ASTM E1142-15(2020)
(Terminology)Standard Terminology Relating to Thermophysical Properties
Standard Terminology Relating to Thermophysical Properties
SCOPE
1.1 This is a compilation of terms and corresponding definitions commonly used in the study of thermophysical properties. Terms that are generally understood or defined adequately in other readily available sources are either not included or their sources identified.
1.2 A definition is a single sentence with additional information included in a Discussion.
1.3 Definitions of terms specific to a particular field (such as dynamic mechanical measurements) are identified with an italicized introductory phrase.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 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.
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Designation: E1142 − 15 (Reapproved 2020)
Standard Terminology
Relating to Thermophysical Properties
This standard is issued under the fixed designation E1142; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope absolute pressure, n—pressure measured relative to zero
pressure corresponding to empty space.
1.1 This is a compilation of terms and corresponding
DISCUSSION—Absolute pressure is atmospheric pressure plus gage
definitions commonly used in the study of thermophysical
pressure.
properties. Terms that are generally understood or defined
adequately in other readily available sources are either not
activation energy (E), n—inchemicalkinetics,theenergythat
included or their sources identified.
must be overcome in order for a chemical reaction to occur.
DISCUSSION—The term activation energy was introduced in 1889 by
1.2 A definition is a single sentence with additional infor-
SvanteArrhenius as a mathematical term in the eponymous, empirical
mation included in a Discussion.
relationship between temperature and reaction rate constant.
1.3 Definitionsoftermsspecifictoaparticularfield(suchas
admittance, Y, n—the reciprocal of impedance.
dynamic mechanical measurements) are identified with an
italicized introductory phrase.
alpha (α) loss peak, n—in dynamic mechanical measurement,
first peak in the damping curve below the melt, in order of
1.4 The values stated in SI units are to be regarded as
decreasing temperature or increasing frequency. E7
standard. No other units of measurement are included in this
standard.
amorphicity, n—a relative measure of amorphous material
1.5 This international standard was developed in accor-
content, expressed as a percent of the total material content.
dance with internationally recognized principles on standard-
angular frequency, ω, n—the number of radians per second
ization established in the Decision on Principles for the
traversedbyarotatingvectorthatrepresentsanyperiodically
Development of International Standards, Guides and Recom-
varying quantity.
mendations issued by the World Trade Organization Technical
DISCUSSION—Angular frequency, ω, is equal to two π times the
Barriers to Trade (TBT) Committee.
frequency, f.
2. Referenced Documents
anisotropic, adj—having different values for a property in
2.1 ASTM Standards:
different directions.
D4092 Terminology for Plastics: Dynamic Mechanical
anti-thixotropy, n—anincreaseoftheapparentviscosityunder
Properties
constant shear stress or shear rate followed by a gradual
E7Terminology Relating to Metallography
recovery when the stress or shear rate is reduced to zero.
E344Terminology Relating to Thermometry and Hydrom-
etry
arrhenius equation, n—a mathematical relationship between
E2744Test Method for Pressure Calibration of Thermal
the specific reaction rate constant and the temperature given
Analyzers
as:
2E/RT
k 5 Ae (1)
3. Terminology
3.1 Definitions:
where:
k = the reaction rate constant,
1 A = the pre-exponential factor,
This terminology is under the jurisdiction of ASTM Committee E37 on
E = the energy of activation,
ThermalMeasurementsandarethedirectresponsibilityofSubcommitteeE37.03on
Nomenclature and Definitions.
R = the gas constant, and
Current edition approved May 1, 2020. Published May 2020. Originally
T = the absolute temperature.
approved in 1988. Last previous edition approved in 2015 as E1142–15. DOI:
10.1520/E1142-15R20.
atmospheric pressure, n—the pressure due to the weight of
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
the atmosphere. E2744
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
DISCUSSION—Atmospheric pressure varies with elevation above sea
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. level, acceleration due to gravity, and weather conditions.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1142 − 15 (2020)
barometer, n—an instrument for measuring atmospheric pres-
G' = storage modulus, measured in shear,
G" = loss modulus, measured in shear,
sure.
K* = complex modulus, measured in compression,
beta (β) loss peak, n—in dynamic mechanical measurement,
K' = storage modulus, measured in compression
second discrete peak in damping curve below the melt, in
K" = loss modulus, measured in compression, and
order of decreasing temperature or increasing frequency.
i 5 21 , measured in compression.
