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ECCC

ECCC RECOMMENDATIONS - VOLUME 2 Part V [Issue 1]

TERMS AND TERMINOLOGY USED FOR THE

GENERATION AND ASSESSMENT OF
MULTI-AXIAL FEATURE SPECIMEN AND
COMPONENT TEST DATA
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ECCC RECOMMENDATIONS - VOLUME 2 Part V [Issue 1]

TERMS AND TERMINOLOGY USED FOR THE GENERATION AND

ASSESSMENT OF MULTI-AXIAL FEATURE SPECIMEN AND
COMPONENT TEST DATA

PREPARED BY ECCC – WG4

Dr P Auerkari VTT, Finland (2001- ) [Convenor]

Mr T B Brown Mitsui Babcock, UK (2001- )
Dr D Dean British Energy, UK (2001- )
Prof B Dogan GKSS, Germany (2004- )
Dr R Hales ETD, UK (2001-04)
Dr S R Holdsworth ALSTOM Power, UK (2001- )
Dr A Klenk MPA Stuttgart, Germany (2001- )
Dr N Le Mat Hamata ETD, UK (2004- ) [Secretary]
Dr R Patel British Energy, UK (2001- )
Dr A Thomas Siempelkamp, Germany (2001- )
Dr A Tonti ISPESL, Italy (2001- )
Mr T Vilhelmsen ELSAM, Denmark (2001-03)

EDITED BY: S R HOLDSWORTH & T B BROWN

APPROVED DATE 31/8/05

On behalf of ECCC
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ABSTRACT

ECCC Recommendations Volume 2 Part V gives the terms and terminology to be used for
the generation, collation and assessment of multi-axial feature specimen and component test
data within ECCC.

ECCC Recommendations Volume 2 Part V user feedback is encouraged and should be sent
to:

Dr S R Holdsworth [Document Controller]

ALSTOM Power
Willans Works
Newbold Road
Rugby, CV21 2NH, UK
Tel: +44 1788 531138
Fax: +44 1788 531469
E-mail: stuart.holdsworth@power.alstom.com

ECCC may from time to time re-issue this document in response to new developments. The
user is advised to consult the Document Controller for confirmation that reference is being
made to the latest issue.

This document shall not be published without the written permission of

the ECCC Management Committee
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1. FOREWORD
ECCC Volume 2 Part V covers the terms and terminology relating to the generation, and
assessment of multi-axial feature and component test data. The document specifically
supports the testing guidance Volume 3 Part V [1], Volume 8 providing guidance for the
assessment of multi-axial specimen data [2] and Volume 9 which covers high temperature
component analysis [3]. For generic terms and terminology, reference should be made to
Part 1 of Volume 2.

Following a general introduction, nomenclature is listed in sections relating to material

details, testing details, test results and assessed results. Finally, a list of load functions are
defined.

2. GENERAL
Multi-axial feature specimen tests and component tests are conducted for a variety of
reasons. For example they may be performed to directly evaluate the likely performance of
engineering structures in service under closely controlled laboratory conditions or to provide
the evidence to test the effectiveness of assessment procedures. In addition, multi-axial
tests are performed to assess the applicability and effectiveness of:
- representative stress models to characterise material multi-axial rupture behaviour, and/or
- multi-axial rupture ductility models to characterise material multi-axial rupture behaviour.

Some general terms are defined in the following listing,

NAME UNIT(S) SYMBOL

Time h t
Temperature °C T
Strain % ε
Strain rate %/h ε&
Stress, initial stress MPa σ, σo

3. MATERIAL DETAILS
For this issue of Part V, the reader is referred to Volume 2 Part I for more comprehensive
guidance on the ECCC recommended terms and terminology for material pedigree data.
However, the symbols needed to characterise the uniaxial material properties necessary for
the assessment of multi-axial feature specimen and component test data are listed in the
following section.
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3.1 Material Properties

3.1.1 Tensile

NAME UNIT(S) SYMBOL

Tensile fracture elongation % A
Elastic modulus, elastic modulus at temperature GPa E, ET
E ' equals E for plane stress, and E/(1-ν2) for plane strain GPa E'
0.2% proof strength MPa Rp0.2
Tensile strength MPa Rm
Tensile fracture reduction of area % Z
Poissons ratio ν

3.1.2 Creep

NAME UNIT(S) SYMBOL

Constant in Norton or Norton-Bailey creep equations D
Creep damage fraction Dc
Stress exponent in Norton or Norton-Bailey creep equations n
Time exponent in Norton-Bailey creep equation p
0.2% creep (plastic strain) strength at time, t, and MPa Rp0.2/t/T
temperature, T
1% creep (plastic strain) strength at time, t, and temperature, MPa Rp1/t/T
T
2% creep (plastic strain) strength at time, t, and temperature, MPa Rp2/t/T
T

