Mechanical modeling of a stitched sandwich thermal protection structure with ceramic-fiber-reinforced SiO2 aerogel as core layer

Ceramic-fiber-reinforced SiO2 aerogel (CFRSA) composite was used as core layer to prepare a stitched sandwich thermal protection structure (SSTPS). Mechanical properties of the SSTPS were experimentally investigated and compared with that of CFRSA, including flatwise tension, flatwise compression, edgewise compression and shear. Research results showed that the SSTPS can greatly improve the mechanical properties of CFRSA. To further understand the non-linear, tension-compression asymmetric and transversely isotropic properties of the SSTPS, inner configurations were investigated by X-ray computed tomography and scanning electron microscopy. Mechanical models were established to predict the overall properties of the SSTPS through performance of each component, including theoretical model and finite element analysis (FEA) model. Mixed series-parallel spring models were constructed to theoretically predict the effective elasticity modulus of the SSTPS. Representative volume element (RVE) was selected for FEA modeling of the SSTPS, which can not only predict the equivalent elastic modulus of SSTPS, but also predict the nonlinear flatwise compression behavior. In order to verify whether the mechanical properties of large area SSTPS under complex stress can be represented by the properties of uniform materials through RVE analysis, four-point bending test and FEA modeling were carried out on a large scale SSTPS specimen. Results showed that when analyzing the macro bending behavior of large area SSTPS, the method of equivalent SSTPS to uniform material were of relatively high accuracy and efficiency.

Exploration on application of dredging thermal protection in the leading edge of the wing

Aiming at the severe aerodynamic heating problem in the leading edge of the hypersonic vehicle, in order to ensure the sharp shape of the leading edge of the wing, a dredging thermal protection structure is proposed, and the built-in high-temperature heat pipe structure is used to provide thermal protection for the leading edge of the wing. By means of numerical simulation and arc wind tunnel test, the dredging thermal protection structure of the leading edge of the wing is analyzed, and the thermal protection effect of the built-in high-temperature heat pipe is obtained. The numerical results show that under certain thermal conditions, the temperature at the leading edge of the wing decreases by 304 K, and the minimum temperature of the tail increases by 130 K. The heat flow is dredged from the high-temperature zone to the low-temperature zone, and the thermal load of the leading edge of the wing is weakened. The same result can be obtained by the arc wind tunnel test, which verifies the accuracy of the numerical method and the feasibility of the dredging thermal protection structure with high-temperature heat pipe embedded in the leading edge of the wing.

THE INFLUENCE OF PERMEABILITY ON THE ABLATION PROCESS FOR AN ABLATIVE MATERIAL

The heat and mass transfer in the ablation process is of great importance for the ablation protection engineering. Accurate temperature assessment can provide effective support for the design of thermal protection structure and ablative material of reentry hypersonic vehicle. In this work, we studied the effect of permeability on heat and mass transfer and ablation thermal protection of gases produced during ablation. Since the carbide formed by ablation of material is a typical porous medium, its structure has self-similarity and can be described by fractal theory. Taking into account the angle of global coordinates and the local coordinates, this paper derived the permeability in any direction as a function of three different fractal dimensions in [Formula: see text], [Formula: see text] and [Formula: see text] directions. In order to verify the correctness of this method, the new model is introduced into the ablation process. Aiming at the ablation process and the diffusion equation of pyrolysis gas in the carbide layer, the temperature, material density and pyrolysis gas density distribution of three-dimensional spherical head under different permeability were simulated numerically. It is found that the permeability of carbides formed by ablative reaction of ablative materials related to fractal structure has an effect on ablation process. From our preliminary results, the higher the permeability, the faster the ablation speed, and the more obvious the overall temperature rise is.