EN IEC 62506:2023

SLOVENSKI STANDARD
01-februar-2024
Metode za pospešeno preskušanje proizvodov (IEC 62506:2023)
Methods for product accelerated testing (IEC 62506:2023)
Verfahren für beschleunigte Produktprüfungen (IEC 62506:2023)
Méthodes d'essais accélérés de produits (IEC 62506:2023)
Ta slovenski standard je istoveten z: EN IEC 62506:2023
ICS:
03.120.01 Kakovost na splošno Quality in general
19.020 Preskuševalni pogoji in Test conditions and
postopki na splošno procedures in general
21.020 Značilnosti in načrtovanje Characteristics and design of
strojev, aparatov, opreme machines, apparatus,
equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 62506

NORME EUROPÉENNE
EUROPÄISCHE NORM December 2023
ICS 03.120.01; 21.020 Supersedes EN 62506:2013
English Version
Methods for product accelerated testing
(IEC 62506:2023)
Méthodes d'essais accélérés de produits Verfahren für beschleunigte Produktprüfungen
(IEC 62506:2023) (IEC 62506:2023)
This European Standard was approved by CENELEC on 2023-12-12. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2023 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 62506:2023 E
European foreword
The text of document 56/2000/FDIS, future edition 2 of IEC 62506, prepared by IEC/TC 56
"Dependability" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2024-09-12
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2026-12-12
document have to be withdrawn
This document supersedes EN 62506:2013 and all of its amendments and corrigenda (if any).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 62506:2023 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standard indicated:
IEC 62740:2015 NOTE Approved as EN 62740:2015 (not modified)
IEC 60812 NOTE Approved as EN IEC 60812
IEC 61163-2 NOTE Approved as EN IEC 61163-2
IEC 60300-3-4 NOTE Approved as EN IEC 60300-3-4
IEC 60068 (series) NOTE Approved as EN 60068 (series)
IEC 61014 NOTE Approved as EN 61014
IEC 61163-1 NOTE Approved as EN 61163-1
IEC 61164:2004 NOTE Approved as EN 61164:2004 (not modified)
IEC 61125:2018 NOTE Approved as EN IEC 61125:2018 (not modified)
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
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.
NOTE 1 Where an International Publication has been modified by common modifications, indicated by (mod), the
relevant EN/HD applies.
NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cencenelec.eu.
Publication Year Title EN/HD Year
IEC 60050-192 - International electrotechnical vocabulary - - -
Part 192: Dependability
IEC 60300-3-5 - Dependability management - Part 3-5: - -
Application guide - Reliability test
conditions and statistical test principles
IEC 60605-2 - Equipment reliability testing - Part 2: - -
Design of test cycles
IEC 60721 series Classification of environmental conditions EN 60721 series
IEC 61123 2019 Reliability testing - Compliance test plans EN IEC 61123 2020
for success ratio
IEC 61124 2023 Reliability testing - Compliance tests for EN IEC 61124 2023
constant failure rate and constant failure
intensity
IEC 61649 2008 Weibull analysis EN 61649 2008
IEC 61709 - Electric components - Reliability - EN 61709 -
Reference conditions for failure rates and
stress models for conversion
IEC 61710 - Power law model - Goodness-of-fit tests EN 61710 -
and estimation methods
IEC 62429 - Reliability growth - Stress testing for early EN 62429 -
failures in unique complex systems

