Multi-scale composite mechanism of sandwich-structure TPS composites

Abstract

This study comprehensively investigates the composite mechanism of an integrated thermal protection system (TPS) with a hydrophobically modified silica aerogel core and fiber-reinforced SiO_2f/SiO₂ face-sheets, fabricated via multi-cycle sol-gel impregnation and high-temperature sintering. Raw material specifications, sol parameters and detailed sintering schedules were fully quantified, and supplementary characterizations including thermal conductivity, TG-DSC thermal stability, pore size distribution, hydrophobic contact angle and interfacial shear strength were supplemented to support mechanism analysis. We systematically studied the effects of 1–11 impregnation cycles on the macrostructure, density, mechanical properties and microstructural evolution of the core and face-sheets. Results show the aerogel core has exceptional stability, with density at 0.38–0.41 g/cm³ and compressive stress (3% strain) at 0.13–0.19 MPa, due to hydrophobicity that resists sol infiltration; the water contact angle of modified aerogel reaches 132.5° ± 2.1°, directly verifying the anti-infiltration effect. In contrast, the face-sheet densifies progressively, with density increasing from 1.20 to 1.54 g/cm³ and stitched samples reaching a tensile strength of 120 MPa after 11 cycles; mercury intrusion testing quantifies the gradual decline of face-sheet porosity throughout cyclic impregnation. Microstructural characterization reveals the sol-gel process enables SiO₂ matrix to encapsulate fiber bundles, forming a dense ceramic composite after sintering. SiO_2f stitching enhances the face-sheet's tensile strength by ∼20% via a "pinning" effect without altering the microscale sol-gel mechanism, and measured interfacial shear strength confirms stable interfacial bonding between core and face-sheet. Sintering-induced microcracks effectively raise composite fracture toughness from 1.31 MPa m¹ᐟ² to 1.92 MPa m¹ᐟ² by energy dissipation. Combining mechanical performance and thermal insulation property (core thermal conductivity stabilized at 0.032∼0.035 W/(m·K), 11 impregnation cycles are verified as the optimal preparation parameter. This study reveals the decoupled evolution mechanism of the core and face-sheet in sandwich TPS composites under repeated sol-gel cycles, determines the optimal fabrication process combined with multi-scale structural evolution rules, and provides important experimental and theoretical references for the process design and targeted performance regulation of high-performance thermal protection composites.