œ
D4092
The complex modulus may be measured in tension or
flexure, (E*), compression, (K*), or in shear, (G*). D4092
boiling pressure, n—at a specific temperature, the value of the
vapor pressure of the liquid at which it is equal to the
complex shear compliance, J*, n—reciprocal of complex
external pressure.
shear modulus, where J* =1/G*. D4092
boiling temperature, n—at a specific pressure, the tempera-
complex tensile compliance, D*, n—reciprocal of complex
ture at which the vapor pressure of the liquid is equal to the
tensile modulus, where D*=1⁄E*. D4092
external pressure.
complex viscosity,η*,n—thecomplexmodulusdividedbythe
capacitance, n—that property of a system of conductors and
imposed frequency in rad/s.
dielectrics that permits the storage of electrical charge when
compliance, J, n—the strain divided by the corresponding
a potential difference exists between the conductors.
stress.
DISCUSSION—Capacitance is the ratio of a quantity of electric charge,
DISCUSSION—Compliance is the reciprocal of modulus.
Q, to a potential difference, V. A capacitance value is always positive.
The unit of capacitance is the farad, F, which is equivalent to one
composition, n—quantity of the components of a mixture;
coulomb per volt.
usually expressed in terms of the weight percentage, or the
catalyst, n—a substance that increases the rate of a chemical
atomic percentage of each of the components in the mixture.
reaction but is not consumed or changed by that reaction.
E7
Celsius, n—designation of the degree on the International
conductivity, electrical (volume), σ, n—the ratio of the
-2
Practical Temperature Scale; also used for the name of the
current density (A·cm ) through a specimen to the potential
scale, as “Celsius Temperature Scale.” Formerly (prior to
gradient (V/cm) in the same direction as the current.
1948) called “Centigrade.” The Celsius temperature scale is DISCUSSION—Conductivity is normally expressed in units
-1
(ohm·cm) , but the correct SI units are Siemen·m.
related to the International Kelvin Temperature Scale by the
equation: T =T−273.16K.
c
congruent phases, n—those states of matter of unique com-
position that co-exist at equilibrium at a single point in
Centigrade, n—see Celsius.
temperature and pressure; for example, the two coexisting
coeffıcient of expansion, n—see coefficient of linear thermal
phases of a two-phase equilibrium. E7
expansion.
congruent transformation, n—an isothermal, or isobaric,
coefficient of linear thermal expansion, α , n—change in
l
phasechangeinwhichbothofthephasesconcernedhavethe
length, relative to the length of the specimen, accompanying
same composition throughout the process; the order of a
a unit change of temperature, at a specified temperature.
system becomes unary at a composition of congruency. E7
coefficient of viscosity, n—the ratio between an infinitesimally
constitutional diagram, n—graphical representation of the
small increase in stress and the corresponding increase in
compositions, temperatures, pressures, or combinations
strain rate.
thereof at which the heterogeneous equilibria of a system
occur.
coefficient of volume thermal expansionα , n—for a solid or
v
liquid, the change in volume, relative to the volume of the
cooling curve, n—graphical representation of specimen tem-
specimen, accompanying a change of temperature at a
perature or temperature change as a function of time or
specified temperature.
decreasing environment temperature.
color temperature, n—temperature in degrees Kelvin (K) at
cooling rate, n—average slope of the time-temperature curve
whichablackbodymustbeoperatedtogiveacolorequalto
taken over a specific time and temperature interval as the
that of the source in question.
temperature is decreased.
complex modulus, E*, G*, or K*, n—ratio of the stress to
critical curve, n—in a binary, or higher order, phase diagram,
strain where each is a factor that may be represented by a
a locus of points along which two or more phases exist in
complex number as follows: E* = E' + iE", G* = G' + iG",
stable thermodynamic equilibrium.
and K* = K' + iK".
critical point, n—inabinaryphasediagram,thatspecificvalue
where:
of composition, temperature, pressure, or combinations
E* = complex modulus, measured in tension or flexure,
E' = storage modulus, measured in tension or flexure, thereof at which the phases of a heterogeneous equilibrium
E" = loss modulus, measured in tension or flexure,
become identical.