IEC 62506 ®
Edition 2.0 2023-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Methods for product accelerated testing
Méthodes d'essais accélérés de produits
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 03.120.01, 21.020 ISBN 978-2-8322-7727-0
– 2 – IEC 62506:2023 © IEC 2023
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms, definitions, symbols and abbreviated terms . 9
3.1 Terms and definitions . 9
3.2 Symbols and abbreviated terms . 11
4 General description of the accelerated test methods . 12
4.1 Cumulative damage model . 12
4.2 Classification, methods and types of test acceleration . 14
4.2.1 General . 14
4.2.2 Type A: qualitative accelerated tests . 15
4.2.3 Type B: quantitative accelerated tests . 15
4.2.4 Type C: quantitative time and event compressed tests . 16
5 Accelerated test models . 17
5.1 Type A, qualitative accelerated tests . 17
5.1.1 Highly accelerated limit tests (HALT) . 17
5.1.2 Highly accelerated stress test (HAST) . 21
5.1.3 Highly accelerated stress screening or audit (HASS or HASA) . 22
5.1.4 Engineering aspects of HALT and HASS . 23
5.2 Types B and C – Quantitative accelerated test methods. 23
5.2.1 Purpose of quantitative accelerated testing . 23
5.2.2 Physical basis for the quantitative accelerated Type B test methods . 23
5.2.3 Type C tests, time (C ) and event (C ) compression . 25
1 2
5.3 Failure mechanisms and test design . 27
5.4 Determination of stress levels, profiles and combinations in use and test –
Stress modelling . 27
5.4.1 General . 27
5.4.2 Step-by-step procedure . 28
5.5 Multiple stress acceleration methodology – Type B tests . 28
5.6 Single and multiple stress acceleration for Type B tests . 31
5.6.1 Single stress acceleration methodology . 31
5.6.2 Stress models with stress varying as a function of time – Type B tests . 38
5.6.3 Stress models that depend on repetition of stress applications – Fatigue
models. 40
5.6.4 Other acceleration models . 41
5.7 Acceleration of quantitative reliability tests. 42
5.7.1 Reliability requirements, goals, and use profile . 42
5.7.2 Accelerated testing for reliability demonstration or life tests . 44
5.7.3 Testing of components for a reliability measure . 55
5.7.4 Reliability measures for components and systems . 56
5.8 Accelerated reliability compliance or evaluation tests . 57
5.9 Accelerated reliability growth testing . 58
5.10 Guidelines for accelerated testing . 59
5.10.1 Accelerated testing for multiple stresses and the known use profile . 59
5.10.2 Level of accelerated stresses . 59
5.10.3 Accelerated reliability and verification tests . 59

IEC 62506:2023 © IEC 2023 – 3 –
6 Accelerated testing strategy in product development . 60
6.1 Accelerated testing sampling plan . 60
6.2 General discussion about test stresses and durations . 60
6.3 Testing components for multiple stresses. 61
6.4 Accelerated testing of assemblies . 61
6.5 Accelerated testing of systems . 61
6.6 Analysis of test results . 62
7 Limitations of accelerated testing methodology . 62
Annex A (informative) Highly accelerated limit test (HALT) . 63
A.1 HALT procedure . 63
A.2 HALT step-by-step procedure . 63
A.3 Example 1 – HALT test results for a DC/DC converter. 65
A.4 Example 2 – HALT test results for a medical item . 65
A.5 HALT test results for a Hi-Fi equipment . 67
Annex B (informative) Accelerated reliability compliance and growth test design . 68
B.1 Use environment and test acceleration . 68
B.2 Determination of stresses and stress duration . 68
B.3 Overall acceleration of a reliability test . 69
B.4 Example of reliability compliance test design assuming constant failure rate
or failure intensity . 70
B.4.1 General . 70
B.4.2 Thermal cycling . 71
B.4.3 Thermal exposure, thermal dwell . 72
B.4.4 Humidity . 72
B.4.5 Vibration test . 73
B.4.6 Accelerations summary and overall acceleration . 73
B.5 Example of reliability compliance test design assuming non-constant failure

rate or failure intensity (wear-out) . 75
Annex C (informative) Estimating the activation energy, E . 76
a
Annex D (informative) Calibrated accelerated life testing (CALT) . 78
D.1 Purpose of test . 78
D.2 Test execution . 78
Annex E (informative) Example of how to estimate empirical factors . 80
Annex F (informative) Determination of acceleration factors by testing to failure . 83
F.1 Failure modes and acceleration factors . 83
F.2 Example of determination of acceleration factor . 83
Annex G (informative) Median rank tables 95 % rank . 87
Bibliography . 89

Figure 1 – Probability density functions (PDF) for cumulative damage, degradation,
and test types . 13
Figure 2 – Relationship of PDFs of the item strength versus load in use . 18
Figure 3 – How HALT tests detect the design margin . 19
Figure 4 – PDFs of operating and destruct limits as a function of applied stress . 20
Figure 5 – Line plot for Arrhenius reaction model . 35
Figure 6 – Plot for determination of the activation energy . 36
Figure 7 – Bathtub curve . 47

