Thermomechanical characteristics of X-core thermal protection structures with various shape and arrangement of lightening holes

The present study proposes an X-shaped sandwich panel with multiple layers and rows of lightening holes, aiming to improve the performance of integrated thermal protection system (ITPS). The thermal protection properties and load-bearing capacity of the panel are investigated by the sequential thermomechanical coupling method. Numerical calculations demonstrate that the X-shaped sandwich panel effectively reduces the maximum temperature of the bottom sheet, achieving a 61.4 K reduction compared to a solid corrugated panel. Moreover, the X-shaped panel enhances the maximum temperature difference between the top and bottom panels up to 632.05 K with rectangular lightening holes. The introduction of these lightening holes modifies the temperature distribution on the bottom sheet from a striped to a dotted pattern, leading to a more uniform temperature field. Furthermore, it is observed that different shapes of lightening holes significantly influence both heat transfer rate and path. Elliptical holes increase peak bottom panel temperature by 9.55 K, while triangular holes decrease it by 3.87 K. In addition, combining various trapezoidal lightening hole designs affects heat transfer characteristics and leads to lower and more uniformly distributed bottom panel temperature. The sandwich structures exhibit stress concentration at the bolt positions and along the periphery of the lightening holes. The structure maximum von Mises stress of 706.72 MPa is within the maximum permissible stress of the material, while the maximum total displacement reaches 1.313 mm. Changing the shape of the holes from triangular to elliptical reduced the maximum stress by 9.18%. Considering both thermal protection and load-bearing capacities, the trapezoid is the optimal shape for lightening holes.