A European Code-of-Practice for Strain-Controlled ... - TMF-Workshop

GROWTH Project n° GRD2-2000-30014 

TMF-Standard 

Final Meeting/Workshop, 20-23/09/05, Berlin 

A European Code-of-Practice for 

Strain-Controlled Thermo-Mechanical Fatigue Testing 

Peter Hähner, JRC Institute for Energy, Petten, (NL) 

Claudia Rinaldi, and Valerio Bicego, CESI, Milan (I) 

Ernst Affeldt, MTU Aero Engines, München (D) 

Henrik Andersson, KIMAB, Stockholm (S) 

Tilmann Beck, University of Karlsruhe (D) 

Thomas Brendel, MTU Aero Engines, München (D) 

Hellmuth Klingelhöffer, BAM, Berlin (D) 

Alain Köster, Ecole Nationale Superieure des Mines de Paris (F) 

Hans-Joachim Kühn, BAM, Berlin (D) 

Malcolm Loveday, NPL, Teddington (UK) 

Massimo Marchionni, CNR-IENI, Milan (I) 

Catherine Rae, University of Cambridge (UK)

survey 

WP1 1 st draft 




WP6: Drafting of CoP 

prel. CoP val.CoP 

WP2 WP3 WP4 WP5 

Material Pre-normative R&D Validation tests Statist. analysis 

2002 2003 2004 2005 

WP7 

Dissemination

Table of Contents of CoP 




1- INTRODUCTION 

1.1 SCOPE AND USE 

1.2 DEFINITIONS AND DESCRIPTION OF TERMS 

1. 3 NORMATIVE REFERENCES 

2- EXPERIMENTAL: Set-up and specimens 

2.1 APPARATUS 

2.2 SPECIMENS 

3- TEST PREPARATORY ISSUES 

3.1 EVALUATION OF E MODULUS 

3.2 OPTIMISATION OF TEMPERATURE CONTROL LOOP 

3.3 THERMAL STRAIN MEASUREMENT 

3.4 ZERO STRESS TEST 

4- TEST EXECUTION 

4.1 TEST START 

4.2 TEST STOP AND RESTART 

4.3 TEST MONITORING 

4.4 TERMINATION OF TEST 

5- ANALYSIS AND REPORTING 

5.1 ANALYSIS OF RECORDED DATA 

5.2 REPORTING OF TEST METHODS 

5.3 REPORTING OF RESULTS 

Acknowledgements 

References 

Annex A Specimens (Informative) 

Annex B Relevant material properties and experimental characteristics (Informative) 

Annex C Representative TMF cycles frequently used (Informative) 

Annex D Measurement scatter and uncertainties (Informative)

Mechanical strain % 

0.4 

0.3 

0.2 

0.1 

0 

-0.1 

-0.2 

-0.3 

-0.4 

E 

M 

A 

D 

45° 90° 

N 




Definition of TMF cycles 

H L 

P 

F 

300 400 500 600 700 800 900 1000 

Temperature °C 

Mech. strain vs. temperature for typical TMF cycles 

with R = �1 

I 

O 

G 

C 

B 

T = T 0 + �T F(�t) 

� m = � m,0 + �� F(�t ��) 

F(x) = F(x + 2�), � x 

0 < � < 180° means that 

� lags behind T

tubular 

solid cyclindrical 




Examples of specimens used in the 

“inner-circle” validation round robin 

flat

Spot-welding of TCs 




Dynamic T measurement and control 

Use of ribbon TCs 

Stability of T profile

Definitions 




Comparison of tolerances and recommendations (1) 

issue TMF-Standard 

CoP 

Definition of � 

phase angle 

m lags behind, 

if � > 0 

Start point of at �m = 0 (R�0) or 

first TMF cycle T = Tmin (R>0), 

always increasing T; 

gradual increase of 

�� m not foreseen 

ISO 12111.1 ASTM E 2368 - 04 

No definition �m at �m = 0 (R�0) or 

� 

lags behind, 

if � > 0 

m = min| �m| (R>0), 

always same 

at �m = 0 (R�0) or 

� 

direction; 

