ISO/TR 16194:2017

TECHNICAL ISO/TR
REPORT 16194
First edition
2017-04
Pneumatic fluid power — Assessment
of component reliability by
accelerated life testing — General
guidelines and procedures
Transmissions pneumatiques — Évaluation de la fiabilité du
composant par essai de durée de vie accélérée — Lignes directrices
générales et modes opératoires
Reference number
©
ISO 2017
© ISO 2017, Published in Switzerland
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ii © ISO 2017 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and units . 3
5 Concepts of reliability and accelerated life testing . 3
6 Failure mechanism and mode . 4
7 Strategy of conducting accelerated life testing . 4
8 Design of accelerated life testing . 5
8.1 Normal use conditions . 5
8.2 Preliminary tests . 5
8.3 Levels of accelerated stress . 6
8.4 Sample size . 7
8.5 Data observation and measurement . 7
8.6 Types of stress loading . 7
9 End of test . 8
9.1 Minimum number of failures required . 8
9.2 Termination cycle count. 8
9.3 Suspended or censored test units . 8
10 Statistical analysis . 9
10.1 Analysis of failure data . 9
10.2 Life distribution. 9
10.3 Accelerated life testing model .10
10.4 Data analysis and parameter estimation .10
11 Reliability characteristics from the test data .11
12 Test report .12
Annex A (informative) Determining stress levels when stress is time-dependent .13
Annex B (informative) Life-stress relationship models .17
Annex C (informative) Verification of compromise Weibull slopes .26
Annex D (informative) Calculation procedures for censored data .32
Annex E (informative) Examples of using accelerated life testing in industrial applications .35
Annex F (informative) Palmgren-Miner’s rule .37
Annex G (informative) ALT experimental results for pneumatic cylinder .39
Bibliography .59
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
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URL: w w w . i s o .org/ iso/ foreword .html
ISO/TR 16194 was prepared by Technical Committee ISO/TC 131, Fluid power systems.
iv © ISO 2017 – All rights reserved

Introduction
This document is being released to document progress that the working group has developed for
accelerated testing. It is a new method with which the working group members have very little
experience, but has been used by institutional laboratories and taught at academic levels.
Some experimentation on air cylinders has been done at the Korean Institute of Machinery and
Materials (KIMM), but the application to pneumatic components in general has not been evaluated.
This document is offered to members as a reference and model procedure, so that they can develop
experience with its use in their own laboratories.
TECHNICAL REPORT ISO/TR 16194:2017(E)
Pneumatic fluid power — Assessment of component
reliability by accelerated life testing — General guidelines
and procedures
1 Scope
This document provides general procedures for assessing the reliability of pneumatic fluid power
components using accelerated life testing and the method for reporting the results. These procedures
apply to directional control valves, cylinders with piston rods, pressure regulators, and accessory
devices – the same components covered by the ISO 19973 series of standards.
This document does not provide specific procedures for accelerated life testing of components.
Instead, it explains the variability among methods and provides guidelines for developing an
accelerated test method.
The methods specified in this document apply to the first failure, without repairs.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 5598, ISO 19973-1 and
the following apply. ISO and IEC maintain terminological databases for use in standardization at the
following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
3.1
B life
x
life of a component or assembly that has not been altered since its production, where its reliability is (
100− x) %; or the time at which (100− x) % of the population has survived
Note 1 to entry: The cumulative failure fraction is x %. For example, if x = 10, the B life has a cumulative failure
probability of 10 %.
3.2
acceleration factor
AF
ratio between the life at the normal use stress level and the life at the accelerated stress level
3.3
accelerated life test
ALT
process in which a component is forced to fail more quickly that it would have under normal use
conditions and which provides information about the component’s life characteristics
3.4
destruct limit
stress level at which one or more of the component’s operating characteristics is no longer within
specification or the component is damaged and cannot recover when the stress is reduced
Note 1 to entry: Destruct limits are classified as a lower destruct limit and upper destruct limit.
3.5
failure mechanism
physical or chemical process that produces instantaneous or cumulative damage to the materials from
which the component is made
3.6
failure mode
manifestation of the failure mechanism resulting from component failure or degradation
Note 1 to entry: The failure mode is the symptom of the aggressive activity of the failure mechanism in the
component’s areas of weakness, where stress exceeds strength.
3.7
failure rate
λ
frequency at which a failure occurs instantaneously at time t, given that no failure has occurred before t
3.8
highly accelerated life test
HALT
process in which components are subjected to accelerated environments to find weaknesses in the
design and/or manufacturing process
Note 1 to entry: The primary accelerated environments include pressure and heat.
3.9
model for accelerated life testing
model that consists of a life distribution that represents the scatter in component life and a relationship
between life and stress
Note 1 to entry: Life distribution examples: Weibull, Lognormal, Exponential, etc.
Note 2 to entry: Life and stress examples: Arrhenius, Eyring, Inverse Power Law, etc.
3.10
normal use conditions
test conditions at which a component is commonly used in the field, which can be less strenuous than
rated conditions
3.11
termination cycle count
number of cycles on a test item when it reaches a threshold level for the first time
2 © ISO 2017 – All rights reserved

4 Symbols and units
a
Symbol Definition
B Time at which 10 % of the population is estimated to fail
η Scale parameter (characteristic life) of the Weibull distribution
F(t) Probability of failure of a component up to time t
β Shape parameter (slope) of the Weib
...