前驱体浸渍裂解过程中SiC/SiC复合材料微观工艺应力模拟研究

Research on Stress Simulation of the Microscale Process of SiC/SiC Composite in PIP Process

前驱体浸渍裂解工艺(PIP)是SiC/SiC复合材料的一种近净成形制备方法,但前驱体裂解过程中产生的应力阻碍了该工艺的产业化应用。本文构建了一种化学-力学耦合模型来研究前驱体裂解过程中应力的产生和演化机理。首先以反应动力学模型描述了前驱体的裂解过程;其次基于三相球模型建立了一个解析模型计算基体的均匀化力学性质;最后结合上述模型构建了有限元模型,在微观尺度模拟计算了代表性体积单胞(RVC)内的工艺应力演变。结果表明:基体在贫基体的界面处承受显著的环向拉伸应力;对于由纯前驱体组成的基体,基体内的工艺应力主要是由裂解过程引起的化学收缩导致的,受温度引起的热膨胀影响较小;随着PIP循环次数的增加,化学收缩和热膨胀的角色发生互换。

The precursor impregnation pyrolysis process(PIP)was a near-net-shape preparation method for SiC/SiC composites,but the stress generated during the precursor pyrolysis process hindered the industrialization of the process.In this study,a chemical-mechanical couple model was proposed to study the mechanism of process stress and simulate the stress evolution during pyrolysis.The pyrolysis process of precursor was described by a kinetic model.An analytical model derived from the three-phase sphere model was developed to determine the homogenized properties and behavior of matrix.A finite element model integrating the kinetic model and the analytical model was established to compute the process stress of a microscale representative volume cell(RVC).The results show that the matrix sustains significant tensile circumferential stress at the interface of matrix-poor area.For the matrix composed by pure precursor,the evolution of the process stress is dominated by the chemical shrink due to the pyrolysis process and slightly influenced by the thermal expansion due to the process temperature.With the increasing of PIP cycle numbers,the roles of chemical shrink and of thermal expansion inverse.