ASTM E6-23a

Standard Terminology Relating to Methods of Mechanical Testing

SCOPE
1.1 This terminology covers the principal terms relating to methods of mechanical testing of solids. The general definitions are restricted and interpreted, when necessary, to make them particularly applicable and practicable for use in standards requiring or relating to mechanical tests. These definitions are published to encourage uniformity of terminology in product specifications.  
1.2 Terms relating to fatigue and fracture testing are defined in Terminology E1823.  
1.3 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Jan-2023
• ICS: 01.040.19 - Testing (Vocabularies)
• ICS: 19.060 - Mechanical testing
• Technical Committee: E28 - Mechanical Testing
• Drafting Committee: E28.91 - Terminology

Relations

• Refers: ASTM E1823-24a - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 15-Feb-2024
• Refers: ASTM E1823-24 - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 01-Feb-2024
• Refers: ASTM E8/E8M-24 - Standard Test Methods for Tension Testing of Metallic Materials
• Effective Date: 01-Jan-2024
• Refers: ASTM E1823-20 - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 01-Feb-2020
• Refers: ASTM E8/E8M-16 - Standard Test Methods for Tension Testing of Metallic Materials
• Effective Date: 15-Jul-2016
• Refers: ASTM E8/E8M-15 - Standard Test Methods for Tension Testing of Metallic Materials
• Effective Date: 01-Feb-2015
• Refers: ASTM E8/E8M-13 - Standard Test Methods for Tension Testing of Metallic Materials
• Effective Date: 01-Jun-2013
• Refers: ASTM E74-13a - Standard Practice of Calibration of Force-Measuring Instruments for Verifying the Force Indication of Testing Machines
• Effective Date: 01-May-2013
• Refers: ASTM E74-13 - Standard Practice of Calibration of Force-Measuring Instruments for Verifying the Force Indication of Testing Machines
• Effective Date: 01-Mar-2013
• Refers: ASTM E1823-12e - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 15-Dec-2012
• Refers: ASTM E74-12 - Standard Practice of Calibration of Force-Measuring Instruments for Verifying the Force Indication of Testing Machines
• Effective Date: 01-Dec-2012
• Refers: ASTM E1823-12d - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 15-Nov-2012
• Refers: ASTM E1823-12c - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 01-Sep-2012
• Refers: ASTM E1823-12b - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 01-Aug-2012
• Refers: ASTM E1823-12a - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 15-May-2012

Overview

ASTM E6-23a, "Standard Terminology Relating to Methods of Mechanical Testing," is an international standard developed by ASTM Committee E28.91. This terminology document establishes consistent definitions of principal terms associated with the mechanical testing of solids. By standardizing mechanical testing terminology, ASTM E6-23a supports clear communication, harmonizes test methods, and fosters uniformity across industries and product specifications. The document is recognized globally and aligns with World Trade Organization (WTO) principles to support international trade and regulatory compliance for mechanical testing standards.

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Key Topics

• Mechanical Testing Terms: Defines fundamental terms related to the mechanical testing of solids, such as force, strain, stress, modulus of elasticity, ductility, hardness, and more.
• Testing Methods: Covers vocabulary for common mechanical test types, including tension, compression, bend, hardness, and creep tests.
• Measurement and Calibration: Presents essential terminology for calibration, measurement accuracy, traceability, and error assessment, referencing related metrology guides and technical notes.
• Strain and Stress Concepts: Clarifies different strains (axial, bending, engineering, true, residual, etc.) and stresses (compressive, tensile, shear, etc.) used in various mechanical tests.
• Hardness and Ductility: Explains types of hardness tests (Brinell, Knoop, Rockwell), definitions of ductility, and related test-specific terms.
• Test Equipment and Systems: Standardizes terms relating to extensometers, force-measuring systems, and other key mechanical testing instruments.
• Cross-Referenced Definitions: Provides an index connecting closely related and fundamental mechanical testing concepts for ease of reference and optimal usage.

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Applications

ASTM E6-23a is indispensable wherever consistent and precise mechanical testing terminology is required. Its practical applications include:

• Materials Testing Laboratories: Ensuring accurate mechanical property evaluation and clear reporting by using standardized terminology.
• Quality Assurance and Product Specification: Specifying, interpreting, and enforcing uniform terminology in product standards and certifications.
• Test Method Development and Revision: Assisting committees and organizations in drafting or updating mechanical testing standards with harmonized definitions.
• Academic and Industrial Research: Facilitating effective communication and reproducibility in mechanical behavior studies of metals, polymers, ceramics, and composites.
• Regulatory Compliance: Supporting international market access by complying with harmonized WTO technical barriers to trade requirements.
• Equipment Manufacturing: Ensuring that manufacturers refer to standard terms for user manuals, calibration procedures, and technical documentation.
• Training and Education: Providing a reference for students and professionals to learn the language of mechanical testing and ensure industry-wide understanding.

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Related Standards

• ASTM E8/E8M: Test Methods for Tension Testing of Metallic Materials
• ASTM E74: Practices for Calibration and Verification for Force-Measuring Instruments
• ASTM E1823: Terminology Relating to Fatigue and Fracture Testing
• ISO/IEC Guide 99 (VIM): International Vocabulary of Metrology-Basic and General Concepts and Terms
• JCGM 200: International Vocabulary of Metrology (VIM)
• NIST Technical Note 1297: Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results

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ASTM E6-23a is the authoritative source for terminology in mechanical testing. By adopting the standard vocabulary it establishes, organizations can improve the reliability of mechanical test data, eliminate ambiguity, enhance compliance, and support global collaboration in material testing and evaluation.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E6 − 23a
Standard Terminology Relating to
Methods of Mechanical Testing
This standard is issued under the fixed designation E6; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope 2.2 BIPM Standard:
JCGM 200 : International vocabulary of metrology — Basic
1.1 This terminology covers the principal terms relating to
and general concepts and associated terms (VIM).
methods of mechanical testing of solids. The general defini-
tions are restricted and interpreted, when necessary, to make
3. Index of Cross-References and Associated Definitions
them particularly applicable and practicable for use in stan-
3.1 The terms listed below are associated with terminology
dards requiring or relating to mechanical tests. These defini-
that is fundamental or commonly used. The definition for the
tions are published to encourage uniformity of terminology in
term of interest is related to or is given below the definition for
product specifications.
the fundamental term cited.
1.2 Terms relating to fatigue and fracture testing are defined
Term
in Terminology E1823.
angular strain indexed under strain
axial strain indexed under strain
1.3 This international standard was developed in accor-
bending strain indexed under strain
dance with internationally recognized principles on standard-
chord modulus see modulus of elasticity
ization established in the Decision on Principles for the direct verification indexed under verification
compressive stress indexed under stress
Development of International Standards, Guides and Recom-
elastic constants see modulus of elasticity and Poisson’s
mendations issued by the World Trade Organization Technical
ratio
Barriers to Trade (TBT) Committee. elastic modulus use modulus of elasticity
elastic true strain indexed under strain
engineering strain indexed under strain
2. Referenced Documents
engineering stress indexed under stress
fracture stress indexed under stress
2.1 ASTM Standards:
indirect verification indexed under verification
E8/E8M Test Methods for Tension Testing of Metallic Ma-
initial tangent modulus see modulus of elasticity
terials
instantaneous strain see initial strain
linear (tensile or compressive) strain indexed under strain
E74 Practices for Calibration and Verification for Force-
load use force
Measuring Instruments
malleability see ductility
E796 Test Method for Ductility Testing of Metallic Foil
modulus of rigidity see shear modulus
movable Brinell hardness testing indexed under Brinell hardness testing
(Withdrawn 2009)
machine machine
E1823 Terminology Relating to Fatigue and Fracture Testing
movable Rockwell hardness testing indexed under Rockwell hardness machine
machine
nominal stress indexed under stress
This terminology is under the jurisdiction of ASTM Committee E28 on normal stress indexed under stress
Mechanical Testing and is the direct responsibility of Subcommittee E28.91 on permanent set see set
physical properties see mechanical properties
Terminology except where designated otherwise. A subcommittee designation in
parentheses following a definition indicates the subcommittee with responsibility for plastic true strain indexed under strain
portable Brinell hardness testing indexed under Brinell hardness testing
that definition.
machine machine
Current edition approved Feb. 1, 2023. Published March 2023. Originally
portable Rockwell hardness testing indexed under Rockwell hardness machine
approved in 1923. Last previous edition approved in 2023 as E6 – 23. DOI:
machine
10.1520/E0006-23A.
principal stress (normal) indexed under stress
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. Available from BIPM - Pavillon de Breteuil F-92312 Sèvres Cedex FRANCE.
