TECHNIQUES FOR MULTIAXIAL CREEP TESTING

UK High TemperattK8 Mechanical Testing Committee

Based on the edited proceedings of a symposium held at Central Electricity Research Laboratories, Leatherhead, UK, 25-26 September 1985.

Programme Committee and Editorial Panel:

Dr B.J. Cane Dr B. F. Dyson Dr D. J. Gooch Professor D. R. Hayhurst Mr I. M. How Dr R. C. Hurst Dr S. T. Kimmins Mr M. S. Loveday Dr G. A. Webster*

*Editorial panel only

ERA Technology Ltd NPL CEGB-CERL (Chairman) Sheffield University ERA Technology Ltd JRC Petten CEGB-CERL NPL Imperial College

UK High Temperature Mechanical Testing Committee:

Dr B. F. Dyson Professor E. G. EllisonjDr W. Plumbridge Mr R. B. Evans Dr D. J. Gooch Professor D. R. Hayhurst Mr I. M. How Dr R. D. Lohr Mr M. S. Loveday Mr J. Orr Mr R. W. Suhr Dr G. Sumner Mr G. B. Thomas Mr D. S. Thorn Dr G. A. Webster

NPL (Chairman) Bristol University NEI-IRD CEGB-CERL Sheffield University ERA Technology Ltd Instron Ltd NPL (Secretary) BSC GEC UKAEA ERA Technology Ltd Rolls Royce Imperial College

TECHNIQUES FOR MULTIAXIAL CREEP

TESTING

Edited by

D. J. GOOCH

CEGB, Central Electricity Research Laboratories, Leatherhead, UK

and

I. M. HOW

ERA Technology Ltd, Leatherhead, UK

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WITH 18 TABLES AND 170 ILLUSTRATIONS

© ELSEVIER APPLIED SCIENCE PUBLISHERS LTD 1986

© CROWN COPYRIGHT 1986--Chapters 2,8 and 10 Softcover reprint of the hardcover 1st edition 1986

British Library Cataloguing in Publication Data

Techniques for multi axial creep testing. 1. Materials-Creep 2. Materials at high temperatures I. Gooch, D. J. II. How, I. M. 620.1'1233 TA418.22

Library of Congress Cataloging in Publication Data

Techniques for multiaxial creep testing.

"Based on the edited proceedings of a symposium held at Central Electricity Research Laboratories, Leatherhead, UK, 25-26 September 1985"­

Bibliography: p. Includes index. 1. Metal&--Creep--Congresses. 2. Metals--Testing­

Congresses. 3. Metals at high temperatures--Testing­Congresses. I. Gooch, D. J. II. How, I. M. TA460.T359 1986 620.1'633 86-16818

ISBN-13: 978-94-010-8027-9 e-ISBN-13: 978-94-009-3415-3 001: 10.1007/978-94-009-3415-3

The selection and presentation of material and the opinions expressed are the sole responsibility of the author(s) concerned

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Introduction

The design and assessment of modern high temperature plant demands an understanding of the creep and rupture behaviour of materials under multi axial stress states. Examples include thread roots in steam turbine casing bolts, branch connections in nuclear pressure vessels and blade root fixings in gas or steam turbine rotors. At one extreme the simple notch weakening/notch strengthening characterization of the material by circumferentially vee-notched uniaxial rupture tests, as specified in many national standards, may be sufficient. These were originally intended to model thread roots and their conservatism is such that they frequently are considered adequate for design purposes. At the other extreme full size or model component tests may be employed to determine the safety margins built into design codes. This latter approach is most commonly used for internally pressurized components, particularly where welds are involved. However, such tests are extremely expensive and the use of modern stress analysis techniques combined with a detailed knowledge of multiaxial properties offers a more economic alternative.

Design codes, by their nature, must ensure conservatism and are based on a material's minimum specified properties. In the case of high temperature components the extension of life beyond the nominal design figure, say from 100000 to 200000 h, offers very significant economic benefits. However, this may require a more detailed understanding of the multiaxial behaviour of a specific material than was available at the design stage.

