Code of practice for creep/fatigue testing of cracked components

The scope of ISO/TTA 5:2006 is to recommend and establish standardized techniques for measuring and analysing Creep Crack Initiation (CCI), Creep Crack Growth (CCG), and Creep Fatigue Crack Growth (CFCG) characteristics using a wide range of pre-cracked standard and non-standard "feature" geometries.

Code de bonne pratique pour les essais de fluage/fatigue des composants fissurés

General Information

Status
Replaced
Publication Date
04-Dec-2006
Withdrawal Date
04-Dec-2006
Current Stage
6060 - International Standard published
Start Date
20-Nov-2006
Completion Date
05-Dec-2006
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TECHNOLOGY ISO/TTA 5
TRENDS
ASSESSMENT
First edition
2006-12-15
Code of practice for creep/fatigue testing
of cracked components
Code de bonne pratique pour les essais de fluage/fatigue des
composants fissurés
Reference number
ISO/TTA 5:2006(E)
ISO 2006
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ISO/TTA 5:2006(E)
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© ISO 2006

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© ISO 2006 – All rights reserved
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ISO/TTA 5:2006(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies

(ISO member bodies). The work of preparing International Standards is normally carried out through ISO

technical committees. Each member body interested in a subject for which a technical committee has been

established has the right to be represented on that committee. International organizations, governmental and

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International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting. Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote.

To respond to the need for global collaboration on standardization questions at early stages of technological

innovation, the ISO CounciI, following recommendations of the ISO/IEC Presidents' Advisory Board on

Technological Trends, decided to establish a new series of ISO publications named ‘Technology Trends

Assessments” (ISO/TTA). These publications are the results of either direct cooperation with

prestandardization organizations or ad hoc Workshops of experts concemed with standardization needs and

trends in emerging fields.

Technology Trends Assessments are thus the result of prestandardization work or research. As a condition of

publication by ISO, ISO/TTAs shall not conflict with existing International Standards or draft International

Standards (DIS), but shall contain information that would normally form the basis of standardization. ISO has

decided to publish such documents to promote the harmonization of the objectives of ongoing

prestandardization work with those of new initiatives in the Research and Development environment. It is

intended that these publications will contribute towards rationalization of technological choice prior to market

entry. Whilst ISO/TTAs are not Standards, it is intended that they will be able to be used as a basis for

standards development in the future by the various existing standards agencies.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO/TTA 5 was prepared by VAMAS TWA25 and published under a memorandum of understanding

concluded between ISO and VAMAS.
iii
© ISO 2006 – All rights reserved
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ISO/TTA 5:2006(E)
TABLE OF CONTENTS

1. EXECUTIVE SUMMARY .......................................................................................................................... 1

2. SCOPE...................................................................................................................................................... 1

3. SPECIFIC OBJECTIVES.......................................................................................................................... 2

4. INTRODUCTION....................................................................................................................................... 3

4.1 BACKGROUND TO VAMAS CREEP CRACK GROWTH INITIATIVES................................................................ 3

4.2 BACKGROUND TO INDUSTRIAL NEEDS FOR VALIDATED TEST DATA.............................................................. 3

4.3 RELEVANCE OF TESTING METHODS TO LIFE ASSESSMENT CODES............................................................. 4

4.3.1 Background to Life Assessment Codes ......................................................................................... 4

4.3.2 Relation between laboratory tests and Component Assessment Codes....................................... 5

4.3.3 Factors involved in the development of assessment codes........................................................... 6

4.4 REQUIREMENTS FOR THE VAMAS TWA 25 COP...................................................................................... 6

4.5 ISO REQUIREMENTS................................................................................................................................7

4.5.1 ISO Technology Trend Assessment (ISO/TTA)............................................................................. 7

5. ACKNOWLEDGEMENTS......................................................................................................................... 8

5.1 LIST OF PARTICIPANTS IN VAMAS TWS25............................................................................................... 8

6. NOMENCLATURE AND ABBREVIATIONS............................................................................................ 9

6.1 NOMENCLATURES ................................................................................................................................... 9

