Shakedown boundaries of multilayered thermal barrier systems considering interface imperfections

Xiaotao Zheng, Haofeng Chen, Zhiyuan Ma

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Abstract

Thermal barrier coatings (TBCs) usually have complex structures and operate in cyclic high temperatures. The cracking phenomenon is usually observed at the interface with microscopic imperfections between the bond and the thermally grown oxide (TGO) layer owing to the cyclic plasticity around the defect interface under the cyclic thermal loading. Shakedown limits of TBCs with interface imperfections are investigated based on the proposed linear matching method considering the effect of temperature-dependent material properties. The influences of geometric parameters ho, R/ho and H/R as well as the thermal expansion coefficient ratio α/αr are discussed in detail. Results present that the thickness of the TGO has no effect and the geometric factor R/ho shows a little influence on shakedown limits of the multilayered systems. However, the geometric parameter H/R and the thermal expansion coefficient ratio α/αr have a remarkable impact on shakedown limits. This indicates that the depth of the defect influences shakedown limits greatly, while the transition radius at the corner of the imperfection shows slight effect. This is obviously different from the common phenomenon that the transition radius usually has an important influence on shakedown limits. Based on the calculated data, the shakedown assessment approach of TBCs considering various factors mentioned above is proposed. It is of great interest that the simulated effective plastic strain occurs at the defect interface between the TGO and the bond layer when the applied load exceeds the shakedown limit. It is the crack failure region of cracked TBCs according to the microscopic morphology observation.
Original languageEnglish
Number of pages21
JournalInternational Journal of Mechanical Science
Early online date18 May 2018
DOIs
Publication statusE-pub ahead of print - 18 May 2018

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Keywords

  • shakedown
  • thermal barrier coatings
  • imperfections
  • temperature- dependent material
  • linear matching methods

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