gradual cyclic 

increase of ��m for 

large strain 

amplitude tests or in 

case of serrated 

yielding 

m = min| �m| (R>0), 

always same 

direction 

gradual cyclic 

increase of ��m for 

large strain 

amplitude tests or in 

case of serrated 

yielding

Apparatus & Specimens 






CoP 

ISO 12111.1 ASTM E 2368 - 04 

Extensometry ISO 9513 Class 1 ISO 9513 Class 1 E83 Class B-2 

(for l0 < 15mm (for l0 < 15mm 

Class 0.5 recomm.) Class 0.5 recomm.) 

Alignment: 5% of mech. Strain 5% of both max. E 606 (LCF): 

max. allowable range 

AND min. mech. 5% of min. mech. 

bending 

strain 

strain range 

Dynamic T Detailed 

Direct contact: Direct contact: 

measurement recommendations binding, pressure, binding, pressure, 

and control on appropr. methods spot welding spot welding 

of fixing; 

outside GL; outside GL; 

No pyrometry Pyrometry Pyrometry 

Humidity of air Not an issue Not an issue Control of rel. air 

humidity strongly 

recommended 

(extensometry) 

Specimen Detailed geometries Detailed geometries 

geometries and machining 

tolerances 

recommended for 

and machining 

tolerances 

recommended for 

�� Solid cylindrical, 

�� tubular, 

�� flat specimens 

�� Solid 

Examples for 

��Solid cylindrical, 

��Tubular specimens 

Tubular 

specimens 

5 < o.d. / w.t. < 10 

cylindrical, 

�� tubular, 

�� flat specimens 

10 < o.d. / w.t. < 30 

Tubular specimens 

preferred 

No recommendation

Max. Allowable Tolerances 




Comparison of tolerances and recommendations (3a) 


CoP 

Max. 

The greater of 

temperature ± 5°C or 

deviation ��T [°C] 

throughout test at 

center of GL 

Max. 


temperature 

gradients 

within GL 

�� ± 10°C or 

��T [°C] 

(axial) 

�� ± 5°C or 

��T [°C] 

(radial, & 

circumferential) 

�� ± 7°C 

(transverse 

gradient in flat 

specimens) 

ISO 12111.1 ASTM E 2368 - 04 

± 2°C 

throughout test as 

indicated by control 

sensor 


± 5°C or 

± 1.5% Tmax [°C] 

(axial, radial, & 

circumferential) 

± 2°C 

throughout test as 

indicated by control 

sensor 


± 3K or 

± 1% Tmax [K] 

(axial)




Comparison of tolerances and recommendations (3b) 


CoP 

Max. 

thermal strain 

hysteresis 

5% ��th Max. 

No mention, as not a 

mechanical directly controlled 

strain deviation variable 

Max. 

between 

phase angle ±2° at Tmax and 

deviation ±5° at Tmin 

Max. 

stress during 

zero-stress test 

| � |max < 5% ��and �� < ±2% �� 

ISO 12111.1 ASTM E 2368 - 04 

2.5% max( � th) 

? definition ? 

2% �� m 

±5° ±5° 

< 2% of max. 

tensile or 

compressive stress 

anticipated 

5% �� th 

2% �� m 

“Insignificant” as 

compared to tensile 

or compressive 

stresses anticipated

TMF Practice Recommendations 






CoP 

Young’s Static and pseudo- 

modulus E dynamic methods 

measurement described for the 

determination of 

E(T) before each 

series of tests 

Young’s Verification of 

modulus TMF system 

verification recommended by 

measuring the Emod 

at 

RT, Tmin, Tmax and 

one intermed. T 

before each test: 

< ± 5% deviation 

from reference 

value 

Thermal strain Single-valued T 

compensation based NOT 

recommended 

Thermal pre- extra water cooling 

cycling at specimen ends 

recommended 

(cf. T control 

outside GL) 

