基于界面端奇异性理论的单纤维拔出试验的试件设计

Specimen Design for Fiber Pullout Test Based on Stress Singularity Analysis of Interface End

在单纤维拔出试验中,由于试件的界面端存在应力奇异性,这使试验所得到的界面剪切强度数据失去合理性[1]。但从文献[1]关于微珠脱粘试验研究的结论中可以发现当基体的楔形角小于某临界角度后,微珠试件界面端应力奇异性几乎消失。由此启发我们设计出一种楔形角小于该纤维／基体系统临界角的锥面的拔出试件,这样即可以防止出现传统拔出试件在界面端的强应力奇异性,又可以避免微珠脱粘试验自身的缺陷。界面端具有任意楔形角的轴对称模型被用于分析和确定纤维／基体系统的临界角,对方程进行渐近展开和分离变量处理,根据边界条件可以得到关于特征值λ的特征方程,针对确定的纤维／基体系统可以得到特征值和楔形角的关系曲线,我们把应力奇异性指数等于-0.005时所对应的楔形角定义为临界角,以及根据临界角设计锥面拔出试件的方法。

Since stress singularity was found at the interface end in current specimen of pullout test, interface stress strength (IFSS) obtained from the tests loses its rationality. But an useful conclusion is that when the wedge angle of the matrix is less than a critical angle, the singularity of stress field at the interface end of the specimen in micro-debond test nearly disappears. Following this conclusion, a conic specimen shown in Figure 1 is presented, in which the wedge angle of the specimen is designed less than a critical angle to preventing the singular stress field occurred at interface end. The conic specimen is designed for pullout test to avoid disadvantages exhibiting in the micro-debond test. An axisymmetric model of fiber/matrix system with arbitrary wedge angles at the interface end is used for the determination of critical wedge angle. With the aid of asymptotic expansion and variable separation, eigenvalue, λ , could be determined by a characteristic determinant. For a given fiber/matrix system, the curve of the stress singularity index vs. wedge angle can be obtained by solving the characteristic determinant. We define the critical wedge angle, θcr corresponding to the singularity index of - 0.005. The design of a conic pullout specimen is also discussed.