6.2 LISTING OF ABBREVIATIONS.................................................................................................................... 10

7. DESCRIPTION OF CREEP AND FATIGUE CRACKING...................................................................... 11

7.1 FAILURE DUE CREEP CRACK GROWTH (CCG)........................................................................................ 11

7.2 CREEP CRACK INITIATION (CCI)............................................................................................................. 11

7.3 TRANSIENT CRACK GROWTH CONDITIONS ............................................................................................... 11

7.4 STEADY STATE CREEP CRACKING (CCG)............................................................................................... 11

7.5 FATIGUE AND CREEP/FATIGUE CRACK GROWTH (FCG AND CFCG) ........................................................ 12

7.5.1 Failure due to fatigue.................................................................................................................... 12

7.5.2 Creep/Fatigue interaction............................................................................................................. 12

7.6 FACTORS AFFECTING CCI, CCG AND CFCG.......................................................................................... 12

7.6.1 Creep properties........................................................................................................................... 12

7.6.2 Metallurgical effects...................................................................................................................... 13

7.6.3 Presence of residual stress fields................................................................................................. 13

7.6.4 Aggressive environments ............................................................................................................. 13

7.6.5 Anisotropic and inhomogeneous material characteristics............................................................ 13

8. TEST METHODS .................................................................................................................................... 13

8.1 OVERVIEW ............................................................................................................................................ 14

8.2 TEST GEOMETRIES................................................................................................................................14

8.3 EXPERIMENTAL TEST METHODS............................................................................................................. 15

8.3.1 Material procurement ................................................................................................................... 15

8.3.2 Specimen selection ...................................................................................................................... 15

8.3.3 Crack-plane orientation ................................................................................................................ 15

8.3.4 Specimen machining ................................................................................................................... 15

8.3.5 Specific size requirements ........................................................................................................... 16

8.3.6 Specific side-grooving requirements ............................................................................................ 16

8.3.7 Shape of the crack front ............................................................................................................... 16

8.3.8 Pre-cracking to introduce a sharp flat crack front........................................................................ 16

8.3.9 Pre-cracking for CCI tests ............................................................................................................ 16

8.3.10 Crack length measurements ........................................................................................................ 17

8.3.11 The use of Potential Drop (PD) .................................................................................................... 17

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ISO/TTA 5:2006(E)

8.3.12 Preparing the specimens for PD leads ........................................................................................ 17

8.3.13 Specimen setup ........................................................................................................................... 17

8.3.14 Loading and creep displacement measurements ........................................................................ 17

8.3.15 Displacement gauge .................................................................................................................... 18

8.3.16 Heating of the specimens............................................................................................................. 18

8.3.17 Initial pre-load............................................................................................................................... 18

8.3.18 Monitoring the temperature.......................................................................................................... 18

8.3.19 Unplanned temperature excursions ............................................................................................. 18

8.3.20 Initial pre-load............................................................................................................................... 18

8.3.21 Specimen loading......................................................................................................................... 19

8.4 DATA COLLECTION.................................................................................................................................19

8.4.1 Detailed test and data monitoring ................................................................................................ 19

8.4.2 Data logging ................................................................................................................................. 19

8.4.3 Displacement measurements.......................................................................................................19

8.5 POST-TEST MEASUREMENTS..................................................................................................................20

8.5.1 Measurement of the final crack front............................................................................................20

8.5.2 Crack tip bowing........................................................................................................................... 20

8.5.3 Crack extension criteria................................................................................................................ 20

8.5.4 Crack deviation criteria................................................................................................................. 20

8.6 RECOMMENDED MINIMUM NUMBER AND DURATION FOR TESTS................................................................21

8.6.1 Batch to batch variability .............................................................................................................. 21

8.6.2 Minimum test requirements.......................................................................................................... 21

8.6.3 Single point data per test ............................................................................................................. 22

8.6.4 Multiple points data per test ........................................................................................................ 22

8.6.5 Test duration requirements .......................................................................................................... 22

8.7 SENSITIVITY AND ACCURACY LIMITS OF THE RESULTS..............................................................................22

