Fracture Toughness of Engineering Materials by Kim Wallin

Fracture Toughness of Engineering Materials by Kim Wallin


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The publication should provide an aid to both fracture mechanics experts and those engineers and scientists who use fracture mechanics in their daily work. It also offers an insight for the standards that need to be developed in the area of structural integrity methodologies. The intention is also to challenge and inspire the scientific experts in the field to develop possibly competing and improved fracture mechanics solutions, because fracture mechanics is still, by and large, a maturing discipline.

Professor K R W Wallin is a recognised expert in the field of fracture mechanics. Indeed his work has provided a major input to the currently accepted ASTM Standard on the Master Curve Method , E1921. This method facilitates characterisation of ductile to brittle fracture for ferritic steels.
ISBN: 978 0 9552994 6 9.

Fracture Toughness of Engineering Materials – estimation and application
Kim Wallin

Professor K R W Wallin is a recognised expert in the field of fracture mechanics. Indeed his work has provided a major input to the currently accepted ASTM Standard on the Master Curve Method , E1921. This method facilitates characterisation of ductile to brittle fracture for ferritic steels. The book “Fracture Toughness of Engineering Materials – Estimation and Application” was written by Kim Wallin during his five year tenure as an Academy Professor funded by the Academy of Finland,and provides an authoritative guide and practical handbook for advanced students, fracture mechanics practitioners and R&D specialists.

Fracture Toughness of Engineering Materials – Estimation and Application provides a valuable and up-to-date addition to the bookshelf of both specialist and practicing scientists and engineers wishing to increase their knowledge of how fracture toughness is estimated and fracture mechanics is applied in structural integrity assessments.


Review by Dr David Lidbury, Serco TAS

Defect assessments are conducted routinely in many industries to assess the integrity or fitness for purpose of components whose failure would have unacceptable consequences, in terms of safety and economics. An essential feature of any defect assessment is an evaluation of the stability of a known or postulated flaw, which involves a comparison of load and resistance. Thus, proximity to crack initiation or unstable crack growth is assessed by calculating the crack driving force and comparing it with the material fracture toughness. This presents a major difficulty which is only partially addressed by current fracture toughness test standards. While fracture mechanics procedures for calculating the crack driving are relatively well developed, the material fracture toughness appropriate to a particular assessment can be much more difficult to estimate. Often this is because only an indirect guide as to the correct value to use is available, e.g. via knowledge of a transition temperature or impact energy. Even if fracture toughness data are available, there is the complication that the mechanisms of ductile and brittle fracture are quite different and that they respond differently to parameters such as temperature, loading rate, structural size, and geometry and load configuration (constraint). Moreover, variations in fracture toughness values from heat to heat or batch to batch can be considerable, requiring different statistical considerations for brittle and ductile fracture. This is further compounded if fracture toughness has to be evaluated over a range of temperatures for which a transition from ductile to brittle behaviour is possible.

The basic outline of the book is as follows:

The aims and objectives are set out clearly in the Introduction, where it is noted that the text is primarily concerned with the fracture toughness of metals, particularly structural ferritic steels. The following chapter introduces the major elastic and elastic-plastic crack driving force parameters and the corresponding definitions of fracture toughness, classified according to the extent of ductile tearing which precedes macroscopic failure. Chapter 3 covers the testing of bend specimens, and reviews some standard expressions used in the elastic and elastic-plastic regimes for the estimation of stress intensity factor (KI) and J-integral values. Added-value advice is given on adjustments which may be considered, as required, to extend the range of applicability of the standard expressions. Chapter 4 will be of particular interest to many practitioners, since it comprises valuable background to, and a very detailed description of, Wallin’s acknowledged Master Curve description of brittle fracture, covering the fracture toughness of both homogeneous and inhomogeneous materials. Chapter 5 deals with ductile fracture toughness and, like the preceding chapter, includes coverage of specimen measuring capacity, data scatter, temperature dependence, effects of specimen side-grooving, and size and constraint effects. The following three chapters respectively consider: loading rate effects on brittle fracture and ductile tearing, and crack arrest; engineering interpretation of the Charpy impact test; and indirect estimations of fracture toughness – covering various ductile-brittle transition temperature concepts, as well as estimation of ductile tearing properties from Charpy-V tests and other impact tests, such as the drop-weight tear test (DWTT). (The exposition in Chapter 7 is particularly thorough and detailed.) Against the background provided by the first eight chapters, the final four chapters address a number of important application areas. Chapter 9 briefly introduces the methodology of structural integrity assessment and outlines the European SINTAP/FITNET procedures. Chapter 10 covers a number of issues affecting the transferability of fracture toughness test results to the assessment of the integrity of components and structures, specifically: the relevance of J-based fracture toughness measurements to the assessment of ductile tearing and cleavage in large-scale tests or real components; constraint effects, based on a two-parameter description of fracture behaviour; and the effects of warm prestressing (WPS) on effective cleavage fracture toughness. Chapter 11 provides a brief overview of statistical methods in fracture toughness estimation, with a focus on the measurement of cleavage initiation fracture toughness. The concluding chapter presents a number of examples (including the analysis of thermal shock and pressurised thermal shock tests) based on the methods presented in the previous chapters, again with emphasis on fracture toughness at temperatures in the brittle failure regime.

