1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS ISO 23788:2012Metallic materials Verification of the alignment offatigue testing machinesBS ISO 23788:2012 BRITISH STANDARDNational forewordThis British Standard is the UK imp
2、lementation of ISO 23788:2012.The UK participation in its preparation was entrusted to TechnicalCommittee ISE/101/6, Fatigue testing of metals and metal matrixcomposites.A list of organizations represented on this committee can beobtained on request to its secretary.This publication does not purport
3、 to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. The British Standards Institution 2012. Published by BSI StandardsLimited 2012ISBN 978 0 580 69953 5ICS 77.040.10Compliance with a British Standard cannot confer immunity fromlegal obligations.Th
4、is British Standard was published under the authority of theStandards Policy and Strategy Committee on 31 August 2012.Amendments issued since publicationDate Text affectedBS ISO 23788:2012 ISO 2012Metallic materials Verification of the alignment of fatigue testing machinesMatriaux mtalliques Vrifica
5、tion de lalignement axial des machines dessai de fatigueINTERNATIONAL STANDARDISO23788First edition2012-07-01Reference numberISO 23788:2012(E)BS ISO 23788:2012ISO 23788:2012(E)ii ISO 2012 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2012All rights reserved. Unless otherwise specified, no part
6、 of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISOs member body in the country of the requester.ISO copyright officeCase postale 56 C
7、H-1211 Geneva 20Tel. + 41 22 749 01 11Fax + 41 22 749 09 47E-mail copyrightiso.orgWeb www.iso.orgPublished in SwitzerlandBS ISO 23788:2012ISO 23788:2012(E) ISO 2012 All rights reserved iiiContents PageForeword ivIntroduction v1 Scope 12 Normative references . 13 Terms and definitions . 14 Symbols .
8、35 Measurement requirements 45.1 Testing machine . 45.2 Alignment cell . 45.3 Design and manufacturing . 45.4 Machining 65.5 Inspection before attaching the strain gauges . 65.6 Instrumentation with strain gauges . 65.7 System checks . 76 Alignment measurement calculations . 76.1 General . 76.2 Cyli
9、ndrical alignment cell 76.3 Thick rectangular alignment cell . 96.4 Thin rectangular alignment cell . 96.5 Classification of machine alignment 97 Procedure for verification of machine alignment .107.1 Purpose and frequency .107.2 Procedure 108 Reporting . 118.1 Basic information 118.2 Special inform
10、ation .12Annex A (informative) Causes of specimen bending and misalignment in fatigue testing machines 17Annex B (normative) Evaluating uncertainty in the alignment measurement .19Annex C (informative) Method for measuring machine lateral stiffness .22Annex D (informative) Three-strain gauge configu
11、ration 24Annex E (informative) Determination of bending contribution due to inherent imperfections in a cylindrical alignment cell device .26Annex F (informative) Numerical example .27Annex G (normative) Alignment gauge A method for qualitative assessment of alignment of test systems for cylindrical
12、 specimens .28Bibliography .30BS ISO 23788:2012ISO 23788:2012(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 ISO technical com
13、mittees. 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 collaborates closely with the
14、 International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.The main task of technical committees is to prepare International Standards. Draft Internationa
15、l Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.Attention is drawn to the possibility that some of the elements of this document may be the
16、subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights.ISO 23788 was prepared by Technical Committee ISO/TC 164, Mechanical testing of metals, Subcommittee SC 5, Fatigue testing.iv ISO 2012 All rights reservedBS ISO 23788:2012ISO 23788:2012(E)Introd
17、uctionMachine alignment in the context of this International Standard means the coincidence of the geometrical (loading) axes of the grips. Any departure from this ideal situation results in an angular and/or lateral offset (or misalignment) in the load train (see Annex A). Misalignment is manifeste
18、d as an unwanted bending stress/strain field to exist in the test specimen or alignment measuring device (hereinafter “alignment cell”). The bending stress/strain field superimposes on the applied, presumed uniform, stress/strain field. In pure torsion testing, any misalignment results in a biaxial
19、torsion plus bending stress/strain state.Misalignment in the load train in axial fatigue test systems has been shown to influence significantly the fatigue test results (see References 1, 2 and 3).The main causes of bending due to misalignment are invariably a combination of poor coincidence of the
