ASTM E6-99e1
(Terminology)Standard Terminology Relating to Methods of Mechanical Testing
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 E 1823.
General Information
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Standards Content (Sample)
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e1
Designation:E6–99 An American National Standard
Standard Terminology Relating to
Methods of Mechanical Testing
This standard is issued under the fixed designation E 6; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
e NOTE— The term elastic constants was deleted: Section 3.1 and the term initial stress were editorially revised in April 2000.
1. Scope
compressive stress see stress
compressometer see extensometer
1.1 This terminology covers the principal terms relating to
constraint A
methods of mechanical testing of solids. The general defini- creep E
creep recovery E
tions are restricted and interpreted, when necessary, to make
creep rupture strength E
them particularly applicable and practicable for use in stan-
creep strength E
dards requiring or relating to mechanical tests. These defini-
discontinuous yielding B
ductility A
tions are published to encourage uniformity of terminology in
edge distance F
product specifications.
edge distance ratio F
1.2 Terms relating to fatigue and fracture testing are defined
elastic constants see modulus of elasticity and Poisson’s
ratio
in Terminology E 1823.
elastic limit A
elastic true strain A
2. Referenced Documents
elongation B
engineering strain see strain
2.1 ASTM Standards:
engineering stress see stress
E 796 Test Method for Ductility Testing of Metallic Foil
extensometer B
E 1823 Terminology Relating to Fatigue and Fracture Test- fatigue ductility B
fatigue ductility exponent B
ing
fatigue life B
fracture ductility A
3. Index of Terms
fracture strength A
fracture stress see stress
3.1 The definitions of the following terms, which are listed
free bend D
alphabetically, appear in the indicated sections of 4.1.
gage length A
Term Section guided bend D
hardness C
angle of bend D
angular strain see strain indentation hardness C
initial recovery E
axial strain seestrain
bearing area F initial strain E
initial stress E
bearing load B
bearing strain F Knoop hardness number C
bearing strength F Knoop hardness test C
linear strain see 0strain
bearing stress F
bearing yield strength F linear (tensile or compressive) strain A
lower yield strength B
bend test D
break elongation see maximum elongation macrostrain see strain
malleability see ductility
breaking load B
Brinell hardness number C mandrel (in bend testing) D
Brinell hardness test C maximum elongation B
chord modulus see modulus of elasticity mechanical hysteresis A
compressive strength B mechanical properties A
mechanical testing A
microstrain see strain
modulus of elasticity A
1 modulus of rigidity see modulus of elasticity
This terminology is under the jurisdiction of ASTM Committee E-28 on
modulus of rupture in bending D
Mechanical Testing and is the direct responsibility of Subcommittee E28.91 on
modulus of rupture in torsion B
Editorial and Terminology except where designated otherwise. A subcommittee
necking B
designation in parentheses following a definition indicates the subcommittee with
nominal stress see stress
responsibility for that definition.
normal stress see stress
Current edition approved July 10, 1999. Published October 1999. Originally
physical properties see mechanical properties
published as E6–23T. Last previous edition E6–98.
pin see mandrel (in bend testing)
Annual Book of ASTM Standards, Vol 03.01.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E6
elastic limit, measurements of strain, using a small load rather than zero
plastic true strain A
load, are usually taken as the initial and final reference.
plunger see mandrel (in bend testing)
principal stress see stress
fracture ductility, e , n—the true plastic strain at fracture.
f
Poisson’s ratio A
–2
proportional limit A fracture strength, S [FL ], n—the normal stress at the
f
radius of bend D
beginning of fracture. Fracture strength is calculated from
rate of creep E
the load at the beginning of fracture during a tension test and
reduction of area B
relaxation rate E
the original cross-sectional area of the specimen.
relaxed stress E
gage length [L], n—the original length of that portion of the
remaining stress E
specimen over which strain or change of length is deter-
residual strain see strain
residual stress see stress mined. (E28.04)
Rockwell hardness number, HR C
least count, n—the smallest change in indication that can
Rockwell hardness test C
customarily be determined and reported.
