ASTM E2448-06
(Test Method)Standard Test Method for Determining the Superplastic Properties of Metallic Sheet Materials
Standard Test Method for Determining the Superplastic Properties of Metallic Sheet Materials
SIGNIFICANCE AND USE
The determination of the superplastic properties of a metallic sheet material is important for the observation, development and comparison of superplastic materials. It is also necessary to predict the correct forming parameters during an SPF process. SPF tensile testing has peculiar characteristics compared to conventional mechanical testing, which distort the true values of stress, strain, strain hardening, and strain rate at the very large elongations encountered in an SPF pull test, consequently conventional mechanical test methods cannot be used. This test method addresses those characteristics by optimizing the shape of the test coupon and specifying a new test procedure.
The evaluation of a superplastic material can be divided into two parts. Firstly, the basic superplastic-forming (SPF) properties of the material are measured using the four parameters of stress, temperature, strain, and strain rate. These are obtained using conversions from the raw data of a tensile test. Secondly, derived properties useful to define an SPF material are obtained from the basic properties using specific equations.
SCOPE
1.1 This test method describes the procedure for determining the superplastic forming properties (SPF) of a metallic sheet material. It includes tests both for the basic SPF properties and also for derived SPF properties. The test for basic properties encompasses effects due to strain hardening or softening.
1.2 This test method covers sheet materials with thicknesses of at least 0.5 mm but not greater than 6 mm. It characterizes the material under a uni-axial tensile stress condition.
Note 1—Most industrial applications of superplastic forming involve a multi-axial stress condition in a sheet; however it is more convenient to characterize a material under a uni-axial tensile stress condition. Tests should be performed in different orientations to the rolling direction of the sheet to ascertain initial anisotropy.
1.3 This method has been used successfully between strain rates of 10-5 to 10-1 per second.
1.4 This method has been used successfully on Aluminum and Titanium alloys. The use of the method with other metals should be verified.
1.5 The values given in SI units are to be considered the standard.
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.
General Information
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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: E 2448 – 06
Standard Test Method for
Determining the Superplastic Properties of Metallic Sheet
1
Materials
This standard is issued under the fixed designation E 2448; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope E21 Test Methods for Elevated Temperature Tension Tests
of Metallic Materials
1.1 This test method describes the procedure for determin-
E 646 Test Method for Tensile Strain Hardening Exponents
ing the superplastic forming properties (SPF) of a metallic
(n-Values) of Metallic Materials
sheet material. It includes tests both for the basic SPF proper-
E 691 Practice for Conducting an Interlaboratory Study to
ties and also for derived SPF properties. The test for basic
Determine the Precision of a Test Method
properties encompasses effects due to strain hardening or
softening.
3. Terminology
1.2 This test method covers sheet materials with thicknesses
3.1 Definitions—Definitions such as gage length (L and L ),
0
of at least 0.5 mm but not greater than 6 mm. It characterizes
true stress (s), true strain (´), normal engineering stress (S),
the material under a uni-axial tensile stress condition.
and engineering strain (e) are defined in Terminology E6.
NOTE 1—Most industrial applications of superplastic forming involve a
Thus,
multi-axial stress condition in a sheet; however it is more convenient to
´5 ln L/L
~ !
0
characterize a material under a uni-axial tensile stress condition. Tests
should be performed in different orientations to the rolling direction of the
s5 S~1 1 e!
sheet to ascertain initial anisotropy.
NOTE 2—Engineering stress S and strain e are only valid up to the point
1.3 This method has been used successfully between strain
ofneckingorinstabilityofcrosssection.Forsuperplasticdeformation,the
-5 -1
rates of 10 to 10 per second.
coupon undergoes an essentially uniform and constant neck along its
1.4 This method has been used successfully on Aluminum length, and S and e are assumed in this standard to be valid. However at
the junction to the clamp sections of the coupon the cross section reduces
and Titanium alloys. The use of the method with other metals
from the original value to the final value, over a length of approximately
should be verified.
4 % at each end. Also, there are local small instabilities of cross section
1.5 The values given in SI units are to be considered the
over the gauge length.These contribute to an error in the calculated values
standard.
of ´ and s. In the absence of currently available extensometers that could
1.6 This standard does not purport to address all of the
operate in the high temperature environment of an SPF test, ´ and s are
safety concerns, if any, associated with its use. It is the
to be inferred from crosshead extension and force.
responsibility of the user of this standard to establish appro-
3.2 Symbols Specific To This Standard:
priate safety and health practices and determine the applica-
V = machine crosshead velocity, the velocity of the traveling
bility of regulatory limitations prior to use.
member of the test machine to which one of the coupon clamps
is attached
2. Referenced Documents
·
2
´ = strain rate, measured as: V/@L ~1 1 e!#
0
2.1 ASTM Standards:
E4 Practices for Force verification of Testing Machines
NOTE 3—This is an operational definition of strain rate.
E6 Terminology Relating to Methods of Mechanical Test-
·
m = strain rate sensitivity, defined as (ln Ds)/ (ln D´). In
ing
· ·
practical terms, m = log (s /s )/log (´ /´ ) under stated test
2 1 2 1
conditions, see 7.2.1.
1
This test method is under the jurisdiction of ASTM Committee E28 on
NOTE 4—The derived term m is widely used to describe the SPF
Mechanical Testing and is the direct responsibility of Subcommittee E28.02 on
properties of a material. It should be used with caution, as it is dependent
Ductility and Formability.
on strain, strain rate and temperature. Many references in the literature do
Current edition approved May 1, 2006. Published June 2006. Originally
not identify the strain condition at which the readings were taken, or allow
approved in 2005. Last previous edition approved in 2005 as E 2448–05.
2 multiple strains to be used in the determination of m.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
NOTE 5—Many superplastic alloys exhibit strain hardening. However
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
the conventional strain hardening exponent n as defined in Test Method
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. E 646 is
...
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