– 4 – IEC 62506:2023 © IEC 2023
Figure 8 – Test planning with a Weibull distribution. 50
Figure 9 – Example of a test based on the Weibull distribution . 51
Figure 10 – Life time and "tail" of the failure rate or failure intensity . 52
Figure 11 – Reliability as a function of life time ratio L and number of test items . 53
v
Figure 12 – Nomogram for test planning . 54
Figure A.1 – How FMEA and HALT supplement each other . 63
Figure C.1 – Plotting failures to estimate the activation energy E . 77
a
Figure E.1 – Weibull graphical data analysis . 81
Figure F.1 – Weibull plot of the three data sets . 84

Table 1 – Test types mapped to the item development cycle . 14
Table A.1 – Comparison between classical accelerated tests and HALT tests . 63
Table A.2 – Summary of HALT results for a DC/DC converter . 65
Table A.3 – Summary of HALT results for a medical system . 66
Table A.4 – Summary of HALT results for a Hi-Fi equipment . 67
Table B.1 – Environmental stress conditions of an automotive electronic device . 70
Table E.1 – Probability of failure of test samples A and B . 81
Table F.1 – Voltage test failure data for Weibull distribution . 83
Table G.1 – Median rank tables 95 % rank . 87

IEC 62506:2023 © IEC 2023 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
METHODS FOR PRODUCT ACCELERATED TESTING

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
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Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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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) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which
may be required to implement this document. However, implementers are cautioned that this may not represent
the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC 62506 has been prepared by IEC technical committee 56: Dependability. It is an
International Standard.
This second edition cancels and replaces the first edition published in 2013. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) references have been updated;
b) symbols have been revised;
c) errors in 5.7.2.3 and Annex B, mainly, have been corrected;
d) calculation errors in the examples of Annex B and Annex F have been corrected.

– 6 – IEC 62506:2023 © IEC 2023
The text of this International Standard is based on the following documents:
Draft Report on voting
56/2000/FDIS 56/2016/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/publications.
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, or
• revised.
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.

IEC 62506:2023 © IEC 2023 – 7 –
INTRODUCTION
Many reliability or failure investigation test methods have been developed and most of them are
currently in use. These methods are used to either determine product reliability or to identify
potential product failure modes, and have been considered effective as demonstrations of
reliability:
• fixed duration,
• sequential probability ratio,
• reliability growth tests,
• tests to failure, etc.
Such tests, although very useful, are usually lengthy, especially when the product reliability that
has to be demonstrated is high. The reduction in time-to-market periods as well as competitive
product cost, increase the need for efficient and effective accelerated testing. Here, the tests
are shortened through the application of increased stress levels or by increasing the speed of
application of repetitive stresses, thus facilitating a quicker assessment and growth of product
reliability through failure mode discovery and mitigation.
There are two distinctly different approaches to reliability activities:
• the first approach verifies, through analysis and testing, that there are no potential failure
modes in the product that are likely to be activated during the expected life time of the
product under the expected operating conditions and usage profile;
• the second approach estimates how many failures can be expected after a given time under
the expected operating conditions and usage profile.
Accelerated testing is a method appropriate for both cases, but used quite differently. The first
approach is associated with qualitative accelerated testing, where the goal is identification of
potential faults that eventually can result in product field failures. The second approach is
associated with quantitative accelerated testing where the product reliability may be estimated
based on the results of accelerated simulation testing that can be related back to the use of the
environment and usage profile.
Accelerated testing can be applied to multiple levels of items containing hardware and software.
Different types of reliability testing, such as fixed duration, sequential test-to-failure, success
test, reliability demonstration, or reliability growth or improvement tests can be candidates for
accelerated methods. This document provides guidance on selected, commonly used
accelerated test types. This document should be used in conjunction with statistical test plan
standards such as IEC 61123, IEC 61124, IEC 61649 and IEC 61710.
The relative merits of various methods and their individual or combined applicability in
evaluating a given system or item, should be reviewed by the product design team (including
reliability engineering) prior to selection of a specific test method or a combination of methods.
For each method, consideration should also be given to the test time, results produced,
credibility of the results, data required to perform meaningful analysis, life cycle cost impact,
complexity of analysis and other identified factors.
In this document the term "item" is used as defined in IEC 60050-192 covering physical products
as well as software. Services and people are however not covered by this document.

