ASTM E1012-99
(Practice)Standard Practice for Verification of Specimen Alignment Under Tensile Loading
Standard Practice for Verification of Specimen Alignment Under Tensile Loading
SCOPE
1.1 Included in this practice are methods covering the determination of the amount of bending that occurs during the loading of notched and unnotched tensile specimens in the elastic range and to plastic strains less than 0.002. These methods are particularly applicable to rates of loading normally used for tension testing, creep testing, and uniaxial fatigue testing.
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Designation: E 1012 – 99
Standard Practice for
Verification of Specimen Alignment Under Tensile Loading
This standard is issued under the fixed designation E 1012; 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 3.2.6 maximum bending strain—the largest value of bend-
ingstrainatthepositionalongthelengthofthereducedsection
1.1 Included in this practice are methods covering the
of a straight unnotched specimen at which bending is mea-
determination of the amount of bending that occurs during the
sured. (For notched specimens, see 4.9.)
loading of notched and unnotched tensile specimens in the
3.2.7 notched section—the section perpendicular to the
elastic range and to plastic strains less than 0.002. These
longitudinal axis of symmetry of the specimen where the
methods are particularly applicable to the force application
cross-sectional area is intentionally at a minimum value in
rates normally used for tension testing, creep testing, and
order to serve as a stress raiser.
uniaxial fatigue testing.
3.2.8 nominal percent bending in notched specimens—the
2. Referenced Documents percent bending in a hypothetical (unnotched) specimen of
uniform cross section—equal to the minimum cross section of
2.1 ASTM Standards:
the notched specimen, the eccentricity of the applied force in
E 6 Terminology Relating to Methods of Mechanical Test-
the hypothetical, and the notched specimens being the same.
ing
(See 11.5.) (This definition is not intended to define strain at
3. Terminology
the root of the notch.)
3.2.9 percent bending—the bending strain times 100 di-
3.1 The terms in Terminology E 6 apply. Other terms used
vided by the axial strain.
in connection with specimen alignment are defined as follows:
3.2.10 rated force—a force at which the alignment is being
3.2 Definitions:
measured.
3.2.1 alignment—the condition of a testing machine and
3.2.11 reduced section—that part of the specimen length
load train (including the test specimen) which influences the
between the fillets.
introduction of bending moments into a specimen during
tensile loading.
4. Significance and Use
3.2.2 apparatus—the load-train, strain gages, and other
4.1 It has been shown that bending stresses that inadvert-
details of the equipment to be used for testing, excluding the
ently occur due to misalignment between the applied force and
test specimen.
the specimen axes during tensile forces can affect the test
3.2.3 axial strain—the average of the longitudinal strains
results. In recognition of this effect, some test methods include
measured at the surface on opposite sides of the longitudinal
a statement limiting the misalignment which is permitted. The
axis of symmetry of the specimen by two strain-sensing
purpose of this practice is to provide a reference for test
devices located at the mid-length of the reduced section.
methods and practices that require tensile loading under
3.2.4 bending strain—the difference between the strain at
conditions where alignment is important. The objective is to
the surface and the axial strain (see Fig. 1). In general, the
implement the use of common terminology and methods for
bending strain varies from point to point around and along the
verification of alignment of loading fixtures and test speci-
reduced section of the specimen. Bending strain is calculated
mens.
as shown in Section 11.
4.2 Axiality requirements and verifications should be op-
3.2.5 eccentricity—the distance between the line of action
tionalwhentestingisperformedforacceptanceofmaterialsfor
of the applied force and the axis of symmetry of the specimen
minimum strength and ductility requirements. This is because
in a plane perpendicular to the longitudinal axis of the
the effects, if any, especially excessive bending, would be
specimen.
expected to reduce strength and ductility properties and give
conservative results. There may be no benefit from improved
ThispracticeisunderthejurisdictionofASTMCommitteeE-28onMechanical
axiality when testing high ductility materials to determine
TestingandisthedirectresponsibilityofSubcommitteeE28.04onUniaxialTesting.
conformance with minimum properties. Whether or not to
Current edition approved August 10, 1999. Published September 1999. Origi-
improve axiality, should be a matter of negotiation between the
nally published as E 1012 – 89. Last previous edition E 1012 – 97.