G* = complex modulus, measured in shear,
critical pressure, n—that pressure at the critical point.
E1142 − 15 (2020)
critical surface, n—inaternaryorhigherorderphasediagram, suitably charged dielectric to fall from its original value to
the area upon which the phases in equilibrium become 1/e of that value, due to the loss of dipole orientation.
DISCUSSION—Under conditions of an alternating applied field and in
identical. E7
systemswithasingledipolerelaxationtime,itisequalto1/ωattheloss
critical temperature, n—that temperature at the critical point.
factor peak in cases where the peak is caused by a dipole mechanism.
crystal, n—solid composed of atoms, ions, or molecules,
dissipation factor, n—see tangent delta.
arranged in a pattern which is periodic in three dimensions.
dissociation, n—as applied to heterogeneous equilibria, the
E7
transformationofonephaseintotwoormorenewphases,all
crystallinity, n—regulararrangementoftheatomsofasolidin
of different composition. E7
space.
dynamic modulus, n—see complex modulus.
DISCUSSION—In most materials, this state is usually imperfectly
achieved. The crystalline regions (ordered regions) are submicroscopic
elasticity, n—that property of materials that causes them to
volumes in which there is more or less regularity of arrangement of the
return to their original form or condition after the applied
component molecules.
force is removed. D4092
crystallite, n—crystalline grain not bounded by habit planes.
elastic limit, n—the greatest stress that can be applied to a
E7
material without permanent deformation.
crystallization, n—arrangement of previously disordered ma-
elastic modulus, n—the ratio of stress to corresponding strain
terial segments of repeating patterns into geometric symme-
within the elastic limit of the stress-strain curve.
try.
DISCUSSION—The elastic modulus may also be measured in tension
(E'), compression (K'), flexure (E'), or shear (G'). (See also complex
crystallization temperature, n—that temperature at which a
modulus.)
specimen undergoes crystallization upon cooling.
enthalpy, n—a thermodynamic function defined by the equa-
Curie point, n—see Curie temperature.
tion H= U +PV where H is the enthalpy, U is the internal
Curie temperature, n—temperature above which a ferromag-
energy, P is the pressure, and V the volume of the system.
netic or ferroelectric material becomes paramagnetic, or
DISCUSSION—At constant pressure the change in enthalpy measures
paraelectric, respectively. the quantity of heat exchanged by the system and its surrounding.
DISCUSSION—There may be more than one if there are multiple
equilibrium diagram, n—see constitutional diagram.
materials.
eutectic point, n—see eutectic.
damping, n—loss in energy, dissipated as heat, that results
when a material or material system is subjected to an
eutectic, adj—mixture of two or more substances which
oscillatory load or displacement. D4092
solidifies as a whole when cooled from the liquid state,
without change in composition.
devitrification, n—crystallization of an amorphous substance.
DISCUSSION—Thetemperatureatwhichtheeutecticmixturesolidifies
E7
is called the eutectic point. This temperature is constant for a given
composition, and represents the lowest melting point of the system.
dielectric constant, n—see permittivity, relative.
expansivity, n—the change in dimension resulting from an
dielectric dissipation factor, D, n—the ratio of the loss factor,
infinitesimal change in an independent variable (such as
ε", to the absolute permittivity, ε', or:
temperature or humidity).
" '
D 5 ε /ε (2)
DISCUSSION—The dielectric dissipation factor is numerically equal to
failure, n—the point beyond which a material ceases to be
thetangentofthedielectriclossangleandmaybereferredtoastheloss
functionally capable of its intended use.
tangent, tan δ, or the cotangent of the phase angle, θ.
failure criterion, n—specification of the chemical, physical,
dielectric loss angle, n—the angle whose tangent is the
mechanical, electrical, or other condition under which a
dissipation factor or arctan ε''/ε'.
materialceasestobefunctionallycapableofitsintendeduse.
DISCUSSION—It is also the difference between 90 degrees and the
phase angle.
failure temperature (T ), n—the temperature at which a
f
material fails.
differential thermocouple, n—see differential thermopile.
Fahrenheit, n—designation of a degree on the Fahrenheit
differential thermopile, n—a number of temperature sensors
temperaturescalethatisrelatedtotheInternationalPractical
connectedinseries-opposingandarrangedsothatthereisan
Temperature Scale by means of the equation:
increase in output signal for a given temperature difference
T 5 1.8 T 132 (3)
between alternate junctions maintained at a reference tem-
F C
perature and the measured temperature.
where:
dilatancy, n—the increase in volume caused by shear.
