纳观界面应力集中对复合晶粒断裂应力的影响

Effect of nano-interface stress concentration on fracture stress of composite grains

为了准确分析纤维增强复合陶瓷内复合晶粒力学性能,提出了一种考虑纳观界面应力集中效应的复合晶粒强度预测方法.基于纤维增强复合陶瓷的显微结构特征,考虑纳米纤维间的相互作用,应用有效自洽法确定纳观界面模型的有效应力场;假设纳观界面处基体和纤维间的应力和位移均连续,利用叠加法将单向拉伸应力状态分解为双向均匀拉伸状态和纯剪切应力状态的组合,根据纤维增强复合陶瓷承受横向载荷的位移函数得到纳观界面附近基体和纤维的位移场和应力场,并计算了纳观界面产生的应力集中因子,综合考虑了复合晶粒内纳观界面和位错塞积相互作用导致的应力集中效应,建立了纤维增强复合陶瓷中复合晶粒的断裂应力预报模型.分析了增强纤维半径和体积分数对复合晶粒断裂应力的影响,结果表明:增强纤维半径越小,断裂应力越大,复合晶粒强度越高,且增强纤维半径大于50 nm后,半径大小对复合晶粒断裂应力影响较小;纤维体积分数越大,断裂应力越小,复合晶粒越易发生破坏.

In order to accurately analyze the mechanical properties of composite grains in fiber reinforced composite ceramics(FRCC), a prediction method of composite grain strength is proposed based on the stress concentration effect of nano-interface. On the basis of the microstructure characteristics of FRCC, considering the interaction between nano-fibers, an effective self-consistent method was applied to determine the effective stress field of the nano-interface model. It was assumed that the stress and the displacement between matrix and fiber were continuous at the interface. The uniaxial tension was decomposed into the combination of biaxial tension and pure shear stress by superposition method. The displacement field and the stress field of the matrix and the fiber on the two sides of the interface were obtained according to the displacement function of the FRCC subjected to transverse load, and the stress concentration factor generated by the nano-interface was calculated. Considering the effect of stress concentration caused by dislocation pile-up and nano-interface, a prediction model for fracture stress of composite grains was established, and the influence of the reinforced fiber radius and the volume fraction on the fracture stress was analyzed. Results show that the smaller the radius is, the greater the fracture stress is, and the higher the grain strength becomes. When the radius is larger than 50 nm, it has little effect on the fracture stress. The larger the fiber volume fraction is, the smaller the fracture stress is, and the lower the grain strength becomes.