ISO INTERNATIONAL STANDARD 12108 Third edition 2018-07 Metallic materials Fatigue testing Fatigue crack growth method Matériaux métalliques - Essais de fatigue - Méthode d'essai de propagation de fissure en fatigue Reference number IS0 12108:2018(E) so @IS02018 IS0 12108:2018(E) COPYRIGHTPROTECTEDDOCUMENT @ IS0 2018 All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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 the address below or Iso's member body in the country of the requester. ISO copyright office CP 401 : Ch. de Blandonnet 8 CH-1214 Vernier, Geneva Phone: +4122 749 0111 Fax: +41 22 749 09 47 Email: copyright@iso.org Website: www.iso.org Published in Switzerland ii @ IS0 2018 - All rights reserved IS0 12108:2018(E) Contents Page Foreword ..V Introduction. ..vi 1 Scope. 2 Normative references 3 Terms and definitions 4 Symbols and abbreviated terms. 4.1 Symbols .4 4.2 Abbreviated terms for specimen identification ..5 5 Apparatus ..5 6 Specimens. .6 6.1 General .6 6.2 Crack plane orientation 6.3 Starter notch precracking details .8 6.4 Stress-intensity factor .10 6.5 Specimen size. .10 6.6 Specimen thickness. 10 6.7 Residual stress ..10 7 Procedure .11 7.1 Fatigue precracking .11 7.2 Crack length measurement .11 7.3 Constant-force-amplitude, K-increasing, test procedure for da/dN > 10-5 mm/cycle ..12 7.4 K-decreasing procedure for da/dN< 10-5 mm/cycle 13 8 Crack length measurement .15 8.1 Resolution .15 8.2 Interruption .15 8.3 Staticforce 15 8.4 Measurement interval .15 8.5 Symmetry.. .16 8.6 Out-of-plane cracking .16 8.7 Crack tip bifurcation. .16 8.8 Non-visual crack length measurement ..16 8.9 Visual crack length measurement ..16 9 Calculations. .16 9.1 Crack-front curvature .16 9.2 Determining the fatigue crack growth rate ..17 9.2.1 General ..17 9.2.2 Secant method ..17 9.2.3 Incremental polynomial method .18 9.3 Determination of the fatigue crack growth threshold ..18 10 Test report. .18 10.1 General .18 10.2 Material ..18 10.3 Test specimen. 10.4 Precracking terminal values 19 10.5 Test conditions. .19 10.6 Test analysis 20 10.7 Presentation of results. ..20 Annex A (normative) Compact tension (cT) specimen .27 Annex B (normative) Centre crack tension (CcT) specimen ..32 @ IS0 2018 - All rights reserved iii