The Crack Tip Opening Displacement in Elastic-Plastic Fracture Mechanics: Proceedings of the Workshop on the CTOD Methodology GKSS-Forschungszentrum Geesthacht, GmbH, Geesthacht, Germany, April 23–25, 1985

364 Pages·1986·5.94 MB·English

by  W. Schmitt

The Crack Tip
Opening Displacement
in Elastic-Plastic
Fracture Mechanics
Proceedings of the Workshop on the CTOD Methodology
GKSS-Forschungszentrum Geesthacht, GmbH,
Geesthacht, Germany, April 23-25, 1985
Editor: K H. Schwalbe
Sponsored by
Studiengesellschaft zur F6rderung der Kemenergieverwertung
in Schiflbau und SchifTahrt e.V. (KEST), Hamburg
Stiftung Volkswagenwerk, Hannover
Springer-Verlag
Berlin Heidelberg New York Tokyo
Prof. Dr.-Ing. K. H. Schwalbe
GKSS Forschungszentrum Geesthacht
Institut fUr Werkstofftechnologie
Max-Planck-StraBe
2054 Geesthacht, FRG
ISBN -13: 978-3-642-82820-1 e-ISBN -13: 978-3-642-82818-8
DOl: 10.1007/978-3-642-82818-8
Library of Congress Cataloging in Publication Data
Workshop on the CTOD Methodology (1985: Gi<'S S-Forschungszentrum Geesthacht)
The crack tip opening displacement in elastic-plastic fracture mechanics.
1. Fracture mechanics--Congresses.
I. Schwalbe, Karlheinz. II. Title.
TA409.w67 1985 620.1'126 86-10066
ISBN-13:978-3-642-82820-l (U.S.)
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Under § 54 ofthe German Copyright Law where copies are made for other than private use, a
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© Springer-Verlag Berlin, Heidelberg 1986
Softcover reprint of the hardcover 1st edition 1986
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Preface
In April 1985 two workshop meetings were arranged in two consecutive
weeks:
the
Second CSNI Informal Workshop on Ductile Fracture Test Methods
was organised and hosted by OECD, Paris, and chaired by F.J. Loss.
It took place on 17th-19th April 1985. It dealt primarily with experimen
tal techniques in elastic-plastic fracture mechanics and standardisation
of JIc and JR-curve tests. In order to enable overseas participants to
attend this meeting and the
Workshop on the CTOD Methodology
the latter was scheduled for 23th-25th April 1985 at the GKSS-Forschungs
zentrum Geesthacht.
Thus, a number of participants took part in the debates on the merits of
the CTOD concept, having the state-of-the-art of the J-integral philosophy
freshly in mind.
In this respect, the twin arrangement was very fruitful.
Three days were planned for the meeting, in order to have sufficient time
for presenting and discussing 27 contributions.
Because of the workshop-type of the meeting several contri butions on on
going research were presented which were not intended to be published.
The Studiengesellschaft zur F5rderung der Kernenergieverwertung in Schiff
bau und Schiffahrt e.V. (KEST) and the Stiftung Volkswagenwerk generously
sponsored the workshop, which is gratefully acknowledged.
Thanks are due to GKSS-Forschungszentrum Geesthacht for hosting
the meeting.
Geesthacht, April 1986
K.-H. Schwalbe
Introduction
Fracture mechanics offers two concepts for the treatment of a cracked body
which behaves in an elastic-plastic manner: the J-integral and the CTaD
concept. Both concepts are of course equivalent, but different methods for
determining the material properties and for transferring them to structural
parts have been developped.
Under certain circumstances, the J -integral is a path-independent contour
integral characterising the crack tip field uniquely. The determination of
the critical value, JIc' which is a measure of the material's resi
stance against the initiation of growth of a pre-existing crack, can be
aChieved by test methods which are already standardised in some countries
(U .S. A., Japan, China) or which are in the stage of standardisation in
other countries. For the J-integral as a driving force parameter, the EPRI
handbook collects J solutions for a number of crack configurations. If the
structural configuration being considered cannot be identified with one of
the cases compiled in the handbook or if the stress-strain behaviour of the
material differs significantly from a power law, individual numerical cal
culations have to be carried out.
The J-integral is also used to correlate a certain amount of crack growth
although this is in principle not in accordance with the assumptions made
for the derivation of J. Consequently, only relatively little crack growth
is supposed to be J-controlled.
The CTaD concept assumes that a characteristic displacement at the crack
tip is a unique measure of the crack tip field and hence of the fracture
behaviour of a cracked body. The user is provided with a concept consisting
of a test standard (BS 5762) and the so-called CTaD Design Curve. The docu
ment BSI PD 6493:1980 contains (among other details) guidelines on how to
apply the CTaD Design Curve to practical cases. Application of the Design
Curve leads normally to conservati ve assessments of the acceptance of de
fects.
Whereas the J-integral is mostly used to characterise the fracture beha
viour of materials in the presence of a ductile tearing mode of crack
growth, the CTaD concept is primarily appl ied to the ductile-to-bri t tIe
transition region of structural steels.
VII
Thus, two different worlds have been developped as has also been demon
strated by the discussions at the two meetings (see Preface).
This is an unnecessary complication and it causes confusion t·o the less
experienced user. Practical application of fracture mechanics will cer
tainly have a greater chance to be accepted also by non-experts if paral
lelisms of this kind can be avoided (and they can!).
Unfortunately, there is no specific displacement at the crack tip which