The last approved version of this historical standard is referenced on this document is available free-of-charge at https://www.bipm.org/en/publications/
www.astm.org. guides/vim.html
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E6 − 23a
bend test, n—a test for ductility performed by bending or
residual strain indexed under strain
residual stress indexed under stress
folding a specimen, usually by steadily applied forces but in
Rockwell hardness standardizing indexed under Rockwell hardness machine
some instances by blows.
machine
DISCUSSION—The bending may be interrupted to examine the bent
Rockwell hardness testing machine see Rockwell hardness machine
surface for cracks.
Rockwell superficial see also Rockwell hardness number
hardness number
DISCUSSION—The ductility is usually judged by whether or not the
secant modulus see modulus of elasticity
specimen cracks under the specified conditions of the test.
shear strain indexed under strain
shear stress indexed under stress
DISCUSSION—There are four general types of bend tests according to
static fatigue strength see creep rupture strength
the manner in which the forces are applied to the specimen to make the
stress-rupture strength see creep rupture strength
bend. These are as follows:
tangent modulus see modulus of elasticity
1. Free Bend
tensile stress indexed under stress
2. Guided Bend
torsional modulus see shear modulus
torsional stress indexed under stress
3. Semi-Guided Bend
transverse strain indexed under strain
4. Wrap-Around Bend
true strain indexed under strain
true stress indexed under stress
DISCUSSION—The specimen has a substantially uniform cross-section
Type 1 extensometer system indexed under extensometer
and a length several times as great as the largest dimension of the
Type 2 extensometer system indexed under extensometer
cross-section. (E28.02)
Type 3 extensometer system indexed under extensometer
ultimate tensile strength (UTS) use tensile strength
biaxial stretching, n—a mode of sheet metal forming in which
yield point use upper yield strength
yield strength see also upper yield strength and lower yield
positive strains are observed in all directions at a given
strength
location. (E28.02)
4. Terminology
breaking force [F], n—the force at which fracture occurs.
DISCUSSION—When used in connection with tension tests of thin
4.1 Terms and Definitions:
materials or materials of small diameter for which it is often difficult to
absorbed energy [FL], n—work spent to fracture a specimen
distinguish between the breaking force and the maximum force
in a single pendulum swing, as measured by a compensated
developed, the latter is considered to be the breaking force. (E28.04)
indicating device (E28.07)
Brinell hardness number, n—a number, which is proportional
accuracy, n—the permissible variation from the correct value.
to the quotient obtained by dividing the test force by the
(E28.01)
curved surface area of the indentation which is assumed to
adjusted length of the reduced section—the length of the be spherical and of the diameter of the ball. (E28.06)
reduced section plus an amount calculated to compensate for
Brinell hardness scale, n—a designation that identifies the
strain in the fillet region. (E28.04)
specific combination of ball diameter and applied force used
alignment, n—the condition of a testing machine that influ- to perform the Brinell hardness test. (E28.06)
ences the introduction of bending moments into a specimen
Brinell hardness standardizing machine—a Brinell hardness
(or alignment transducer) during the application of tensile or
machine used for the standardization of Brinell hardness test
compressive forces. (E28.01)
blocks. The standardizing machine differs from a regular
batch, n—for strain gages, a group of strain gages of the same Brinell hardness testing machine by having tighter toler-
type and lot, manufactured as a set (made at the same time ances on certain parameters. (E28.06)
and under the same conditions). (E28.01)
Brinell hardness test, n—an indentation hardness test using a
verified machine to force an indenter (tungsten carbide ball
bearing area [L ], n—the product of the pin diameter and
specimen thickness. (E28.04) with diameter D), under specified conditions, into the surface
of the material under test.
bearing force [F], n—a compressive force on an interface.
DISCUSSION—The diameter of the resulting indentation d is measured
(E28.04)
after removal of the force. (E28.06)
bearing strain, n—the ratio of the bearing deformation of the
Brinell hardness testing machine—a Brinell hardness ma-
bearing hole, in the direction of the applied force, to the pin
chine used for general testing purposes. (E28.06)
diameter. (E28.04)
movable Brinell hardness testing machine—a Brinell hard-
-2
bearing strength [FL ], n—the maximum bearing stress
ness testing machine that is designed to be moved to different
which a material is capable of sustaining. (E28.04)
locations on a moveable frame, table or similar support that is
-2 integral to the testing machine (for example, securely fixed to
bearing stress [FL ], n—the force per unit of bearing area.
a rolling table), or a Brinell hardness testing machine that is
(E28.04)
designed to move into the testing position prior to a test, (for
-2
bearing yield strength [FL ], n—the bearing stress at which example, securely fixed to a moving support arm), and has
a material exhibits a specified limiting deviation from the been previously verified to ensure that such moves will not
proportionality of bearing stress to bearing strain. (E28.04) affect the hardness result.
E6 − 23a
portable Brinell hardness testing machine—a Brinell hard- is included; for tests on metals, the initial strain is not included.
ness testing machine that is designed to be transported, carried, (E28.04)
set up, and operated by the users, and that measures Brinell
creep recovery, n—the time-dependent decrease in strain in a
hardness by the Brinell hardness test principle.
solid, following the removal of force.
DISCUSSION—Recovery is usually determined at constant tempera-
calibration, n—determination of the values of the significant
ture.
parameters by comparison with values indicated by a refer-
ence instrument or by a set of reference standards. (E28.06)
DISCUSSION—In tests of plastics, the initial recovery is generally
included; for metals, it is not. Thermal expansion is excluded.
calibration, n—operation that, under specified conditions, in a
(E28.04)
first step, establishes a relation between the quantity values
-2
with measurement uncertainties provided by measurement
creep rupture strength [FL ], n—the stress causing fracture
standards and corresponding indications with associated
in a creep test at a given time, in a specified constant
measurement uncertainties and, in a second step, uses this
environment.
information to establish a relation for obtaining a measure-
DISCUSSION—This is sometimes referred to as the stress-rupture
ment result from an indication.
strength or, in glass technology, the static fatigue strength. (E28.04)
DISCUSSION—A calibration may be expressed by a statement, calibra-
-2
creep strength [FL ], n—the stress that causes a given creep
tion function, calibration diagram, calibration curve, or calibration
in a creep test at a given time in a specified constant
table. In some cases, it may consist of an additive or multiplicative
correction of the indication with associated measurement uncertainty.
environment. (E28.04)
DISCUSSION—Calibration should not be confused with adjustment of
deep drawing, n—a metal sheet forming operation in which
a measuring system, often mistakenly called “self-calibration”, nor with
strains on the sheet surface are positive in the direction of the
verification of calibration.
punch travel and negative at 90° to that direction. (E28.02)
DISCUSSION—Often, the first step alone in the above definition is
5 deflectometer, n—a specialized extensometer used for sensing
perceived as being calibration. JCGM 200:2012
of extension or motion, usually without reference to a
(E28.01)
specific gauge length. (E28.01)
calibration factor, n—the factor by which a change in exten-
Demeri Split Ring Test—a test that measures the springback
someter reading must be multiplied to obtain the equivalent
behavior of sheet metal by comparing the diameter of a ring
strain.
extracted from the wall of a flat bottom cup and the diameter
DISCUSSION—For any extensometer, the calibration factor is equal to
of the same ring split to release residual stresses. (E28.02)
the ratio of change in length to the product of the gauge length and the
change in extensometer reading. For direct-reading extensometers the
differential indentation depth hardness test, n—an indenta-
calibration factor is unity. (E28.01)
tion hardness test using a verified hardness testing machine
-2
compressive strength [FL ], n—the maximum compressive
to force a truncated diamond cone indenter, diamond sphero-
stress that a material is capable of sustaining.
conical indenter or tungsten carbide ball indenter, under
DISCUSSION—Compressive strength is calculated by dividing the
specified conditions, into the surface of the material under
maximum force during a compression test by the original cross-
test, and to measure the difference in depth of the indentation
sectional area of the specimen.
as the force on the indenter is increased from a specified
DISCUSSION—In the case of a material which fails in compression by
preliminary test force to a specified total test force and then
a shattering fracture, the compressive strength has a very definite value.
