IEC 60216-6:2022

IEC 60216-6 ®
Edition 3.0 2022-11
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Electrical insulating materials – Thermal endurance properties –
Part 6: Determination of thermal endurance indices (TI and RTE RTI) of an
insulating material using the fixed time frame method

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IEC 60216-6 ®
Edition 3.0 2022-11
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Electrical insulating materials – Thermal endurance properties –
Part 6: Determination of thermal endurance indices (TI and RTE RTI) of an
insulating material using the fixed time frame method
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 17.220.99; 29.035.01 ISBN 978-2-8322-6173-6
– 2 – IEC 60216-6:2022 RLV © IEC 2022
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 7
3 Terms, definitions, symbols and abbreviated terms . 8
3.1 Terms and definitions. 8
3.2 Symbols and abbreviated terms . 11
4 FTFM protocol . 13
4.1 Principles of FTFM protocol . 13
4.2 Objective of FTFM protocol . 13
5 TI determination . 13
5.1 Ageing procedures . 13
5.2 Ageing times and temperatures . 14
5.3 Test specimens . 14
5.3.1 Preparation . 14
5.3.2 Number of specimens . 14
5.4 Diagnostic tests . 15
5.5 Selection of end-points . 15
5.6 Establishment of initial property value . 15
5.7 Ageing conditions . 16
5.7.1 Ageing ovens . 16
5.7.2 Environmental conditions . 16
5.7.3 Conditions for property measurement . 16
5.8 Procedure for ageing . 16
6 Calculation procedures . 17
6.1 General principles . 17
6.1.1 Thermal endurance calculation . 17
6.1.2 Property value – equivalent temperature transform (Calculation of
hypothetical ageing temperature derived from the value of a property) . 17
6.2 Precision of calculations . 18
6.3 Derivation of temperatures equivalent to property values . 18
6.3.1 General . 18
6.3.2 Preliminary calculations . 18
6.3.3 Regression calculations (property on temperature) . 18
6.3.4 Linearity test . 20
6.3.5 Estimation of end-point temperatures equivalent to property values . 21
6.4 Regression analysis (temperature on time) . 21
6.4.1 General . 21
6.4.2 Group means and variances . 22
6.4.3 General means and variances . 22
6.4.4 Regression . 23
6.5 Statistical tests . 23
6.5.1 Variance equality test . 23
6.5.2 Linearity test (F-test) . 24
6.5.3 Estimates of x and y and their confidence limits . 25
6.6 Thermal endurance graph . 26
7 Calculation and requirements for results . 26

– 3 – IEC 60216-6:2022 RLV © IEC 2022

7.1 Calculation of thermal endurance characteristics . 26
7.2 Reporting of results. 27
7.2.1 Summary of statistical tests and reporting . 27
7.2.2 Report format . 27
8 Report . 28
9 RTE RTI determination . 28
10 Additional symbols . 28
11 Experimental procedures . 29
11.1 Selection of control material reference EIM . 29
11.2 Selection of diagnostic test for extent of ageing . 29
11.3 Ageing procedures . 29
12 Calculation procedures . 30
12.1 General principles . 30
12.2 Input data . 30
12.3 RTE RTI. 30
12.4 Confidence limits . 31
12.5 Extrapolation . 33
13 Results and report . 33
13.1 Results of statistical and numerical tests . 33
13.2 Result . 33
13.3 Report . 33
Annex A (normative) Decision flow chart . 34
Annex B (normative) Decision table . 36
Annex C (informative) Statistical tables . 37
Annex D (informative) Suggested ageing times and temperatures . 41
D.1 TI determination . 41
D.1.1 Correlation time (TI) = 20 000 h . 41
D.1.2 Other correlation times for TI calculation (see 12.3) . 41
D.2 RTE RTI determination . 41
Annex E (informative) Figures . 43
Annex F (normative) Statistical significance of the difference between two regression

estimates . 46
Annex G (informative) Computer programs for IEC 60216-6 . 47
G.1 General . 54
G.1.1 Overview . 54
G.1.2 Convenience program execution . 55
G.2 Data files . 56
G.2.1 Content of file Control6.ftd . 57
G.2.2 Report . 59
G.2.3 Thermal endurance graph . 61