Rockwell superficial hardness num- see Rockwell hardness number
ber
DISCUSSION—In machines with close graduations it may be the value
Rockwell superficial hardness test C
of a graduation interval; with open graduations or with magnifiers for
semi-guided bend D
set A reading, it may be an estimated fraction, rarely as fine as one tenth, of
secant modulus see modulus of elasticity
a graduated interval; and with verniers it is customarily the difference
shear fracture B
between the scale and vernier graduation measured in terms of scale
shear modulus see modulus of elasticity
units. In the indicating mechanism includes a stepped detent, the detent
shear strain see strain
action may determine the least count.
shear strength B
shear stress see stress
mechanical hysteresis, n—the energy absorbed in a complete
slenderness ratio B
cycle of loading and unloading. (E28.03)
strain A
stress A
DISCUSSION—A complete cycle of loading and unloading includes
stress relaxation E
any stress cycle regardless of the mean stress or range of stress.
stress-strain diagram A
tangent modulus see modulus of elasticity
mechanical properties, n—those properties of a material that
tensile strength B
tensile stress see stress are associated with elastic and inelastic reaction when force
torsional modulus see modulus of elasticity
is applied, or that involve the relationship between stress and
torsional stress see stress
strain.
total elongation B
transverse strain see strain
DISCUSSION—These properties have often been referred to as “physi-
true strain see strain
cal properties,” but the term “mechanical properties” is much to be
true stress see strain
ultimate elongation see maximum elongation preferred.
uniform elongation B
mechanical testing, n—the determination of mechanical prop-
upper yield strength B
Vickers hardness number C erties. (E28.90)
–2
Vickers hardness test C
modulus of elasticity [FL ], n—the ratio of stress to corre-
wrap-around bend D
sponding strain below the proportional limit.
yield point B
–2
yield point elongation B tension or compression, E [FL ], n—Young’s modulus
yield strength B
(modulus in tension or modulus in compression).
Young’s modulus see modulus of elasticity
–2
shear or torsion, G [FL ], n—commonly designated as
zero time E
modulus of rigidity, shear modulus, or torsional modulus.
4. Terminology
DISCUSSION—The stress-strain relations of many materials do not
4.1 Terms and Definitions:
conform to Hooke’s law throughout the elastic range, but deviate
therefrom even at stresses well below the elastic limit. For such
A. GENERAL DEFINITIONS
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
constraint, n—any restriction to the deformation of a body.
specified point on the stress-strain curve, or the chord connecting any
(E28.11)
two specified points on the stress-strain curve is usually taken to be the
ductility, n—the ability of a material to deform plastically
“modulus of elasticity.” In these cases the modulus should be desig-
before fracturing. (E28.02)
nated as the “tangent modulus,” the“ secant modulus,” or the “chord
modulus,” and the point or points on the stress-strain curve described.
DISCUSSION—Ductility is usually evaluated by measuring (1) the
Thus, for materials where the stress-strain relationship is curvilinear
elongation or reduction of area from a tension test, (2) the depth of cup
rather than linear, one of the four following terms may be used:
from a cupping test, (3) the radius or angle of bend from the bend test,
–2
(a) initial tangent modulus [FL ], n—the slope of the stress-strain
or (4) the fatigue ductility from the fatigue ductility test (see Test
curve at the origin.
Method E 796).
–2
(b) tangent modulus [FL ], n—the slope of the stress-strain curve at
DISCUSSION—Malleability is the ability to deform plastically under
any specified stress or strain.
repetitive compressive forces.
–2
(c) secant modulus [FL ], n—the slope of the secant drawn from the
–2
elastic limit [FL ], n—the greatest stress which a material is origin to any specified point on the stress-strain curve.
–2
(d) chord modulus [FL ], n—the slope of the chord drawn between
capable of sustaining without any permanent strain remain-
any two specified points on the stress-strain curve.
ing upon complete release of the stress.
DISCUSSION—Modulus of elasticity, like stress, is expressed in force
DISCUSSION—Due to practical considerations in determining the per unit of area (pounds per square inch, etc.).
E6
Poisson’s ratio, μ, n—the absolute value of the ratio of angular strain, n—use shear strain.
transverse strain to the corresponding axial strain resulting shear strain, n—the tangent of the angular change, due to
from uniformly distributed axial stress below the propor- force, between two lines originally perpendicular to each
tional limit of the material. (E28.03) other through a point in a body. (E28.04)
true strain, e, n—in a body subjected to axial force, the natural
DISCUSSION—Above the proportional limit, the ratio of transverse
logarithm of the ratio of the gage length at the moment of
strain to axial strain will depend on the average stress and on the stress
observation to the original gage length.
range for which it is measured and, hence should not be regarded as
elastic true strain, e , n—elastic component of the true strain.