Annual Book of ASTM Standards, Vol 03.01. material producer and the user.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E 1012
NOTE 1—Abending strain, 6B, is superimposed on the axial strain, a, for low-axial strain (or stress) in (a) and high-axial strain (or stress) in (b). For
the same bending strain 6B, a high-percent bending is indicated in (a) and a low-percent bending is indicated in (b).
FIG. 1 Schematic Representations of Bending Strains (or Stresses) That May Accompany Uniaxial Loading
5. Verification of Alignment 5.3.2 Verifications of Type T shall be made on the specimen
to be tested just prior to or during the testing and without
5.1 For ease of reference in other practices, test methods,
removing the specimen from the testing machine or making
and product specifications, the most commonly used methods
any other adjustments that would affect alignment during the
for verifying alignment are listed in Section 6.
period between verification and testing.
5.2 A numerical requirement for alignment should specify
the force, specimen dimensions, and temperature at which the
NOTE 3—Maintaining a small force on the specimen between verifica-
measurement is to be made.
tion and testing is necessary to retain alignment.
5.2.1 The force at which the bending strain is specified may
bestatedintermsofayieldstrengthorothernominalspecimen
6. Methods of Verification of Alignment
stress.
6.1 The following methods may be applied to either the
NOTE 1—For an offset-load train, percent bending decreases with
verification of alignment of the apparatus or during a specific
increasing applied force. (See CurvesA, B, and C in Fig. 2.) However, in
test. (In general, they are in order of decreasing rigor and cost.)
some instances, percent bending may increase with increasing applied
force. (See Curve D in Fig. 2.)
6.1.1 Method 1—The specification measure of alignment is
determined either at the test conditions (Type A) or during the
5.3 Alignmentrequirementscanrefertotheapparatus(Type
test (Type T). This requires an array of strain sensors (for
A) or to a single test (Type T). Those applied to the test
example, see Fig. 3 and 10.6) at two or more longitudinal
apparatus should be referred to as follows: ASTM Standard
Practice E 1012, Type A, Method (followed by the suitable positions along the reduced section. The strain sensors or
number from 6.1). Those applied to a specific test should be components of the strain sensors must be attached to the
similar with a “T” substituted for the “A.”
specimen. Position the strain sensors so as to minimize the
5.3.1 Verifications of Type A shall be made using a speci-
portion of the measured strain due to notches or fillets. (If a
men and apparatus made to the same drawing and of the same
specific specimen configuration is required, specify the loca-
materials as those that will be used during testing, except that
tion of the strain sensors.)
any specimen notches be eliminated. The same specimen may
NOTE 4—When verifying alignment for apparatus (Type A), bending
be used for successive verifications. The materials and design
values may be considered to vary linearly with temperature at tempera-
should be such that only elastic strains occur at the rated force.
tures between those at which alignment was measured.
NOTE 2—To avoid damage to the verification specimen, the sum of the
6.1.2 Method 2—Identical to Method 1, with the following
axialstrain(seesection4.4)andthemaximumbendingstrain(seesection
exceptions:
4.8 ) should not exceed the elastic limit.
E 1012
NOTE 1—Curve A: Machine 1, threaded grip ends (11)
NOTE 2—Curve B: Machine 2, buttonhead grip ends (11)
NOTE 3—Curve C: Machine 3, grips with universal couplings (7)
NOTE 4—Curve D: schematic representation of a possible response from an offset load train (16)
FIG. 2 Effects of Applied Force on Percent Bending for Different Testing Machines and Gripping Methods
NOTE 1—w equals width of specimen.
NOTE 2—d equals distance from edge of specimen to centerline of strain sensor.
FIG. 3 Locations of Strain Sensors on Specimens of Rectangular Cross Section (Numbers Indicate Positions of Strain Sensors)
6.1.2.1 An array of strain sensors are centered at the 6.1.2.3 Note 4 does not apply.
mid-length of the reduced section of an unnotched specimen,
6.1.3 Method 3—Test fixtures, machine, and specimens are
or over the notch of a notched specimen (Note 2 applies).
dimensionally inspected for compatibility with good alignment
6.1.2.2 If an extensometer is used on a notched specimen,
and are examined visually or with suitable instrumentation to
the gage length should be at least 1.5 times the distance from
establish that wear, distortion, or other damage do not signifi-
the notch to the nearest fillet, but no closer to the tangent point
cantly affect alignment.
of the nearest fillet than one-half of the reduced section
diameter or width.