returned to the preliminary test force. (E28.06)
In the case of materials which do not fail in compression by a shattering
fracture, the value obtained for compressive strength is an arbitrary differential indentation depth hardness number, n—a num-
value depending upon the degree of distortion which is regarded as
ber derived from the net increase in the depth of indentation
indicating complete failure of the material. (E28.04)
as the force on an indenter is increased from a specified
preliminary test force to a specified total test force and then
compressometer, n—a specialized extensometer used for sens-
returned to the preliminary test force. (E28.06)
ing negative or compressive strain. (E28.01)
differential indentation depth hardness testing machine,
constraint, n—any restriction to the deformation of a body.
n—a machine capable of performing a Differential Indenta-
(E28.91)
tion Depth hardness test and displaying the resulting hard-
creep, n—the time-dependent strain that occurs after the
ness number. (E28.06)
application of a force which is thereafter maintained con-
discontinuous yielding, n—in a uniaxial test, a hesitation or
stant.
fluctuation of force observed at the onset of plastic
DISCUSSION—Creep tests are usually made at constant force and
deformation, due to localized yielding.
temperature. For tests on plastics, the initial strain – however defined–
DISCUSSION—The stress-strain curve need not appear to be
discontinuous. (E28.04)
This definition is reproduced here from JCGM 200:2012 International vocabu-
discontinuous yielding stress, σ , n—the peak stress at the
i
lary of metrology – Basic and general concepts and associated terms (VIM) with
initiation of the first measurable serration on the curve of
permission from the Director of BIPM. The text has been put in ASTM Interna-
tional’s form and style. stress-versus-strain.
E6 − 23a
DISCUSSION—The parameter σ is a function of test variables and is DISCUSSION—The increase in gauge length may be determined either
i
at or after fracture, as specified for the material under test.
not a material constant. (E28.04)
DISCUSSION—The term elongation, when applied to metals, generally
ductility, n—the ability of a material to deform plastically
means measurement after fracture; when applied to plastics and
before fracturing.
elastomers, measurement at fracture. Such interpretation is usually
DISCUSSION—Ductility is usually evaluated by measuring (1) the
applicable to values of elongation reported in the literature when no
elongation or reduction of area from a tension test, (2) the depth of cup
further qualification is given.
from a cupping test, (3) the radius or angle of bend from the bend test,
or (4) the fatigue ductility from the fatigue ductility test (see Test DISCUSSION—In reporting values of elongation, the gauge length shall
Method E796). be stated.
DISCUSSION—Elongation is affected by specimen geometry (area and
DISCUSSION—Malleability is the ability to deform plastically under
shape of cross section, parallel length, parallelism, fillet radii, etc.),
repetitive compressive forces. (E28.02)
preparation (degree to which surfaces within the reduced section are
dynamic elastic modulus, E , n—the elastic modulus, either smooth and free of cold work), and test procedure (alignment and test
d
Young’s modulus or shear modulus, that is measured in a speed, for example). (E28.04)
dynamic mechanical measurement. (E28.04)
elongation after fracture, n—the elongation measured by
fitting the two halves of the broken specimen together.
dynamic mechanical measurement, n—a technique in which
either the modulus or damping, or both, of a substance under (E28.04)
oscillatory applied force or displacement is measured as a
elongation at fracture, n—the elongation measured just prior
function of temperature, frequency, or time, or a combina-
to the sudden decrease in force associated with fracture.
tion thereof. (E28.04)
(E28.04)
-2
dynamic shear modulus, G [FL ], n—the value of the shear
d
error, n—for a measurement or reading, the amount it deviates
modulus determined using an oscillatory applied force or
from a known or reference value represented by a measure-
displacement and in conformance with this test method.
ment standard.
(E28.04)
DISCUSSION—Mathematically, the error is calculated by subtracting
-2
dynamic Young’s modulus, E [FL ], n—the value of the
d the accepted value from the measurement or reading. (See also percent
Young’s modulus determined using an oscillatory applied
error.) (E28.91)
force or displacement and in conformance with this test
expanded uncertainty, n—a statistical measurement of the
method. (E28.04)
probable limits of error of a measurement.
eccentricity [L], n—the distance between the line of action of DISCUSSION—NIST Technical Note 1297 treats the statistical ap-
proach including the expanded uncertainty. (E28.91)
the applied force and the axis of symmetry of the specimen
in a plane perpendicular to the longitudinal axis of the
extensometer, n—a device for sensing strain. (E28.01)
specimen. (E28.01)
extensometer system, n—a system for sensing and indicating
edge distance [L], n—the distance from the edge of a bearing
strain.
specimen to the center of the hole in the direction of applied
DISCUSSION—The system will normally include an extensometer,
force. (E28.04)
conditioning electronics, and auxiliary device (recorder, digital readout,
computer, etc.). However, completely self-contained mechanical de-
edge distance ratio, n—the ratio of the edge distance to the pin
vices are permitted. An extensometer system may be one of three types.
diameter. (E28.04)
(E28.01)
elastic force measurement standard, n—system consisting of
Type 1 extensometer system, n—an extensometer system
an elastic member combined with an appropriate device for
which both defines gauge length, and senses extension, for
indicating the magnitude (or a quantity proportional to the
example, a clip-on strain gauge type with conditioning
magnitude) of deformation of the member under an applied
electronics. (E28.01)
force. (E28.01)
Type 2 extensometer system, n—an extensometer which
-2
senses extension and the gauge length is defined by specimen
elastic limit [FL ], n—the greatest stress that a material is
geometry or specimen features such as ridges or notches.
capable of sustaining without any permanent strain remain-
DISCUSSION—A Type 2 extensometer is used where the extensometer
ing upon complete release of the stress.
gauge length is determined by features on the specimen, for example,
DISCUSSION—Due to practical considerations in determining the
ridges, notches, or overall height (in case of compression test speci-
elastic limit, measurements of strain using a small force, rather than
men). The precision associated with gauge length setting for a Type 2
zero force, are usually taken as the initial and final reference.
extensometer should be specified in relevant test method or product
(E28.04)
standard. The position readout on a testing machine is not recom-
mended for use in a Type 2 extensometer system. (E28.01)
elongation, El, n—the increase in gauge length of a body
subjected to a tension force, referenced to a gauge length on
the body.
DISCUSSION—Usually elongation is expressed as a percentage of the
Available from National Institute of Standards and Technology (NIST), 100
original gauge length. Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http://www.nist.gov.
E6 − 23a
Type 3 extensometer system, n—an extensometer system forming limit diagram, (FLD), n—a graph on which the
which intrinsically senses strain (ratiometric principle), for measured major and associated minor strain combinations
example, video camera system. (E28.01) are plotted to develop a forming limit curve. (E28.02)
exercise, v—apply the maximum force to be used in the gage factor, n—for strain gages, the ratio between the unit
change of strain gage resistance due to strain and the causing
verification to either a force-measuring instrument or the
force-sensing device of a testing machine or to both, to strain.
DISCUSSION—The gage factor is dimensionless and is expressed as
reestablish the hysteresis pattern that tends to disappear
follows:
during periods of disuse, or with the change of mode of force
application, as from compression to tension. (E28.01) R 2 R
R 1 ΔR
force [F], n—in mechanical testing, a vector quantity of
K 5 5 (1)
L 2 L ε R
0 0
fundamental nature characterized by a magnitude, a
L
direction, a sense, and a discrete point of application, that
acts externally upon a test object and creates stresses in it. where:
DISCUSSION—Force is a derived unit of the SI system. Units of force
K = gage factor,
in the SI system are newtons (N).
R = strain gage resistance at test strain,
R = strain gage resistance at zero or reference strain,
DISCUSSION—Where applicable, the noun force is preferred to load in 0
L = test structure length under the strain gage at test strain,
terminology for mechanical testing. (E28.91)
L = test structure length under the strain gage at zero or
force indicator, n—of a testing machine, a component of a
reference strain,
force-measuring system that presents, in force units, the
ΔR = change in strain gage resistance when strain is changed
force measured by the force-measuring system. (E28.01)
from zero (or reference strain) to test strain, and
L2L
=
ε
the mechanical strain
force measurement error, E, n—in the case of a testing
L
(E28.01)
machine, the difference obtained by subtracting the force
indicated by the force measurement standard from the
gauge length [L], n—the original length of that portion of the
indicated force of the testing machine.
specimen over which strain or change of length is deter-
DISCUSSION—In a certificate and report of calibration and verification,
mined.