NAME UNIT(S) SYMBOL

Elastic strain % εe
Creep strain % εc, εf
Instantaneous plastic strain % εi
Plastic strain (εi + εf) % εp
Permanent strain % εper

3.1.3 Rupture

NAME UNIT(S) SYMBOL

Creep rupture elongation for time, t, and temperature, T % Au/t/T
Time to rupture h tu
Rupture strength for time, t, and temperature, T MPa Ru/t/T
Creep rupture reduction of area for time, t, and temperature, % Zu/t/T
T

4. TESTING DETAILS
4.1 Overview
In multi-axial feature specimen or component tests, a constant force (F), moment (M),
internal pressure (p) and/or torque (τ) is applied to the structure at a constant temperature, T.
The loading is applied as quickly as practical. However, where a component test is
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attempting to simulate service conditions, the rate of loading will be dictated by service
loading rates.

With a small number of exceptions (e.g. [4-6]), multi-axial feature specimen and component
tests are not covered by published standard procedures. Testing practices are therefore
dependent on specific data requirements and the expertise of the individual test laboratory.

The recorded response variable(s) will depend on the nature of the test and the requirement
of the test initiator and range from failure time to a comprehensive package including local
and global strain measurement and crack development monitoring (involving both on-line
and off-line techniques).

4.2 Multi-axial Testpieces

4.2.1 Types
The most commonly used specimen geometries used for multi-axial testing are the
circumferentially notched round tensile testpiece, with either a v-notch or a semi-circular
(Bridgeman) notch [4], or the thin walled tube testpiece subject to various combinations of
axial, torsional, and/or internal pressure loading [5,6]. However, other geometries may be
employed, and examples of these are listed in the following table.

NAME UNIT(S) SYMBOL

Circumferentially notched round tensile testpiece, v-notched, CNRT
semi-circular notched
Biaxial plate
Compact tension testpiece, (with side grooves) CT, (Cs)
Cruciform
Tube, pressurised, without and with end-loading (axial T(p), T(p,F)
loading)
Tube, end loaded (axial loaded) T(F)
Tube, torsion loaded, without and with end-loading (axial T(τ), T(τ,F)
loading)
Tube, torsion loaded with internal pressure, without and with T(τ,pi),
end-loading (axial loading) T(τ,pi,F)
Tube, moment T(M)

4.2.2 Dimensions: CNRT testpieces

The most commonly used multi-axial testpiece is the circumferentially notched round tensile
testpiece. This testpiece configuration with a v-notch geometry is widely used for material
characterisation, e.g. to characterise notch sensitivity [4,7]. With a semi-circular (Bridgeman)
notch geometry, the CNRT configuration may be used to investigate the creep properties of
materials over a much wider range of triaxial tensile stress states and to give an indication of
how creep strain accumulates under these circumstances [4].

NAME UNIT(S) SYMBOL

Circumferentially notched round tensile testpiece CNRT
Notch root diameter mm dno
Outer diameter mm D
Notch root radius mm rno
Notch flank angle ° α
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4.2.3 Dimensions: Tube testpieces

Tube testpieces, without or with external circumferential notches in the gauge length, provide
the means of generating a wider spectrum of multi-axial stress states than the CNRT
geometry. The results from multi-axial tests involving this geometry are therefore necessary
to identify the most effective representative stress and ductility models for characterizing the
multi-axial creep deformation and rupture behaviour of a given material.

NAME UNIT(S) SYMBOL

Tube testpiece (see options in 4.2.1) T( )
Inner diameter of gauge length mm di
Outer diameter of gauge length mm do
Notch root diameter mm dno
Mean diameter of gauge length mm dm
Diameter of end plug mm dplug
Diameter ratio, R = do/ di R
Wall thickness of gauge length mm t1
Wall thickness of test piece end mm t2
Parallel length of test section mm l
Length of end cap mm L
Transition radius mm r
Notch root radius mm rno
Notch flank angle ° α

4.2.4 Dimensions: CT(Cs) testpieces

Compact tension testpieces are more commonly regarded as a fracture mechanics testpiece
(e.g. [8]). However, the geometry is the preferred multi-axial testpiece geometry for the
LICON methodology [9].

