1、BSI Standards PublicationBS EN ISO 16808:2014Metallic materials Sheetand strip Determinationof biaxial stress-strain curveby means of bulge test withoptical measuring systems (ISO16808:2014)BS EN ISO 16808:2014 BRITISH STANDARDNational forewordThis British Standard is the UK implementation of EN ISO
2、16808:2014.The UK participation in its preparation was entrusted to TechnicalCommittee ISE/101/2, Ductility testing.A list of organizations represented on this committee can beobtained on request to its secretary.This publication does not purport to include all the necessaryprovisions of a contract.
3、 Users are responsible for its correctapplication. The British Standards Institution 2014. Published by BSI StandardsLimited 2014ISBN 978 0 580 76890 3ICS 77.040.10Compliance with a British Standard cannot confer immunity fromlegal obligations.This British Standard was published under the authority
4、of theStandards Policy and Strategy Committee on 31 August 2014.Amendments issued since publicationDate Text affectedEUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN ISO 16808 July 2014 ICS 77.040.10 English Version Metallic materials - Sheet and strip - Determination of biaxial stress-strain cu
5、rve by means of bulge test with optical measuring systems (ISO 16808:2014) Matriaux mtalliques - Tles et bandes - Dtermination de la courbe contrainte-dformation biaxiale au moyen de lessai de gonflement hydraulique avec systmes de mesure optiques (ISO 16808:2014) Metallische Werkstoffe - Bleche und
6、 Bnder - Bestimmung der biaxialen Spannung/Dehnung-Kurve durch einen hydraulischen Tiefungsversuch mit optischen Messsystemen (ISO 16808:2014) This European Standard was approved by CEN on 4 July 2014. CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the cond
7、itions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN member. This European Standard exist
8、s in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same status as the official versions. CEN members are the national stan
9、dards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Sl
10、ovenia, Spain, Sweden, Switzerland, Turkey and United Kingdom. EUROPEAN COMMITTEE FOR STANDARDIZATION COMIT EUROPEN DE NORMALISATION EUROPISCHES KOMITEE FR NORMUNG CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels 2014 CEN All rights of exploitation in any form and by any means reserv
11、ed worldwide for CEN national Members. Ref. No. EN ISO 16808:2014 EBS EN ISO 16808:2014EN ISO 16808:2014 (E) 3 Foreword This document (EN ISO 16808:2014) has been prepared by Technical Committee ISO/TC 164 “Mechanical testing of metals” in collaboration with Technical Committee ECISS/TC 101 “Test me
12、thods for steel (other than chemical analysis)” the secretariat of which is held by AFNOR. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by January 2015, and conflicting national standards shall be
13、 withdrawn at the latest by January 2015. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN and/or CENELEC shall not be held responsible for identifying any or all such patent rights. According to the CEN-CENELEC Internal Regula
14、tions, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Ita
15、ly, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom. Endorsement notice The text of ISO 16808:2014 has been approved by CEN as EN ISO 16808:2014 without any modification. BS EN ISO 168
16、08:2014ISO 16808:2014(E) ISO 2014 All rights reserved iiiContents PageForeword iv1 Scope . 12 Symbols and abbreviated terms . 13 Principle 24 Test equipment. 25 Optical measurement system 66 Test piece 66.1 General . 66.2 Application of grid . 67 Procedure. 78 Evaluation methods for the determinatio
17、n of the curvature and strains at the pole . 79 Calculation of biaxial stress-strain curves . 810 Test report . 9Annex A (informative) International comparison of symbols used in the determination of the bulge test flow curve 11Annex B (normative) Test procedure for a quality check of the optical me
18、asurement system .13Annex C (informative) Computation of the curvature on the basis of a response surface 16Annex D (informative) Determination of the equi-biaxial stress point of the yield locus and the hardening curve .18Bibliography .26BS EN ISO 16808:2014ISO 16808:2014(E)ForewordISO (the Interna
19、tional 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 committees. Each member body interested in a subject for which a technical committee has be
20、en 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 International Electrotechnical Commission (IEC) on all matters of electrotechnical stan
21、dardization.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 accord
22、ance 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 patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details
23、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 used in this document is information given for the convenience of users and does not constitute an endors
24、ement.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 WTO principles in the Technical Barriers to Trade (TBT) see the following URL: Foreword - Supplementary informationThe committee responsi
25、ble for this document is ISO/TC 164, Mechanical testing of metals, Subcommittee SC 2, Ductility testing.iv ISO 2014 All rights reservedBS EN ISO 16808:2014INTERNATIONAL STANDARD ISO 16808:2014(E)Metallic materials Sheet and strip Determination of biaxial stress-strain curve by means of bulge test wi
26、th optical measuring systems1 ScopeThis International Standard specifies a method for determination of the biaxial stress-strain curve of metallic sheets having a thickness below 3 mm in pure stretch forming without significant friction influence. In comparison with tensile test results, higher stra
27、in values can be achieved.NOTE In this document, the term “biaxial stress-strain curve” is used for simplification. In principle, in the test the “biaxial true stress-true strain curve” is determined.2 Symbols and abbreviated termsThe symbols and designations used are given in Table 1.Table 1Symbol
28、Designation UnitddieDiameter of the die (inner) mmdBHDiameter of the blank holder (inner) mmR1Radius of the die (inner) mmh Height of the drawn blank (outer surface) mmt0Initial thickness of the sheet (blank) mmt Actual thickness of the sheet mmp Pressure in the chamber MParms Standard deviation (ro