“force measurement error” shall be used with numerical values, for
DISCUSSION—If the device is used for sensing extension or motion,
example, “At a force of 300 kN [60 000 lbf], the force measurement
and gauge length is predetermined by the specimen geometry or
error of the testing machine was + 67 N [+ 15 lbf].” (E28.01)
specific test method, then only resolution and strain error for a specified
gauge length should determine the class of extensometer system.
force measurement standard, n—a standard weight, an equal-
(E28.01)
arm balance and a standard weight, or an elastic force
measurement standard used as a reference, with associated
gauge length [L], n—the original length of that portion of the
measurement uncertainty, in compliance Practices E74.
specimen over which strain, elongation, or change of length
are determined.
DISCUSSION—A force measurement standard is a specific type of
“measurement standard” as defined in JCGM 200: International vo- DISCUSSION—Typically, this length is also the distance between gauge
cabulary of metrology — Basic and general concepts and associated marks, if gauge marking is used to facilitate measurement of the
elongation after fracture.
terms (VIM). (E28.01)
DISCUSSION—When sensing extension or motion with a gauge length
force-measuring instrument—a system consisting of an elas-
that is predetermined by the specimen geometry or specific test method,
tic member combined with an appropriate instrument for
then only resolution and strain error for the specified gauge length
indicating the magnitude (or a quantity proportional to the
should determine the class of the extensometer system. (E28.04)
magnitude) of deformation of the member under an applied
guided bend, n—the bend obtained by using a mandrel to
force. (E28.01)
guide and force the portion of the specimen being bent
force-measuring system, n—of a testing machine, a compo-
between two faces of a die. (E28.02)
nent of a testing machine that measures and indicates the
hardness, n—the resistance of a material to deformation,
force applied by the testing machine. (E28.01)
particularly permanent deformation, indentation, or scratch-
force-sensing device, n—of a testing machine, a component of
ing.
the force-measuring system, that measures through deforma-
DISCUSSION—Different methods of evaluating hardness give different
tion or other means the force applied by the testing machine.
ratings because they are measuring somewhat different quantities and
DISCUSSION— Examples of a force-sensing device include a strain- characteristics of the material. There is no absolute scale for hardness;
gage force transducer (commonly called a load cell) and a pressure therefore, to express hardness quantitatively, each type of test has its
transducer. (E28.01) own scale of arbitrarily defined hardness. (E28.06)
forming limit curve, (FLC), n—an empirically derived curve indentation hardness, n—the hardness as evaluated from
showing the biaxial strain levels beyond which localized measurements of area or depth of the indentation made by
through-thickness thinning (necking) and subsequent failure pressing a specified indenter into the surface of a material
occur during the forming of a metallic sheet. (E28.02) under specified static loading conditions. (E28.06)
E6 − 23a
may not always be desirable when used as a verb, adjective, or other
indicated temperature [Θ], n—the temperature indicated by
part of speech. For example, it is appropriate to refer to loading a
the temperature-measuring system that meets the require-
specimen, a loading rate, a load cell, or a load–line displacement.
ments of this standard. (E28.04)
(E28.91)
initial strain, n—the strain introduced into a specimen by the
lot, n—for strain gages, a group of strain gages with grid
given loading conditions, before creep takes place.
elements from a common melt, subjected to the same
DISCUSSION—This is sometimes referred to as instantaneous strain.
mechanical and thermal processes during manufacturing.
(E28.04)
(E28.01)
instrumented absorbed energy, W [FL], n—work spent to
t
-2
fracture a specimen in a single pendulum swing, as calcu-
lower yield strength, LYS [FL ], n—in a uniaxial test, the
lated by integrating the force-displacement curve. (E28.07) minimum stress recorded during discontinuous yielding,
ignoring transient effects. (E28.04)
Knoop hardness number, HK, n—the calculated result from a
Knoop hardness test, which is proportional to the test force
measurement accuracy, n—closeness of agreement between a
applied to the Knoop indenter divided by the projected area
measured quantity value and a true quantity value of a
of the permanent indentation made by the indenter after
measurand
removal of the test force.
DISCUSSION—The concept ‘measurement accuracy’ is not a quantity
DISCUSSION—The projected area of the permanent indentation made
and is not given a numerical quantity value. A measurement is said to
by the Knoop indenter is calculated based partly on the measured length
be more accurate when it offers a smaller measurement error.
of the long diagonal of the projected area of the indentation. (E28.06)
DISCUSSION—The term “measurement accuracy” should not be used
Knoop hardness test, n—an indentation test in which a Knoop
for measurement trueness and the term “measurement precision”
rhombic-based pyramidal diamond indenter having specified
should not be used for ‘measurement accuracy’, which, however, is
edge angles, is forced under specified conditions into the
related to both these concepts.
surface of the test material, and, after removal of the test
force, the length of the long diagonal of the projected area of DISCUSSION—‘Measurement accuracy’ is sometimes understood as
closeness of agreement between measured quantity values that are
the indentation is measured to calculate the Knoop hardness
being attributed to the measurand. JCGM 200:2012 (E28.01)
number. (E28.06)
mechanical hysteresis, n—the energy absorbed in a complete
lateral expansion [L], n—the maximum increase in thickness
of the specimen as a result of the impact test, expressed in cycle of loading and unloading.
mm. DISCUSSION—A complete cycle of loading and unloading includes
DISCUSSION—lateral expansion is used as a measure of ductility. any stress cycle regardless of the mean stress or range of stress.
(E28.07) (E28.91)
lead wire, n—for strain gages, an electrical conductor used to
mechanical properties, n—those properties of a material that
connect a sensor to its instrumentation. (E28.01)
are associated with elastic and inelastic reaction when force
is applied, or that involve the relationship between stress and
least count, n—the smallest change in indication that can
strain.
customarily be determined and reported.
DISCUSSION—These properties have often been referred to as “physi-
DISCUSSION—In machines with close graduations the least count may
cal properties,” but the term “mechanical properties” is preferred.
be the value of a graduation interval; with open graduations or with
magnifiers for reading, it may be an estimated fraction, rarely as fine as (E28.91)
one tenth, of a graduated interval; and with verniers it is customarily the
difference between the scale and vernier graduation measured in terms mechanical testing, n—determination of the properties or the
of scale units. If the indicating mechanism includes a stepped detent,
mechanical states of a material that are associated with
the detent action may determine the least count.
elastic and inelastic reactions to force or that involve
relationships between stress and strain. (E28.91)
length of the reduced section—the distance between the
tangent points of the fillets that bound the reduced section.
metallic resistance bonded strain gage, n—a resistive
(E28.04)
element, with or without a matrix that is attached to a solid
body by cementing, welding, or other suitable techniques so
limiting dome height (LDH) test, n—an evaluative test for
that the resistance of th
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E6 − 23 E6 − 23a
Standard Terminology Relating to
Methods of Mechanical Testing
This standard is issued under the fixed designation E6; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope
1.1 This terminology covers the principal terms relating to methods of mechanical testing of solids. The general definitions are
restricted and interpreted, when necessary, to make them particularly applicable and practicable for use in standards requiring or
relating to mechanical tests. These definitions are published to encourage uniformity of terminology in product specifications.
1.2 Terms relating to fatigue and fracture testing are defined in Terminology E1823.
1.3 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
E8/E8M Test Methods for Tension Testing of Metallic Materials
E74 Practices for Calibration and Verification for Force-Measuring Instruments
E796 Test Method for Ductility Testing of Metallic Foil (Withdrawn 2009)
E1823 Terminology Relating to Fatigue and Fracture Testing
2.2 ISO Standard:
ISO/IEC Guide 99:2007 International Vocabulary of metrology—Basic and general concepts and terms (VIM)
2.3 NIST Technical Notes:
NIST Technical Note 1297 Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results
2.2 BIPM Standard:
JCGM 200 : International vocabulary of metrology — Basic and general concepts and associated terms (VIM).
3. Index of Cross-References and Associated Definitions
3.1 The terms listed below are associated with terminology that is fundamental or commonly used. The definition for the term of
interest is related to or is given below the definition for the fundamental term cited.
This terminology is under the jurisdiction of ASTM Committee E28 on Mechanical Testing and is the direct responsibility of Subcommittee E28.91 on Terminology
except where designated otherwise. A subcommittee designation in parentheses following a definition indicates the subcommittee with responsibility for that definition.
ɛ4
Current edition approved Jan. 15, 2023Feb. 1, 2023. Published March 2023. Originally approved in 1923. Last previous edition approved in 20152023 as E6 – 15E6 – 23. .
