A Review of Thermo-Mechanical Fatigue ... - TMF-Workshop
A Review of Thermo-Mechanical Fatigue ... - TMF-Workshop
A Review of Thermo-Mechanical Fatigue ... - TMF-Workshop
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A <strong>Review</strong> <strong>of</strong> <strong>Thermo</strong>-<strong>Mechanical</strong><br />
<strong>Fatigue</strong> behaviour in<br />
Polycrystalline Nickel Superalloys<br />
Dr M. Whittaker, Dr R. Lancaster<br />
12 th May 2011<br />
Rolls-Royce University Technology Centre in Materials
<strong>Thermo</strong>-mechanical fatigue at Swansea UTP<br />
Induction heated, forced air cooled<br />
tension/torsion (100kN/400Nm) ESH<br />
servo-hydraulic test machine.<br />
Controlled by IMPAC pyrometry<br />
Previous investigations on IN718<br />
Focus on Nickel Superalloys for disc<br />
applications<br />
Rolls-Royce University Technology Centre in Materials
Rationale for investigation <strong>of</strong> PX Ni superalloys<br />
Increased turbine entry temperatures (TET) in conjunction with thinner<br />
disc rims means that <strong>TMF</strong> at disc rims requires consideration.<br />
Development <strong>of</strong> lifing methodologies under <strong>TMF</strong> loading is critical for safe<br />
operation <strong>of</strong> gas turbine engines.<br />
Extrapolation <strong>of</strong> isothermal fatigue (IF) results shows limited success.<br />
Loading conditions within gas turbine lead to complex loading regimes –<br />
Need to investigate the effect <strong>of</strong> phase angle.<br />
Complex interaction <strong>of</strong> phase angle, peak temperature, strain range,<br />
mean stress and environmental/creep damage.<br />
Rolls-Royce University Technology Centre in Materials
RR1000 test material (Coarse grain)<br />
50μm<br />
However, the <strong>TMF</strong> properties <strong>of</strong><br />
the alloy have not yet been widely<br />
examined.<br />
RR1000 is a heavily γ’ stabilised<br />
nickel alloy which is expected to<br />
be widely used in high<br />
temperature applications in the<br />
coming years.<br />
20μm<br />
Rolls-Royce University Technology Centre in Materials
Isothermal <strong>Fatigue</strong><br />
• Specimen subjected to an alternating mechanical load under a<br />
stabilised temperature<br />
Rolls-Royce University Technology Centre in Materials
<strong>Thermo</strong>-<strong>Mechanical</strong> <strong>Fatigue</strong><br />
• Specimen simultaneously subjected to alternating mechanical AND<br />
thermal loads<br />
Rolls-Royce University Technology Centre in Materials<br />
In-Phase Test Out-<strong>of</strong>-Phase Test
Investigation <strong>of</strong> phase angle effects<br />
Rolls-Royce University Technology Centre in Materials<br />
• Tests keep a<br />
constant strain<br />
range <strong>of</strong> 1%<br />
• R ratio and mean<br />
strain vary from test<br />
to test<br />
• Investigate the<br />
effects <strong>of</strong> direction<br />
around the cycle
A model for qualitative <strong>TMF</strong> prediction<br />
Rolls-Royce University Technology Centre in Materials<br />
For intermediate temperatures<br />
the model seems to provide an<br />
useful qualitative approach for<br />
rationalizing <strong>TMF</strong> data.<br />
Model is essentially mean stress<br />
dependent, in that at these<br />
temperatures (300-700⁰C) ⁰ fatigue<br />
life is inversely proportional to<br />
mean stress.<br />
Crossover occurs near slightly<br />
above yield strain, influenced by<br />
the effect <strong>of</strong> reverse yielding.<br />
At higher temperatures the influence <strong>of</strong> environment/creep seems to<br />
reduce the fatigue life <strong>of</strong> IP specimens.
Mean stress effect on fatigue life in RR1000<br />
Stress (MPa)<br />
Cycles<br />
Rolls-Royce University Technology Centre in Materials<br />
Max Stress stress 4 IP IP<br />
Min Stress stress 4 IP IP<br />
Max Stress stress 5 OOP<br />
Min stress OOP<br />
Min Stress 5 OOP
<strong>Review</strong>ing existing PX Ni superalloy data<br />
Evans et al (2005) – IN718, 300-680⁰C<br />
Rolls-Royce University Technology Centre in Materials<br />
Yield in IN718 occurs at<br />
approximately 0.4% strain.<br />
Large amount <strong>of</strong> plasticity in<br />
these tests and reverse yielding.<br />
IP s<strong>of</strong>tens on tensile portion<br />
and OOP s<strong>of</strong>tens on<br />
compressive portion<br />
Resultant tensile mean stress<br />
in OOP (-∞) tests, compressive<br />
mean stress in IP (R=0) tests.<br />
Therefore reduced fatigue<br />
lives in OOP tests.
Effects at increased peak temperatures<br />
Marchionni et al (2007) – Nimonic 90,<br />
300-680⁰C<br />
Rolls-Royce University Technology Centre in Materials<br />
Initially difficult to rationalize<br />
• Testing conducted under R = -1<br />
loading conditions<br />
• Would potentially expect to see<br />
a crossover in IP/OOP results.<br />
• However the expected shorter<br />
response for OOP tests at higher<br />
strains does not occur.<br />
• Early cracking and life<br />
dominated by fatigue crack<br />
propagation.