could be regarded as "the natural crack tip opening displacement". This
was once again confirmed by the workshop discussions: at least seven dif
ferent definitions of the GTOD were presented, which is certainly a weak
ness of the concept.
It may be beneficial to the reader of the present proceedings to bear in
mind that the workshop discussion can be structured as outlined below. This
structure can be used like a grid which can be laid on the various papers
in order to get a reasonable overview on what was presented.
- As mentioned above, the GTOD is very much a matter of definition. Each
of the definitions presented at the workshop makes sense, but it is im
portant to establish correlations between the various GTODs.
The symbols used in the presentations, Le. 6115, 60, 65, 6T, 6t,vR. .. ,
show that there is much to do in order to unify the various philo
sophies.
- The remote techniques for determining a cri tical GTOD do not seem to
yield values which correspond in all cases with the displacement at the
very crack tip.
- There is an increasing tendency for correlating stable crack growth with
the GTOD, i.e. for determining 6-R-curves in contrast to J-R-curves. This
seems to be attractive since some limited findings suggest that there are
less stringent size requirements for a 6-R-curve than for a J-R-curve. On
the other hand, a recently introduced modification of the J-integral
seems to improve the ability of J to correlate crack growth.
VIII
- Although in principle both the J-integral and the CTOD philosophies and
their techniques are compatible, this compatibility must be demonstrated
by as many practical examples as possible in order to make visible that
there is no real borderline between these two worlds. Empirical and theo
retical correlations between J and 15 show that there can indeed be a
unique relation between these quantities.
- Like J, the CTOD can be predicted as a dri ving force parameter by full
finite element calculations. It would, however, be very attractive if
simple formulae could be developped in order to simplify the practical
application. In this context, the Dugdale model - although strongly
simplifying the reality - is still being used.
- Application to a structural part can be done as follows:
• The dri ving force parameter, 15 ,can be calculated numerically and
app
compared with the material property, 15mat
• The CTOD Design Curve yields conservative estimates for the acceptance
of defects; it is not aimed at predicting failure. This drawback is
balanced by the bulk of practical experience showing that the Design
Curve works for the purpose it was developped for.
• Procedures are under development which are easy to use (without nume
rics) but which are nevertheless capable of predicting failure situa
tions with reasonable accuracy. By incorporating the R-curve methodolo
gy in such procedures one can take advantage of the increase of the ma
terial's resistance against crack growth with the crack growth process.
Thus, the merits of the CTOD concept can be characterised by slightly
easier measurement of 15 compared to J - in particular in the presence of
crack growth - and by the availability of simple application tools.
Participants
Aeberli, K.E. FRG GKSS-Forschungszentrum
Geesthacht GmbH
2054 Geesthacht
Amstutz, H. FRG Technische Hochschule
Darmstadt
6100 Darmstadt
Andrews, W.R. USA General Electric Company,
Schenectady, NY 12345
Blauel, J .G. FRG Fraunhofer-Institut
fur Werkstoffmechanik
7800 Freiburg
Burget, W. FRG Fraunhofer-Institut
fur Werkstoffmechanik
7800 Freiburg
Cornec, A. FRG GKSS-Forschungszentrum
Geesthacht GbmH
2054 Geesthacht
Dawes, M.G. UK The Welding Institute
Abington
Cambridge CBl 6AL
Dormagen, D. FRG Rheinisch-Westf§lische
Technische Hochschule
5100 Aachen
Ernst, H. USA Westinghouse Research &
Development Center
Pittsburgh, PA 15235
Fontaine, A. F IRSID, 78105 St Germain
en Laye
Fossati, C. I CISE, 20090 Segrate
Milano
Garwood, S.J. UK The Welding Institute
Abington
Cambridge CBl 6AL
Heerens, J. FRG GKSS-Forschungszentrum
Geesthacht GmbH
2054 Geesthacht
x
Hellmann, D. FRG GKSS-Forschungszentrum
Geesthacht GmbH
2054 Geesthacht
Heuser, A. FRG Rheinisch-Westf§lische
Technische Hochschule
5100 Aachen
Hoffmann, M. FRG Technische Hochschule
Darmstadt
6100 Darmstadt
Kanninen, M.F. USA Southwest Research
Institute, San Antonio
Texas 78284
K. FRG Technische Hochschule
K~ttgen,
Darmstadt
6100 Darmstadt
Loss, F.J. USA Materials Engineering
Associates
Lanham MD 20706
McCabe, D.E. USA Westinghouse Research &
Development Center
Pittsburgh, PA 15235
Mattheck, C. FRG Kernforschungszentrum
Karlsruhe
7500 Karlsruhe
Morawietz, P. FRG Rheinisch-Westf§l. TUV
4300 Essen
Newman, J.C. USA NASA Langley Research
Center, Hampton VA 23665
Schmitt, W. FRG Fraunhofer-Institut
fUr Werkstoffmechanik
7800 Freiburg
Schwalbe, K.-H. FRG GKSS-Forschungszentrum
Geesthacht GmbH
2054 Geesthacht
Contributions to the Workshop
Session: Crack Tip Examination
W. Schmitt Numerical Evaluation of CTOD: 2D and 3D Applications.
H. Amstutz Problems of Numerical CTOD Analysis.
T. Seeger
J. Heerens Experimental and Theoretical Investigation of
A. Cornec Crack Tip Blunting.
C. Mattheck Theoretical Calculation of CTOD Using a Dugdale
D. Munz Model Including Strain Hardening.
M. Hoffmann Dugdale Solution for Strain Hardening Materials
T. Seeger
M.F. Kanninen ASTM Computational Round Robin.
Session: Experimental Techniques
D. E. McCabe Geometry Dependence of Hinge Methods.
D.E. McCabe The ASTM Round Robin.
K.-H. Schwalbe Introduction to GKSS work on CTOD.
D. Hellmann Compatibility of 65 with BS 5762.
J. Heerens On the Relationships Between Various Definitions
K.-H. Schwalbe of the Crack Tip Opening Displacement.
D. Hellmann
A. Cornec