Figure A.1 – Decision flow chart . 35
Figure E.1 – Property-temperature graph with regression line . 43
Figure E.2 – Thermal endurance graph . 43
Figure E.3 – Ageing times and temperatures in relation to thermal endurance graph . 44
Figure E.4 – Ageing times and temperatures in relation to thermal endurance graph . 44
Figure E.5 – Ageing times and temperatures in relation to thermal endurance graph . 45

– 4 – IEC 60216-6:2022 RLV © IEC 2022
Figure G.1 – Shortcut property dialog for program launch . 56
Figure G.2 – Thermal endurance graph . 61

Table 1 – Intermediate data values . 30
Table B.1 – Decision table . 36
Table C.1 – χ -function . 37
Table C.2 – t-function . 37
Table C.3 – F-function, P = 0,05 . 38
Table C.4 – F-function, P = 0,005. 39
Table D.1 – Ageing temperatures and times. 41

– 5 – IEC 60216-6:2022 RLV © IEC 2022

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICAL INSULATING MATERIALS –
THERMAL ENDURANCE PROPERTIES –

Part 6: Determination of thermal endurance indices (TI and RTE RTI)
of an insulating material using the fixed time frame method

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
This redline version of the official IEC Standard allows the user to identify the changes made to
the previous edition IEC 60216-6:2006. A vertical bar appears in the margin wherever a change
has been made. Additions are in green text, deletions are in strikethrough red text.

– 6 – IEC 60216-6:2022 RLV © IEC 2022
IEC 60216-6 has been prepared by IEC technical committee 112: Evaluation and qualification
of electrical insulating materials and systems. It is an International Standard.
This third edition cancels and replaces the second edition published in 2006. This
edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) clarification of definition of index properties vs. endurance properties;
b) complete rework of Annex G and the corresponding program.
The text of this International Standard is based on the following documents:
Draft Report on voting
112/583/FDIS 112/589/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
A list of all parts in the IEC 60216 series, published under the general title Electrical insulating
materials – Thermal endurance properties, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The "colour inside" logo on the cover page of this document indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.

– 7 – IEC 60216-6:2022 RLV © IEC 2022

ELECTRICAL INSULATING MATERIALS –
THERMAL ENDURANCE PROPERTIES –

Part 6: Determination of thermal endurance indices (TI and RTE RTI)
of an insulating material using the fixed time frame method

1 Scope
This part of IEC 60216 specifies the experimental and calculation procedures for deriving the
thermal endurance characteristics, temperature index (TI) and relative thermal endurance index
(RTE) relative temperature index (RTI) of an electrical insulating material (EIM) using the “fixed
time frame method (FTFM)”.
In this protocol, the ageing takes place for a small number of fixed times, using the appropriate
number of ageing temperatures throughout each time, the properties of the specimens being
measured at the end of the relevant time interval. This differs from the procedure of IEC 60216-
1, where ageing is conducted at a small number of fixed temperatures, property measurement
taking place after ageing times dependent on the progress of ageing.
The diagnostic tests employed in the fixed time frame method are restricted to destructive tests.
The method has not yet been applied to non-destructive or proof test procedures.
Both the TI and the RTE RTI determined according to the FTFM protocol are derived from
experimental data obtained in accordance with the instructions of IEC 60216-1 and IEC 60216-2
as modified in this part of IEC 60216. The calculation procedures and statistical tests are
modified from those of IEC 60216-3 and IEC 60216-5.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60212, Standard conditions for use prior to and during the testing of solid electrical
insulating materials
IEC 60216-1:20012013, Electrical insulating materials – Thermal endurance properties – Part
1: Ageing procedures and evaluation of test results
IEC 60216-2, Electrical insulating materials – Thermal endurance properties – Part 2:
Determination of thermal endurance properties of electrical insulating materials – Choice of test
criteria
IEC 60216-3:20022021, Electrical insulating materials – Thermal endurance properties – Part
3: Instructions for calculating thermal endurance characteristics
IEC 60216-4-1, Electrical insulating materials – Thermal endurance properties – Part 4-1:
Ageing ovens – Single-chamber ovens
IEC 60216-4-2, Electrical insulating materials – Thermal endurance properties – Part 4-2:
Ageing ovens – Precision ovens for use up to 300 °C