29、ot mean square) - Radius of curvature mmr1Surface radius for determining curvature mmr2Surface radius for determining strain mmr1_100Surface radius to determine curvature with a die diam-eter of 100 mmmmai , biCoefficients for response surface -Biaxial stress MPae Engineering strain -1Major true str
30、ain -2Minor true strain -3True thickness strain -Equivalent true strain -lsCoordinate and length of a section mmdz Displacement in the z-direction mmdzmvDisplacement after movement correction mm ISO 2014 All rights reserved 1BS EN ISO 16808:2014ISO 16808:2014(E)3 PrincipleA circular blank is complet
31、ely clamped at the edge in a tool between die and blank holder. A bulge is formed by pressing a fluid against the blank until final fracture occurs (Figure 1). During the test, the pressure of the fluid is measured and the evolution of the deformation of the blank is recorded by an optical measuring
32、 system.1,2,3Based on the recorded deformation of the blank, the following quantities near the centre of the blank are determined: the local curvature, the true strains at the surface, and, by assuming incompressible deformation of the material, the actual thickness of the blank. Furthermore, assumi
33、ng the stress state of a thin-walled spherical pressure vessel at the centre of the blank, the true stress is calculated from the fluid pressure, the thickness and the curvature radius.NOTE In addition to the bulge test procedures with optical measurement systems introduced in Reference 1 and descri
34、bed in the following, there are also laser systems4,5,6or tactile systems7,8,9valid for bulge test investigation, which are not covered in this International Standard.Keyh height of the drawn blank (outer surface) radius of curvaturep pressure in the chamber t0initial thickness of the sheet (blank)3
35、true thickness strain (at the apex of the dome) t actual thickness of the sheetddiediameter of the die (inner)Figure 1 Principle of the bulge testThe coordinate origin shall be in the centre of the blank holder. The XY-plane should be parallel to the surface of the blank holder (parallel to the clam
36、ped metal sheet before forming). Herein, the x-direction corresponds to the rolling direction. The z-direction shall be normal to the clamped metal sheet before forming, with the positive direction towards the optical sensor.4 Test equipment4.1 The bulge test shall be carried out on a machine equipp
37、ed with a die, a blank holder and a fluid chamber. The proposed equipment is illustrated in Figure 2.2 ISO 2014 All rights reservedBS EN ISO 16808:2014ISO 16808:2014(E)Key1 deformation measurement system 3 chamber with fluid2 lock bead 4 pressure measurement systemFigure 2 Proposal of a testing equi
38、pment (principle drawing)4.2 The lay out of the test equipment shall be such that it is possible to continuously measure the outside surface of the test piece continuously during the test, i.e. to be able to determine the deformation of the geometry by recording the evolution of X, Y, Z coordinates
39、of a grid of points on the bulging blank surface, in order to calculate the shape and the true strains in the central area of interest until failure occurs.4.3 During the test, the system shall be able to measure optically (without contact) the X, Y, Z coordinates of a grid of points on the bulging
40、surface of the specimen. Out of these coordinates, the true strains 1and 2for each point of the selected area, the thickness strain 3and the curvature radius for the apex of the dome are calculated.4.4 The system should be equipped with a chamber fluid pressure measurement system. An indirect measur
41、ement system is also possible. Starting from 20 % of the maximum measured pressure value, the precision should be 1 % of the actual measured value.4.5 The die, the blank holder and the fluid chamber shall be sufficiently rigid to minimize deformation during testing. The blank-holder force shall be h
42、igh enough to keep the blank holder closed. Any movement of the test piece between the blank holder and die should be prevented. Typically during the test, the bulge pressure is acting on parts of the blank holder reducing the effective blank-holder force. This shall be taken in consideration when d
43、efining the necessary blank-holder force.4.6 The fluid shall be in contact with the blank surface (without any air bubbles) to prevent energy storage during the test through compressed air bubbles which would lead to higher energy release and greater oil splashing at failure. No fluid shall be lost
44、through the blank holder, die and sheet or elsewhere during the test until failure occurs.4.7 A lock bead (or comparable geometry in the circular surface), designed to suppress any material flow, is recommended. The lock bead shall not initiate cracks in the material. The lock bead shall be located
45、between blank holder and die. A location close to the die radius is recommended. The lock bead geometry should avoid a curvature and a wrinkling of the blank when closing the tool and prevent the sliding of the blank during the test. ISO 2014 All rights reserved 3BS EN ISO 16808:2014ISO 16808:2014(E
46、)4.8 It is recommended to place glass plates in front of the lenses and the illumination in order to protect the optical measuring system from oil splashing due to blank failure at the end of the test.7,12The plates can be fixed on the blank holder (thick glass) or near the camera lenses and illumin
47、ation (thinner glass); see Figure 3. The inserted protection shall not to disturb the optical measurement quality (see Clause 5). After each test, the glass plates shall be well cleaned without damaging or scratching them and precisely repositioned to not alter calibration. Typically, a calibration
48、of the optical system including the protection increases the measurement quality.4.9 The smallest die diameter recommended should have a ratio of die diameter to initial thickness ddie/ t0 33 (see Figure 2). The radius of the die should not lead to cracks in the blank during the test. A recommendati
49、on is (5 t0) to (15 t0) (maximum 15 mm).4 ISO 2014 All rights reservedBS EN ISO 16808:2014ISO 16808:2014(E)a) b)c)Key1 lamp 4 test piece2 cameras 5 fluid3 glass platesFigure 3 Examples for possible positions of oil shielding plates and lamps ISO 2014 All rights reserved 5BS EN ISO 16808:2014ISO 16808:2014(E)5 Optical measurement systemFor the determination of the radius of curvature , and the true strains 1and 2, an optical-deformation field measurement system with the following characteri