– 8 – IEC 62506:2023 © IEC 2023
METHODS FOR PRODUCT ACCELERATED TESTING

1 Scope
This document provides guidance on the application of various accelerated test techniques for
measurement or improvement of item reliability. Identification of potential failure modes that
can be experienced in the use of an item and their mitigation is instrumental to ensure
dependability of an item.
The object of the methods is to either identify potential design weakness or provide information
on item reliability, or to achieve necessary reliability and availability improvement, all within a
compressed or accelerated period of time. This document addresses accelerated testing of non-
repairable and repairable systems. It can be used for probability ratio sequential tests, fixed
duration tests and reliability improvement/growth tests, where the measure of reliability can
differ from the standard probability of failure occurrence.
This document also extends to present accelerated testing or production screening methods
that would identify weakness introduced into the item by manufacturing error, which can
compromise item reliability. Services and people are however not covered by this document.
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 60050-192 – International Electrotechnical Vocabulary (IEV) – Part 192: Dependability,
available at http://www.electropedia.org
IEC 60300-3-5, Dependability management – Part 3-5: Application guide – Reliability test
conditions and statistical test principles
IEC 60605-2, Equipment reliability testing – Part 2: Design of test cycles
IEC 60721 (all parts), Classification of environmental conditions
IEC 61123:2019, Reliability testing – Compliance test plans for success ratio
IEC 61124:2023, Reliability testing – Compliance tests for constant failure rate and constant
failure intensity
IEC 61649:2008, Weibull analysis
IEC 61709, Electric components – Reliability – Reference conditions for failure rates and stress
models for conversion
IEC 61710, Power law model – Goodness-of-fit tests and estimation methods
IEC 62429, Reliability growth – Stress testing for early failures in unique complex systems