DOI: 10.1520/E0006-23.10.1520/E0006-23A.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Available from National Institute of Standards and Technology (NIST), 100 Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http://www.nist.gov.
Available from BIPM - Pavillon de Breteuil F-92312 Sèvres Cedex FRANCE. this document is available free-of-charge at https://www.bipm.org/en/publications/guides/
vim.html
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E6 − 23a
Term
angular strain see strain
angular strain indexed under strain
axial strain see strain
axial strain indexed under strain
bending strain see strain
bending strain indexed under strain
chord modulus see modulus of elasticity
direct verification see verification
direct verification indexed under verification
compressive stress see stress
compressive stress indexed under stress
elastic constants see modulus of elasticity and Poisson’s
ratio
elastic modulus see modulus of elasticity
elastic modulus use modulus of elasticity
elastic true strain indexed under strain
engineering strain see strain
engineering strain indexed under strain
engineering stress see stress
engineering stress indexed under stress
fracture stress see stress
fracture stress indexed under stress
indirect verification see verification
indirect verification indexed under verification
initial tangent modulus see modulus of elasticity
instantaneous strain see initial strain
linear (tensile or compressive) strain see strain
linear (tensile or compressive) strain indexed under strain
macrostrain see strain
load use force
malleability see ductility
microstrain see strain
modulus of rigidity see modulus of elasticity
modulus of rigidity see shear modulus
movable Brinell hardness testing indexed under Brinell hardness testing
machine machine
movable Rockwell hardness testing indexed under Rockwell hardness machine
machine
nominal stress see stress
nominal stress indexed under stress
normal stress see stress
normal stress indexed under stress
permanent set see set
physical properties see mechanical properties
pin see mandrel (in bend testing)
plastic true strain indexed under strain
plunger see mandrel (in bend testing)
portable Brinell hardness testing indexed under Brinell hardness testing
machine machine
portable Rockwell hardness testing indexed under Rockwell hardness machine
machine
principal stress see stress
principal stress (normal) indexed under stress
residual strain see strain
residual strain indexed under strain
residual stress see stress
residual stress indexed under stress
Rockwell hardness standardizing indexed under Rockwell hardness machine
machine
Rockwell hardness testing machine see Rockwell hardness machine
Rockwell superficial see also Rockwell hardness number
hardness number
secant modulus see modulus of elasticity
shear strain see strain
shear strain indexed under strain
shear stress see stress
shear stress indexed under stress
static fatigue strength see creep rupture strength
stress-rupture strength see creep rupture strength
tangent modulus see modulus of elasticity
tensile stress see stress
tensile stress indexed under stress
torsional modulus see modulus of elasticity
torsional modulus see shear modulus
torsional stress see stress
torsional stress indexed under stress
E6 − 23a
transverse strain see strain
transverse strain indexed under strain
true strain see strain
true strain indexed under strain
true stress see stress
true stress indexed under stress
Type 1 extensometer system indexed under extensometer
Type 2 extensometer system indexed under extensometer
Type 3 extensometer system indexed under extensometer
ultimate tensile strength (UTS) see tensile strength
ultimate tensile strength (UTS) use tensile strength
yield point use upper yield strength
yield strength see also upper yield strength and lower yield
strength
4. Terminology
4.1 Terms and Definitions:
absorbed energy [FL],n—work spent to fracture a specimen in a single pendulum swing, as measured by a compensated
indicating device (E28.07)
accuracy, n—the permissible variation from the correct value. (E28.01)
adjusted length of the reduced section—the length of the reduced section plus an amount calculated to compensate for strain
in the fillet region. (E28.04)
alignment, n—the condition of a testing machine that influences the introduction of bending moments into a specimen (or
alignment transducer) during the application of tensile or compressive forces. (E28.01)
angle of bend, n—the change in the angle between the two legs of the specimen during a bend test, measured before release
of the bending forces.
DISCUSSION—
The angle of bend is measured before release of the bending force, unless otherwise specified. (E28.02)
batch, n—for strain gages, a group of strain gages of the same type and lot, manufactured as a set (made at the same time and
under the same conditions). (E28.01)
bearing area [L ],n—the product of the pin diameter and specimen thickness. (E28.04)
bearing force [F],n—a compressive force on an interface. (E28.04)
bearing strain, n—the ratio of the bearing deformation of the bearing hole, in the direction of the applied force, to the pin
diameter. (E28.04)
-2
bearing strength [FL ],n—the maximum bearing stress which a material is capable of sustaining. (E28.04)
-2
bearing stress [FL ]], , n—the force per unit of bearing area. (E28.04)
-2
bearing yield strength [FL ],n—the bearing stress at which a material exhibits a specified limiting deviation from the
proportionality of bearing stress to bearing strain. (E28.04)
bend test, n—a test for ductility performed by bending or folding a specimen, usually by steadily applied forces but in some
instances by blows.
DISCUSSION—
The bending may be interrupted to examine the bent surface for cracks.
E6 − 23a
DISCUSSION—
The ductility is usually judged by whether or not the specimen cracks under the specified conditions of the test.
DISCUSSION—
There are four general types of bend tests according to the manner in which the forces are applied to the specimen to make the bend. These are as
follows:
1. Free Bend
2. Guided Bend
3. Semi-Guided Bend
4. Wrap-Around Bend
DISCUSSION—
The specimen has a substantially uniform cross-section and a length several times as great as the largest dimension of the cross-section. (E28.02)
biaxial stretching, n—a mode of sheet metal forming in which positive strains are observed in all directions at a given location.
(E28.02)
breaking force [F],n—the force at which fracture occurs.
DISCUSSION—
When used in connection with tension tests of thin materials or materials of small diameter for which it is often difficult to distinguish between the
breaking force and the maximum force developed, the latter is considered to be the breaking force. (E28.04)
Brinell hardness number, n—a number, which is proportional to the quotient obtained by dividing the test force by the curved
surface area of the indentation which is assumed to be spherical and of the diameter of the ball. (E28.06)
Brinell hardness scale, n—a designation that identifies the specific combination of ball diameter and applied force used to
perform the Brinell hardness test. (E28.06)
Brinell hardness standardizing machine—a Brinell hardness machine used for the standardization of Brinell hardness test
blocks. The standardizing machine differs from a regular Brinell hardness testing machine by having tighter tolerances on certain
parameters. (E28.06)
Brinell hardness test, n—an indentation hardness test using a verified machine to force an indenter (tungsten carbide ball with
diameter D), under specified conditions, into the surface of the material under test. The diameter of the resulting indentation d
is measured after removal of the force.
DISCUSSION—
The diameter of the resulting indentation d is measured after removal of the force. (E28.06)
Brinell hardness testing machine—a Brinell hardness machine used for general testing purposes. (E28.06)
movable Brinell hardness testing machine—a Brinell hardness testing machine that is designed to be moved to different locations
on a moveable frame, table or similar support that is integral to the testing machine (for example, securely fixed to a rolling table),
or a Brinell hardness testing machine that is designed to move into the testing position prior to a test, (for example, securely fixed
to a moving support arm), and has been previously verified to ensure that such moves will not affect the hardness result.
portable Brinell hardness testing machine—a Brinell hardness testing machine that is designed to be transported, carried, set up,
and operated by the users, and that measures Brinell hardness by the Brinell hardness test principle.
calibration, n—determination of the values of the significant parameters by comparison with values indicated by a reference
instrument or by a set of reference standards. (E28.06)
calibration, n—operation that, under specified conditions, in a first step, establishes a relation between the quantity values with
measurement uncertainties provided by measurement standards and corresponding indications with associated measurement
uncertainties and, in a second step, uses this information to establish a relation for obtaining a measurement result from an
indication.
DISCUSSION—
A calibration may be expressed by a statement, calibration function, calibration diagram, calibration curve, or calibration table. In some cases, it may
consist of an additive or multiplicative correction of the indication with associated measurement uncertainty.
E6 − 23a
DISCUSSION—
Calibration should not be confused with adjustment of a measuring system, often mistakenly called “self-calibration”, nor with verification of
calibration.
DISCUSSION—
Often, the first step alone in the above definition is perceived as being calibration. JCGM 200:2012
(E28.01)
calibration factor, n—the factor by which a change in extensometer reading must be multiplied to obtain the equivalent strain.
DISCUSSION—
For any extensometer, the calibration factor is equal to the ratio of change in length to the product of the gauge length and the change in extensometer
reading. For direct-reading extensometers the calibration factor is unity. (E28.01)
-2
compressive strength [FL ],n—the maximum compressive stress that a material is capable of sustaining.