8.7.1 Effects of data variability on correlation for FCG, CCG and CCI................................................. 22

8.8 PREPARATION OF TEST DATA .................................................................................................................23

8.8.1 Data collection.............................................................................................................................. 23

8.8.2 Time at which the test should be stopped.................................................................................... 23

8.8.3 Smoothing the PD output data..................................................................................................... 23

8.8.4 Deriving the crack length from the PD output .............................................................................. 23

8.8.5 Recommended number of data points......................................................................................... 24

8.8.6 Calculating cracking and displacement rates............................................................................... 24

9. DATA ANALYSIS PROCEDURES .........................................................................................................24

9.1 CHOOSING AN APPROPRIATE CCI OR CCG RATE CORRELATING PARAMETER ...........................................24

9.1.1 Choice of parameter for correlating CCG .................................................................................... 24

9.1.2 Choice of the C* term for CCG rate ............................................................................................. 25

9.1.3 Choice of parameter for CCI ........................................................................................................ 25

9.2 DEFINITIONS FOR THE RELEVANT FRACTURE MECHANICS PARAMETERS ...................................................25

9.2.1 Stress intensity factor, K .............................................................................................................. 25

9.2.2 J-integral....................................................................................................................................... 25

9.2.3 The C* parameter......................................................................................................................... 25

9.2.4 Creep zone................................................................................................................................... 26

9.2.5 Steady state creep ....................................................................................................................... 27

9.2.6 The C parameter ......................................................................................................................... 27

9.2.7 Small-scale creep......................................................................................................................... 27

9.2.8 Interpretation of C* parameter...................................................................................................... 27

9.2.9 Time Dependant Failure Assessment Diagram (TDFAD) for CCI ............................................... 28

9.2.10 The Q* Parameter ........................................................................................................................ 28

9.3 CRITERIA FOR VALIDITY CHECKS OF C* AND K.........................................................................................28

9.3.1 Check for validity of C*................................................................................................................. 28

9.3.2 Components of displacement rates ............................................................................................. 29

9.3.3 Validity criteria for C* for highly ductile materials......................................................................... 29

9.3.4 Validity criteria for creep brittle materials..................................................................................... 30

9.3.5 Transition time criteria for C*........................................................................................................ 30

10. REPORTING PROCEDURES .................................................................................................................31

10.1 DETAILS OF TEST INFORMATION TO BE REPORTED....................................................................................31

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ISO/TTA 5:2006(E)

10.1.1 Report of findings ......................................................................................................................... 31

10.1.2 Pedigree of the material ............................................................................................................... 31

10.1.3 Material properties to be logged................................................................................................... 31

10.1.4 Test machine description ............................................................................................................. 31

10.1.5 Details of starter crack.................................................................................................................. 31

10.1.6 Details for loading......................................................................................................................... 32

10.1.7 Report of data analysis................................................................................................................. 32

10.1.8 Plots of data.................................................................................................................................. 32

10.1.9 Tabulation of results ..................................................................................................................... 32

10.1.10 Photographic/micrographic evidence ....................................................................................... 32

10.1.11 Treatment of anomalous data................................................................................................. 32

11. CORRELATING CRACK GROWTH USING FRACTURE MECHANICS .............................................. 32

11.1 CCG RATE ANALYSIS............................................................................................................................ 33

11.2 CRACK INITIATION (CCI) ANALYSIS ........................................................................................................ 33

11.3 FCG RATE ANALYSIS............................................................................................................................ 34

11.4 CREEP/FATIGUE CRACK GROWTH RATE ANALYSIS.................................................................................... 34

12. METHODS FOR CALCULATING THE C* PARAMETER ................................................................... 34

12.1 EXPERIMENTAL ESTIMATES OF C*.......................................................................................................... 35

12.2 REFERENCE STRESS METHOD OF ESTIMATING C* .................................................................................. 36

13. APPENDIX I ............................................................................................................................................ 37

13.1 TEST SPECIMEN GEOMETRIES ............................................................................................................... 37