Much effort has been devoted in recent years to quantifying the state of stress in multi axial specimen geometries and to studying the defor­mation and rupture mechanisms and their dependence upon stress state. However, comparatively little attention has been paid to the practical

v

vi Introduction

difficulties associated with multiaxial testing. This may be contrasted with the situation which exists for uniaxial testing which is covered by national standards, largely because of the historical dependence of design procedures on reliable uniaxial data. In the future, increasing importance will be attached to multi axial data and it is essential that testing techniques are soundly based in theory and are adequately controlled. It is also important to develop simplified techniques which may be used to generate the required volume of data economically. It is therefore an appropriate time to review the state of the multiaxial testing art both from a theoretical and practical standpoint.

For this reason the UK High Temperature Mechanical Testing Committee (UKHTMTC), whose secretariat is at the National Physical Laboratory (NPL), organized a symposium on Techniquesfor Multiaxial Creep Testing in September 1985. The meeting was held at the Central Electricity Research Laboratories (CERL) under the auspices of the Central Electricity Generating Board and ERA Technology Ltd. The primary aim of the UKHTMTC is to promote discussion, development and, where appropriate, standardization of testing techniques. This meet­ing was the third in a series devoted to techniques in pursuance of that aim. The first was held at NPL in 1981 and the proceedings were published as Measurement of High Temperature Mechanical Properties of Materials edited by M. S. Loveday, M. F. Day and B. F. Dyson (HMSO, London, 1982). The second was held at Preston in 1983 under the auspices of Springfields Nuclear Power Development Laboratories, the proceedings being published as Techniquesfor High Temperature Fatigue Testing edited by G. Sumner and V. B. Livesey (Elsevier Applied Science Publishers, London, 1985). The present volume comprises the edited proceedings of the 1985 meeting. The majority of papers were invited although a number of shorter contributed papers which highlight specific aspects are also included. It is hoped that the book will prove a valuable reference work for all concerned with the design and execution of multiaxial creep tests.

The introductory chapter outlines the theory of deformation and rupture under multi axial conditions and gives examples of component studies for which an understanding of multiaxial behaviour is necessary. Following this the book is divided into three sections as at the con­ference. The first deals with biaxial techniques which are the most readily interpretable but which generally require purpose-built testing machines. The most common technique is the tension/torsion of thin-walled tubes which permits the application of stresses ranging from pure shear to pure

Introduction vii

tension. Accurate extensometry poses a particular problem in these tests and detailed descriptions of techniques developed to overcome this are given. A simplified double shear test which may be performed using standard creep machines is described in Chapter 2 and the ultimate biaxial test, the cruciform test, is the subject of Chapter 7.

The second section is concerned with triaxial techniques and Chapter 9 gives a comprehensive overview of the theory behind the most common of these, the circumferentially notched bar test, with the next two chapters covering the practical aspects. Triaxiality may also be induced by the superimposition of a hydrostatic stress upon a tensile test and Chapter 13 describes how this may be achieved. Finally, one of the most common causes of triaxiality is the mismatch of creep strength between weld metal and parent material in we1dments and this is dealt with in Chapter 12. This area is of growing importance since the great majority of .creep failures of thick section high temperature components occur at weld­ments where stress triaxiality leading to low ductility frequently is identified as the primary cause.

The last section covers the testing of pressurized tubes and com­ponents, these being the most realistic tests possible for most pressure vessels. They may be used to determine multiaxial stress rupture criteria but also permit the measurement of representative stresses for defor­mation and rupture for direct application to service situations. Chapter 14 summarizes the stress state theory and the subsequent chapters describe how theory is turned into practice. The final chapter culminates in a description of the ultimate multiaxial test, the full sized pressure vessel.

