Ceramic aerogels are attractive for thermal insulation but plagued by poor mechanical stability and degradation under thermal shock. In this study, we designed and synthesized hyperbolic architectured ceramic aerogels with nanolayered double-pane walls with a negative Poisson’s ratio (−0.25) and a negative linear thermal expansion coefficient (−1.8 × 10 −6 per °C). Our aerogels display robust mechanical and thermal stability and feature ultralow densities down to ~0.1 milligram per cubic centimeter, superelasticity up to 95%, and near-zero strength loss after sharp thermal shocks (275°C per second) or intense thermal stress at 1400°C, as well as ultralow thermal conductivity in vacuum [~2.4 milliwatts per meter-kelvin (mW/m·K)] and in air (~20 mW/m·K). This robust material system is ideal for thermal superinsulation under extreme conditions, such as those encountered by spacecraft.

Double-negative-index ceramic aerogels for thermal superinsulation

Probabilistic Physics of Failure-based framework for fatigue life prediction of aircraft gas turbine discs under uncertainty

Aerogels are highly porous structures prepared via a sol-gel process and supercritical drying technology. Among the classes of aerogels, silica aerogel exhibits the most remarkable physical properties, possessing lower density, thermal conductivity, refractive index, and dielectric constant than any solids. Its acoustical property is such that it can absorb the sound waves reducing speed to 100 m/s compared to 332 m/s for air. However, when it comes to commercialization, the result is not as expected. It seems that mass production, particularly in the aerospace industry, has dawdled behind. This paper highlights the evolution of aerogels in general and discusses the functions and significances of silica aerogel in previous astronautical applications. Future outer-space applications have been proposed as per the current research trend. Finally, the implementation of conventional silica aerogel in aeronautics is argued with an alternative known as Maerogel.

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Aerogels in Aerospace: An Overview

Silica aerogels are among the lightest weight solid materials and exhibit other unique properties, in particular an outstanding insulation performance. However, these nanostructured highly porous materials show inherent brittleness that makes their processing and handling difficult and constrains their use in common daily applications. One of the most convincing and effective strategies to reinforce the silica aerogel structure is the manufacturing of aerogel composites with embedded fibres, which significantly contributes to widening their applications. This review encompasses a complete survey on scientific achievements related to silica aerogel composites reinforced with all types of fibres (natural, man-made, organic, inorganic and nanofibres), describing their synthesis approaches and properties. The influence of the embedment of different fibres on the final properties of the composites is thoroughly reported, considering their amount in the matrix and/or their specific characteristics, namely morphology, orientation and optical features. The applications linked to the fibre-reinforced silica aerogel composites are briefly addressed as well, evincing developments in typical functions of aerogels, as thermal and/or acoustic insulators and adsorbents, and also in emerging uses, for example as sensors or technical and protective apparel.

Silica aerogel composites with embedded fibres: a review on their preparation, properties and applications

Heat insulation properties of silica aerogel/glass fiber composites fabricated by press forming

Aerogel has been used for thermal insulation because of its extremely low thermal conductivity, but the application has been restricted to non-loading-bearing structures by its low strength properties. Fiber-reinforced aerogel was prepared with higher strength but without sacrificing much of its thermal conductivity. While fiber-reinforced aerogel performs as load-bearing insulation, two behaviors must be investigated: compression and stress relaxation at evaluated temperature. At first, compression test was performed on a fiber-reinforced aerogel composite at both room and evaluated temperature, then the effects of temperature on compression properties of the fiber-reinforced aerogel were analyzed. Stress Relaxation Test was carried out at a constant strain of 0.1 for 1200 s at both room and evaluated temperature. The experimental results show that the stress relaxations increase with the temperature rise from 200 °C to 800 °C. Previous research and Scanning Electron Microscope (SEM) analysis of specimens showed that two time-dependent behaviors: (1) cracks induced by collapse of the pores, and (2) fiber failures subject to interfaces that debond and slide, might be possible reasons for the stress relaxation and the small inelastic strain of specimen tested at 25 °C. While three time dependent phenomena: (1) fusing of aerogel nanoparticles to form nanoparticle clusters, (2) fiber stress relaxation and (3) fiber failures subject to interfaces that debond and slide, would be possible reasons for the remarkable stress relaxation behavior at 800 °C.

Experimental investigation on mechanical properties of a fiber-reinforced silica aerogel composite

Compression tests were conducted on a ceramic-fiber-reinforced SiO 2 aerogel at high temperature. Anisotropic mechanical property was found. In-plane Young's modulus is more than 10 times higher than that of out-of-plane, but fracture strain is much lower by a factor of 100. Out-of-plane Young's modulus decreases with increasing temperature, but the in-plane modulus and fracture stress increase with temperature. The out-of-plane property does not change with loading rates. Viscous flow at high temperature is found to cause in-plane shrinkage, and both in-plane and out-of-plane properties change. Compression induced densification of aerogel matrix was also found by Scanning Electron Microscope analysis.

Experimental investigation on high temperature anisotropic compression properties of ceramic-fiber-reinforced SiO2 aerogel

Effects of crystallographic orientations and dwell types on low cycle fatigue and life modeling of a SC superalloy

Creep and fatigue lifetime analysis of directionally solidified superalloy and its brazed joints based on continuum damage mechanics at elevated temperature

Duoqi Shi

Papers

Experimental investigation on mechanical properties of a fiber-reinforced silica aerogel composite

Experimental investigation on high temperature anisotropic compression properties of ceramic-fiber-reinforced SiO2 aerogel

Effects of crystallographic orientations and dwell types on low cycle fatigue and life modeling of a SC superalloy

Creep and fatigue lifetime analysis of directionally solidified superalloy and its brazed joints based on continuum damage mechanics at elevated temperature

Constitutive modeling and failure mechanisms of anisotropic tensile and creep behaviors of nickel-base directionally solidified superalloy