Issue 35

K. Slámečka et alii, Frattura ed Integrità Strutturale, 35 (2016) 322-329; DOI: 10.3221/IGF-ESIS.35.37 324 elastic-ideally plastic (BC) behavior. Material properties were obtained from references [10, 11] and the in-house database and they reflect the internal porosity of the YSZ top coat (the stiffness of 15 GPa is assumed being more than an order of magnitude smaller than the Young’s modulus of dense YSZ of 210 GPa). The geometry of the TC/BC interface was modelled based on profilometric measurements of a plasma-sprayed YSZ top coat [12]. The residual data were obtained after subtracting the specimen’s circular shape and were then decomposed into the roughness and the waviness components by using a Gaussian filter with an arbitrarily chosen cut-off wavelength of 200  m. The waviness data of approximately 1 mm 2 in size were used for FE calculations in order to alleviate the demands on CPU power and to diminish the differences between the topographies of TC and BC that are caused mostly by differences in material (ceramic, metal) and powder feedstock properties. Indeed, while the roughness of the bond coat and the top coat, as quantified by the average roughness S a (the average absolute deviation of roughness irregularities from the mean plane), the root mean square roughness S q (the standard deviation of the distribution of height z -coordinates), and the surface roughness R S (a ratio of the ‘‘true’’ and the projected surface area), is considerably different, the waviness in both cases is reasonably similar, Tab. 1. The simulated thermal loading consisted of a single cooling step from a temperature of 1020 °C at which a stress-free state was assumed in all materials. The system was isothermally cooled down to room temperature and the stresses at critical locations (YSZ and interfaces between YSZ, TGO, and BC) were studied. Figure 2 : Residual surface data (top left) of the as-sprayed YSZ top coat, its decomposition into the roughness (top middle) and waviness (top right) components, and rendering of the studied part of waviness data in ANSYS (bottom). Parameters (BC/TC) Data S a (  m) S q (  m) R S (  ) Residual 8.7/5.5 11.0/6.9 1.82/1.28 Roughness 6.3/3.3 8.0/4.2 1.82/1.28 Waviness 4.8/3.8 6.1/5.0 1.01/1.00 Table 1 : Comparison of the topographical parameters obtained for the as-sprayed CoNiCrAlY bond coat and YSZ top coat. The FEMME [9] (Finite Elements Microstructure MEshfree) method allows one to describe a complex graded microstructure, using a Cellular Automata (CA) model, with a generic FEM (Finite Element Model with irregular