– 8 – IEC 60216-6:2022 RLV © IEC 2022
IEC 60216-4-3, Electrical insulating materials – Thermal endurance properties – Part 4-3:
Ageing ovens – Multi-chamber ovens
IEC 60216-5:2022, Electrical insulating materials – Thermal endurance properties – Part 5:
Determination of relative thermal endurance index (RTE) relative temperature index (RTI) of
an insulating material
IEC 60493-1:1974, Guide for the statistical analysis of ageing test data – Part 1: Methods based
on mean values of normally distributed test results
3 Terms, definitions, symbols and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1.1
electrical insulating material
EIM
material of low electric conductivity, used to separate conducting parts at different electric
potentials or to isolate such parts from the surroundings
3.1.2
assessed thermal endurance index
ATE
numerical value of the temperature in degrees Celsius, up to which the control material
possesses known, satisfactory service performance in the specified application
NOTE 1 The ATE of a specific material may vary between different applications of the material.
NOTE 2 ATE is sometimes referred to as “absolute” thermal endurance index.
3.1.2
assessed temperature index
ATI
numerical value of the temperature index in degrees Celsius of the reference EIM
Note 1 to entry: The ATI of a specific material may vary between different applications of the material.
3.1.3
ageing temperature
temperature in degrees Celsius at which a group of specimens is thermally aged
3.1.4
end-point temperature
temperature in degrees Celsius at which a specimen is considered to have reached end-point
after ageing for a specified time

– 9 – IEC 60216-6:2022 RLV © IEC 2022

3.1.5
candidate material EIM
material for which an estimate of the thermal endurance is required to be determined
Note 1 to entry: The determination is made by simultaneous thermal ageing of the material and a control material
reference EIM.
3.1.6
central second moment of a data group
sum of the squares of the differences between the data values and the value of the group mean
divided by the number of data items in the group
3.1.7
95 % confidence limit
statistical parameter, calculated from test data, which with 95 % confidence constitutes an
upper or lower limit for the true value of a quantity estimated by statistical analysis
Note 1 to entry: This implies that there is only 5 % probability that the true value of the quantity estimated is actually
larger (or smaller) than the upper (or lower) confidence limit.
Note 2 to entry: In other connections, confidence values other than 95 % may sometimes be used, e.g. in the
linearity test for destructive test data.
3.1.8
control material reference EIM
material with known assessed thermal endurance index (ATE), preferably derived from service
experience, used as a reference for comparative tests with the candidate material EIM
3.1.9
correlation coefficient
number expressing the completeness of the relation between members of two data sets, equal
to the covariance divided by the square root of the product of the variances of the sets
Note 1 to entry: The value of its square is between 0 (no correlation) and 1 (complete correlation).
Note 2 to entry: In this standard, the two data sets are the values of the independent variable and the means of the
corresponding dependent variable groups.
3.1.10
correlation time (RTE) for RTI
estimated time to end-point of the control material reference EIM at a temperature equal to its
ATE ATI in degrees Celsius
τ
Note 1 to entry: In this document, it is expressed by symbol , see Clause 10.
c
3.1.11
correlation time for TI
hypothetical time to end-point used to calculate TI
Note 1 to entry: Its usual value is 20 000 h, see Clause D.1.
3.1.12
covariance,
for two sets of data with equal numbers of elements where each element in one set corresponds
to one in the other, sum of the products of the deviations of the corresponding members from
their set means, divided by the number of degrees of freedom
3.1.13
degrees of freedom
number of data values minus the number of parameter values