DISCUSSION—
Compressive strength is calculated by dividing the maximum force during a compression test by the original cross-sectional area of the specimen.
DISCUSSION—
In the case of a material which fails in compression by a shattering fracture, the compressive strength has a very definite value. In the case of materials
which do not fail in compression by a shattering fracture, the value obtained for compressive strength is an arbitrary value depending upon the degree
of distortion which is regarded as indicating complete failure of the material. (E28.04)
compressometer, n—a specialized extensometer used for sensing negative or compressive strain. (E28.01)
constraint, n—any restriction to the deformation of a body. (E28.91)
creep, n—the time-dependent strain that occurs after the application of a force which is thereafter maintained constant.
DISCUSSION—
Creep tests are usually made at constant force and temperature. For tests on plastics, the initial strain – however defined– is included; for tests on metals,
the initial strain is not included. (E28.04)
creep recovery, n—the time-dependent decrease in strain in a solid, following the removal of force.
DISCUSSION—
Recovery is usually determined at constant temperature.
DISCUSSION—
In tests of plastics, the initial recovery is generally included; for metals, it is not. Thermal expansion is excluded. (E28.04)
-2
creep rupture strength [FL ],n—the stress causing fracture in a creep test at a given time, in a specified constant environment.
DISCUSSION—
This is sometimes referred to as the stress-rupture strength or, in glass technology, the static fatigue strength. (E28.04)
-2
creep strength [FL ],n—the stress that causes a given creep in a creep test at a given time in a specified constant environment.
(E28.04)
deep drawing, n—a metal sheet forming operation in which strains on the sheet surface are positive in the direction of the punch
travel and negative at 90° to that direction. (E28.02)
deflectometer, n—a specialized extensometer used for sensing of extension or motion, usually without reference to a specific
gauge length. (E28.01)
Demeri Split Ring Test—a test that measures the springback behavior of sheet metal by comparing the diameter of a ring
extracted from the wall of a flat bottom cup and the diameter of the same ring split to release residual stresses. (E28.02)
This definition is reproduced here from JCGM 200:2012 International vocabulary of metrology – Basic and general concepts and associated terms (VIM) with permission
from the Director of BIPM. The text has been put in ASTM International’s form and style.
E6 − 23a
differential indentation depth hardness test, n—an indentation hardness test using a verified hardness testing machine to force
a truncated diamond cone indenter, diamond spheroconical indenter or tungsten carbide ball indenter, under specified conditions,
into the surface of the material under test, and to measure the difference in depth of the indentation as the force on the indenter
is increased from a specified preliminary test force to a specified total test force and then returned to the preliminary test force.
(E28.06)
differential indentation depth hardness number, n—a number derived from the net increase in the depth of indentation as the
force on an indenter is increased from a specified preliminary test force to a specified total test force and then returned to the
preliminary test force. (E28.06)
differential indentation depth hardness testing machine, n—a machine capable of performing a Differential Indentation
Depth hardness test and displaying the resulting hardness number. (E28.06)
discontinuous yielding, n—in a uniaxial test, a hesitation or fluctuation of force observed at the onset of plastic deformation,
due to localized yielding.
DISCUSSION—
The stress-strain curve need not appear to be discontinuous. (E28.04)
discontinuous yielding stress, σ ,n—the peak stress at the initiation of the first measurable serration on the curve of
i
stress-versus-strain.
DISCUSSION—
The parameter σ is a function of test variables and is not a material constant. (E28.04)
i
ductility, n—the ability of a material to deform plastically before fracturing.
DISCUSSION—
Ductility is usually evaluated by measuring (1) the elongation or reduction of area from a tension test, (2) the depth of cup from a cupping test, (3)
the radius or angle of bend from the bend test, or (4) the fatigue ductility from the fatigue ductility test (see Test Method E796).
DISCUSSION—
Malleability is the ability to deform plastically under repetitive compressive forces. (E28.02)
dynamic elastic modulus, E ,n—the elastic modulus, either Young’s modulus or shear modulus, that is measured in a dynamic
d
mechanical measurement. (E28.04)
dynamic mechanical measurement, n—a technique in which either the modulus or damping, or both, of a substance under
oscillatory applied force or displacement is measured as a function of temperature, frequency, or time, or a combination thereof.
(E28.04)
-2
dynamic shear modulus, G [FL ],n—the value of the shear modulus determined using an oscillatory applied force or
d
displacement and in conformance with this test method. (E28.04)
-2
dynamic Young’s modulus, E [FL ],n—the value of the Young’s modulus determined using an oscillatory applied force or
d
displacement and in conformance with this test method. (E28.04)
eccentricity [L],n—the distance between the line of action of the applied force and the axis of symmetry of the specimen in a
plane perpendicular to the longitudinal axis of the specimen. (E28.01)
edge distance [L],n—the distance from the edge of a bearing specimen to the center of the hole in the direction of applied force.
(E28.04)
edge distance ratio, n—the ratio of the edge distance to the pin diameter. (E28.04)
E6 − 23a
elastic force measurement standard, n—system consisting of an elastic member combined with an appropriate device for
indicating the magnitude (or a quantity proportional to the magnitude) of deformation of the member under an applied force.
(E28.01)
-2
elastic limit [FL ],n—the greatest stress that a material is capable of sustaining without any permanent strain remaining upon
complete release of the stress.
DISCUSSION—
Due to practical considerations in determining the elastic limit, measurements of strain using a small force, rather than zero force, are usually taken
as the initial and final reference. (E28.04)
elongation, El,n—the increase in gauge length of a body subjected to a tension force, referenced to a gauge length on the body.
DISCUSSION—
Usually elongation is expressed as a percentage of the original gauge length.
DISCUSSION—
The increase in gauge length may be determined either at or after fracture, as specified for the material under test.
DISCUSSION—
The term elongation, when applied to metals, generally means measurement after fracture; when applied to plastics and elastomers, measurement at
fracture. Such interpretation is usually applicable to values of elongation reported in the literature when no further qualification is given.
DISCUSSION—
In reporting values of elongation, the gauge length shall be stated.
DISCUSSION—
Elongation is affected by specimen geometry (area and shape of cross section, parallel length, parallelism, fillet radii, etc.), preparation (degree to which
surfaces within the reduced section are smooth and free of cold work), and test procedure (alignment and test speed, for example). (E28.04)
elongation after fracture, n—the elongation measured by fitting the two halves of the broken specimen together. (E28.04)
elongation at fracture, n—the elongation measured just prior to the sudden decrease in force associated with fracture. (E28.04)
error, n—for a measurement or reading, the amount it deviates from a known or reference value represented by a measurement
standard.
DISCUSSION—
Mathematically, the error is calculated by subtracting the accepted value from the measurement or reading. (See also percent error.) (E28.91)
expanded uncertainty, n—a statistical measurement of the probable limits of error of a measurement.
DISCUSSION—
NIST Technical Note 1297 treats the statistical approach including the expanded uncertainty. (E28.91)
extensometer, n—a device for sensing strain. (E28.01)
extensometer system, n—a system for sensing and indicating strain.
DISCUSSION—
The system will normally include an extensometer, conditioning electronics, and auxiliary device (recorder, digital readout, computer, etc.). However,
completely self-contained mechanical devices are permitted. An extensometer system may be one of three types. (E28.01)
Type 1 extensometer system, n—an extensometer system which both defines gauge length, and senses extension, for example,
a clip-on strain gauge type with conditioning electronics. (E28.01)
Type 2 extensometer system, n—an extensometer which senses extension and the gauge length is defined by specimen geometry
or specimen features such as ridges or notches.
DISCUSSION—
A Type 2 extensometer is used where the extensometer gauge length is determined by features on the specimen, for example, ridges, notches, or overall
height (in case of compression test specimen). The precision associated with gauge length setting for a Type 2 extensometer should be specified in
relevant test method or product standard. The position readout on a testing machine is not recommended for use in a Type 2 extensometer system.
(E28.01)
E6 − 23a
Type 3 extensometer system, n—an extensometer system which intrinsically senses strain (ratiometric principle), for example,
video camera system. (E28.01)
exercise, v—apply the maximum force to be used in the verification to either a force-measuring instrument or the force-sensing
device of a testing machine or to both, to reestablish the hysteresis pattern that tends to disappear during periods of disuse, or
with the change of mode of force application, as from compression to tension. (E28.01)
force [F],n—in mechanical testing, a vector quantity of fundamental nature characterized by a magnitude, a direction, a sense,
and a discrete point of application, that acts externally upon a test object and creates stresses in it.
