modeling of cavity growth during creep at high ss

MODELING OF CAVITY GROWTH DURING CREEP AT HIGH TEMPERATURE

-by Loïc Renversade

Research project - February 16Tutor : Andras Borbely

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Outline

1) Context of the project:• What is creep ?• Why do we need creep resistant

materials ?• How to assess creep damage ?

2) Presentation of the project:• The starting point.• The approach.

THE CONTEXT

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What is creep ?

time

elo

ng

at

ion

Thermally activated : T > 0.3 Tm.

Time dependant plastic deformation.

0.2 Tm

0.5 Tm

Constant load

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What is creep ?

Failure : nucleation, growth and coalescence of cavities.

Thermally activated : T > 0.3 Tm.

Stresses lower than elastic limit.

Time dependant plastic deformation.

What are the related issues ?

Thermal power plants

Jet engines

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A need for creep resistant materials

Electricity generation : improvement of efficiency.

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A need for creep resistant materials

Electricity generation : improvement of efficiency.

Increasing efficiency = materials in harsher environments.

Development of creep resistant materials: precise chemistry and microstructures control.

Damage assessment techniques

Microscopy sample preparation

(polishing). complex shapes of

voids.

Ultrasonic technique qualitative measures. in-service

components.

X-ray microtomography quantitative

measures. 3D imaging.

Destructive methods Non-destructive methods

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X-ray micro-tomography:

Damage assessment techniques

rotation

Tray

X-ray source

detector

data collectionstep-by-steprotation

volume reconstructi

on

THE PROJECT

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The experiments

Constant load

Constant pressure

Heating element

Measure of extension

Creep experiments performed at MPA, Stuttgart.

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The experiments

Volume for

tomography

Extraction of samples:

Measurements done at European Synchrotron Radiation Facility.

Z

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Reconstruction from tomography

Statistics

38 000h – 600°C

10 000h – 575°C

300 μm

Outer surface

Inner surface

Inner pressure

3D images

Z

5 μm

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Project approach

•Model of cavity growth.•Material parameters of the steels.

Literature review

•Simulation of experiments using finite-elements (experimental measures).•Simulation of cavity growth.

Modeling

•Influence of variables and parameters.•Limits of the model.

Interpretation of results

CONCLUSION

Industrial need for creep resistant materials.

Need for research to better understand creep.

QUESTIONS ?