DIN EN ISO 16808-2014 Metallic materials - Sheet and strip - Determination of biaxial stress-strain curve by means of bulge test with optical measuring systems (ISO 16808 2014) Ger.pdf

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1、November 2014Translation by DIN-Sprachendienst.English price group 14No part of this translation may be reproduced without prior permission ofDIN Deutsches Institut fr Normung e. V., Berlin. Beuth Verlag GmbH, 10772 Berlin, Germany,has the exclusive right of sale for German Standards (DIN-Normen).IC

2、S 77.040.10!%=cK“2266440www.din.deDDIN EN ISO 16808Metallic materials Sheet and strip Determination of biaxial stress-strain curve by means of bulge test withoptical measuring systems (ISO 16808:2014);English version EN ISO 16808:2014,English translation of DIN EN ISO 16808:2014-11Metallische Werkst

3、offe Blech und Band Bestimmung der biaxialen Spannung/Dehnung-Kurve durch einen hydraulischenTiefungsversuch mit optischen Messsystemen (ISO 16808:2014);Englische Fassung EN ISO 16808:2014,Englische bersetzung von DIN EN ISO 16808:2014-11Matriaux mtalliques Tles et bandes Dtermination de la courbe c

4、ontrainte-dformation biaxiale au moyen de lessai degonflement hydraulique avec systmes de mesure optiques (ISO 16808:2014);Version anglaise EN ISO 16808:2014,Traduction anglaise de DIN EN ISO 16808:2014-11www.beuth.deIn case of doubt, the German-language original shall be considered authoritative.Do

5、cument comprises 31 pages10.14 DIN EN ISO 16808:2014-11 2 A comma is used as the decimal marker. National foreword This document (EN ISO 16808:2014) has been prepared by Technical Committee ISO/TC 164 “Mechanical testing of metals”, Subcommittee SC 1 “Uniaxial testing” (Secretariat: AFNOR, France) i

6、n collaboration with Technical Committee ECISS/TC 101 “Test methods for steel (other than chemical analysis)” (Secretariat: AFNOR, France) in accordance with the agreement on technical cooperation between ISO and CEN (Vienna Agreement). The responsible German body involved in its preparation was the

7、 DIN-Normenausschuss Materialprfung (Materials Testing Standards Committee), Working Committee NA 062-01-42 AA Zug- und Duktilittsprfung fr Metalle. EN ISO 16808July 2014 ICS 77.040.10 English Version Metallic materials - Sheet and strip - Determination of biaxial stress-strain curve by means of bul

8、ge 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 - Blech und Band - Bestimmungde

9、r biaxialen Spannung/Dehnung-Kurve durch einenhydraulischen Tiefungsversuch mit optischenMesssystemen (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 conditions for giving this Eu

10、ropean 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 exists in three official versi

11、ons (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 standards bodies of Austria,

12、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, Slovenia, Spain, Sweden, Sw

13、itzerland, Turkey andUnited Kingdom. CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels 2014 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN ISO 16808:2014 EEUROPEAN COMMITTEE FOR STANDARDIZATIONCOMIT EUROPEN DE NORMA

14、LISATIONEUROPISCHES KOMITEE FR NORMUNGEUROPEAN STANDARDNORME EUROPENNEEUROPISCHE NORMContents Page Foreword . 3 1 Scope . 4 2 Symbols and abbreviated terms . 4 3 Principle 5 4 Test equipment . 5 5 Optical measurement system . 9 6 Test piece 9 6.1 General 9 6.2 Application of grid 9 7 Procedure 10 8

15、Evaluation methods for the determination of the curvature and strains at the pole 10 9 Calculation of biaxial stress-strain curves 11 10 Test report . 12 Annex A (informative) International comparison of symbols used in the determination of the bulge test flow curve 14 Annex B (normative) Test proce

16、dure for a quality check of the optical measurement system 16 Annex C (informative) Computation of the curvature on the basis of a response surface 19 Annex D (informative) Determination of the equi-biaxial stress point of the yield locus and the hardening curve . 21 Bibliography 29 2DIN EN ISO 1680

17、8:2014-11 EN ISO 16808:2014 (E) ForewordThis 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 methods for steel (other than chemical analysis)” the secretariat of which is held

18、 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 withdrawn at the latest by January 2015. Attention is drawn to the possibility

19、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 Regulations, the national standards organizations of the following countries are bound

20、 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, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,

21、 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. 3DIN EN ISO 16808:2014-11EN ISO 16808:2014 (E)1 ScopeThis International Standard specifies a

