Aerospace series - Hydraulic tubing joints and fittings - Planar flexure test

ISO 9538:2017 specifies a flexure test procedure for reconnectable and permanent hydraulic tube joints. This procedure is intended for conducting flexure tests on fittings with high-strength hydraulic tubes made of corrosion-resisting steel, titanium and aluminium for use on commercial and military aircraft.

Série aérospatiale — Joints et raccords des tuyauteries hydrauliques — Essai de flexion plane

General Information

Status
Published
Publication Date
24-Apr-2017
Current Stage
9599 - Withdrawal of International Standard
Start Date
19-Jun-2025
Completion Date
13-Dec-2025

Relations

Effective Date
26-Nov-2022
Effective Date
12-Feb-2014

Overview

ISO 9538:2017 specifies a planar flexure test procedure for reconnectable and permanent hydraulic tubing joints and fittings used in aerospace applications. The standard applies to fittings with high‑strength hydraulic tubes made of corrosion‑resisting steel, titanium and aluminium for commercial and military aircraft. It defines test equipment, specimen preparation, instrumentation and a vibration‑based procedure to assess flexure fatigue performance under combined internal pressure and bending loads.

Key topics and requirements

  • Test device and setup
    • Vibrator, manifold (to receive at least six specimens) and hydraulic supply unit with pressure monitoring and shutdown capability.
    • Vibrator capable of up to 300 Hz.
  • Specimens
    • Include the test fitting (e.g., straight union), test tube and end fitting to seal the tube.
  • Instrumentation
    • Strain gauges required on each specimen; gauge placement: approximately 4 mm from attachment point for tube sizes to DN 16, 8 mm for DN 20 and above.
    • Angle gauges and stroboscope recommended for deflection control.
  • Frequency and dynamic tuning
    • Recommended test frequency ≈ 100 Hz.
    • Specimen natural frequency should be 110–120 Hz; test frequency set about 10–20% below natural frequency to avoid resonance.
    • Tube length is adjusted (with gauges and pressure applied) to achieve required natural frequency.
  • Stress determination and calibration
    • Combined stress is the sum of mean axial (from internal pressure) and bending stress; bending stress is determined by strain gauges and calibrated by applying a static load to reproduce the required moment before dynamic testing.
  • Acceptance criteria
    • Test specimens shall withstand 10^7 cycles with no leakages or failures.

Applications

  • Qualification and fatigue validation of aerospace hydraulic tube fittings.
  • Laboratory fatigue testing to demonstrate flexure resistance of fittings on steel, titanium and aluminium tubing.
  • Alternative to rotary flexure methods where planar vibration testing is preferred or required.

Who uses this standard

  • Aerospace component manufacturers and tube‑fitting suppliers
  • Environmental/test laboratories and fatigue test facilities
  • Design and qualification engineers, quality assurance and certification authorities
  • Maintenance and overhaul organizations validating repair fittings

Related standards

  • ISO 7257 - Aircraft - Hydraulic tubing joints and fittings - Rotary flexure test (alternative method)
  • ISO 7169 - Separable tube fittings for aerospace fluid systems (procurement/qualification context)

Keywords: ISO 9538:2017, planar flexure test, hydraulic tubing joints, aerospace, tube fittings, flexure fatigue stress, strain gauges, vibration frequency, natural frequency, test specimens.

Standard

ISO 9538:2017 - Aerospace series -- Hydraulic tubing joints and fittings -- Planar flexure test

English language
6 pages
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Frequently Asked Questions

ISO 9538:2017 is a standard published by the International Organization for Standardization (ISO). Its full title is "Aerospace series - Hydraulic tubing joints and fittings - Planar flexure test". This standard covers: ISO 9538:2017 specifies a flexure test procedure for reconnectable and permanent hydraulic tube joints. This procedure is intended for conducting flexure tests on fittings with high-strength hydraulic tubes made of corrosion-resisting steel, titanium and aluminium for use on commercial and military aircraft.

ISO 9538:2017 specifies a flexure test procedure for reconnectable and permanent hydraulic tube joints. This procedure is intended for conducting flexure tests on fittings with high-strength hydraulic tubes made of corrosion-resisting steel, titanium and aluminium for use on commercial and military aircraft.

ISO 9538:2017 is classified under the following ICS (International Classification for Standards) categories: 49.080 - Aerospace fluid systems and components. The ICS classification helps identify the subject area and facilitates finding related standards.

ISO 9538:2017 has the following relationships with other standards: It is inter standard links to ISO 9538:2025, ISO 9538:1996. Understanding these relationships helps ensure you are using the most current and applicable version of the standard.

You can purchase ISO 9538:2017 directly from iTeh Standards. The document is available in PDF format and is delivered instantly after payment. Add the standard to your cart and complete the secure checkout process. iTeh Standards is an authorized distributor of ISO standards.

Standards Content (Sample)


INTERNATIONAL ISO
STANDARD 9538
Second edition
2017-04
Aerospace series — Hydraulic tubing
joints and fittings — Planar flexure test
Série aérospatiale — Joints et raccords des tuyauteries hydrauliques
— Essai de flexion plane
Reference number
©
ISO 2017
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
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 Device for flexure test . 1
5 Flexure test specimens . 3
6 Stress determination. 3
7 Procedure. 4
7.1 Instrumentation and strain gauges . 4
7.2 Frequency . 5
7.2.1 Test frequency . 5
7.2.2 Natural frequency of the specimens . 5
7.2.3 Determination of tube length. 5
7.3 Bending stress calibration of test specimen . 5
8 Requirements . 5
Bibliography . 6
Foreword
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This document was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles,
Subcommittee SC 10, Aerospace fluid systems and components.
This second edition cancels and replaces the first edition (ISO 9538:1996), of which
...

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