NAME UNIT(S) SYMBOL

Compact tension testpiece (with side grooves) CT (Cs)
Crack depth mm a
Initial crack depth mm ao
Thickness mm B
Net section thickness mm BN
Side-groove depths mm n1, n2
Width mm W

4.2.5 Dimensions: Other testpieces

Other testpieces such as bi-axial plate and cruciform specimens are used to characterise the
multi-axial creep deformation and rupture behaviour of engineering materials (e.g. [10]).
Such tests are performed by specialists and the associated terminology varies with user.

4.3 Components
4.3.1 Types
Component test specimens are by their very nature varied as they are derived from the need
of each particular industry to test or validate component parts of engineering structures. It is
therefore difficult to stipulate specific geometries. However, recent reviews have identified
three generic component types: tube/pipe, bend and nozzle/branch geometries [1,11].
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Weld(s) may or may not be included as an integral part of the component under test. Only
three generic geometries are listed here.

NAME UNIT(S) SYMBOL

Tube See 4.2.1
Tube with weld under test Tw
Pipe P
Pipe with weld under test Pw
Nozzle/Branch, pressurized N(p)
Nozzle/Branch, moment in plane/out of plane N(Mi),
N(Mo)
Nozzle/Branch, pressurized with moment N(p,M)

4.3.2 Dimensions: Tube/Pipe test pieces

One of the most commonly tested components is the tube or pipe geometry with a butt weld.
The weld should be centrally placed in the test section. The terminology for the tube/pipe
test pieces is already given in section 4.2.3.

4.3.3 Dimensions: Bend test pieces

NAME UNIT(S) SYMBOL

Inner diameter of gauge length mm di
Outer diameter of gauge length mm do
Diameter of end plug mm dplug
Wall thickness of gauge length mm t
Mean radius of bend mm Rm
Angle of gauge length mm φ

4.3.4 Dimensions: Nozzle/Branch pieces

This is a common component in the power industry and can be in the form of isolated or
multiple nozzles/branches.

NAME UNIT(S) SYMBOL

Inner diameter of main vessel mm Di
Outer diameter of main vessel mm Do
Mean diameter of main vessel mm Dm
Wall thickness of main vessel mm Tv
Inner diameter of nozzle/branch mm di
Outer diameter of nozzle/branch mm do
Mean diameter of nozzle/branch mm dm
Wall thickness of nozzle/branch mm t
Ratio of vessel/nozzle mean diameters R
Ratio of vessel diameter/vessel thickness RT
Length of vessel mm L
Length of nozzle/branch mm l
Pitch between multiple nozzle/branch centers mm P
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4.4 Test Parameters

NAME UNIT(S) SYMBOL

Force, axial force N F, FA
Pressure, internal pressure MPa p, pi
Time h t
Temperature °C T
Torque Nm τ
Moment, in plane, out of plane Nm Mi, Mo

5. TEST RESULTS
5.1 Multi-axial Tests

NAME UNIT(S) SYMBOL

Alternating current potential drop crack monitoring ACPD
Direct current potential drop crack monitoring DCPD
Crack initiation criterion (e.g. ∆a = 0.5mm) mm x
Time to creep crack initiation h ti,x
time to rupture, time to rupture of notched testpiece h tu, tnu
Reduction of area at rupture, in notch root % Zu, Znu
Axial strain, at crack initiation, at rupture % εa, εai, εau
Hoop strain, at crack initiation, at rupture % εh, εhi, εhu
Strains in x, y and z directions % εx, εy, εz
Axial displacement mm δa
Change in diameter at notch throat mm δd

5.2 Component Tests

The terminology defined in the table below is generic to any component specimen geometry.
Additional terms for specific geometries may be defined in relation to those given below, e.g.
strain results obtained from strain gauges or creep pip measurements.

NAME UNIT(S) SYMBOL

Alternating current potential drop crack monitoring ACPD
Direct current potential drop crack monitoring DCPD
Crack dimensions at initiation, depth, length mm ai, ci
Crack dimensions at rupture, depth, length mm au, cu
Crack initiation criterion (e.g. ∆a = 0.5mm) mm x
Time to creep crack initiation h ti,x
Time to rupture h tu
Strain at crack initiation % εi
Strain at rupture % εu
Displacement mm δ
CTOD at creep crack initiation µm δi,x
Specimen dimensions at rupture, as sect. 4.3 with 'u' suffix mm e.g. Dou
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6. ASSESSED RESULTS
6.1 General
Assessed results are those determined from a knowledge of the loading conditions or the
directly observed observations. Typically these require reference to established solutions for
more commonly adopted testpiece geometries or specific finite element analysis.

