【作者】 李鑫；

【导师】 向维；

【作者基本信息】 西南交通大学 ， 机械工程， 2023， 硕士

【摘要】 陶瓷基复合材料(CMCs)在航空发动机系统、飞行器热防护系统、先进核能系统及高性能制动系统等领域有重要应用价值,纤维/基体界面性能对其细观损伤演化和宏观力学性能起着至关重要的作用。为了深入研究CMCs损伤演化的复杂机制,需要对其细观结构的应力分布进行准确的模拟。剪滞模型被广泛应用于损伤CMCs的应力预测,然而该理论模型是在一系列假设和简化的基础上提出的,具有一定的局限性。相比之下,以有限元法为代表的数值方法可以更有效地模拟复杂甚至极端条件下损伤CMCs的应力场。然而经典的h型有限元方法在模拟界面粘连、滑移和脱粘等复杂界面行为时,需要足够多的连续界面单元来保证界面裂纹尖端应力场的准确性,精细的网格划分对前处理过程提出了较高的要求,而且必然导致计算量巨大。因此,本文引入了升阶谱求积元法(HQEM),将其应用于断裂力学参数的计算和CMCs的界面行为模拟,主要工作如下:1.结合HQEM和虚拟裂纹闭合法准确高效地计算了平面裂纹问题的应变能释放率(SERRs)。提出了适用于HQEM的应变能释放率计算公式,并讨论了该p型方法的网格划分方式和收敛性。数值算例表明,对于I型、II型和界面裂纹问题,HQEM均表现出了远高于传统有限元法和光滑有限元法的精度和效率。2.采用HQEM实现了损伤CMCs特征体元应力分布的准确模拟。研究了基于HQEM的损伤CMCs建模方式,提出了界面粘连系数和脱粘系数的概念,并通过参数分析表明二者分别与纤维体积分数和界面剪应力存在对应关系,从而为其最佳取值的选取提供了依据。通过HQEM模型计算出的CMCs特征体元的应力分布与BHE模型吻合较好,验证了HQEM能够对CMCs的应力分布进行准确预测。3.采用HQEM研究了陶瓷基复合材料损伤过程的应力传递与变形机制。建立了SiC_f/SiC复合材料的整体HQEM模型,包含上游区域、过渡区域和下游区域,并针对CMCs在失效过程中的三种典型状态——基体开裂、界面脱粘和纤维失效,模拟了其轴向应力分布和变形情况,所得结果与理论分析一致,清晰地揭示了CMCs损伤演变过程中的细观机制。更多还原

【Abstract】 Ceramic matrix composites(CMCs)play a crucial role in various applications,including aero-engine systems,aircraft thermal protection systems,advanced nuclear energy systems,and high-performance braking systems,and so on.The performance of the fiber/matrix interface is pivotal to the mesoscopic damage evolution and macroscopic mechanical properties of CMCs.To investigate the complex mechanisms of CMCs damage evolution,accurate simulation of stress distribution in the mesoscopic structures is required.Although the shear-lag model has been widely used for stress prediction in damaged CMCs,it is proposed on basis of a series of assumptions and simplifications,thus limiting its applications.In contrast,numerical methods exemplified by the well-known finite element method(FEM)can more effectively simulate the stress fields in damaged CMCs under complex or even extreme conditions.However,when using the classical h-version FEM to simulate complex interface behaviors such as adhesion,slipping and debonding,sufficient continuum interface elements are required to ensure the accuracy of stress estimation at the interface crack tip.Fine meshing poses high requirements for pre-processing,and inevitably leads to a huge computational burden.Therefore,a hierarchical quadrature element method(HQEM)is introduced to the calculation of fracture mechanics parameters and simulation of CMC interface behaviors in this study.The primary contents are as follows:1.The strain energy release rates(SERRs)of plane crack problems are derived by combining HQEM and the virtual crack closure method.The calculation formula of SERRs suitable for HQEM is proposed,and the meshing scheme and convergence of this p-version method are discussed.Numerical examples show that for mode I,II,and interface crack problems,HQEM exhibits much higher accuracy and efficiency than traditional FEM and smoothed FEM.2.The stress distribution of the unit cell in damaged CMCs is evaluated using HQEM.The modeling method of damaged CMCs based on HQEM is studied,and the interface bonded and debonded coefficients are proposed.Through parameter analysis,it provides a basis for the optimal selection of the interface bonded and debonded coefficients,which are respectively related to the fiber volume fraction and interface shear stress.The stress distribution of the CMCs unit cell calculated by the HQEM model matches well with the BHE model,verifying that HQEM can accurately predict the stress distribution of CMCs.3.The stress transfer and deformation mechanism of CMCs during damage process are investigated by HQEM.An overall HQEM model of SiC_f/SiC composites is established,which includes the upstream region,transition region,and downstream region.Aiming at the three typical states of CMCs during failure:matrix cracking,interface debonding,and fiber failure,the axial stress distribution and deformation are simulated,and the results are consistent with theoretical analysis,revealing the mesoscopic mechanism of CMCs damage evolution.更多还原