22、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 strain values can be achieved.NOTE In this document, the term “biaxial stress-s

23、train 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 Designation UnitddieDiameter of the die (inner) mmdBHDiameter of the blank

24、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 (root mean square) - Radius of curvature mmr1Surface radius for determining cu

25、rvature 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 strain -2Minor true strain -3True thickness strain -Equivalent true strain -ls

26、Coordinate and length of a section mmdz Displacement in the z-direction mmdzmvDisplacement after movement correction mm4DIN EN ISO 16808:2014-11 EN ISO 16808:2014 (E) 3 PrincipleA circular blank is completely clamped at the edge in a tool between die and blank holder. A bulge is formed by pressing a

27、 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 system.1,2,3Based on the recorded deformation of the blank, the following quantities near the

28、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, assuming the stress state of a thin-walled spherical pressure vessel at the centre of the blank, the

29、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 described in the following, there are also laser systems4,5,6or tactile systems7,8,9valid for bulge t

30、est 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)3true thickness strain (at the apex of the dome) t actual thickness of the sheetddiediameter of

31、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 clamped metal sheet before forming). Herein, the x-direction corresponds to the rolling direction.

32、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 equipped with a die, a blank holder and a fluid chamber. The proposed equipment is illustrated in Fig

33、ure 2.5DIN EN ISO 16808:2014-11EN ISO 16808:2014 (E)Key1 deformation measurement system 3 chamber with fluid2 lock bead 4 pressure measurement systemFigure 2 Proposal of a testing equipment (principle drawing)4.2 The lay out of the test equipment shall be such that it is possible to continuously mea

34、sure 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 of a grid of points on the bulging blank surface, in order to calculate the shape and the true strains in the centra

35、l 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 surface of the specimen. Out of these coordinates, the true strains 1and 2for each point of the selected area, the t

36、hickness 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 measurement system is also possible. Starting from 20 % of the maximum measured pressure value, the precision should be 1

37、% 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 high enough to keep the blank holder closed. Any movement of the test piece between the blank holder and die should b

38、e 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 defining the necessary blank-holder force.4.6 The fluid shall be in contact with the blank surface (without any air b

39、ubbles) 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 through the blank holder, die and sheet or elsewhere during the test until failure occurs.4.7 A lock bead (or compar

40、able 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 between blank holder and die. A location close to the die radius is recommended. The lock bead geometry should avoid

41、 a curvature and a wrinkling of the blank when closing the tool and prevent the sliding of the blank during the test.6DIN EN ISO 16808:2014-11 EN ISO 16808:2014 (E) 4.8 It is recommended to place glass plates in front of the lenses and the illumination in order to protect the optical measuring syste

42、m 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 illumination (thinner glass); see Figure 3. The inserted protection shall not to disturb the optical measurement quality (see Clause 5). After

43、each test, the glass plates shall be well cleaned without damaging or scratching them and precisely repositioned to not alter calibration. Typically, a calibration of the optical system including the protection increases the measurement quality.4.9 The smallest die diameter recommended should have a

44、 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 recommendation is (5 t0) to (15 t0) (maximum 15 mm).7DIN EN ISO 16808:2014-11EN ISO 16808:2014 (E)a) b)c)Key1 lamp 4 test piece2 cameras 5 fluid3 gl

45、ass platesFigure 3 Examples for possible positions of oil shielding plates and lamps8DIN EN ISO 16808:2014-11 EN ISO 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 fol

46、lowing characteristics is recommended: Optical sensor based on two or more cameras; Measurement area, whereas dmeasurement area 1/2 ddie;The used measurement area should be larger than a concentric diameter of half the diameter of the blank holder. This area should be observable during the entire fo

47、rming process for all heights of the drawn blank. Local resolution (grid distance between the independent measurement points): The distance gmaxbetween two adjacent points on the unformed blank should follow the requirement:gmax ddie50 The determination of the curvature requires an accuracy of the z

48、-coordinates in an area with a diameter of 1/2 ddieconcentric to the blank holder ofrmsdzrmsdzd()(),ndiemmmm=1000 015 NOTE The accuracy of the shape measurement can be checked with a test of the optical measurement system (see Annex B).Accuracy for strain measurement: rms (1) = 0,003 rms (2) = 0,003

49、For each real strain value for the mentioned rms () above, the acceptable measurement values are:real= 0 acceptable measurement range: 0,003 0,003real= 0,5 acceptable measurement range: 0,497 0,503 Missing measurement points: In order to avoid unbalanced curvature approximations, only the absence of less than 5 % of the measurement points in the concentric area with a diameter = 1/2 ddiei