20、centrelines of the grips, and inherent imperfections in the specimen or alignment cell itself. The bending contribution due to the test machine ideally remains the same for every test specimen or alignment cell. The bending contribution due to the specimen or alignment cell varies from one device to
21、 another.Recent research (see References 4 and 5) has shown that no matter how carefully a specimen or an alignment cell device has been manufactured an inherent bending error always exists. Imperfections (i.e. eccentricity and angularity) arise from geometric asymmetry about the axial centreline in
22、 the device and other measurement errors relating to the chosen type, positioning and performance of the strain gauges. The device inherent bending error can be significant and sometimes even exceed that due to the machine misalignment.In this International Standard, errors due to inherent imperfect
23、ions in the alignment cell itself are eliminated. This is achieved by rotating the alignment device 180 about its longitudinal axis and subtracting its contribution from the overall maximum surface bending strain determined in the measurement. Different devices that are made of the same material and
24、 nominal dimensions should reasonably, therefore, produce the same alignment measurement results; see an example in Reference 2, Figure 10. ISO 2012 All rights reserved vBS ISO 23788:2012BS ISO 23788:2012Metallic materials Verification of the alignment of fatigue testing machines1 ScopeThis Internat
25、ional Standard describes a method for verifying the alignment in a testing machine using a strain-gauged measuring device. It is applicable to dynamic uniaxial tension/compression, pure torsion and combined tension/compression plus torsion fatigue testing machines for metallic materials.The methodol
26、ogy outlined in this International Standard is generic and can be applied to static testing machines and in non-metallic materials testing.2 Normative referencesThe following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For da
27、ted references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.ISO 7500-1, Metallic materials Verification of static uniaxial testing machines Part 1: tension/ compression testing machines Verification and cali
28、bration of force-measuring system3 Terms and definitionsFor the purposes of this document, the following terms and definitions apply.3.1alignmentcoincidence of the loading axes of the load train components, including the test specimenNOTE Departure from such coincidence can introduce bending moments
29、 into the specimen.3.2alignment cellcarefully machined measuring device instrumented with strain gauges for use in verifying the alignment of a testing machine3.3alignment gaugecarefully machined mechanical device made of a split bar and a gauge for pass/fail checking of the correct alignment of the
30、 grips3.4average axial strainoaverage longitudinal axial strain measured at the surface of the alignment cell by a set of strain gauges located in the same cross-sectional planeNOTE The average axial strain represents the strain at the geometrical centre of the cross section.3.5load trainall the com
31、ponents between and including the crosshead and the actuatorNOTE The load train includes the specimen.INTERNATIONAL STANDARD ISO 23788:2012(E) ISO 2012 All rights reserved 1BS ISO 23788:2012ISO 23788:2012(E)3.6bending strainbdifference between the local strain measured by a strain gauge and the aver
32、age axial strainNOTE Bending strain is a vector characterized by a magnitude, a direction and a discrete point of application. In general, it varies from point to point on the surface of the alignment cell.3.7machine alignmentcoincidence of the axes of the grips, which is characterized by the maximu
33、m bending strain component b,max,mcNOTE Machine misalignment is manifested by the existence of a lateral offset and/or an angular offset between the loading axes of the upper and lower grips.3.8machine aspectreference to the test machines front, back, left and right3.9maximum bending strainb,maxvect
34、or quantity with the largest bending strain magnitude in a given cross-sectional planeNOTE Maximum bending strain vector is characterized by a magnitude, a direction and a discrete point of application.3.10percentage bendingmaximum bending strain times 100 and divided by the average axial strain3.11
35、measurement planecross-sectional plane in the alignment cell in which the transverse axes of a set of strain gauges are positioned3.12measurement orientations position of the alignment cell (0, 90, 180 and 270), about its longitudinal axis, which defines the location of gauge 1 or a permanent mark o
36、n the alignment cells surface, with respect to the front of the machine NOTE The front of the machine is the R-direction.3.13parallel lengthLpparallel portion of the reduced section of the alignment cell3.14proportional limitgreatest stress that a material is capable of sustaining elastically, i.e.