The overall aim of the book is stated as to provide advice on how best to estimate a material’s fracture toughness (advising on test procedure and suitable parameter or providing relationships between available parameters) and how to apply the result in a structural integrity assessment. The emphasis is on application of relatively simple, often innovative, analytical models, rather than reliance on heavy-duty computational methods. On the author’s admission, some parts of the book, due to their novelty, may appear outside commonly accepted views and therefore controversial. Although demanding more than a casual familiarity with fracture mechanics concepts, the book contains a wealth of data and illustrative analyses, detail and fresh insights on both familiar and less familiar themes which will be of great value to its intended readership: indeed, the author states that approximately 80-85% of the material presented in just over 500 pages has not been previously published.

A summary at the end of each chapter would have provided the reader with an overview of the various complex issues discussed within it. Moreover, a concluding chapter, drawing together (at least to the extent currently possible) the various threads forming the unified view of fracture toughness estimation that the author set out to explore in the Introduction, would have been useful. It would certainly have enhanced the reader’s appreciation of the extent to which the book had met its original aims. But these are relatively minor points, and might be addressed in a subsequent edition. Overall, “Fracture Toughness of Engineering Materials – Estimation and Application” can be recommended as providing a valuable and up-to-date addition to the bookshelf of any specialist wishing to increase their knowledge of how fracture toughness is estimated in structural integrity assessments.



Notation ix




Introduction 1


1.1 Background 1


1.2 This
book 2


1.3 The
case of the Titanic 3


1.4 Brittle
vs ductile 5


1.5 Structural
materials 6


1.6 References 7




Fracture Mechanical


2.1 General 8


2.2 Crack
driving force parameters 9


2.3 Definitions
of fracture toughness 25


2.4 References 65




Testing of Bend


3.1 General 72


3.2 The
compact tension C(T) specimen 77


3.3 Single-edged
bend specimen SE(B) 90


3.4 Quality
assurance 107


3.5 References 110




4 Brittle Fracture Toughness (the Master Curve)


General 115
4.2 Statistical
modelling of cleavage fracture initiation – derivation of the
Master Curve (MC)
probability distribution 118


4.3 MC
scatter 135


4.4 The
MC statistical size 142


4.5 Temperature
dependence of Kmin 147


4.6 Temperature
dependence of K0 152


4.7 Measuring
capacity of bend specimens for brittle fracture toughness
testing 157


4.8 Effect
of prior stable crack extension on cleavage fracture probability 169


4.9 Pre-fatigue
requirements of brittle fracture toughness testing 173


4.10 Analysis
of inhomogeneous materials 175


4.11 References 186




5 Ductile Fatigue Toughness


5.1 General 192


5.2 Tearing
resistance curve expressions 193


5.3 Scatter
in ductile tearing resistance 200


5.4 Effect
of side-grooving 206


5.5 Measuring
capacity of bend specimens 208


5.6 Extrapolation
of tearing resistance curves 214


5.7 Temperature
dependence of ductile tearing resistance 217


5.8 The
effect of mixed mode loading on the tearing resistance 221


5.9 References 223




6 Loading Rate Effects and Crack Arrest


6.1 General 226


6.2 Effect
of loading rate 226


6.3 Crack
arrest toughness 243


6.4 References 256




7 Engineering Interpretation of Charpy Impact Test


7.1 Introduction 261


7.2 Physical
aspects of the Charpy test 263


7.3 Sub-sized
and miniature specimens 281


7.4 Description
of Charpy transition curves 398


7.5 Instrumented
impact testing 310


7.6 References 313




8 Indirect Fracture Toughness Estimation


8.1 General 321


8.2 Relation
between different transition temperatures 327


8.3 Fracture
toughness correlations 339


8.4 References 366




9 Structural Integrity Assessment Procedures


9.1 General 373


9.2 Plasticity
correlation 378


9.3 Definition
of brittle fracture reference fracture toughness 386


9.4 Simple
plastic collapse criterion 388


9.5 References 392




10 Transferabiltity of Fracture Toughness to Structural Integrity


10.1 General 395


10.2 Parameter
validity 395


10.3 Constraint 401


10.4 Description
of real flaws 424


10.5 Residual
stresses 428


10.6 Warm
pre-stressing 432


10.7 References 438




11 Statistical Methods in Fracture Toughness Estimation


11.1 General 447


11.2 Some
distribution functions 449


11.3 Rank
probability estimation 451


11.4 Maximum
likelihood estimation 459


11.5 Significance
of deterministic lower bound estimates 462


11.6 Statistical
planning 467


11.7 References 476




12 Examples


12.1 Introduction 478


12.2 Assessing
the fracture toughness of a 18MND5 (A533B) steel 478


12.3 Assessment
of the EURO curve material’s fracture toughness 487


12.4 Assessment
of thermal shock experiments 497


12.5 Assessment
of the Point Pleasant Bridge failure 506


12.6 Assessment
of pressurised thermal shock experiments 511


12.7 References 517




13 The Re-analysed EURO Fracture Toughness Data Set




Index 536