13.2 GEOMETRY DEFINITIONS FOR LABORATORY SPECIMENS......................................................................... 37

14. SPECIMEN FRACTURE MECHANICS PARAMETER SOLUTIONS.................................................... 39

14.1 STRESS INTENSITY FACTOR K................................................................................................................ 39

14.2 SOLUTIONS FOR THE Y FUNCTION .......................................................................................................... 40

14.2.1 Y factor for C(T) ......................................................................................................................... 40

14.2.2 Y factor for CS(T)...................................................................................................................... 40

14.2.3 Y factor for for SEN(T) .............................................................................................................. 40

14.2.4 Y factor for SEN(B) (3 Point Bend Specimen) ........................................................................ 40

14.2.5 Y factor for DEN(T) .................................................................................................................... 41

14.2.6 Y factor for M(T)......................................................................................................................... 41

14.3 C* SOLUTIONS ...................................................................................................................................... 41

14.4 REFERENCE STRESS (σ ) SOLUTIONS.................................................................................................. 42

REF

14.4.1 σ for C(T) .................................................................................................................................. 42

ref

14.4.2 σ for CS(T)................................................................................................................................43

ref

14.4.3 σ for SEN(T)............................................................................................................................ 43

ref

14.4.4 σ for SEN(B) (3 Point Bend Specimen) ................................................................................ 43

ref

14.4.5 σ for DEN(T)............................................................................................................................. 43

ref

14.4.6 σ for M(T) ................................................................................................................................. 44

ref

14.5 η FUNCTIONS FOR CRACKED GEOMETRIES.............................................................................................. 44

14.5.1 Nomenclature (see Figure A.I.3)................................................................................................... 44

14.5.2 Solutions for creep crack growth parameter, C* .......................................................................... 45

14.5.3 Best fit solutions of η from finite element calculations................................................................. 45

14.5.4 Choice of η for evaluating C* for material CCI and CCG properties............................................ 46

14.5.5 Choice of η for evaluating C* in life assessment.......................................................................... 46

14.6 η FUNCTION EQUATIONS ....................................................................................................................... 46

14.6.1 η functions for C(T) .................................................................................................................. 46

14.6.2 η functions for CS(T)............................................................................................................... 47

14.6.3 η functions for SEN(T) ............................................................................................................ 47

14.6.4 η functions for SEN(B) — 3PB ............................................................................................... 48

14.6.5 η functions for DEN(T) ............................................................................................................ 48

14.6.6 η functions for M(T)................................................................................................................. 49

LLD

14.7 TABLE FOR Η .................................................................................................................................... 50

CMOD

14.8 TABLE FOR Η .................................................................................................................................. 51

14.9 GEOMETRY DEFINITIONS FOR 'FEATURE’ TYPE SPECIMENS..................................................................... 52

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ISO/TTA 5:2006(E)

14.9.1 Details form Pipe, Plate and Notched bar 'feature specimens'.................................................... 52

14.10 FRACTURE MECHANICS FUNCTIONS FOR FEATURE COMPONENTS............................................................53

14.10.1 K solutions for pipes and plates ............................................................................................... 53

14.10.2 Reference stress solutions for pipes ........................................................................................ 54

14.10.3 Reference stress solutions for plates ....................................................................................... 54

14.10.4 Stress intensity factor K for the round notch bar ...................................................................... 55

14.10.5 C* parameter for the notched bar............................................................................................. 55

15. APPENDIX II :(TDFAD) K APPROACH FOR CCI............................................................................55

mat

15.1 INTRODUCTION.......................................................................................................................................55

15.2 NOMENCLATURE ....................................................................................................................................56

15.3 FAILURE ASSESSMENT DIAGRAM ............................................................................................................57

15.4 MATERIALS DATA REQUIREMENTS ..........................................................................................................58

16. APPENDIX III: THE Q* PARAMETER ....................................................................................................62

16.1 SYMBOLS AND DESIGNATIONS ................................................................................................................62

16.2 SCOPE ..................................................................................................................................................63

16.3 SPECIMEN GEOMETRY .........................................
...

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