1、BS ISO 7257:2016 Aircraft Hydraulic tubing joints and fittings Rotary flexure test BSI Standards Publication WB11885_BSI_StandardCovs_2013_AW.indd 1 15/05/2013 15:06BS ISO 7257:2016 BRITISH STANDARD National foreword This British Standard is the UK implementation of ISO 7257:2016. It supersedes BS M
2、 55:1984 which is withdrawn. The UK participation in its preparation was entrusted to Technical Committee ACE/69, Aerospace hydraulic systems, fluids and com- ponents. A list of organizations represented on this committee can be obtained on request to its secretary. This publication does not purport
3、 to include all the necessary provisions of a contract. Users are responsible for its correct application. The British Standards Institution 2016. Published by BSI Standards Limited 2016 ISBN 978 0 580 79216 8 ICS 49.080 Compliance with a British Standard cannot confer immunity from legal obligation
4、s. This British Standard was published under the authority of the Standards Policy and Strategy Committee on 30 June 2016. Amendments/corrigenda issued since publication Date Text affectedBS ISO 7257:2016 ISO 2016 Aircraft Hydraulic tubing joints and fittings Rotary flexure test Aronautique Joints e
5、t raccords pour tubes hydrauliques Essai de flexion rotative INTERNATIONAL STANDARD ISO 7257 Second edition 2016-06-01 Reference number ISO 7257:2016(E)BS ISO 7257:2016ISO 7257:2016(E)ii ISO 2016 All rights reserved COPYRIGHT PROTECTED DOCUMENT ISO 2016, Published in Switzerland All rights reserved.
6、 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
7、the address below or ISOs 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 copyrightiso.org www.iso.orgBS ISO 7257:2016ISO 7257:2016(E)Foreword iv Introduction v 1 Scope . 1 2
8、Requirements 1 2.1 Flexure test device . 1 2.2 Flexure test specimen . 1 2.3 Specimen length and deflection requirements . 7 2.3.1 Specimen length . 7 2.3.2 Stress determination 7 2.3.3 Deflection . 7 2.4 Method of classification of fittings according to S/N flexure performance 7 2.5 Method of deter
9、mining deflection/fatigue strength 7 3 Procedure. 8 3.1 Preparation for test . 8 3.1.1 Instrumentation, strain gauges . 8 3.1.2 Rotary flexure test set-up centring 8 3.1.3 Flexure stress measurement . 9 3.1.4 Flexure deflection measurement . 9 3.1.5 Operating pressure 9 3.2 S/N testing 9 3.3 Deflect
10、ion/fatigue testing .10 4 Formula .10 5 Equipment 10 Bibliography .12 ISO 2016 All rights reserved iii Contents PageBS ISO 7257:2016ISO 7257:2016(E) Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work
11、of preparing International Standards is normally carried out through 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-government
12、al, in liaison with ISO, also take part in the work. 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
13、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). Attention is drawn to the possib
14、ility that some of the elements of this document may be the subject of 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
15、patent declarations received (see www.iso.org/patents). Any trade name 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 conformit y assessment, as well as
16、 information about ISOs adherence to the World Trade Organization (WTO) principles 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
17、 systems and components. This second edition cancels and replaces the first 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) Introduction Thi
18、s International Standard describes a flexure fatigue test procedure which allows 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 tes
19、t methods may be used as long as they develop the same data as the rotary flexure test. ISO 2016 All rights reserved vBS ISO 7257:2016BS ISO 7257:2016Aircraft Hydraulic tubing joints and fittings Rotary flexure test 1 Scope This International Standard specifies a flexure test procedure to determine
20、and classify the fatigue strengths of reconnectable or permanent hydraulic tube 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, Nimonic 1) , titanium and aluminium alloy hydr
21、aulic tube for use on commercial and military aircraft. A mean stress is applied by holding system pressure in the specimens and then flexing in a rotary bending test machine. 2 Requirements 2.1 Flexure test device The test device should be capable of testing in-line or bulkhead union test specimens
22、 and other configurations such as elbows and tees. The rotary flexure test device should 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 main
23、taining the required operating pressure during the test. The test fluid shall be water or 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 even
24、t of failure or pressure drop. The device should be capable of testing at controlled constant 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 manif
25、old. The rotating headstock should have a low- friction, self-aligning bearing and should be designed to permit total deflections of up to 25 mm/1 inch, and a constant rotational frequency within the range of 1 500 min 1to 3 600 min 1 . The base should be of rigid construction. 2.2 Flexure test spec
26、imen The test specimen should be consisting of an adapter fitting (headstock end), a section of 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) Ni
27、monic is the trademark of a product supplied by Special Metals Corporation. This information is 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. IN