T = the temperature in degree Fahrenheit, and
F
T = the temperature in degrees Celsius.
C
dipole relaxation time, γ, n—the exponential decay time
required for the electric polarization of any point of a freezing temperature, n—see crystallization temperature.
E1142 − 15 (2020)
frequency, f, n—thenumberofcyclesperunittimeofperiodic invariant equilibrium, n—stable state among a number of
process. phases exceeding by two the number of components in the
system and in which more of the external variables
DISCUSSION—The unit is Hertz (Hz) which is equal to 1 cycle per/s.
(pressure, temperatures, or concentrations) may be varied
frequency profile, n—in dynamic mechanical meas
...
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: E1142 − 15 E1142 − 15 (Reapproved 2020)
Standard Terminology
Relating to Thermophysical Properties
This standard is issued under the fixed designation E1142; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This is a compilation of terms and corresponding definitions commonly used in the study of thermophysical properties.
Terms that are generally understood or defined adequately in other readily available sources are either not included or their sources
identified.
1.2 A definition is a single sentence with additional information included in a Discussion.
1.3 Definitions of terms specific to a particular field (such as dynamic mechanical measurements) are identified with an
italicized introductory phrase.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 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:
D4092 Terminology for Plastics: Dynamic Mechanical Properties
E7 Terminology Relating to Metallography
E344 Terminology Relating to Thermometry and Hydrometry
E2744 Test Method for Pressure Calibration of Thermal Analyzers
3. Terminology
3.1 Definitions:
absolute pressure, n—pressure measured relative to zero pressure corresponding to empty space.
DISCUSSION—
Absolute pressure is atmospheric pressure plus gage pressure.
activation energy (E), n—in chemical kinetics, the energy that must be overcome in order for a chemical reaction to occur.
DISCUSSION—
The term activation energy was introduced in 1889 by Svante Arrhenius as a mathematical term in the eponymous, empirical relationship between
temperature and reaction rate constant.
admittance, Y,n—the reciprocal of impedance.
alpha (α) loss peak, n—in dynamic mechanical measurement, first peak in the damping curve below the melt, in order of
decreasing temperature or increasing frequency. E7
This terminology is under the jurisdiction of ASTM Committee E37 on Thermal Measurements and are the direct responsibility of Subcommittee E37.03 on
Nomenclature and Definitions.
Current edition approved May 1, 2015May 1, 2020. Published June 2015May 2020. Originally approved in 1988. Last previous edition approved in 20142015 as
E1142 – 14b.E1142 – 15. DOI: 10.1520/E1142-15.10.1520/E1142-15R20.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1142 − 15 (2020)
amorphicity, n—a relative measure of amorphous material content, expressed as a percent of the total material content.
angular frequency, ω, n—the number of radians per second traversed by a rotating vector that represents any periodically varying
quantity.
DISCUSSION—
Angular frequency, ω, is equal to two π times the frequency, f.
anisotropic, adj—having different values for a property in different directions.
anti-thixotropy, n—an increase of the apparent viscosity under constant shear stress or shear rate followed by a gradual recovery
when the stress or shear rate is reduced to zero.
arrhenius equation, n—a mathematical relationship between the specific reaction rate constant and the temperature given as:
2E/RT
k 5 Ae (1)
where:
k = the reaction rate constant,
A = the pre-exponential factor,
E = the energy of activation,
R = the gas constant, and
T = the absolute temperature.
atmospheric pressure, n—the pressure due to the weight of the atmosphere. E2744
DISCUSSION—
Atmospheric pressure varies with elevation above sea level, acceleration due to gravity, and weather conditions.
barometer, n—an instrument for measuring atmospheric pressure.
beta (β) loss peak, n—in dynamic mechanical measurement, second discrete peak in damping curve below the melt, in order of
decreasing temperature or increasing frequency. D4092
boiling pressure, n—at a specific temperature, the value of the vapor pressure of the liquid at which it is equal to the external
pressure.
boiling temperature, n—at a specific pressure, the temperature at which the vapor pressure of the liquid is equal to the external
pressure.
capacitance, n—that property of a system of conductors and dielectrics that permits the storage of electrical charge when a
potential difference exists between the conductors.