IEC 62506:2023 © IEC 2023 – 9 –
3 Terms, definitions, symbols and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-192 and the
following apply.
ISO and IEC maintain terminology 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
NOTE Symbols for reliability, availability and maintainability measures follow those of IEC 60050-192, where
available.
3.1.1
activation energy
E
a
empirical factor for estimating the acceleration caused by a change in absolute temperature
Note 1 to entry: Activation energy is usually measured in electron volts per degree Kelvin.
3.1.2
detection screen
low stress level exposure to detect intermittent faults
3.1.3
event compression
increasing stress repetition frequency to be at considerably higher levels than it is in the field
3.1.4
highly accelerated limit test
HALT
test or sequence of tests intended to identify the most likely failure modes of the product in a
defined stress environment
Note 1 to entry: HALT is sometimes spelt out as the highly accelerated life test (as it was originally named in error).
However, as a non-measurable accelerated test, it does not provide information on life duration, but on the magnitude
of stress which represents the limit of the design.
3.1.5
highly accelerated stress audit
HASA
process monitoring tool where a sample from a production lot is tested to detect potential
weaknesses in a product caused by manufacturing
3.1.6
highly accelerated stress screening
HASS
screening intended to identify latent defects in a product caused by manufacturing process or
control errors
– 10 – IEC 62506:2023 © IEC 2023
3.1.7
item
subject being considered
Note 1 to entry: The item may be an individual part, component, device, functional unit, equipment, subsystem, or
system.
Note 2 to entry: The item may consist of hardware, software, people or any combination thereof.
Note 3 to entry: The item is often comprised of elements that may each be individually considered. See "sub-item"
(IEV 192-01-02) and "indenture level" (IEV 192-01-05).
Note 4 to entry: IEC 60050-191:1990 (now withdrawn; replaced by IEC 60050-192:2015) identified the term "entity"
as an English synonym, which is not true for all applications.
Note 5 to entry: The definition for "item" in IEC 60050-191:1990 (now withdrawn; replaced by IEC 60050-192:2015)
is a description rather than a definition. This new definition provides meaningful substitution throughout this
document. The words of the former definition form the new Note 1 to entry.
Note 6 to entry: In this document people and services are excluded.
[SOURCE: IEC 60050-192:2015, 192-01-01, modified – Note 6 to entry has been added.]
3.1.8
life time
time interval from first use until user requirements are no longer met
Note 1 to entry: The end of life time is usually called failure of the component.
Note 2 to entry: The end of life is often defined as the time where a specified percentage of the components have
failed, for example stated as a B or L value for 10 % accumulated failures.
10 10
3.1.9
precipitation screen
screening profile to precipitate, through failure, conversion of latent faults into revealed faults
3.1.10
step-stress test
test in which the applied stress is increased, after each specified interval, until failure occurs or
a predetermined stress level is reached
Note 1 to entry: The ‘interval’ could be specified in terms of number of stress applications, durations, or test
sequences.
Note 2 to entry: The test should not alter the basic failure modes, failure mechanisms, or their relative prevalence.
[SOURCE: IEC 60050-192:2015,192-09-10]
3.1.11
test acceleration factor
ratio of the stress response rate of the test specimen under the accelerated conditions, to the
stress response rate under specified operational conditions
Note 1 to entry: Both stress response rates refer to the same time interval in the life of the tested items.
Note 2 to entry: Measures of stress response rate are, for example, operating time to failure, failure intensity, and
rate of wear.
[SOURCE: IEC 60050-192:2015,192-09-09]
3.1.12
time compression
removal of exposure time at low or deemed non damaging stress levels from a test for the
purpose of acceleration
IEC 62506:2023 © IEC 2023 – 11 –
3.2 Symbols and abbreviated terms
ADT accelerated degradation test(ing)
AF acceleration, acceleration factor
AF overall acceleration in a test
Test
CALT calibrated accelerated life testing
B life time, the time where 10 % of the items have failed
C confidence
CD compact disc player in a HiFi equipment
DL destruct limit
DSL design specification limit
FIT failure in time (failure per 10 hours)
HALT highly accelerated limit test
HASA highly accelerated stress audit
HASS highly accelerated stress screening test
HAST highly accelerated stress test
L load
L life time ratio
v
LDL lower destruct limit
LDT lower destruct temperature
LOL lower operating limit
LOT lower operating temperature
LRTL lower reliability test limit
MTBF mean operating time between failures
MTTF mean operating time to failure
OL operating limit
OVL operation vibration limit
P acceptance probability
A
PDF probability density functions
PWB printed wiring board
R(t) reliability as a function of time; probability of survival to the time t
RTL reliability test level
S strength
SL specification limit
SPRT sequential probability ratio test
t time denoted time 0
t a specified time, e.g. life
L
THB temperature humidity bias test
TTF time to failure
UDL upper destruct limit
UDT upper destruct temperature
UOL upper operating limit
UOT upper operating temperature

– 12 – IEC 62506:2023 © IEC 2023
URTL upper reliability test limit
UUT unit under test
VDL vibration destruct limit
λ(S) failure rate as a function of a stress
λ(t) failure rate as a function of time
4 General description of the accelerated test methods
4.1 Cumulative damage model
Accelerated testing of any type is based on the cumulative damage principle. The stresses of
the item in its life cause progressive damage that accumulates throughout the item life. This
damage can, or not, result in an item’s failure in the field.
The strategy of any type of accelerated testing is to produce, by increasing stress levels during
testing, cumulative damage equivalent to that expected in the item’s life for the type of expected
stress. The determination of item destruct limits, without reliability estimation, provides
information on whether there exists a sufficient margin between those destruct limits and item
specification limits, thus providing assurance that the item will survive its predetermined life
period without failure related to that specific stress type. This technique can, but not
necessarily, quantify a probability of item survival for its life, and just provides assurance that
the necessary adjustments in item strength would help eliminate such failure in item use. Where
sufficient margins are determined unrelated to the probability of survival, the type of test is
qualitative. In tests where this probability of survival is determined, the magnitude of the stress
is correlated to the probability that the item would survive that stress type beyond the
predetermined life, and this test type is quantitative.
Figure 1 depicts the principle of cumulative damage in both qualitative and quantitative
accelerated tests.
In Figure 1, for simplicity, all stresses, operating limits, destruct limits, etc. are shown as
absolute values. The specification values for an item are usually given in both extremes, upper
and lower, thus the upper and lower (or low) specification limit, USL and LSL with the
corresponding design limits (DSL), UDL and LDL, the upper and lower operating limits, UOL
and LOL, and also the reliability test limits, URTL and LRTL. The rationale is that the opposite
(negative stresses), can also cause cumulative damage probably with a different failure
mechanism, thus the relationship between the expected and specified limits can be illustrated
in the same manner as for the high or positive stress. As an example, cold temperature
extremes can produce the same or different failure modes in an item. To avoid clutter, the
positive and the negative thermal or any other stresses are not separately shown in Figure 1,
thus the magnitudes of stresses are either positive or negative, and thus represented as
absolute values only as upper or lower limits.