28、TERNATIONAL ST ANDARD ISO 7257:2016(E) ISO 2016 All rights reserved 1BS ISO 7257:2016ISO 7257:2016(E) Key 1 adjustment for deflection 8 adapter fitting 2 self-aligning bearing (without torsion on test joint) 9 10 mm/0,400 inch max 3 test length, L 10 (5 1) mm/(0,200 0,040) inch 4 tailstock 11 hydrau
29、lic pressure 5 tailstock alignment bolt 12 deflection, D 6 dial indicator, alternate for strain gauge (horizontal and vertical adjustment) 13 strain gauges 7 headstock 14 test joint (specimen separable joint) Figure 1 Typical rotary flexure test schematic2 ISO 2016 All rights reservedBS ISO 7257:201
30、6ISO 7257:2016(E) Key 1 tailstock 2 hydraulic pressure 3 accumulator to suit pressure 4 nitrogen pressure 5 actuator 2:1 ratio 6 laboratory test gauge, approximatively 35 000 kPa 7 laboratory test gauge, approximatively 14 000 kPa 8 needle valve 9 microswitch (to stop motor and cycle counter) Figure
31、 2 Typical rotary flexure test hydraulic schematic ISO 2016 All rights reserved 3BS ISO 7257:2016ISO 7257:2016(E) a) Permanent bulkhead union b) Buttweld c) Permanent joint d) Permanent joint e) Permanent joint f) Reconnectable, butt welded joint g) Reconnectable, internal swaged joint4 ISO 2016 All
32、 rights reservedBS ISO 7257:2016ISO 7257:2016(E) h) Reconnectable, external swaged joint i) Reconnectable or permanent tee piece j) Reconnectable or permanent elbow k) Reconnectable union, flanged bulkhead Key 1 boss 2 12 mm/0,500 inch max. 3 clamp Figure 3 Alternate specimen mounting for permanent
33、joints ISO 2016 All rights reserved 5BS ISO 7257:2016ISO 7257:2016(E) Key S bending stress N cycles to failure NOTE Such curves could be established to illustrate possible observations in comparison testing of different materials or fitting attachments. Figure 4 S/N curves for characterizing various
34、 types of tubing or fitting joints Key D deflection N cycles to failure NOTE The correlation between the strain gauge reading and deflection 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.
35、 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 resistant 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 r
36、equirements 2.3.1 Specimen length The length, L, of the specimens for rotary flexure testing shall be as shown in the Tables 1 and 2 and measured 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 dete
37、rmination The desired strain or bending stress level for each set of specimens is induced by deflection of the specimen in the headstock. The bending stress levels for the various deflection settings should be determined prior to applying pressure, using strain gauges and procedures as outlined in C
38、lause 4. Strain gauges should always be used unless continual use of the same specimens and equipment makes settings by dial indicator acceptable. 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 te
39、st equipment is used. A typical stress cycle is illustrated in Figure 6. 2.3.3 Deflection The specimen deflections required to induce the stress levels 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
40、 stress determination by strain gauge whenever qualification tests are being conducted, or when deflection plotting is of particular interest for example, to compare steel and titanium tubing. 2.4 Method of classification of fittings according to S/N flexure performance Fitting/tubing combinations s
41、hould be classified by the characteristic curves as shown in Figure 4, above which all S/N failure data points lie. Characteristic curves should be established as outlined in 3.2, showing cycles to failure for various bending stress levels. 2.5 Method of determining deflection/fatigue strength Cycle
42、s to failure should be plotted as shown in Figure 5, showing cycles to failure for various deflection settings (deflection settings may correspond with 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
43、 fittings or compare the flexibility of different tubing materials such as corrosion-resistant steel and titanium. Table 1 Test specimen length (tube size) Dimensions in millimetres Tube size a DN 05 DN 06 DN 08 DN 10 DN 12 DN 14 DN 16 DN 18 DN 20 DN 22 DN 25 DN 28 DN 32 DN 40 Length, L b 130 155 18
44、0 190 230 245 255 265 280 295 305 330 355 400 aSelected from ISO 2964. The “DN” designates nominal tube outside diameters, for example, DN 05 designates a 5-mm tube outside diameter. bThe length, L, may vary by 5 mm. ISO 2016 All rights reserved 7BS ISO 7257:2016ISO 7257:2016(E) Table 2 Test specime
45、n length (dash size) Dimensions in inches Dash size a 03 04 05 06 08 10 12 14 16 20 24 32 40 Length, L b 5 6,25 7 7, 5 9 10,75 11,5 12 12 14 15,25 b b aSelected from ISO 8575. Dash size 1/16 inch, example 05 = 5/16 inch diameter. bLength shall be as specified by the user or procuring agency. cThe le
46、ngth, L, may vary by 0,2 inch. Key 1 maximum stress 2 minimum stress S p mean axial stress produced by internal pressure S b stress caused by bending S f combined stress, S p+ S b Figure 6 Typical alternating stress cycle with internal pressure 3 Procedure 3.1 Preparation for test 3.1.1 Instrumentat
47、ion, strain gauges Strain 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 tube sizes DN 20/12 and above: approximately 8 mm (0,32 inch). Location: The gauges should be
48、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 centring The exact outside diameter and wall thickness of the test specimen should be measured and recorded before the test. It is also recommended to che
49、ck 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 should 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 t
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