DISCUSSION—
Capacitance is the ratio of a quantity of electric charge, Q, to a potential difference, V. A capacitance value is always positive. The unit of capacitance
is the farad, F, which is equivalent to one coulomb per volt.
catalyst, n—a substance that increases the rate of a chemical reaction but is not consumed or changed by that reaction.
Celsius, n—designation of the degree on the International Practical Temperature Scale; also used for the name of the scale, as
“Celsius Temperature Scale.” Formerly (prior to 1948) called “Centigrade.” The Celsius temperature scale is related to the
International Kelvin Temperature Scale by the equation: T = T − 273.16 K.
c
Centigrade,n—see Celsius.
coeffıcient of expansion,n—see coefficient of linear thermal expansion.
coefficient of linear thermal expansion, α ,n—change in length, relative to the length of the specimen, accompanying a unit
l
change of temperature, at a specified temperature.
coefficient of viscosity, n—the ratio between an infinitesimally small increase in stress and the corresponding increase in strain
rate.
coefficient of volume thermal expansion α ,n—for a solid or liquid, the change in volume, relative to the volume of the specimen,
v
accompanying a change of temperature at a specified temperature.
E1142 − 15 (2020)
color temperature, n—temperature in degrees Kelvin (K) at which a black body must be operated to give a color equal to that
of the source in question.
complex modulus, E*,G*, or K*,n—ratio of the stress to strain where each is a factor that may be represented by a complex
number as follows: E* = E' + iE", G* = G' + iG",E* = E' + iE", G* = G' + iG", and K* = K' + iK".K* = K' + iK".
where:
E* = complex modulus, measured in tension or flexure,
E' = storage modulus, measured in tension or flexure,
E9 = loss modulus, measured in tension or flexure,
E" = loss modulus, measured in tension or flexure,
G* = complex modulus, measured in shear,
G' = storage modulus, measured in shear,
G9 = loss modulus, measured in shear,
G" = loss modulus, measured in shear,
K* = complex modulus, measured in compression,
K' = storage modulus, measured in compression
K9 = loss modulus, measured in compression, and
K" = loss modulus, measured in compression, and
i 5 21 , measured in compression.
œ
The complex modulus may be measured in tension or flexure, (E*), compression, (K*), or in shear, (G*). D4092
complex shear compliance, J*,n—reciprocal of complex shear modulus, where J* = 1/G*. D4092
complex tensile compliance, D*,n—reciprocal of complex tensile modulus, where D* = 1 ⁄E*. D4092
complex viscosity, η*, n—the complex modulus divided by the imposed frequency in rad/s.
compliance, J,n—the strain divided by the corresponding stress.
DISCUSSION—
Compliance is the reciprocal of modulus.
composition, n—quantity of the components of a mixture; usually expressed in terms of the weight percentage, or the atomic
percentage of each of the components in the mixture. E7
−2-2
conductivity, electrical (volume), σ, n—the ratio of the current density (A·cm ) through a specimen to the potential gradient
(V/cm) in the same direction as the current.
DISCUSSION—
−1-1
Conductivity is normally expressed in units (ohm·cm) , but the correct SI units are Siemen·m.
congruent phases, n—those states of matter of unique composition that co-exist at equilibrium at a single point in temperature
and pressure; for example, the two coexisting phases of a two-phase equilibrium. E7
congruent transformation, n—an isothermal, or isobaric, phase change in which both of the phases concerned have the same
composition throughout the process; the order of a system becomes unary at a composition of congruency. E7
constitutional diagram, n—graphical representation of the compositions, temperatures, pressures, or combinations thereof at
which the heterogeneous equilibria of a system occur.
cooling curve, n—graphical representation of specimen temperature or temperature change as a function of time or decreasing
environment temperature.
cooling rate, n—average slope of the time-temperature curve taken over a specific time and temperature interval as the temperature
is decreased.
critical curve, n—in a binary, or higher order, phase diagram, a locus of points along which two or more phases exist in stable
thermodynamic equilibrium.
critical point, n—in a binary phase diagram, that specific value of composition, temperature, pressure, or combinations thereof at
which the phases of a heterogeneous equilibrium become identical.
critical pressure, n—that pressure at the critical point.
critical surface, n—in a ternary or higher order phase diagram, the area upon which the phases in equilibrium become identical.
