Kriteria stability obecných singulárních koncentrátorů napětí, Část IV: Aplikace na lomové chování povlaků

Crack initiation kriteria for singular stress concentrators, Part IV: Applications to fracture of coated structures. Engineering Mechanics

journal article - other

en

The influence of through crack in the protective surface layer on damage of coated structure is investigated. The coated structure is modeled as a particular case of a bi-material body consisting of thin surface layer on the substrate. The problem is studied under the assumptions corresponding to small scale yielding conditions and calculations are performed by the finite element method. Specific attention is devoted to the case of a through coating crack with its tip at the interface between coating and the substrate. To estimate how the coating crack with its tip at the interface influences the substrate failure the general approach described in (Part I,II III of this contribution) is applied. An approximate approach based on calculations of crack mouth opening displacement for thin protective layers is suggested and developed. It is concluded that in the case of a stiffer coating on a more compliant substrate, the through coating cracks represent dangerous stress concentrators and, as a consequence of elastic mismatch of both materials, the critical applied stress for substrate failure decreases. Traditional approaches may have underestimated this effect and estimations of the service life of coated structures neglecting this phenomenon could lead to non-conservative values, with unexpected failures.

Práce se zabývá šířením trhlin v povlacích. Specielni pozornost je věnována konfiguraci, kdy se vrchol trhliny nachází na rozhraní mezi ochrannou vrstvou a podkladovým materiálem. Práce navazuje na části I-III věnované šíření trhliny přes materiálové rozhraní.

The influence of through crack in the protective surface layer on damage of coated structure is investigated. The coated structure is modeled as a particular case of a bi-material body consisting of thin surface layer on the substrate. The problem is studied under the assumptions corresponding to small scale yielding conditions and calculations are performed by the finite element method. Specific attention is devoted to the case of a through coating crack with its tip at the interface between coating and the substrate. To estimate how the coating crack with its tip at the interface influences the substrate failure the general approach described in (Part I,II III of this contribution) is applied. An approximate approach based on calculations of crack mouth opening displacement for thin protective layers is suggested and developed. It is concluded that in the case of a stiffer coating on a more compliant substrate, the through coating cracks represent dangerous stress concentrators and, as a consequence of elastic mismatch of both materials, the critical applied stress for substrate failure decreases. Traditional approaches may have underestimated this effect and estimations of the service life of coated structures neglecting this phenomenon could lead to non-conservative values, with unexpected failures.

Fracture mechanics, bi-material body, thin layers, fracture of coated structures

2008

30.09.2008

Engineering Academy of the Czech Rep.

Praha

1802-1484

Engineering Mechanics

15

4

263–270

8