It remains to thank all those who contributed to the preparation of this book and the many people who assisted in the organization of the 1985 symposium. Particular thanks are due to the Organizing Committee, who also constituted the majority of the Editorial Panel, for many hours of their time. The support and assistance of colleagues at CERL and ERA, without whom the symposium would not have taken place, is also gratefully acknowledged. However, at the end of the day the success of a conference and its subsequent publication depends on the authors and it is to these that we extend our especial gratitude.

D. J. GOOCH

I. M. How

Contents

Introduction . v

List of Contributors xiii

PART I: DATA REQUIREMENTS

1. Multiaxial Data Requirements for Structural Integrity Assessments in Creep. 3

I. w. GOODALL

PART II: BIAXIAL TESTING

2. The Application of Torsional and Double Shear Tests 31 J. HENDERSON

3. Requirements for Thin-walled Torsion Testing. 53 D. W. A. REEs

4. A Tension-Torsion Testing Technique 79

W. TR~MPCZYNSKI and Z. KOWALEWSKI

5. A Biaxial Tension-Torsion, Constant Stress, Creep Testing Machine 93

P. DELOBELLE, D. VARCHON and C. OYTANA

6. Torsion Testing in an Inert Atmosphere . 103 M. S. SHAMMAS and K. D. MARCHANT

ix

x Contents

7. Biaxial Testing Using Cruciform Specimens 111 C. J. MORRISON

8. Effects of Overloads and Creep on the Yield Surface of a Nickel-based Superalloy 127

M. R. WINSTONE and G. F. HARRISON

PART III: TRIAXIAL TESTING

9. An Overview on Studies of Stress State Effects During Creep of Circumferentially Notched Bars 137

D. R. HAYHURST and G. A. WEBSTER

10. Practical Aspects of Testing Circumferential Notch Specimens at High Temperature 177

M. S. LoVEDAY

11. Creep Tests on Axisymmetric Notched Bars: Global Displacement Measurements and Metallographic Determination of Local Strain and Damage 199

C. LEVAILLANT, A. PINEAU, M. YOSHIDA and R. PIQUES

12. Computer Modelling of Creep Damage in Components with Variable Metallurgical Structure 209

R. W. EVANS and B. WILSHIRE

13. Multiaxial Creep Testing Using Uniaxially Loaded Specimens with a Superimposed Hydrostatic Pressure 223

D. LoNSDALE and P. E. J. FLEWITT

Editors' Note: Creep Rupture Testing under Triaxial Tension 241

PART IV: PRESSURISED TUBES AND COMPONENTS

14. Stress State Distributions in Thick-walled Pressurised Tubes under Creep Loading

B. J. CANE 245

Contents xi

15. Potential for Standardisation of Techniques for Creep Testing of Internally Pressurised Tubular Components 267

R. C. HURST and I. M. How

16. Experiments on Multiaxial Creep Above 800°C. 295 M. R6DIG, W. HANNEN, H. HELLWIG, J. KLOMFASS

17. Some Experiences in the Creep Testing of Piping Elbows 305 K. RAE, J. T. BoYLE and J. SPENCE

18. Creep Rupture Testing of Tubular Model Components 311 R. J. BROWNE

19. Full Size Component Testing under Creep Conditions 333 M. C. CoLEMAN, R. FIDLER and J. A. WILLIAMS

Index. 357

List of Contributors

J. T. BoYLE

Department of Mechanics of Materials, University of Strathclyde, 75 Montrose St, Glasgow GIIXJ, UK

R. J. BROWNE

CEGB, SE Region Scientific Services Department, Canal Road, Gravesend, Kent DA12 2RS, UK

B. J. CANE

ERA Technology Ltd., Cleeve Road, Leatherhead, Surrey KT22 7SA, UK

M. C. CoLEMAN

CEGB, Marchwood Engineering Laboratories, Marchwood, Southampton S04 4ZB, UK

P. DELOBELLE

Laboratoire de M ecanique Appliquee, F aculte des Sciences et des Techniques, Route de Gray, La Bouloie, 25030 Besan~on Cedex, France