E7
E1142 − 15 (2020)
critical temperature, n—that temperature at the critical point.
crystal, n—solid composed of atoms, ions, or molecules, arranged in a pattern which is periodic in three dimensions. E7
crystallinity, n—regular arrangement of the atoms of a solid in space.
DISCUSSION—
In most materials, this state is usually imperfectly achieved. The crystalline regions (ordered regions) are submicroscopic volumes in which there is
more or less regularity of arrangement of the component molecules.
crystallite, n—crystalline grain not bounded by habit planes. E7
crystallization, n—arrangement of previously disordered material segments of repeating patterns into geometric symmetry.
crystallization temperature, n—that temperature at which a specimen undergoes crystallization upon cooling.
Curie point,n—see Curie temperature.
Curie temperature, n—temperature above which a ferromagnetic or ferroelectric material becomes paramagnetic, or paraelectric,
respectively.
DISCUSSION—
There may be more than one if there are multiple materials.
damping, n—loss in energy, dissipated as heat, that results when a material or material system is subjected to an oscillatory load
or displacement. D4092
devitrification, n—crystallization of an amorphous substance. E7
dielectric constant,n—see permittivity, relative.
dielectric dissipation factor, D,n—the ratio of the loss factor, ε",ε", to the absolute permittivity, ε', or:
D 5ε"/ε' (2)
" '
D 5ε /ε (2)
DISCUSSION—
The dielectric dissipation factor is numerically equal to the tangent of the dielectric loss angle and may be referred to as the loss tangent, tan δ, or the
cotangent of the phase angle, θ.
dielectric loss angle, n—the angle whose tangent is the dissipation factor or arctan ε"/ε'.ε''/ε'.
DISCUSSION—
It is also the difference between 90 degrees and the phase angle.
differential thermocouple,n—see differential thermopile.
differential thermopile, n—a number of temperature sensors connected in series-opposing and arranged so that there is an increase
in output signal for a given temperature difference between alternate junctions maintained at a reference temperature and the
measured temperature.
dilatancy, n—the increase in volume caused by shear.
dipole relaxation time, γ, n—the exponential decay time required for the electric polarization of any point of a suitably charged
dielectric to fall from its original value to 1/e of that value, due to the loss of dipole orientation.
DISCUSSION—
Under conditions of an alternating applied field and in systems with a single dipole relaxation time, it is equal to 1/ω at the loss factor peak in cases
where the peak is caused by a dipole mechanism.
dissipation factor,n—see tangent delta.
E1142 − 15 (2020)
dissociation, n—as applied to heterogeneous equilibria, the transformation of one phase into two or more new phases, all of
different composition. E7
dynamic modulus,n—see complex modulus.
elasticity, n—that property of materials that causes them to return to their original form or condition after the applied force is
removed. D4092
elastic limit, n—the greatest stress that can be applied to a material without permanent deformation.
elastic modulus, n—the ratio of stress to corresponding strain within the elastic limit of the stress-strain curve.
DISCUSSION—
The elastic modulus may also be measured in tension (E ´), '), compression (K ´), '), flexure (E ´), '), or shear (G ´). '). (See also complex modulus.)
enthalpy, n—a thermodynamic function defined by the equation H = U + PV where H is the enthalpy, U is the internal energy,
P is the pressure, and V the volume of the system.
DISCUSSION—
At constant pressure the change in enthalpy measures the quantity of heat exchanged by the system and its surrounding.
equilibrium diagram,n—see constitutional diagram.
eutectic point,n—see eutectic.
eutectic, adj—mixture of two or more substances which solidifies as a whole when cooled from the liquid state, without change
in composition.
DISCUSSION—
The temperature at which the eutectic mixture solidifies is called the eutectic point. This temperature is constant for a given composition, and represents
the lowest melting point of the system.
expansivity, n—the change in dimension resulting from an infinitesimal change in an independent variable (such as temperature
or humidity).
failure, n—the point beyond which a material ceases to be functionally capable of its intended use.
failure criterion, n—specification of the chemical, physical, mechanical, electrical, or other condition under which a material
ceases to be functionally capable of its intended use.
failure temperatur
...
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