IEC 62506:2023 © IEC 2023 – 13 –

Figure 1 – Probability density functions (PDF) for
cumulative damage, degradation, and test types
The graph in Figure 1 shows the required strength of an item regarding a stress for the duration
, through the end of
of its life time, from beginning of life (e.g. time when the item is made), t
life, t . The strength and stresses in tests are also assumed to have a Gaussian distribution.
L
The different types of accelerated tests can now be illustrated using Figure 1 as a conceptual
model.
Functional testing is carried out within the range of the requirement specification and at the
level of the specification. In this area no failures should occur during the test; design is validated
to allow operation within the upper and lower specification limits. Accelerated testing of Types
B and C (4.2.3 and 4.2.4), i.e. accelerated degradation testing (ADT) or cumulative damage
testing can be illustrated as the distance between the design specification limit (DSL) and the
level where the reliability demonstration test should be performed (RTL). When the degradation
reduces the performance below the requirement specifications, the item can be declared as
failed, if this behaviour is defined as a failure. When testing the item at time t no failures should
be expected for stress levels up to and including the design specification limit (DSL).
The item design specification should take into consideration certain degradation during the
item’s life which is resultant from the cumulative damage of the stresses expected in life, thus
its limit is the design specification limit (DSL) which is higher than the requirement limit (RL) in
order to provide the necessary margin. After item degradation resultant from the cumulative
damage caused by expected stresses, the reliability test provides information on the existing
margin between the test level (the remaining strength) and the requirement. This margin is a
measure of reliability at the end of required period, t .
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– 14 – IEC 62506:2023 © IEC 2023
The ultimate strength of the design is considerably higher than the design specifications and
this is the level determined in the qualitative accelerated test where the goal is to identify design
weaknesses which can compromise item reliability, i.e. the weaknesses that can occur in the
item’s life span, as the item degrades. Thus, the strength in the qualitative test is demonstrated
at operating limit (OL).
The destruct limit is above (beyond) the operating limit, and is denoted as DL. This is where a
permanent failure is observed. If the OL or DL are close to the DSL or the standard deviation
of the OL or DL distributions are high, then the test will indicate a potential weakness in the
design as indicated in Figure 1.
Item reliability is a function of time, usually predetermined life time, t .
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The cumulative normal distribution of the margin (difference of stress means divided by their
common standard deviation) between the specified strength (use conditions) which is
represented by the requirement and the reliability test level (RTL) determines item reliability.
The test level and its duration are chosen so as to cause cumulative damage during testing
corresponding to the degradation due to cumulative damage in the item’s life span. The
calculated value produces the item required reliability, which is then a quantitative measure.
A summary of listed tests and the mapping of their applications to the item life cycle is presented
in Table 1.
Table 1 – Test types mapped to the item development cycle
TTypypee DDesesiiggnn IIntnteegrgraattiionon VVaalidlidaattioionn AAccepccepttananccee MMaanufnufaaccttururiingng SSerervviicceses
FFMEMECCAA
HHALALTT HHAASS/SS/HHAASSAA
AA
QQuualaliittatatiiveve
Maturity Building Maturity Confirmation
RReleliiaabibilliittyy G Grrowowtth h RReelialiabbililitityy RReleliiaabibilliittyy
...