Poisson’s ratio. If this ratio is reported, nevertheless, as a value of
e
“Poisson’s ratio” for stresses beyond the proportional limit, the range of
plastic true strain, e , n—the inelastic component of true
p
stress should be stated.
strain.
DISCUSSION—Poisson’s ratio will have more than one value if the
macrostrain, n—the mean strain over any finite gage length of
material is not isotropic.
measurement large in comparison with interatomic dis-
–2
proportional limit [FL ], n—the greatest stress which a
tances. (E28.13)
material is capable of sustaining without any deviation from
DISCUSSION—Macrostrain can be measured by several methods,
proportionality of stress to strain (Hooke’s law).
including electrical-resistance strain gages and mechanical or optical
extensometers. Elastic macrostrain can be measured by X-ray diffrac-
DISCUSSION—Many experiments have shown that values observed for
tion.
the proportional limit vary greatly with the sensitivity and accuracy of
DISCUSSION—When either of the terms macrostrain or microstrain is
the testing equipment, eccentricity of loading, the scale to which the
first used in a document, it is recommended that the physical dimension
stress-strain diagram is plotted, and other factors. When determination
or the gage length, which indicate the size of the reference strain
of proportional limit is required, the procedure and the sensitivity of the
volume involved, be stated.
test equipment should be specified.
set—strain remaining after complete release of the load pro-
microstrain, n—the strain over a gage length comparable to
ducing the deformation.
interatomic distances. (E28.13)
DISCUSSION—Due to practical considerations, such as distortion in the
DISCUSSION—These are the strains being averaged by the macrostrain
specimen and slack in the strain indicating system, measurements of
measurement. Microstrain is not measurable by existing techniques.
strain at a small load rather than zero load are often taken.
Variance of the microstrain distribution can, however, be measured by
DISCUSSION—Set is often referred to as permanent set if it shows no
X-ray diffraction.
further change with time. Time elapsing between removal of load and
DISCUSSION—When either of the terms macrostrain or microstrain is
final reading of set should be stated.
first used in a document, it is recommended that the physical dimension
or the gage length, which indicate the size of the reference strain
strain, e, n—the per unit change, due to force, in the size or
volume involved, be stated.
shape of a body referred to its original size or shape. Strain
is a nondimensional quantity, but it is frequently expressed
residual strain, n—strain associated with residual stress.
in inches per inch, metres per metre, or percent.
(E28.13)
DISCUSSION—Strain, as defined here is sometimes called “engineering
DISCUSSION—Residual strains are elastic.
strain,” to emphasize the difference from true strain.
–2
stress [FL ], n—the intensity at a point in a body of the forces
DISCUSSION—In this standard, “original” refers to dimensions or
shape of cross section of specimens at the beginning of testing. or components of force that act on a given plane through the
DISCUSSION—Strain at a point is defined by six components of strain:
point. Stress is expressed in force per unit of area (pounds-
three linear components and three shear components referred to a set of
force per square inch, megapascals, and so forth).
coordinate axes.
DISCUSSION—In the usual tension, compression, or torsion test it is DISCUSSION—As used in tension, compression, or shear tests pre-
customary to measure only one component of strain and to refer to this scribed in product specifications, stress is calculated on the basis of the
as “the strain.” In a tension or a compression test this is usually the original dimensions of the cross section of the specimen. This stress is
axial component. sometimes called “engineering stress,” to emphasize the difference
DISCUSSION—Strain has an elastic and a plastic component. For small from true stress.
strains the plastic component can be imperceptibly small.
–2
engineering stress, S [FL ], n—the stress calculated on the
DISCUSSION—Linear thermal expansion, sometimes called “thermal
basis of the original dimensions of the specimen.
strain,” and changes due to the effect of moisture are not to be
–2
considered strain in mechanical testing. nominal stress [FL ], n—the stress at a point calculated on the
net cross section by simple elastic theory without taking into
linear (tensile or compressive) strain, n—the chan
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