paren- NOTE 1—Dimensions in inches with millimetre dimensions in paren-
theses. theses.
FIG. 3 Machined Sharp Edge-Notch Specimen, DE(T) FIG. 5 Reinforcing Plate for Specimen Head
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E 338
hardened 6-mm ( ⁄4-in.) diameter pins having a length that will 7.4 Fracture Appearance—The appearance of the fracture
permit them to enter the slot in the loading clevises (see Fig. 1). is valuable subsidiary information and shall be briefly noted for
If the plates are 3 mm ( ⁄8 in.) thick and made of a material each specimen. One common type of fracture is shown in Fig.
having a 1380-MPa (200 000-psi) minimum yield strength, 6(a). This consists of a central flat band, transverse to the
they may be used in any test covered by this method. specimen axis, and bordered by relatively narrow oblique
6.2 The sharpness of the machined notches is a critical bands. If the oblique bands are fairly uniform, measure the
feature of the sharp edge-notched specimen, DE(T), of Fig. 3 average width, b, of the transverse band and record the ratio
and special care is required to prepare them. Finish machining (B − b)/B as the proportion of oblique fracture per unit
of the notch may be completed either before or after final heat thickness, or oblique fraction. In the case of test specimen
treatment. For each specimen the notch root radii and notch DE(T), the measurement b shall be at a point within the middle
location with respect to the pin-hole centers shall be measured third of the specimen width. For specimen M(T), make
prior to testing, and specimens that do not meet the require- measurements on each side of the center slot at points not
ments of Fig. 3 shall be discarded or reworked. closer than one plate thickness to the edge nor farther than 8
6.3 Center-cracked specimens having high notch acuity mm ( ⁄16in.) from the edge. Average these measurements to
have been prepared by machining with sh
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