1、BS ISO 7257:2016Aircraft Hydraulic tubingjoints and fittings Rotaryflexure testBSI Standards PublicationWB11885_BSI_StandardCovs_2013_AW.indd 1 15/05/2013 15:06BS ISO 7257:2016 BRITISH STANDARDNational forewordThis British Standard is the UK implementation of ISO 7257:2016.It supersedes BS M 55:1984
2、 which is withdrawn.The UK participation in its preparation was entrusted to TechnicalCommittee ACE/69, Aerospace hydraulic systems, fluids and com-ponents.A list of organizations represented on this committee can beobtained on request to its secretary.This publication does not purport to include al
3、l the necessaryprovisions of a contract. Users are responsible for its correctapplication. The British Standards Institution 2016.Published by BSI Standards Limited 2016ISBN 978 0 580 79216 8ICS 49.080Compliance with a British Standard cannot confer immunity fromlegal obligations.This British Standa
4、rd was published under the authority of theStandards Policy and Strategy Committee on 30 June 2016.Amendments/corrigenda issued since publicationDate Text affectedBS ISO 7257:2016 ISO 2016Aircraft Hydraulic tubing joints and fittings Rotary flexure testAronautique Joints et raccords pour tubes hydra
5、uliques Essai de flexion rotativeINTERNATIONAL STANDARDISO7257Second edition2016-06-01Reference numberISO 7257:2016(E)BS ISO 7257:2016ISO 7257:2016(E)ii ISO 2016 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2016, Published in SwitzerlandAll rights reserved. Unless otherwise specified, no part
6、 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 ISOs member bod
7、y in the country of the requester.ISO copyright officeCh. de Blandonnet 8 CP 401CH-1214 Vernier, Geneva, SwitzerlandTel. +41 22 749 01 11Fax +41 22 749 09 47copyrightiso.orgwww.iso.orgBS ISO 7257:2016ISO 7257:2016(E)Foreword ivIntroduction v1 Scope . 12 Requirements 12.1 Flexure test device . 12.2 F
8、lexure test specimen . 12.3 Specimen length and deflection requirements . 72.3.1 Specimen length . 72.3.2 Stress determination 72.3.3 Deflection . 72.4 Method of classification of fittings according to S/N flexure performance 72.5 Method of determining deflection/fatigue strength 73 Procedure. 83.1
9、Preparation for test . 83.1.1 Instrumentation, strain gauges . 83.1.2 Rotary flexure test set-up centring 83.1.3 Flexure stress measurement . 93.1.4 Flexure deflection measurement . 93.1.5 Operating pressure 93.2 S/N testing 93.3 Deflection/fatigue testing . 104 Formula .105 Equipment 10Bibliography
10、 .12 ISO 2016 All rights reserved iiiContents PageBS ISO 7257:2016ISO 7257:2016(E)ForewordISO (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 through
11、 ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborate
12、s 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 crit
13、eria 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).Attention is drawn to the possibility that some of the elements of this document may be the subject of
14、 patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent rights identified during the development of the document will be in the Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents).Any trade name
15、used in this document is information given for the convenience of users and does not constitute an endorsement.For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISOs adherence to the World Trade Organization (WTO) p
16、rinciples in the Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.The committee responsible for this document is ISO/TC 20, Aircraft and space vehicles, Subcommittee SC 10, Aerospace fluid systems and components.This second edition cancels and replaces the first
17、 edition (ISO 7257:1983), which has been technically revised to add imperial unit equivalents, three DN sizes, and for additional clarifications.iv ISO 2016 All rights reservedBS ISO 7257:2016ISO 7257:2016(E)IntroductionThis International Standard describes a flexure fatigue test procedure which all
18、ows evaluation of various tube fitting designs or material combinations. This evaluation is performed by fatigue testing the tube joints over a spectrum of bending stresses and then plotting the cycles to failure. Other test methods may be used as long as they develop the same data as the rotary fle
19、xure test. ISO 2016 All rights reserved vBS ISO 7257:2016BS ISO 7257:2016Aircraft Hydraulic tubing joints and fittings Rotary flexure test1 ScopeThis International Standard specifies a flexure test procedure to determine and classify the fatigue strengths of reconnectable or permanent hydraulic tube
