5.5.2. Corrugated Core ITPS

For the corrugated core ITPS, the optimised configuration obtained from the thermal study is considered in the mechanical analysis. A quasi-isotropic laminate layup is considered. The same mechanical boundary conditions described for the honeycomb structure of the ablative TPS are applied (see Figure 7), and the commercial solver ANSYS® APDL is used. To take into account the thermal deformation, a coupled thermo-mechanical analysis is performed. The thermal solver is used to obtain the temperature field on the whole structure for the time point at which the maximum outer facesheet temperature is reached, which also corresponds to the maximum thermal gradient. The analysis leads to the results shown in Figure 18. The material properties are reported in Table A5. Due to the lack of established failure criteria for CMCs, the Von Mises equivalent stress on the component is reported. Widespread failure in several parts of the component is detected. The material tensile strength of 260 MPa is exceeded in several points of the structure, even far from the constraints where a local, artificial increase in stress is observed. This is mainly due to the high thermal gradient acting on the structure. The sandwich structure offers a high bending stiffness, which, although advantageous for the mechanical loading of the component, leads to high thermally induced stresses. Although the material exhibits a low coefficient of thermal expansion (CTE), the thermal stresses still exceed the allowable values in several sections of the component. Future design involving different fibre orientations that achieve a three-dimensional tailoring of the CTE might mitigate the incurred failures while retaining high bending stiffness.

**Figure 18.** Von Mises stress [MPa] for the corrugated core ITPS subjected to coupled pressure and thermal loads.