E 1012
NOTE 5—When there is disagreement over the results of this test, NOTE 7—When multiple extensometers are used, the strain may be
Methods 1 or 2 for verifying alignment are recommended as the preferred determined by arithmetically averaging outputs. Electrical outputs are
method. thought to be more accurate and reproducible than mechanical outputs.
8. Test Specimen
7. Apparatus
8.1 This practice refers to cylindrical specimens, thick
7.1 The readings from the individual strain sensors shall be
rectangular specimens, and thin rectangular specimens.
repeatable at the rated force within 10 % of the permitted
8.2 This practice is valid for metallic and nonmetallic test
bending strain, during five successive force applications made
specimens.
after the first force application without reducing the applied
8.3 Quality of machining of test specimens is critical, for
force to less than 5 % of the rated force.
example, straightness, concentricity, flatness, and surface fin-
7.2 When multiple strain sensors are used as in 6.1.1 and
ish.
6.1.2, specimen size limitations may dictate the use of electri-
calresistancestraingagesratherthanextensometersemploying
NOTE 8—Geometry and dimensions of test specimens taken from
mechanical linkages. Strain sensors, such as mechanical, opti- different product forms are described in the Test Specimen section of Test
Methods E 8.
cal, or electrical extensometers, as well as wire resistance or
foil strain gages, can provide useful displacement data. The
9. Calibration and Standardization
sensitivity of displacement measurement required by an appli-
9.1 When three or more strain measurements are made at
cable standard or specification depends on the amount of
one or more longitudinal positions, the bending strains are
bending permitted.
determined from ratios of strain measurements. Consequently,
7.3 For verification by Method 2, a single extensometer of
theabsoluteaccuraciesoftheextensometersarenotsignificant.
the nonaveraging type may be used by rotating it to various
The sensitivities and reproducibilities of the instruments used
positions around the perimeter during successive force appli-
are significant. All sensors should be calibrated by the same
cationsandrepeatingthemeasurementsasdescribedin10.5.In
means (see Method E 83) and correction factors should be
general, repeated force applications are not permitted in Type
applied, if necessary, to bring their readings into agreement.
T tests (see 5.3) because they may affect the subsequently
measured results.
10. Procedure
NOTE 6—Repositioningtheextensometeraroundthespecimendoesnot
10.1 Temperature variations during the verification test
usually give highly precise and reproducible results, but nevertheless is a
shouldbewithinthelimitsspecifiedinthemethodsorpractices
technique which is useful for detecting large amounts of bending.
which require the alignment verification.
7.4 FordeterminingmaximumbendingstrainduringTypeT
10.2 The zero-force reference value of the strain sensors
Tests (see 5.3), the use of three or four separate extensometers
should be measured at a force no greater than approximately
or an extensometer with multiple strain sensors which reads
1 % of that force at which the alignment verification is to be
strain at three or more positions about the perimeter is
made.
recommended.
10.3 To verify the alignment of the testing apparatus,
7.5 In most cases, the strain sensors will reference displace- repeated force applications are necessary. The amount of
ments between points on the specimen surfaces. However, it is bending introduced by the load-train depends on the relative
also possible to reference displacements of surfaces attached to position of the various components which transmit force to the
the specimen. Such an arrangement might consist of two plates specimen and also on the care with which these parts are
firmlyfixedtoeachendofthegagelengthofaspecimenwhich machined and assembled.Aspects of the test specimen, such as
is free of initial bending. Displacement measurements are straightness and concentricity, are critical.
made between corresponding pairs of points on these plates. 10.4 Repeated force should include assembly and disassem-
bly of the components of the load-train, including the test
Each pair of points is in a plane containing the specimen axis
and is equally distant from this axis. For specimens of circular specimen. Rotation in 90° increments (0°, 90°, 180°, 270°,
cross section, it is recommended that three or four pairs of repeat 0°) are recommended for a systematic study of the
points be used. A suitable extensometer may then be used to effects of rotational position of components of the load-train.
measure the displacement of the pairs of points as force is Calculate the bending value for each combination of the
applied to the specimen. The strain at the specimen surface in components of the load-train. The maximum value should not
the plane containing the pairs of points may, for small exceed the specified values in the standard practices, testing
displacements, be taken equal to the strain computed at the metho
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