ISO 12111.1 ASTM E 2368 - 04 

Static method 

described for the 




Verification of 

extensometry 

recommended by 

measuring the Emod 

at RT before 

each test 

Static method 

described for the 




No recommendation 

T based preferred T based or t based 

Usually 3 – 4 precycles 

to dynamic T 

equilibrium

Other Practices 






CoP 

Test 

Programmed stop: 

interruption 

Restart like 

procedure 

new test; 

Unexpected stop: 

Restart only 

if last cycle 

has been 

recorded 

Failure criteria 

associated with 

force drop 

Nf, x: 

�� or �max decrease 

by x% below 

sloping tangent line 

to previous 

inflection point 

ISO 12111.1 ASTM E 2368 - 04 

Programmed stop 

described 

5 – 50% peak 

tensile force drop 

from stabilized 

value or projected 

straight line 

Programmed stop 

described 

5 – 50% force drop 

from previously 

recorded peak force




Conclusions 

TMF-Standard CoP on strain-controlled TMF 

contains the “essence” of 4 years work of 20 European laboratories 

has been validated by ~ 120 TMF tests (OOP and IP) 

comprises a lot of informative material and practical recommendations 

has contributed to improving & harmonizing the partners’ in-house TMF practices 

provides technical underpinning to the ISO standard 

is disseminated to all interested parties 

Dissemination 

Original plan to run own CWA abandoned 

CoP to be published as a EUR Report 

To be distributed to all workshop participants



Final Meeting/Workshop, 20-23/09/05, Berlin










ANNEX C (Informative) Exemplary compilation of relevant material properties and experimental characteristics 

Material properties of Nimonic90 1 

Property Symbol Unit Indicative 

value 

Mechanical properties 

Density � g/cm 3 

8.2 

Yield stress at Tmax � y MPa 440 @ 850°C 

Young’s modulus of elasticity E GPa 150 

Poisson ratio � 1 0.3 

Thermal properties 

Gibbs free enthalpy of plastic deformation Gpl eV 1.9 ??? 

Gibbs free enthalpy of oxidation (800 – 1000°C) Gox eV 1.1 

Specific heat cp J / kg °C 650 

Thermal conductivity � W / m °C 24 

Lin. coefficient of thermal expansion (400 – 850°C) � 10-6 °C �1 15 

Electrical conductivity 

Electromagnetic properties 

� 

( �� 

m) �1 

Magnetic permeability � 1 1.1 

0.76




Characteristics of experimental setup and TMF conditions 

Parameter Symbol Unit Indicative 

value 

Specimen radius r mm 3 

Frequency of induction heating �ind kHz 200 

Heating/cooling rate T � °C / s 5 

Minimum temperature Tmin °C 400 

Maximum temperature Tmax °C 850 

Quantity 

Derived quantities 

Symbol Formula Unit Indic. 

value 

Skin effect penetration depth of power 

density 

d (4��0��)�1/2 mm 0.61 

Characteristic temperature of plastic deform. Tc,pl Gpl/kB °C 22000 

Characteristic temperature of oxidation Tc,ox Gox/kB °C 12500 

Thermal relaxation time � ( � cp/ � )r 2 s 2.0 

Radial temperature gradient 1. T’ ( � cp/ � )rT � °C/mm 3.3 

Radial stress deviation �� (E/(1-�)) � T’r MPa 31 

Characteristic temperature deviation � T 0.1 T2 max / Tc,ox °C 10

WP3: Pre-normative R&D 




Task 1: Pre-cycling, start, interrupt, restart procedures 

Task 2: Dynamic T measurement and control 

Task 3: Thermal strain comp., deviations from nominal T 

Task 4: T gradient effects in 3 sample geometries 

(solid cylindrical, hollow cyl., solid rectangular) 

Task 5: Deviations from nominal phase angle

WP4: Validation Tests: 

1.) symmetrical triangular OOP 

R � = - 1, � = 180° 

T min = 400°C, T max = 850°C 

tcycle = 180s � dT/dt = � 5K/s 

��m = 0.8% � Nf � 1000 

2.) symmetrical triangular IP 




mech. strain [%] 