DISCUSSION—
Force is a derived unit of the SI system. Units of force in the SI system are newtons (N).
DISCUSSION—
Where applicable, the noun force is preferred to load in terminology for mechanical testing. (E28.91)
force indicator, n—of a testing machine, a component of a force-measuring system that presents, in force units, the force
measured by the force-measuring system. (E28.01)
force measurement error, E,n—in the case of a testing machine, the difference obtained by subtracting the force indicated by
the force measurement standard from the indicated force of the testing machine.
DISCUSSION—
In a certificate and report of calibration and verification, “force measurement error” shall be used with numerical values, for example, “At a force of
300 kN [60 000 lbf], the force measurement error of the testing machine was + 67 N [+ 15 lbf].” (E28.01)
force measurement standard, n—a standard weight, an equal-arm balance and a standard weight, or an elastic force
measurement standard used as a reference, with associated measurement uncertainty, in compliance Practices E74.
DISCUSSION—
A force measurement standard is a specific type of “measurement standard” as defined in JCGM 200: International vocabulary of metrology — Basic
and general concepts and associated terms (VIM). (E28.01)
force-measuring instrument—a system consisting of an elastic member combined with an appropriate instrument for
indicating the magnitude (or a quantity proportional to the magnitude) of deformation of the member under an applied force.
(E28.01)
force-measuring system, n—of a testing machine, a component of a testing machine that measures and indicates the force
applied by the testing machine. (E28.01)
force-sensing device, n—of a testing machine, a component of the force-measuring system, that measures through deformation
or other means the force applied by the testing machine.
DISCUSSION—
Examples of a force-sensing device include a strain-gage force transducer (commonly called a load cell) and a pressure transducer. (E28.01)
forming limit curve, (FLC), n—an empirically derived curve showing the biaxial strain levels beyond which localized
through-thickness thinning (necking) and subsequent failure occur during the forming of a metallic sheet. (E28.02)
forming limit diagram, (FLD), n—a graph on which the measured major and associated minor strain combinations are plotted
to develop a forming limit curve. (E28.02)
fracture ductility, ε ,n—the true plastic strain at fracture.
f
free bend, n—the bend obtained by applying forces to the ends of a specimen without the application of force at the point of
maximum bending.
E6 − 23a
DISCUSSION—
In making a free bend, lateral forces first are applied to produce a small amount of bending at two points. The two bends, each a suitable distance from
the center, are both in the same direction. (E28.02)
force [F],n—in mechanical testing, a vector quantity of fundamental nature characterized by a magnitude, a direction, a sense,
and a discrete point of application, that acts externally upon a test object and creates stresses in it.
DISCUSSION—
Force is a derived unit of the SI system. Units of force in the SI system are newtons (N).
DISCUSSION—
Where applicable, the noun force is preferred to load in terminology for mechanical testing. (E28.91)
gage factor, n—for strain gages, the ratio between the unit change of strain gage resistance due to strain and the causing strain.
DISCUSSION—
The gage factor is dimensionless and is expressed as follows:
R 2 R
R 1∆R
K 5 5 (1)
L 2 L ε R
0 0
L
where:
K = gage factor,
R = strain gage resistance at test strain,
R = strain gage resistance at zero or reference strain,
L = test structure length under the strain gage at test strain,
L = test structure length under the strain gage at zero or reference strain,
∆R = change in strain gage resistance when strain is changed from zero (or reference strain) to test strain, and
L2L
=
ε
the mechanical strain
L
(E28.01)
gauge length [L],n—the original length of that portion of the specimen over which strain or change of length is determined.
DISCUSSION—
If the device is used for sensing extension or motion, and gauge length is predetermined by the specimen geometry or specific test method, then only
resolution and strain error for a specified gauge length should determine the class of extensometer system. (E28.01)
gauge length [L],n—the original length of that portion of the specimen over which strain, elongation, or change of length are
determined.
DISCUSSION—
Typically, this length is also the distance between gauge marks, if gauge marking is used to facilitate measurement of the elongation after fracture.
DISCUSSION—
When sensing extension or motion with a gauge length that is predetermined by the specimen geometry or specific test method, then only resolution
and strain error for the specified gauge length should determine the class of the extensometer system. (E28.04)
guided bend, n—the bend obtained by using a mandrel to guide and force the portion of the specimen being bent between two
faces of a die. (E28.02)
hardness, n—the resistance of a material to deformation, particularly permanent deformation, indentation, or scratching.
DISCUSSION—
Different methods of evaluating hardness give different ratings because they are measuring somewhat different quantities and characteristics of the
material. There is no absolute scale for hardness; therefore, to express hardness quantitatively, each type of test has its own scale of arbitrarily defined
hardness. (E28.06)
indentation hardness, n—the hardness as evaluated from measurements of area or depth of the indentation made by pressing
a specified indenter into the surface of a material under specified static loading conditions. (E28.06)
E6 − 23a
indicated temperature [Θ],n—the temperature indicated by the temperature-measuring system that meets the requirements of
this standard. (E28.04)
initial strain, n—the strain introduced into a specimen by the given loading conditions, before creep takes place.
DISCUSSION—
This is sometimes referred to as instantaneous strain. (E28.04)
instrumented absorbed energy, W [FL],n—work spent to fracture a specimen in a single pendulum swing, as calculated by
t
integrating the force-displacement curve. (E28.07)
Knoop hardness number, HK,n—the calculated result from a Knoop hardness test, which is proportional to the test force
applied to the Knoop indenter divided by the projected area of the permanent indentation made by the indenter after removal
of the test force.
DISCUSSION—
The projected area of the permanent indentation made by the Knoop indenter is calculated based partly on the measured length of the long diagonal
of the projected area of the indentation. (E28.06)
Knoop hardness test, n—an indentation test in which a Knoop rhombic-based pyramidal diamond indenter having specified
edge angles, is forced under specified conditions into the surface of the test material, and, after removal of the test force, the
length of the long diagonal of the projected area of the indentation is measured to calculate the Knoop hardness number.
(E28.06)
lateral expansion [L],n—the maximum increase in thickness of the specimen as a result of the impact test, expressed in mm.
DISCUSSION—
lateral expansion is used as a measure of ductility. (E28.07)
lead wire, n—for strain gages, an electrical conductor used to connect a sensor to its instrumentation. (E28.01)
least count, n—the smallest change in indication that can customarily be determined and reported.
DISCUSSION—
In machines with close graduations the least count may be the value of a graduation interval; with open graduations or with magnifiers for reading,
it may be an estimated fraction, rarely as fine as one tenth, of a graduated interval; and with verniers it is customarily the difference between the scale
and vernier graduation measured in terms of scale units. If the indicating mechanism includes a stepped detent, the detent action may determine the
least count.
length of the reduced section—the distance between the tangent points of the fillets that bound the reduced section. (E28.04)
limiting dome height (LDH) test, n—an evaluative test for metal sheet deformation capability employing a hemispherical
punch and a circumferential clamping force sufficient to prevent metal in the surrounding flange from being pulled into the die
cavity. (E28.02)
load [F],n—in mechanical testing, an external force or system of forces or pressures, acting upon the test specimen or sample.
DISCUSSION—
Load is a deprecated term and, where practical, should be replaced by force, particularly when used as a noun. For reasons of editorial simplicity or
traditional usage, replacement of load by force may not always be desirable when used as a verb, adjective, or other part of speech. For example, it
is appropriate to refer to loading a specimen, a loading rate, a load cell, or a load–line displacement. (E28.91)
lot, n—for strain gages, a group of strain gages with grid elements from a common melt, subjected to the same mechanical and
thermal processes during manufacturing. (E28.01)
-2
lower yield strength, LYS[FL ],n—in a uniaxial test, the minimum stress recorded during discontinuous yielding, ignoring
transient effects. (E28.04)
E6 − 23a
mandrel (in bend testing), n—the tool used to control the strain on the concave side of a bend in a wrap-around bend test and
also to apply the bending force in a semi-guided or guided bend test.
DISCUSSION—
The terms “pin” and “plunger” have been used in place of mandrel.
DISCUSSION—
In free bends or semi-guided bends to an angle of 180° a shim or block of the proper thickness may be placed between the legs of the specimen as
bending is completed. This shim or block is also referred to as a pin or mandrel. (E28.02)
measurement accuracy, n—closeness of agreement between a measured quantity value and a true quantity value of a measurand
DISCUSSION—
The concept ‘measurement accuracy’ is not a quantity and is not given a numerical quantity value. A measurement is said to be more accurate when
it offers a smaller measurement error.
