PSI - Issue 61

Mehmet N. Balci et al. / Procedia Structural Integrity 61 (2024) 331–339 Balci and Yalcin / Structural Integrity Procedia 00 (2019) 000 – 000

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and substrate is the metallic alloy which is designated to resist against mechanical load. The length of flaws, pores or microcracks existing in the interface regions can increase and reach to a considerable level, forming a crack at the interface.

Fig. 1. Crack configurations for surface coating, bond coating and substrate system, (a) Case-A: crack between surface coating and bond coating, (b) Case-B: crack between bond coating and substrate.

These cracks lead to stress concentration and may be a reason of failure due to delamination under thermal shock loading. Hence, thorough understanding of the toughness of multilayered TBCs under thermal shock is crucial. The thicknesses of the surface coating and bond coating were assumed as 231 and 186 m, respectively (Bumgardner et al., 2017). In the present study, the thicknesses of the surface coating and bond coating were assumed as 450 and 150 , respectively. Due to the symmetric boundary conditions, one-half of the problem can be modeled. The thermal and mechanical boundary conditions are assumed as follows: ( ) , , , 0, i o sc i Q h A T T x y   = − −  = (1) In the cold thermal shock loading case, the initial temperature of the entire model is 1323 i T K = and temperature of the surrounding fluid 298 T K  = without any stress field in the TBC system. In the hot thermal shock loading case, 298 i T K = and 1323 . T K  = The convection heat transfer coefficient 2 3000 . h W m K  = It is assumed that the substrate, bond coating and surface coating are perfectly bonded to each other. ( ) 0, 0, , Case-A, f sc q y y t = −  (2) ( ) 0, 0, , Case-B, f bc sc q y y t t = −  + (3) ( ) , 0, , Case-A, f sc q y y t  = −  (4) ( ) , 0, , Case-B, f bc sc q y y t t  = −  + (5) Crack faces are thermally insulated which necessitates: ( ) ,0 0, 0 , f q x x a + =   (6) ( ) ,0 0, 0 . f q x x a − =   (7) The far field temperature of the coating system for hot thermal load is assumed as room temperature which is: ( ) , 298 , 0 . T x K x − =   (8) Mechanical boundary conditions can be written based on the symmetry condition at 0, x = as follows: ( ) 0, 0, , Case-A, sc u y y t = −  (9) ( ) 0, 0, ,Case-B. bc sc u y y t t = −  + (10) ( ) , 0, 0 , v x x − =   ( ) ( ) , , 0. u v x  − = − = (11) 3. Modelling of delamination behavior based on finite element method Delamination behavior is modelled through the use of finite element method (FEM) in ANSYS (2016). In Fig. 2, utilized finite elements are described in detail. In simulations, 82544 quadrilateral finite elements involving 96 quarter-