6.2 Parameters

NAME UNIT(S) SYMBOL

Elastic stress concentration factor (ratio of maximum axial kt
stress calculated for elastic conditions to the net stress at the
same load) – determined from existing solutions (e.g. [12]) or
by finite element analysis
Principal strains, ε1 is maximum principal strain % ε1, ε2, ε3
von Mises strain % εVM
Principal stresses, σ1 is maximum principal stress MPa σ1, σ2, σ3
Principal stresses at skeletal point MPa σ1*, σ2*, σ3*
Mean (hydrostatic) stress MPa σm
Mean (hydrostatic) stress at skeletal point MPa σm*
Net section stress MPa σnet
Reference stress MPa σref
Representative stress MPa σrep
von Mises stress MPa σVM
von Mises stress at skeletal point MPa σVM*

7. CHARACTERISING FUNCTIONS
7.1 General
The following section reviews and defines various functions used to characterise multi-axial
rupture strength and ductility.

7.2 Classical

σ VM =
1
2
[
⋅ (σ 1 − σ 2 ) + (σ 2 − σ 3 ) + (σ 3 − σ 1 )
2 2
]
2 0. 5

σ1 + σ 2 + σ 3
σm =
3

ε VM =
3
2
[
⋅ (ε1 − ε 2 ) + (ε 2 − ε 3 ) + (ε 3 − ε1 )
2 2 2
]
0.5

7.2.1 Representative Rupture Stresses

−ν
t nu = C (T )σ rep

7.2.1.1 Sdobyrev []

σ rep = α .σ 1 + (1 − α ).σ VM (0 ≤ α ≤ 1)
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7.2.1.2

σ rep = 3.β .σ m + (1 − β ).σ VM (0 ≤ β < 1)

7.2.1.3 Cane [13]

σ rep = (σ 1 / σ VM )γ / ν σ VM (0 ≤ γ ≤ν )

7.2.1.4

σ rep = (3.σ m / σ VM )γ / ν σ VM (0 ≤ γ <ν )

7.2.1.5 Hayhurst [14]

σ rep = α .σ 1 + 3.β .σ m + (1 − α − β ).σ VM (0 ≤ α + β ≤ 1)

and where α, β and γ are material parameters

7.2.1.6 Huddleston [15]

a
3  2σ VM   J 
σ rep = S1   expb 1 − 1
2  3S1    S S 
where S1 is maximum deviatoric stress and J1, the
first invariant of the stress tensor

7.2.2 Multi-axial Rupture Ductility Models

7.2.2.1 Manjoine [16]

εf
= 2 (1−3σ m / σ VM )
ε fu

7.2.2.2 Rice & Tracey [17]

εf  1 3σ m 
= exp − 
ε fu  2 2σ VM 
matrix hole growth

7.2.2.3 Cocks & Ashby [18]

εf  2(n − 1/ 2)   2(n − 1/ 2)σ m 

= sinh  sinh (n + 1/ 2)σ 
ε fu  3 (n + 1 / 2 )   VM 
grain boundary cavity growth

7.2.2.4 Marlof [19]

εf 1 σ 3 σ −σm   σ  1 (σ 1 − σ m )
= ⋅ VM =  ⋅ 1   3 ⋅ m  = ⋅
ε fu 3 σ m 2 σ VM   σ VM  2 σm

7.2.2.5 Ewald [20]

εf 3 (σ − σ m )
= ⋅ 1
ε fu 2 σ1

7.2.2.6 Sheng [21]

3 (σ − σ m )  σ VM 
m
εf
= ⋅ 1 ⋅  
ε fu 2 σ VM  σ1 
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7.2.2.7 Hales [22]

Diffusion controlled cavity growth

m +1
ε f  σ VM 
= 
ε fu  σ 1 

7.2.2.8 Hales [22]

Constrained cavity growth

m +1
εf 2σ 1  σ VM 
=  
ε fu 3S1  σ 
 1 

7.2.2.9 Spindler [23]

εf   σ   1 3σ m 
= exp p1 − 1  + q  − 
ε fu   σ VM   2 2σ VM 
Where p and q are parameters affecting multi-axial stress influence on material ductility

