Metallic integrated thermal protection structures inspired by the Norway spruce stem: Design, numerical simulation and selective laser melting fabrication

Abstract

With the development of hypersonic vehicles and reusable launch vehicles, the design of integrated thermal protection (ITP) structures needs to meet the demanding requirement of thermal protection. More complex geometries, such as lattice structures and bio-inspired structures, have been introduced into the design of ITP structures, aiming to enhance the thermal protection performance. Additive manufacturing holds high flexibility in processing and enables more complex designs, which is suitable for the fabrication of complex ITP structures. In this paper, inspired by the structures of Norway spruce stem, a series of ITP structures with different gradient hollow designs was proposed and manufactured by selective laser melting (SLM). The steady-state and transient thermal behavior of those bio-inspired ITP structures were investigated by finite element method (FEM). To verify the accuracy of the FEM simulation results, Ti6Al4V components with different bio-inspired ITP structures were fabricated by SLM and thermal conductivities of those SLM-processed components were experimentally measured. The FEM thermal simulation revealed that the gradient-structure with larger hollow tubes near the top and bottom plates and smaller hollow tubes in the center possessed the lowest bottom surface temperature of 262.8 °C, which was 21.4 °C lower than the structure with the highest bottom surface temperature. The thermal conductivity measurement revealed that the gradient-structure, with the lowest bottom surface temperature obtained by FEM thermal simulation, had the lowest thermal conductivity of 2.321 W/(m⋅K), which was about 29% lower than that of the structure possessing the highest thermal conductivity.