37、without any deviation from proportionality of stress to strain3.15R-directionfixed reference direction with respect to the frame of the testing machineNOTE Typically, it is the direction from the centre towards the front of the machine.3.16strain gauge axial separationLgaxial distance on the alignme
38、nt cell between the upper and lower measurement planes2 ISO 2012 All rights reservedBS ISO 23788:2012ISO 23788:2012(E)3.17strain gauge transverse separationWgtransverse distance on the broad face of a thin rectangular alignment cell between the centres of the strain gauges4 SymbolsFor the purposes o
39、f this document, the following symbols apply.Symbol DescriptionA1 A4B1 B4dupper set of strain gaugeslower set of strain gaugesminimum diameter of cylindrical alignment cell; inner diameter of alignment gaugeDediameter at grip end of cylindrical alignment celleccentricity or lateral offsetLpparallel
40、lengthLgaxial separation of strain gaugesLzoverall length of alignment cell, alignment gauge or test specimenr fillet radius between the parallel length and the grip end of the alignment cell or test speciment thickness of reduced section of rectangular alignment cellw width of reduced section of re
41、ctangular alignment cellWwgwidth at grip end of rectangular alignment celltransverse separation of strain gauges percentage bendingacpercentage bending due to inherent imperfections in the alignment cellmcpercentage bending due to machine misalignmentoaverage axial strain1, 2, etc. readings of indiv
42、idual strain gauges (i.e. local strain)bbending strain (combined value)b,acbending strain component due to inherent imperfections in the alignment cellb,mcbending strain component due to machine misalignmentb,maxmaximum bending strain (combined value)b,max,acmaximum bending strain component due to i
43、nherent imperfections in the alignment cellb,max,mcmaximum bending strain component due to machine misalignment angular offset ISO 2012 All rights reserved 3BS ISO 23788:2012ISO 23788:2012(E)acangle (clockwise where seen from above) of the location of b,max,acwith respect to gauge 1 (or a permanent
44、mark on the alignment cells surface)mcangle (clockwise where seen from above) of the location of b,max,mcwith respect to front of the machine (the R-direction)5 Measurement requirements5.1 Testing machineThe testing system shall have a force-measuring system comprising force transducer (load cell),
45、conditioner and readout units. This system shall meet the requirements of ISO 7500-1.NOTE 1 Class 1 requires that force indicated errors do not exceed 1 % of the reading over the verification range.It is essential that the grips enable rotating the alignment cell 180 about its longitudinal axis. It
46、shall also adequately enable repeatable positioning and gripping of the alignment cell with minimal variation in the misalignment (see Annex B).It is recommended, but not essential, that the machine be equipped with means for adjusting the lateral and angular offsets of one part of the load train. I
47、t is also recommended toa) minimize the number of components of which these gripping devices are composed in order to reduce the number of mechanical interfaces, andb) maximize the lateral stiffness of the fatigue testing machine in order to reduce the effects of any so-called reversed bending on fa
48、tigue test results in tests involving reversed tension-compression loading (see Reference 1).NOTE 2 See Annex C for a method for measuring machine lateral stiffness.5.2 Alignment cellAlignment measurement can be slightly affected by the stiffness of the alignment cell used in the measurement (see Fi
49、gure 13 in Reference 2); the lower the stiffness of the device, the higher its measurement sensitivity of machine alignment. A good alignment cell should also be sufficiently robust to last and enable successive usage over a long period of time (i.e. years). Care should be taken to ensure both requirements are adequately fulfilled.A suitable material for an alignment cell should ideally have:a) a sufficiently high linear elastic range;b) a high degree of metallurgical stability;c) freedom fr
