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Fracture mechanics analysis of an APS applied TBC
Linköping University, Department of Mechanical Engineering. Linköping University, The Institute of Technology.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

An air plasma sprayed thermal barrier coating is investigated by fracture-mechanical analysis. The virtual crack extension method is used to calculatethe energy release rate, G, and the displacements of the crack surfaces are used to split the energy release rate into mode 1 and 2 stress intensity factors, K1 and K2 . The results of the investigation are evolutions of G, K1 and K2 as functions of delamination crack length for small delamination cracks.

An approximation of a hot spot is investigated by applying an out-of-phase load at room temperature. The results show that the out-of-phase load results in a more open crack compared with only a thermal load on the TBC system. This can explain why the out-of-phase load is dangerous.

The results show that it might be possible to base a delamination life model on fracture-mechanical data of an interface crack in the top/bond coat interface. If so, it is important that the mode mixity effects on crack growth rate is included in the life model.

Keyword [en]
Thermal barrier coating, Virtual crack extension, Interface crack, Crack initiation, Life modelling
National Category
Engineering and Technology
URN: urn:nbn:se:liu:diva-87826OAI: diva2:600176
Available from: 2013-01-23 Created: 2013-01-23 Last updated: 2013-01-23
In thesis
1. Delamination in APS applied thermal barrier coatings: life modelling
Open this publication in new window or tab >>Delamination in APS applied thermal barrier coatings: life modelling
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Thermal barrier coatings, TBCs, are used in gas turbines as a thermal shield resulting in lower temperature in coated components. The decrease of temperature allows higher gas temperatures in the turbine, which increase the efficiency. The bimaterial construction with an outer ceramic layer applied onto a metallic material give rice to problems during thermal cycling. Thermal induced stresses will gradually break down the coating. The ceramic layer will delaminate from the substrate, resulting in spallation, and the component will break down due to overheating.

The delamination process is investigated in this thesis by finite element simulations. The growth of an internal alumina layer in the top/bond coat interface is investigated by 3D finite element simulations which show that the local stress state change in such way that the alumina growth help nucleation and growth of small delamination cracks. Finite element simulations, in which t he energy release rate and stress intensity factors are calculated, investigate the growth of small delamination cracks in or close to the top/bond coat interface. Experiments show that these cracks grow parallel to or in the sinusoidal top/bond coat interface and the results of the simulations show that the mode mixity changes as the delamination cracks grow.

A new delamination life model is proposed which is based on results of the fracture mechanical simulations and experimental observations. The model predicts the growth of small cracks in the TBC before they form a large delamination crack. The model is based on a modified Paris law where a mode mixity dependence on the crack growth rate is included, meaning lower crack growth rate in mode 2 load compared with mode 1. Parameters of the model are obtained by optimisation of the model against experimental data, describing the delamination damage evolution in the TBC. The data are obtained from interrupted thermal cycling tests and the prediction of the model corresponds well with these data.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2004. 20 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 902
National Category
Engineering and Technology
urn:nbn:se:liu:diva-24067 (URN)3627 (Local ID)91-85295-55-8 (ISBN)3627 (Archive number)3627 (OAI)
Public defence
2004-10-27, Sal C3, Fysikhuset, Linköpings Universitet, Linköping, 10:15 (Swedish)
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2013-01-23

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