20、 joints.The procedure is intended for conducting flexure tests of fittings and joints with high-strength hydraulic tubes of various alloys such as corrosion resistant steel, Nimonic1), titanium and aluminium alloy hydraulic tube for use on commercial and military aircraft.A mean stress is applied by
21、 holding system pressure in the specimens and then flexing in a rotary bending test machine.2 Requirements2.1 Flexure test deviceThe test device should be capable of testing in-line or bulkhead union test specimens and other configurations such as elbows and tees.The rotary flexure test device shoul
22、d be similar to that shown in Figure 1. Each rotary flexure test device should be capable of testing one specimen, but several specimens may be mounted on one plate.The device should be capable of constantly maintaining the required operating pressure during the test. The test fluid shall be water o
23、r system fluid (working fluid) unless otherwise specified by the responsible authorities. A typical pressurization and automatic shutdown system is shown in Figure 2. The shut-down should be automatic in the event of failure or pressure drop. The device should be capable of testing at controlled con
24、stant temperature, if specified by the procuring agency. The tailstock of the test device should be designed to permit alignment during initial installation and specimen mounting, and to serve as a pressure manifold. The rotating headstock should have a low-friction, self-aligning bearing and should
25、 be designed to permit total deflections of up to 25 mm/1 inch, and a constant rotational frequency within the range of 1 500 min1to 3 600 min1. The base should be of rigid construction.2.2 Flexure test specimenThe test specimen should be consisting of an adapter fitting (headstock end), a section o
26、f straight tubing, and a test fitting at the tailstock end. Typical test specimens are shown in Figure 3. The tubing shall be of a size and wall thickness as specified by the user or procuring agency.1) Nimonic is the trademark of a product supplied by Special Metals Corporation. This information is
27、 given for the convenience of users of this document and does not constitute an endorsement by ISO of the product named. Equivalent products can be used if they can be shown to lead to the same results.INTERNATIONAL STANDARD ISO 7257:2016(E) ISO 2016 All rights reserved 1BS ISO 7257:2016ISO 7257:201
28、6(E)Key1 adjustment for deflection 8 adapter fitting2 self-aligning bearing (without torsion on test joint) 9 10 mm/0,400 inch max3 test length, L 10 (5 1) mm/(0,200 0,040) inch4 tailstock 11 hydraulic pressure5 tailstock alignment bolt 12 deflection, D6 dial indicator, alternate for strain gauge (h
29、orizontal and vertical adjustment)13 strain gauges7 headstock 14 test joint (specimen separable joint)Figure 1 Typical rotary flexure test schematic2 ISO 2016 All rights reservedBS ISO 7257:2016ISO 7257:2016(E)Key1 tailstock2 hydraulic pressure3 accumulator to suit pressure4 nitrogen pressure5 actua
30、tor 2:1 ratio6 laboratory test gauge, approximatively 35 000 kPa7 laboratory test gauge, approximatively 14 000 kPa8 needle valve9 microswitch (to stop motor and cycle counter)Figure 2 Typical rotary flexure test hydraulic schematic ISO 2016 All rights reserved 3BS ISO 7257:2016ISO 7257:2016(E)a) Pe
31、rmanent bulkhead union b) Buttweldc) Permanent joint d) Permanent jointe) Permanent jointf) Reconnectable, butt welded joint g) Reconnectable, internal swaged joint4 ISO 2016 All rights reservedBS ISO 7257:2016ISO 7257:2016(E)h) Reconnectable, external swaged joint i) Reconnectable or permanent tee
32、piecej) Reconnectable or permanent elbowk) Reconnectable union, flanged bulkheadKey1 boss2 12 mm/0,500 inch max.3 clampFigure 3 Alternate specimen mounting for permanent joints ISO 2016 All rights reserved 5BS ISO 7257:2016ISO 7257:2016(E)KeyS bending stressN cycles to failureNOTE Such curves could
33、be established to illustrate possible observations in comparison testing of different materials or fitting attachments.Figure 4 S/N curves for characterizing various types of tubing or fitting jointsKeyD deflectionN cycles to failureNOTE The correlation between the strain gauge reading and deflectio
34、n may vary for different fitting designs. For example, a mechanically attached fitting may show some movement in the fitting, whereas a weld joint will be rigid. Also, a significant difference is noted if the S/N and D/N curves are compared for different tubing such as titanium alloy and corrosion r