– 10 – IEC 60216-6:2022 RLV © IEC 2022
3.1.14
destructive test
diagnostic property test, where the test specimen is irreversibly changed by the property
measurement, in a way which precludes a repeated measurement on the same specimen
Note 1 to entry: An example of a destructive test is the measurement of electric strength. An example of a non-
destructive test is the measurement of tg dissipation factor tan δ.
3.1.15
end-point line
line parallel to the temperature axis intercepting the property axis at the end-point value
3.1.16
halving interval
HIC
numerical value of the temperature interval in Kelvin which expresses the halving of the time to
end-point taken at a time equal to TI
3.1.17
regression analysis
process of deducing the best fit line expressing the relation of corresponding members of two
data groups by minimizing the sum of squares of deviations of members of one of the groups
from the line
3.1.18
regression coefficients
coefficients of the equation of the best fit line derived by regression analysis
3.1.18
relative thermal endurance index
RTE
estimate of the thermal endurance of a candidate material, made by thermal ageing
simultaneously with the control material, as described in this standard
NOTE The value of RTE is the value of the temperature in degrees Celsius at which the estimated time to end-point
of the candidate material is the same as the estimated time to end-point of the control material at a temperature
equal to its ATE.
3.1.19
relative temperature index
RTI
determined by test in relation to the thermal performance of a known reference EIM
3.1.20
significance
probability of a value of a statistical function greater than a specified value
Note 1 to entry: The value is equal to (1–p) where p is the cumulative distribution function value. Significance is
conventionally printed in upper case (P).
3.1.21
standard deviation
square root of the variance of a data group or sub-group
3.1.22
standard error of an estimate of the true value of a data group property
value of the standard deviation of the hypothetical sampling population of which the group
property may be considered to be a member
Note 1 to entry: For an estimate of the group mean, the standard error is equal to the group standard deviation
divided by the square root of the number of data items in the group, and indicates the uncertainty in the estimate of
the true value of the mean. This standard is concerned only with means and the difference between two means.

– 11 – IEC 60216-6:2022 RLV © IEC 2022

3.1.23
temperature index
TI
numerical value of the temperature in degrees Celsius derived from the thermal endurance
relationship at a time of 20 000 h (or other specified time) determined by test by itself
Note 1 to entry: This rating is based on 20 000 h life, unless otherwise specified, based on one of the end-of-life
criteria listed in IEC 60216-2.
3.1.24
temperature group,
number of specimens being exposed together to thermal ageing at the same temperature in the
same oven
Note 1 to entry: Where there is no risk of ambiguity, either temperature groups or test groups may be referred to
simply as “groups”.
3.1.25
test group,
number of specimens removed together from a temperature group for destructive testing
Note 1 to entry: Where there is no risk of ambiguity, either temperature groups or test groups may be referred to
simply as “groups”.
3.1.26
thermal endurance graph
graph in which the logarithm of the time to reach a specified end-point in a thermal endurance
test is plotted against the reciprocal thermodynamic (absolute) test temperature
3.1.27
thermal endurance graph paper
graph paper having a logarithmic time scale as the ordinate and values proportional to the
reciprocal of the thermodynamic (absolute) temperature as the abscissa
Note 1 to entry: The ordinate is usually graduated in powers of ten (from 10 h to 100 000 h is often a convenient
range). The abscissa is usually graduated in a non-linear (Celsius) temperature scale oriented with temperature
increasing from left to right.
3.1.28
time group,
all test groups removed for testing at the same time
3.1.29
variance of a data group
sum of the squares of the deviations of the data from a reference level defined by one or more
parameters divided by the number of degrees of freedom
Note 1 to entry: The reference level may can, for example be a mean value (1 parameter) or a line (2 parameters,
here intercept on the axis of the independent variable and slope).
3.2 Symbols and abbreviated terms
The following symbols are used in the calculations of Clauses 6, 7, 12 and Annex A, Annex B
and Annex C.
Symbol Description Clause
a Regression coefficient: intercept of regression line with x-axis 6.4.4
b Regression coefficient: slope of regression line relative to y-axis 6.4.4
6.5.3
ˆ
b
r
Y
Parameter derived from b for calculation of
c
b
p Regression coefficient for destructive test calculations 6.3.5