DISCUSSION—
The term “measurement accuracy” should not be used for measurement trueness and the term “measurement precision” should not be used for
‘measurement accuracy’, which, however, is related to both these concepts.
DISCUSSION—
‘Measurement accuracy’ is sometimes understood as closeness of agreement between measured quantity values that are being attributed to the
measurand. JCGM 200:2012 200:2012 (E28.01)
(E28.01)
mechanical hysteresis, n—the energy absorbed in a complete cycle of loading and unloading.
DISCUSSION—
A complete cycle of loading and unloading includes any stress cycle regardless of the mean stress or range of stress. (E28.04)(E28.91)
mechanical properties, n—those properties of a material that are associated with elastic and inelastic reaction when force is
applied, or that involve the relationship between stress and strain.
DISCUSSION—
These properties have often been referred to as “physical properties,” but the term “mechanical properties” is preferred. (E28.91)
mechanical testing, n—determination of the properties or the mechanical states of a material that are associated with elastic and
inelastic reactions to force or that involve relationships between stress and strain. (E28.91)
metallic resistance bonded strain gage, n—a resistive element, with or without a matrix that is attached to a solid body by
cementing, welding, or other suitable techniques so that the resistance of the element will vary as the surface to which it is
attached is deformed.
DISCUSSION—
These test methods apply to gages where the instantaneous gage resistance, R, is given by the equation:
R 5 R 11εK (2)
~ !
o
where:
R = element resistance at reference strain and temperature levels (frequently initial test or balanced circuit conditions),
o
ε = linear strain of the surface in the direction of the measurement axis of the strain gage produced either by a stress field
(mechanical strain) or by a temperature change (thermal expansion), and
K = the gage factor.
(E28.01)
metrological traceability, n—property of a measurement result whereby the result can be related to a reference through a
documented unbroken chain of calibrations, each contributing to the measurement uncertainty.
DISCUSSION—
For this definition, a ‘reference’ can be a definition of a measurement unit through its practical realization, or a measurement procedure including the
measurement unit for a non-ordinal quantity, or a measurement standard.
E6 − 23a
DISCUSSION—
Metrological traceability requires an established calibration hierarchy.
DISCUSSION—
Specification of the reference must include the time at which this reference was used in establishing the calibration hierarchy, along with any other
relevant metrological information about the reference, such as when the first calibration in the calibration hierarchy was performed.
DISCUSSION—
For measurements with more than one input quantity in the measurement model, each of the input quantity values should itself be metrologically
traceable and the calibration hierarchy involved may form a branched structure or a network. The effort involved in establishing metrological
traceability for each input quantity value should be commensurate with its relative contribution to the measurement result.
DISCUSSION—
Metrological traceability of a measurement result does not ensure that the measurement uncertainty is adequate for a given purpose or that there is
an absence of mistakes.
DISCUSSION—
A comparison between two measurement standards may be viewed as a calibration if the comparison is used to check and, if necessary, correct the
quantity value and measurement uncertainty attributed to one of the measurement standards. JCGM 200:2012
(E28.01)
-2
modulus of elasticity [FL ],n—the ratio of stress to corresponding strain below the proportional limit.
DISCUSSION—
The stress-strain relationships of many materials do not conform to Hooke’s law throughout the elastic range, but deviate therefrom even at stresses
well below the elastic limit. For such materials, the slope of either the tangent to the stress-strain curve at the origin or at a low stress, the secant drawn
from the origin to any specified point on the stress-strain curve, or the chord connecting any two specified points on the stress-strain curve is usually
taken to be the “modulus of elasticity.” In these cases, the modulus should be designated as the “tangent modulus,” the “secant modulus,” or the “chord
modulus,” and the point or points on the stress-strain curve described. Thus, for materials where the stress-strain relationship is curvilinear rather than
linear, one of the four following terms may be used:
-2
(a) initial tangent modulus [FL ], n—the slope of the stress-strain curve at the origin.
-2
(b) tangent modulus [FL ], n—the slope of the stress-strain curve at any specified stress or strain.
-2
(c) secant modulus [FL ], n—the slope of the secant drawn from the origin to any specified point on the stress-strain curve.
-2
(d) chord modulus [FL ], n—the slope of the chord drawn between any two specified points on the stress-strain curve below
the elastic limit of the material.
DISCUSSION—
Modulus of elasticity, like stress, is expressed in force per unit of area (pounds per square inch, etc.). (E28.04)
necking, n—the onset of nonuniform or localized plastic deformation, resulting in a localized reduction of cross-sectional area.
(E28.02)
percent error, n—the ratio, expressed as a percent, of an error to the known accepted value represented by a measurement
standard. (See also, error.) (E28.91)
pile-up—a buildup of material around the edge of an indent that is the result of the indentation process. (E28.06)
precision, n—the degree of mutual agreement among individual measurements made under prescribed like conditions. (E28.04)
primary force standard, n—a deadweight force applied directly without intervening mechanisms such as levers, hydraulic
multipliers, or the like, whose mass has been determined by comparison with reference standards traceable to the International
System of Units (SI) of mass. (E28.01)
Poisson’s ratio, μ,n—the negative of the ratio of transverse strain to the corresponding axial strain resulting from an axial stress
below the proportional limit of the material.
DISCUSSION—
Poisson’s ratio can be negative for some materials, for example, a tensile transverse strain will result from a tensile axial strain.
DISCUSSION—
Poisson’s ratio will have more than one value if the material is not isotropic. (E28.04)
E6 − 23a
portable testing machine (force-measuring type), primary force standard, n—a device specifically designed to be moved
from place to place and for applying a force (load) to a specimen.deadweight force applied directly without intervening
mechanisms such as levers, hydraulic multipliers, or the like, whose mass has been determined by comparison with reference
standards traceable to the International System of Units (SI) of mass. (E28.01) (E28.01)
primary torque measurement standard, n—A deadweight force applied through a moment arm, all with metrological
traceability to the International System of Units (SI). (E28.01)
-2
proportional limit [FL ],n—the greatest stress that a material is capable of sustaining without deviation from proportionality
of stress to strain (Hooke’s law).
DISCUSSION—
Many experiments have shown that values observed for the proportional limit vary greatly with the sensitivity and accuracy of the testing equipment,
eccentricity of loading, the scale to which the stress-strain diagram is plotted, and other factors. When determination of proportional limit is required,
the procedure and the sensitivity of the test equipment should be specified.
radius of bend, n—the radius of the cylindrical surface of the pin or mandrel that comes in contact with the inside surface of
the bend during bending.
DISCUSSION—
In the case of free or semi-guided bends to 180° in which a shim or block is used, the radius of bend is one half the thickness of the shim or block.
(E28.02)
rapid indentation hardness test—an indentation hardness test using calibrated machines to force a tungsten carbide ball, under
specified conditions, into the surface of the material under test and to measure the depth of the indentation.
DISCUSSION—
The depth measured can be from the surface of the test specimen or from a reference position established by the application of a preliminary test force.
The depth measurement is usually correlated to another scale or Brinell hardness number. (E28.06)
rate of creep, n—the slope of the creep-time curve at a given time. (E28.04)
reading, n—a quantity (typically a measurement or test result) indicated by a piece of equipment, such that it can be read by
a user. (E28.91)
reduced parallel section, A,n—the central portion of the specimen that has a nominally uniform cross section, with an optional
small taper toward the center, that is smaller than that of the ends that are gripped, not including the fillets.
DISCUSSION—
This term is often called the parallel length in other standards.
DISCUSSION—
Previous versions of E8/E8M defined this term as “reduced section.” (E28.04)
reduced section, n—the central portion of the specimen that has a cross section smaller than the gripped ends.
DISCUSSION—
The cross section is uniform within prescribed tolerances. (E28.04)
reduction of area, n—the difference between the original cross-sectional area of a tension test specimen and the area of its
smallest cross section.
DISCUSSION—
The reduction of area is usually expressed as a percentage of the original cross-sectional area of the specimen.
DISCUSSION—
The smallest cross section may be measured at or after fracture as specified for the material under test.
DISCUSSION—
The term reduction of area when applied to metals generally means measurement after fracture; when applied to plastics and elastomers, measurement
E6 − 23a
at fracture. Such interpretation is usually applicable to values for reduction of area reported i
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