化学气相渗透的边界奇点法建模
Modeling of Chemical Vapor Infiltration Using Boundary Singularity Method
AI总结：
本研究采用边界奇点法模拟纤维预制体的化学气相渗透过程，通过计算纤维表面浓度与沉积速率，实现了纤维生长和孔隙填充的动态建模，并与解析解、实验及水平集方法结果对比验证，为CVI材料质量评估提供依据。
摘要：
采用边界奇点法（BSM）对纤维预制体中的化学气相渗透（CVI）过程进行了建模。将具有不同横截面几何形状的直长纤维（代表预制体中的纤维）放置在预定尺寸的域内。以制备致密纤维增强碳化硅（SiC）复合材料作为CVI方法的典型代表，其中甲基三氯硅烷（MTS）同时作为碳化硅基体的硅源和碳源。随后，在域边界设定MTS的浓度，随着时间推移，域逐渐被MTS渗透。采用所采用的BSM计算预制体纤维表面的MTS浓度。对于所考虑的准平衡状态，固体表面的反应速率等于向表面的扩散速率。Robin或第三类边界条件（即函数值与其在域边界上的导数值的线性组合）被开发并应用于BSM。根据BSM获得的纤维表面浓度，计算沉积速率，并更新几何形状以反映时间步长内的纤维生长，从而随时间模拟纤维尺寸增长和孔隙填充。通过将BSM分析与已知的同心圆柱解析解（外圆柱设定浓度，内圆柱发生反应）进行比较，验证了BSM分析的正确性。BSM解还与实验数据以及通过水平集方法（LSM）获得的计算结果进行了比较。获得的孔隙尺寸和位置的动态变化将有助于评估通过CVI制造的材料质量。获得了孔隙率瞬态，以显示随时间推移初始孔隙率与当前孔隙率之间的关系。
英文摘要：
Boundary Singularity Method (BSM) was used to model Chemical Vapor Infiltration (CVI) in a fibrous preform. Straight, long fibers of varying cross-sectional geometry, representing fibers of a preform, were placed within a domain of a pre-determined size. The preparation of dense fiber-reinforced Silicon-Carbon (SiC) composites was considered as a representative of CVI methodology, where methyl-trichlorosilane (MTS) was used as both the silicon and carbon donor for the silicon carbide matrix. Concentrations of MTS were then set at the domain boundaries, and the domain was gradually infiltrated with MTS as time progressed. The concentration of MTS at the surface of the preform fibers was calculated using the adopted BSM. For quasi-equilibrium considered, the reaction rate at solid surface is equal to the diffusion rate towards the surface. The Robin or third type boundary condition, which is a linear combination of the values of a function and the values of its derivative on the boundary of the domain, are developed and implemented to BSM. From the fibers surface concentrations obtained by BSM, deposition rates were calculated, and the geometry was updated to reflect the fiber growth during the time step, therefore, the fiber size growth and pore filling was modeled over time. The BSM analysis was verified by comparisons to a known analytical solution of concentric cylinders with a concentration set at the outer cylinder and a reaction at the inner. BSM solutions were also compared to experimental data as well as computational results obtained by a Level-Set Method (LSM). Obtained dynamics of pore size and location will help to evaluate quality of material manufactured by CVI. Porosity transients were obtained to show the relation between initial and current porosities as time progresses.
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