– 12 – IEC 60216-6:2022 RLV © IEC 2022
Symbol Description Clause
6.5.1
c
Parameter in calculation of χ
6.3.4,
F F-distributed variance ratio for linearity test
6.5.2
g, h, i, j Indexing parameters for regression calculations 6.3, 6.4
HIC Halving interval 7.1
k Number of ageing times 6.1.1
Total number of x values 6.4.3
N
ij
n Number of x values in time group i 6.1.1
i ij
Annex A,
Annex B
P Significance of the value of a statistical test function
and
Annex C
p 6.3
End-point property value
e
p 6.3
Property value h in temperature group g (time group i implied)
gh
6.3
p
Mean property value in temperature group g (time group i implied)

g
6.5.1
q Base of logarithms in calculation of χ
r Number of temperature groups selected in time group i 6.3.3
6.4.4
r Square of correlation coefficient
6.5.2
Total (non-regression) variance of x-values
s
2 Variance of property values in temperature group g (time group i 6.3.3
s
1g
implied)
6.5.2
Value of s adjusted to allow for acceptable non-linearity
s
a
6.5.3
2 ˆ
Y
Parameter derived from s for calculation of
s
c
r
t Student's t-distributed stochastic variable 6.5.3
7.1
TC, TC
a s
Lower confidence limit of TI or TI (see above)
a
a
t 6.5.3
Value of t with probability p and N degrees of freedom
p,N
x 6.3.5
Value of x, index number j, in time group i
ij
x
General mean of x-values 6.4.3
6.5.3
ˆˆ
XX, Estimate of x, and its confidence limit

c
y 6.1.1
Value of y for time group i
i
y
General mean of y-values 6.4.3
ˆˆ 6.5.3
YY,
Estimate of y, and its confidence limit
c
Reciprocal kelvin temperature for 6.1.1
z
ϑ
ij ij
nd
µ (y)
6.4.3
2 Central 2 moment of y values

Total number of property values in time group (i implied) 6.3.3
ν
2 2
6.5.1
χ χ distributed variable for variance equality (Bartlett's) test

ϑ
ij
Ageing temperature for specimen group j in time group i 6.1.1

– 13 – IEC 60216-6:2022 RLV © IEC 2022

Symbol Description Clause
Θ
6.1.1
0 273,15 K (corresponding to 0 °C)

τ
Ageing time for time group i 6.1.1
i
4 FTFM protocol
4.1 Principles of FTFM protocol
The FTFM (fixed time frame method) protocol is based upon the principle that thermal ageing
for determination of thermal endurance characteristics is carried out over a small number of
fixed times, with a sufficient range of ageing temperatures at each time to ensure that the
property values determined reach the end-point in a satisfactory manner.
In this it differs from the fixed temperature frame procedure of IEC 60216-1, where a small
number of ageing temperatures is employed, with ageing being carried out with testing at
intervals, until the end-point has been reached.
4.2 Objective of FTFM protocol
The objective of The protocol is to shall achieve the following advantages:
The determination of thermal endurance characteristics is completed in a fixed, predetermined
time.
This enables much more efficient planning of the determination and will often have substantial
commercial advantage. A simple TI determination will can be completed in 5 kh, whereas by
the fixed temperature frame procedure, it may can be necessary for ageing to be considerably
prolonged past this time to achieve the end-point at the lowest chosen ageing temperature.
Each temperature to end-point (i.e. time-group mean) in the thermal endurance regression is
based on the temperatures selected in a time group. The number of temperatures selected may
be any number between three and the number of temperature groups in a time group.
Since the largest source of systematic error in the fixed temperature frame procedure is
temperature error (actual indication error or temperature distribution error), systematic errors
can be considerably reduced. Errors from this source can lead to results which are either
inaccurate or invalid through incorrect assessment of linearity.
5 TI determination
5.1 Ageing procedures
Each test procedure shall specify the shape, dimensions and number of the test specimens, the
times of exposure, the property to which TI is related, the methods of its determination, the end-
point, and the derivation of the thermal endurance characteristics from the experimental data.
The chosen property should, if possible, reflect in a significant fashion a function of the material
EIM in practical use. A choice of properties is given in IEC 60216-2.
To provide uniform conditions, the conditioning of specimens after removal from the oven and
before measurement may need to should be specified.