8. REFERENCES
1 ECCC Recommendations Volume 3, 2005, 'Part V: Testing practices for multi-axial
features and components', eds. Brown, T.B. & Holdsworth, S.R., publ. ETD.
2 ECCC Recommendations Volume 8, 2005, 'Guidance for the assessment of multi-
axial creep test data', ed. Holdsworth, S.R., publ. ETD
3 ECCC Recommendations Volume 9, 2005, 'High temperature component analysis',
eds. Auerkari, P., Patel, R., Thomas, A. & Dean, D., publ. ETD.
4 Webster, G.A., Holdsworth, S.R., Loveday, M.S., Nikbin, K., Perrin, I.J., Purper, H.,
Skelton, R.P. & Spindler, M.W., 2004, 'A code of practice for conducting notched bar
creep tests and for interpreting the data, Issue 3', Fatigue & Fracture of Engineering
Materials & Structures, 27, 4, 319-342.
5 How, I.M. et al, 1992, 'A code of practice for internal pressure testing of tubular
components at elevated temperatures', Proc. HTMTC Symp. on Harmonisation of
Testing Practice for High Temperature Material, ISPRA Italy, 18-19/10/90, eds.
Loveday, M.S. & Gibbons, T.B., Elsevier App. Sci., 363-400.
6 Rees, D.W.A. et al. et al, 1992, 'A code of practice for torsional creep testing of
tubular testpieces at elevated temperatures', ibid., 331-361.
7 Scholz, A., Schwienheer, M. & Morris, P.F., 2003, 'European notched testpiece for
creep rupture testing', Proc. 21st Symp. on German Iron & Steel Inst. & DVM,
Herausforderung durch den industriellen Fortschritt, 4-5/12/03, Bad Neuenaber Ed.
Buchholz, W.O. & Geisler, S.), Stahleisen, ISBN 3-514-00703-9, 308-314.
8 E1457, 2000, 'Standard test method for measurement of creep crack growth rates in
metals', ASTM Standards, v03.01.
9 Mendes-Martins, V. & Holdsworth, S.R., 2002, 'The LICON methodology for
predicting the long term service behaviour of new steels', Materials at High
Temperature, 19, 2, 99-104.
10 Morrison, C.J., 1986, 'Biaxial testing using cruciform specimens', Proc. HTMTC
Symp. on Techniques for Multi-axial Creep Testing, CERL-CEGB Leatherhead, 25-
26/9/85, eds. Gooch, D.J. & How, I.M., Elsevier App. Sci., 111-126.
11 Holdsworth, S.R., 2002, 'Overview of activities of the structural mechanics cluster of
the Plant Life Assessment Network', Materials at High Temperature, 2002 19(2), 69-
74.
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12 Peterson, R.E., 1974, Stress Concentration Factors, Wiley-Interscience, New York.

13 Cane, B.J., 1979, 'Creep cavitation and rupture in 2¼CrMo steel under uniaxial and
mulit-axial stresses', Proc. Int. Conf. on Mechanical Behaviour of Materials, ed. Miller,
K.J. & Smith, R.A., 2, Pergamon Press, Oxford, 173-182.
14 Hayhurst, D.R., 1972, 'Creep rupture under multi-axial states of stress', J. Mech.
Phys. Solids, 20, 381-390.
15 Huddleston, R.L., 1985, 'An improved multi-axial creep rupture strength criterion',
Trans ASME J. Press. Vessel Technol., 107, 412-429.
16 Manjoine, M.J., 1975, 'Ductility indices at elevated temperatures', ASME J. Engng.
Mater. Technol., 156-161.
17 Rice, J.R. & Tracey, D.M., 1969, 'On the ductile enlargement of voids in triaxial stress
fields', J. Mech. Phys. Solids, 17, 201-217.
18 Cocks, A.C.F. & Ashby, M.F., 1980, 'Intergranular fracture during power law creep
under multi-axial stress', Met. Sci., 14, 395-402.
19 Marloff, R.H., Leven, M. & Sankey, G.O., 1981, 'Creep of Rotors under Triaxial
Tension', Proc. Int. Conf. om Measurements in Hostile Environments, Brit. Soc. for
Strain Measurement, Newcastle-upon-Tyne.
20 Ewald, J., 1991, 'Verminderung des Verformungsvermögens bei mehrachsigen Span-
nungszuständen im plastischen Zustand und bei Kriechbeanspruchung', Mat.-wiss. u.
Werkstofftech. 22, 359-369.
21 Sheng, S., 1992, 'Anwendung von Festigkeitshypothesen im Kriechbereich bei mehr-
achsigen Spannungs-Formänderungszuständen', Dissertation Universität Stuttgart.
22 Hales, R., 1994, 'The role of cavity growth mechanisms in determining creep-rupture
under multi-axial stresses', Fatigue Fract. Engng. Struct., 17, 279-291.
23 Spindler, M.W., 2004, 'The multi-axial creep ductility of austenitic stainless steel',
Fatigue. Fract. Engng. Mater. Struct., 27, 4, 273-281.