NACE TM0177 Method D (DCB) test allows the determination of the critical stress intensity factor KISSC, below which the propagation of a sulfide stress crack in the material is stopped. For a given severity of the sour medium (pH, PH2S, T, [Cl-]…), KISSC is not a material constant since it depends for instance on the testing arm displacement. Recently, the Klimit concept was proposed to circumvent this issue. Klimit is a conservative KISSC value and would be more representative of the material corrosion resistance. For an accurate determination of Klimit it is necessary to know KIapplied, the KI value when the test starts. In the proposed revision of the NACE TM0177 standard, it is recommended to use the compliance of the DCB specimen and the calculated arm displacement value for the determination of KIapplied.

This work is dedicated to analyzing the methodology to calculate KIapplied values. Experimental measurements of the initial compliance of chevron notched specimens (before the SSC crack propagation) have been performed, assisted by a numerical model of the DCB specimen. The validity of the compliance equation for the wedge insertion, the necessity to correct the lift-off load value for the compensation of the wedge compression and the definition that should apply for the initial crack length are discussed. Recommendations for an accurate determination of KIapplied values are then proposed.

Subject
Materials, Modeling, Compression, Geometry, Compliance, Notches, Tolerances, Lead, Precracking, Crack length, Cracks, Plasticity, Yield strength
Keywords:
DCB, KIapplied, Klimit, T95, C125
© 2013 Association for Materials Protection and Performance (AMPP). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of AMPP. Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
2013
Association for Materials Protection and Performance (AMPP)
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