– 14 – IEC 60216-6:2022 RLV © IEC 2022
5.2 Ageing times and temperatures
In the majority of cases, the required thermal endurance characteristics are for a projected
duration of 20 000 h. However, there is often a need for such information related to other, longer
or shorter times. In cases of longer times, the times given as requirements or recommendations
in the text of this standard (e.g. 5 kh for the minimum value of the longest ageing time) shall be
increased in the ratio of the actual specification time to 20 kh.
In cases of shorter specification times, the related times may be decreased in the same ratio if
necessary.
Particular care will be needed for very short specification times, since the higher ageing
temperatures may can lead into temperature regions which include transition points, e.g. glass
transition temperature or partial melting, with consequent non-linearity. Very long specification
times may can also lead to non-linearity.
Recommendations for ageing times and temperatures are given in Annex D and illustrated in
Figure E.3 to Figure E.5.
5.3 Test specimens
5.3.1 Preparation
The specimens used for the ageing test shall constitute a random sample from the population
investigated and shall be treated uniformly.
Since processing conditions may significantly affect the ageing characteristics of some
materials EIMs, it shall be ensured that, for example, sampling, cutting sheet from the supply
roll, cutting of anisotropic material in a given direction, moulding, curing, preconditioning, are
performed in the same manner for all specimens.
The material specifications or the standards for the diagnostic test methods will contain all
necessary instructions for the preparation of specimens.
The thickness of specimens is in some cases specified in the list of property measurements for
the determination of thermal endurance. See IEC 60216-2. If not, the thickness shall be
reported. Some physical properties are sensitive even to minor variations of specimen
thickness. In such cases the thickness after each ageing period may need to be determined
and reported if required in the relevant specification.
The thickness is also important because the rate of ageing may can vary with thickness. Ageing
data of materials EIMs with different thicknesses are not always comparable. Consequently, a
material may an EIM can be assigned more than one thermal endurance characteristic derived
from the measurement of properties at different thicknesses.
The tolerances of specimen dimensions shall be the same as those normally used for general
testing. Where specimen dimensions need smaller tolerances than those normally used, these
special tolerances shall be given.
Screening measurements ensure that specimens are of uniform quality and typical of the
material EIM to be tested.
5.3.2 Number of specimens
The accuracy of endurance test results depends largely on the number of specimens aged at
each temperature.
The total number of specimens (N) is derived as follows:

– 15 – IEC 60216-6:2022 RLV © IEC 2022

N = a × b × c + d
where
a is the number of specimens in a test group undergoing identical treatment at one
temperature and discarded after determination of the property (usually five);
b is the number of treatments, i.e. total number of exposure temperatures, at one time;
c is the number of ageing time levels;
d is the number of specimens in the group used to establish the initial value of the property.
Normal practice is to select d = 2a when the diagnostic criterion is a percentage change of
the property from its initial level. When the criterion is an absolute property level, d is usually
given the value of zero, unless reporting of the initial value is required.
It is good practice to prepare additional specimens, or at least to provide a reserve from the
original material batch from which such specimens may can subsequently be prepared. In this
way any required ageing of additional specimens in case of unforeseen complications will
introduce a minimum risk of producing systematic differences between groups of specimens.
Such complications may can arise, for example, if the thermal endurance relationship turns out
to be non-linear, or if specimens are lost due to thermal runaway of an oven.
5.4 Diagnostic tests
If IEC material specifications are available, property requirements in terms of acceptable lower
limits of TI values are usually given. If such material specifications are not available, a selection
of properties and methods for the evaluation of thermal endurance is given in IEC 60216-2.
If such a method cannot be found, an international, national or institution standard or a specially
devised method should be used in that order of preference. In this case, the diagnostic test
shall be stated in the report, including the property, measurement procedure and end-point.
5.5 Selection of end-points
The thermal endurance of materials may need to EIMs can be characterized by different
endurance data (derived using different properties and/or end-points), in order to facilitate the
adequate selection of the material in respect of its particular application. See IEC 60216-2.
There are two alternative ways in which the end-point may can be defined:
a) as a percentage increase or decrease in the measured value of the property from the original
level. This approach will provide comparisons among materials EIMs but bears a poorer
relationship than item b) to the property values required in normal service. For the
determination of the initial value, see 5.6;
b) as a fixed value of the property. This value might be selected with respect to usual service
requirements. End-points of proof tests are predominantly given in the form of fixed values
of the property.
The end-point should be selected to indicate a deg
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