R. W. EVANS

Department of Metallurgy and Materials Technology, University College of Swansea, Singleton Park, Swansea SA2 8P P, UK

xiii

xiv List of Contributors

R. FIDLER

CEGB, Marchwood Engineering Laboratories, Marchwood, Southampton S04 4ZB, UK

P. E. J. FLEWITT

CEGB, SE Region Scientific Services Department, Canal Road, Gravesend, Kent DAl2 2RS, UK

I. W. GOODALL

CEGB, Berkeley Nuclear Laboratories, Berkeley, Gloucestershire GL13 9PB, UK

W. HANNEN

Nuclear Research Centre, liilich Institutefor Reactor Materials, 5170 Jiilich, Federal Republic of Germany

G. F. HARRISON

Royal Aircraft Establishment, Pyestock, Farnborough, Hampshire GU14 OLS, UK

D. R. HAYHURST

Department of Mechanical Engineering, University of Sheffield, Mappin Street, Sheffield, Yorkshire S1 3lD, UK

H. HELLWIG

Nuclear Research Centre, liilich Institutefor Reactor Materials, 5170 lulich, Federal Republic of Germany

J. HENDERSON

National Engineering Laboratory, East Kilbride, Glasgow G75 OQU, UK. Present address: 43 Fernleigh Road, Newlands, Glasgow G43 2UD, UK

I. M. How ERA Technology Ltd., Cleeve Road, Leatherhead, Surrey KT22 7SA, UK

List of Contributors xv

R. C. HURST

Joint Research Centre, 1755 ZG Petten, The Netherlands

J. KLOMFASS

Nuclear Research Centre, Jiilich 1nstitutefor Reactor Materials, 5170 Jiilich, Federal Republic of Germany

z. KOWALEWSKI

Polish Academy of Sciences, Swietokryzska 21, 00-049 Warsaw, Poland

C. LEVAILLANT

Ecole Nationale Superieure des Mines de Paris, Centre des Materiaux, BP87, 91003 Evry Cedex, France

D. LoNSDALE

CEGB, SE Region Scientific Services Department, Canal Road, Gravesend, Kent DA12 2RS, UK

M. S. LoVEDAY

National Physical Laboratory, Division of Materials Applications, Teddington, Middlesex TWll OLW, UK

K. D. MARCHANT

CEGB, Central Electricity Research Laboratories, Kelvin Avenue, Leatherhead, Surrey KT22 7SE, UK

C. J. MORRISON

Department of Engineering, University of Leicester, Leicester LE17RH, UK

C. ()YTANA

Laboratoire de M ecanique Appliquee, F acuite des Sciences et des Techniques, Route de Gray, La Bouloie, 25030 Besan~on Cedex, France

xvi List of Contributors

A. PINEAU

Ecole Nationale Superieure des Mines de Paris, Centre des Matl?riaux, BP87, 91003 Evry Cedex, France

R. PIQUES

Ecole Nationale Superieure des Mines de Paris, Centre des Materiaux, BP87, 91003 Evry Cedex, France

K. RAE Ferranti Pic, Ferry Road, Edinburgh, UK

D. W. A. REES

Faculty of Engineering, University of Surrey, Guildford, Surrey GU2 5XH, UK. Present address: Department of Manufacturing and Engineering Systems, Brunei University, Uxbridge, Middlesex UB8 3PH, UK

M. RODIG

Nuclear Research Centre, Jiilich Institutefor Rellctor Materials, 5170 Jiilich, Federal Republic of Germany

M. S. SHAMMAS

CEGB, Central Electricity Research Laboratories, Kelvin Avenue, Leatherhead, Surrey KT22 7SE, UK

J. SPENCE

Department of Mechanics of Materials, University of Strathclyde, 75 Montrose St., Glasgow G1 1XJ, UK

W. TRAMPCZYNSKI

Polish Academy of Sciences, Swietokryzska 21, 0~49 Warsaw, Poland

D. VARCHON

Laboratoire de M ecanique Appliquee, F aculte des Sciences et des Techniques, Route de Gray, La Bouloie, 25030 Besan90n Cedex, France