ICF13B

13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- For the fracture-mechanical computations, a least representative cell has been defined, consisting of a substrate+bond coat+TGO+top coat cell, having the width ܮ ( = half the period of the idealised cosine wave of Fig. 3). This cell has been given boundary conditions corresponding to symmetry along the left-hand vertical boundary. The model bases on an idealised (sinusoidal) bond coat (BC)/top coat (TC) interface profile, in which the thermally grown oxide (TGO) is assumed to grow. See Fig. 3. Equal cracks grow symmetrically from all profile tops, i.e., when D = a/L = 1.0, cracks extend along the whole interface, leading to complete failure. Further essential model assumptions:  Plane strain  Stress-free TBC system at the end of the high-temperature part of the cycle  The maximum damage-driving energy release rate G and stress intensity factors KI and KII appear after cooling down from the maximum temperature (low thermal expansion of the TC)  The material behaviour of all components of the TBC aggregate during the cooling down from maximum temperature is assumed to be linearly elastic G, KI and KII are computed by a virtual crack extension method and by interface crack theory (see [3] and appendix) Fig 4 shows examples of the FE geometry and of the stress pattern in the interface region for 4 typical ݄ ܮ/ cases Figure 4. Examples of the FE geometry and of the stress pattern in the interface region for 4 typical h/L cases. Most of the FE computations so far have been done in an in-house code. We have, however, moved over to the commercial code Abaqus for a planned continuation, which will, among other things, inh L Material No. 1 Material No. 2 1 2

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