35、esistant steel.Figure 5 D/N curve deflection/fatigue strength6 ISO 2016 All rights reservedBS ISO 7257:2016ISO 7257:2016(E)2.3 Specimen length and deflection requirements2.3.1 Specimen lengthThe length, L, of the specimens for rotary flexure testing shall be as shown in the Tables 1 and 2 and measur
36、ed as shown in Figures 1 or 3, depending on the fitting design. For intermediate sizes, the length, L, may be interpolated from the tables.2.3.2 Stress determinationThe desired strain or bending stress level for each set of specimens is induced by deflection of the specimen in the headstock. The ben
37、ding stress levels for the various deflection settings should be determined prior to applying pressure, using strain gauges and procedures as outlined in Clause 4. Strain gauges should always be used unless continual use of the same specimens and equipment makes settings by dial indicator acceptable
38、. Such settings by dial indicator, however, shall be established in prior testing by the use of strain gauges. Strain gauges should be used whenever new test equipment is used. A typical stress cycle is illustrated in Figure 6.2.3.3 DeflectionThe specimen deflections required to induce the stress le
39、vels indicated in 3.2 are measured by dial indicator at the length, L, as shown in Figures 1 or 3.Established deflection settings may be used in lieu of stress determination by strain gauge whenever qualification tests are being conducted, or when deflection plotting is of particular interest for ex
40、ample, to compare steel and titanium tubing.2.4 Method of classification of fittings according to S/N flexure performanceFitting/tubing combinations should be classified by the characteristic curves as shown in Figure 4, above which all S/N failure data points lie. Characteristic curves should be es
41、tablished as outlined in 3.2, showing cycles to failure for various bending stress levels.2.5 Method of determining deflection/fatigue strengthCycles to failure should be plotted as shown in Figure 5, showing cycles to failure for various deflection settings (deflection settings may correspond with
42、bending stress levels used as outlined in 2.4).NOTE Plotting of deflection in lieu of stress over cycles may be of interest to evaluate rigidity of fittings or compare the flexibility of different tubing materials such as corrosion-resistant steel and titanium.Table 1 Test specimen length (tube size
43、)Dimensions in millimetresTube sizeaDN 05DN 06DN 08DN 10DN 12DN 14DN 16DN 18DN 20DN 22DN 25DN 28DN 32DN 40Length, Lb130 155 180 190 230 245 255 265 280 295 305 330 355 400aSelected from ISO 2964. The “DN” designates nominal tube outside diameters, for example, DN 05 designates a 5-mm tube outside di
44、ameter.bThe length, L, may vary by 5 mm. ISO 2016 All rights reserved 7BS ISO 7257:2016ISO 7257:2016(E)Table 2 Test specimen length (dash size)Dimensions in inchesDash sizea03 04 05 06 08 10 12 14 16 20 24 32 40Length, Lb5 6,25 7 7, 5 9 10,75 11,5 12 12 14 15,25b baSelected from ISO 8575. Dash size
45、1/16 inch, example 05 = 5/16 inch diameter.bLength shall be as specified by the user or procuring agency.cThe length, L, may vary by 0,2 inch.Key1 maximum stress2 minimum stressSpmean axial stress produced by internal pressureSbstress caused by bendingSfcombined stress, Sp+ SbFigure 6 Typical altern
46、ating stress cycle with internal pressure3 Procedure3.1 Preparation for test3.1.1 Instrumentation, strain gaugesStrain gauges should be mounted on each test specimen. The strain gauge type and location should be as follows:Types: For tube size through DN 16/10: approximately 4 mm (0,16 inch).For tub
47、e sizes DN 20/12 and above: approximately 8 mm (0,32 inch).Location: The gauges should be mounted as shown in Figure 1, 90 apart.NOTE Mounting of four gauges, in pairs, on the X and Y axis is optional.3.1.2 Rotary flexure test set-up centringThe exact outside diameter and wall thickness of the test
48、specimen should be measured and recorded before the test. It is also recommended to check straightness, and if not straight, to reject or at least to mark the specimen in the plane where the tube end is not aligned.8 ISO 2016 All rights reservedBS ISO 7257:2016ISO 7257:2016(E)The tube assembly shoul
49、d be installed into the tailstock and the separate fittings hand tightened to permit subsequent adjustments. The setup procedure is detailed as follows. Free-state microstrain readings for the tube specimen should be measured and recorded prior to installation and tightening of the fitting nut. The self-aligning bearing at the headstock end should be roughly centred and the adapter inserted. The tailstock end should then be carefully tightened so as to avoid moving the test specimen out of li