Stress response <strong>of</strong> Nimonic 90 (IP and OOP tests)<br />
Rolls-Royce University Technology Centre in Materials<br />
• Based on mean stresses<br />
it would be expected that<br />
the IP tests should show a<br />
longer fatigue life.<br />
• <strong>Fatigue</strong> crack<br />
propagation must<br />
dominate the fatigue life<br />
• Infers that crack<br />
propagation at 350-400MPa<br />
at 850C is faster than at<br />
700MPa at 400C.
Effect <strong>of</strong> peak temperature on IP/OOP ordering<br />
Beck et al (1997) – IN792<br />
Rolls-Royce University Technology Centre in Materials<br />
• According to the lines<br />
drawn, IP loading gives<br />
longer fatigue lives at lower<br />
temperatures.<br />
• Based on mean stress<br />
arguments this fits with<br />
earlier results.<br />
• At higher temperatures IP<br />
fatigue lives shorter than<br />
OOP – most likely<br />
dominated by crack<br />
propagation again.<br />
• Variability in results<br />
however, other<br />
interpretations could be<br />
made.
Characterisation <strong>of</strong> <strong>TMF</strong> effects in RR1000<br />
Investigate the behaviour <strong>of</strong> the alloy using a constant strain<br />
range (1%), but differing phase angles.<br />
Cycle temperature <strong>of</strong> 300-700⁰C.<br />
Eventually examine the effect <strong>of</strong> changes in strain range.<br />
Also vary peak temperature to see what effect it has on the<br />
ordering <strong>of</strong> tests.<br />
Generation <strong>of</strong> high quality stress-strain data to enable<br />
development <strong>of</strong> modelling procedures.<br />
Rolls-Royce University Technology Centre in Materials
Stress (MPa)<br />
In-Phase test<br />
<strong>Mechanical</strong> Strain (%)<br />
Loop 1<br />
Loop 2<br />
Loop 3<br />
Loop 4<br />
Loop 5<br />
Loop 10<br />
Loop 100<br />
Loop 500<br />
Typical <strong>of</strong> IP tests, stress<br />
relaxation due to creep at peak<br />
strain/temperature.<br />
Characterised by intergranular<br />
cracking.<br />
Rolls-Royce University Technology Centre in Materials<br />
50μm<br />
Stress (MPa)<br />
Max Stress<br />
Min Stress<br />
Number <strong>of</strong> <strong>Fatigue</strong> Cycles
Stress (MPa)<br />
Out-<strong>of</strong> phase (180⁰) test<br />
Loop 1<br />
Loop 2<br />
Loop 3<br />
Loop 4<br />
Loop 5<br />
Loop 10<br />
Loop 100<br />
Loop 1000<br />
Strain (%)<br />
Transgranular failure as peak strain<br />
is applied at 300⁰C. Increasing mean<br />
stress throughout the test at creep<br />
occurs to increase the minimum<br />
stress on the compressive part <strong>of</strong> the<br />
cycle<br />
Rolls-Royce University Technology Centre in Materials<br />
Stress (MPa)<br />
50μm<br />
Cycles<br />
Max Stress<br />
Min Stress
Generation <strong>of</strong> test data<br />
Loop 1<br />
Loop 2<br />
Loop 3<br />
Loop 5<br />
Loop 10<br />
Stress (MPa)<br />
<strong>Mechanical</strong> Strain (%)<br />
Clockwise 45⁰ Anticlockwise 135⁰<br />
Anticlockwise 90⁰<br />
Rolls-Royce University Technology Centre in Materials<br />
Loop 1<br />
Loop 2<br />
Loop 3<br />
Loop 5<br />
Loop 10<br />
Loop 100<br />
Loop 1000<br />
High quality data allowing for<br />
test to test data comparison.<br />
Clear evidence <strong>of</strong> differences<br />
appearing in mean stress is<br />
evident.
Comparison with isothermal data<br />
Strain range (%)<br />
Cycles to failure<br />
Traditional isothermal<br />
approaches do not seem to yield<br />
a relationship.<br />
Rolls-Royce University Technology Centre in Materials<br />
Stabilsed stress range (MPa)<br />
Comparison with isothermal data<br />
reveals the detrimental effect <strong>of</strong><br />
<strong>TMF</strong>, but also the spread in<br />
results that can occur as a<br />
function <strong>of</strong> phase angle.<br />
Cycles to failure
Effect <strong>of</strong> phase angle on <strong>TMF</strong> life<br />
Also clear is that this relationship is<br />
strongly dependent on mean<br />
stress, as described by the model<br />
proposed earlier.<br />
Rolls-Royce University Technology Centre in Materials<br />
It can be seen that <strong>TMF</strong> lives increase<br />
with increasing phase angle.<br />
Although scatter in the data needs to<br />
be considered, this relationship<br />
seems to be well defined by this data.
Conclusions<br />
<strong>TMF</strong> facility development is a difficult process and small errors may lead<br />
to significant issues in valid test data.<br />
Based on results in the open literature, the ordering <strong>of</strong> IP and OOP tests<br />
is strongly affected by the mean stress achieved during the test.<br />
Other influences, such as early crack development may lead to<br />
differences in the expected response.<br />
A crossover would be expected in the IP and OOP results as sufficient<br />
plastic strain is generated the significantly vary the mean stress.<br />
Phase angle is shown to have a significant effect on <strong>TMF</strong> life, with a<br />
power law relationship existing between the two.<br />
Ongoing work is anticipated to reveal further insights about the effects <strong>of</strong><br />
strain range, peak temperature, environmental interaction etc...<br />
Rolls-Royce University Technology Centre in Materials
Thank you for your attention<br />
Any questions?<br />
Rolls-Royce University Technology Centre in Materials