Shengbo Shi

Modeling of one-dimensional thermal response of silica-phenolic composites with volume ablation

The silica-phenolic composites experience volume ablation when exposed to a radiant heat flux. Based on the analysis of mechanisms during volume ablation, a mathematical model was developed to predict the one-dimensional thermal response of the ablative material in this paper. After discretizing the space and time domain, the governing equations were described using the implicit finite differential form. Both the heat-mass transfer process and the moving boundary caused by thermal expansion, as well as the variation of pore pressure due to concentration and flow of the decomposition gases were considered in the formulation of the model. The thermal response of silica-phenolic composites during the volume ablation, including temperature distribution, pore pressure distribution, volume fraction of the phase components and degree of decomposition, were calculated by the proposed model. The time-dependent temperature progressions at different material depths were measured using a solar radiation heating experiment platform. The experimental and calculated temperature profiles are in good agreement.

Degradation in compressive strength of silica/phenolic composites subjected to thermal and mechanical loading

Reduction to the mechanical properties of fiber-reinforced polymer composites occurs when the material is exposed to radiant heat flux and compressive loading. A thermo-mechanical model was developed to predict the compressive strength and the failure time of silica fiber-reinforced phenolic composites. The coupling heat and mass transfer processes, generation of pyrolysis gases, and their subsequent diffusion process were considered in the model. The thermal softening, thermal decomposition of the matrix material, and phase transition of the reinforced fibers, which reduce the strength of the material, were also taken into account in the formulation of the model. Pyrolysis kinetics of phenolic resin, volume fraction of phase component, temperature profile, compressive strength, and time-to-failure of silica/phenolic composites were predicted using the developed model. The calculated temperature-dependent strength curve was compared with the experimental results measured by a high-temperature compression testing, and the agreement is good. The material fracture morphology was analyzed for silica-phenolic composite specimen after high-temperature compression testing.

Ablation mechanism and properties of silica fiber-reinforced composite upon oxyacetylene torch exposure

The mechanism of mass loss and endothermic properties of silica fiber-reinforced phenolic composites during ablation were investigated in this paper. A theoretical prediction model combining the surface ablation theory and heat transfer theory of heat shield was developed to study the surface ablation behavior. In the formulation of the mathematical model, the effect of the moving boundary on the thermal response was considered, which results from the surface recession of the material in the thickness direction during ablation. The surface ablation recession rate and wall temperature of silica fiber-reinforced phenolic composite specimen were measured using an oxyacetylene torch experimental platform. Then, the efficiency of the model was verified by comparing calculation and experimental results. According to the principles of energy conservation on the ablated surface of the material, the proportion formulas of the heat absorption induced by individual endothermic mechanisms and the total heat absorption were derived. Similarly, the proportions of the mass loss caused by individual mass loss mechanisms were also given. Finally, variations of the ablation properties of the silica fiber-reinforced phenolic composites versus thermal exposure time were calculated and analyzed.

Design and optimization of an integrated thermal protection system forspace vehicles

The relationships of multi-discipline in the thermal protection system (TPS) design were developed and a design process of TPS has been established. The optimization design of integrated thermal protection system (ITPS) was formulated with mass per unit area of the ITPS as the objective function. An area of wing component of space vehicle was selected and corrugated-core sandwich integrated thermal protection structure scheme was adopted in this design zone. Heat transfer and structural analysis of the ITPS were carried out by using the finite element method. The predicted results show that the design of ITPS could satisfy the requirements of thermal protection and load bearing capacity of space vehicles. Furthermore, hear transfer processes and thermally induced stresses of structure/thermal protection independent design scheme were analyzed, and subsequently compared with the ITPS design. The simulated results show that structure weight of the ITPS design is 6.5 kg lighter than the conventional TPS scheme in a 0.8 m 2 design zone.

Modeling of Coupled Temperature-Displacement-Diffusion Problem for Silica-Phenolic Composite under High Temperature

Volume ablation process of resin-matrix thermoprotective composite is, generally, associated with complex physico-chemical changes, heat and mass transfer processes and irreversible changes of thermomechanical and thermophysical properties. The thermomechanical behavior of resin-matrix thermoprotective material during volume ablation can be analyzed as the coupled temperature-displacement- diffusion problem of porous elastomers under high temperature. Based on the ablative and thermoprotective mechanisms of silica-phenolic composite, the governing equations of the porous elastomers, such as equation of motion of solid phase, gas diffusion equation and energy conservation equation, were established. These governing equations were further modified using finite element method to obtain the element stiffness equation for each element. Additionally, the global stiffness equations were assembled and solved by Gaussian elimination method. The temperature distribution, pore pressure, strain and stress field in plane strain state were calculated when silica-phenolic composite was exposed to a constant radiant heat flux.