0.4 

0.2 

0.0 

-0.2 

-0.4 

400 500 600 700 800 900 

R� = - 1, � = 0° 

temperature [°C] 

Tmin = 400°C, Tmax = 850°C used by 

tcycle = 180s � dT/dt = � 5K/s “inner circle” and 

��m = 0.6% � Nf � 1000 “outer circle” round robin participants




From these data various dimensionless parameters derive, which can be used to estimate the 

lower bounds of systematic errors induced by the experimental set-up and the thermo-mechanical 

fatigue conditions imposed, and to assess the influences of the various parameters affecting those 

errors. 

The induction heating of the above set-up causes a skin effect with very limited direct 

bulk heating, as the ratio of the penetration depth to the specimen radius 

d 

r 

� 

1 1 

� 

4�� 

�� r 

0 

20% 

amounts to some 20 percent only. Accordingly, the specimen bulk is heated by heat 

conduction with finite thermal relaxation time �� 2s, causing a temperature difference �T � 10°C between inside and outside temperature. 

The relative stress deviation associated with the radial temperature gradient induced by 

surface heating and heat conduction to the bulk (lamp furnace or induction heater with 

small penetration depth) reads 

�� 

��c 

� 

� � 

y 

p 

E 

( 1�� 

) � 

y 

2 

r T� 

� 

7 % 

. 

On top of these systematic errors due to thermal relaxation there will always be 

measurement and control uncertainties, which must be kept as low as possible by 

appropriate maintenance and calibration of the measurement equipment as well as by an 

optimization of the TMF testing techniques. In particular, the relative overall temperature 

deviation in the gauge length should not exceed 

T 

max 

�T 

� T 

min 

� �0. 

1 

T 

c, ox 

T 

2 

max 

�T�T� max 

min 

� �2. 

2 % , 

if the rate of the relevant thermally activated process (here: oxidation) is to be maintained 

ithi 10%




Schematic of various coil configurations




Dynamic T measurement and control: 

Major issues in dynamic T control by thermocouples: 

Inductive heating & resistive heating: 

Radiation heating 

Heat transfer coefficient from specimen surface to TC 

Heat conduction through TC wire: cold spot 

=> appropriate TC attachment is crucial 

Reflectivity coefficients of TC and specimen 

=> appropriate shielding of TC 

=> Need for comprehensive trials using a combination of different methods




Dynamic T measurement and control (cont’d): 

1. Temperature control by ribbon TC within GL 

(a) (b) 

Ribbon type thermocouples, applied to (a) a round specimen with 8 mm 

diameter, and (b) a flat specimen 12 mm wide and 4 mm thick




Dynamic T measurement and control (cont’d) 

4. Prevention of “cold spot” 

Wrapping configuration of spot-welded thermocouple




TC type R/S K/N 

Material Pt-based Ni-based 

Thermal contact good poor 

Thermal conductivity high low 

Error governed by heat conduct. therm. contact 

Recommended ribbon or SW 

attachment SW wrapping

Stress Range, MPa 

1200 

1000 

800 

600 

400 

200 

0 




Failure criterion 

0 200 400 600 800 1000 1200 1400 

N, cycles 

Example of end of life criterion, based on 10% stress range drop below a 

sloping tangent line to the saturated portion of the curve 

Nf10




Web-enabled Mat-DB - TMF-Standard data sets 

To get access to TMF Standard data and documentation please register on the JRC Petten ODIN 

website (https://odin.jrc.nl), register for Mat-DB and DoMa and mention under comments that you 

request access to the TMF-Standard project data sets. 

Selection of TMF-Standard data within the web-enabled Mat-DB data retrieval part




Selection of TMF Standard data within the web-enabled Mat-DB data retrieval part




Graphical output of TMF Standard data within the web-enabled Mat-DB data retrieval part

A European Code-of-Practice for Strain-Controlled ... - TMF-Workshop

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