STUDY OF FRACTURE SURFACE BRIDGING EFFECT IN CERAMICS

一些增韧陶瓷基复合材料(含少量体积%不锈钢颗粒的多晶氧化铝、含30%镍或钴金属的β锂辉石微晶玻璃、含20体积%碳化硅晶须的氮化硅陶瓷等)。已经做好了准备。我们试图通过1)微观尺度的光谱技术，2)R曲线评价，3)裂纹轮廓观察来阐明增韧机理。评价了这些复合材料的R曲线行为和裂纹张开位移(COD)曲线，并对其抗断裂机理进行了探讨。这些复合材料在1 mm的短裂纹扩展范围内表现出明显的R曲线行为。结合复合材料的微观组织特征和断口几何形状，对实验结果进行了讨论。对于玻璃或陶瓷单晶中的COD剖面观察，没有观察到断口之间的相互作用。另一方面，在韧性增强陶瓷基复合材料的COD分布中，裂纹尖端附近的实验值低于理论值(欧文抛物线)，导致断口相互作用增强。尤其是在高韧性复合材料中，裂纹尖端附近的外应力屏蔽作用更为明显。研究发现，基体颗粒尺寸的增大和金属粉末或晶须的加入都能增强断口之间的相互作用。外加应力强度与裂纹尖端应力强度随K(APPL)/K(TIP)的变化关系表明，增强剂在增韧陶瓷基复合材料中起着弹性桥联元件的作用。明确了每个样品在COD剖面上的桥接区大小，以对应于R曲线特征中上升延伸的大小。

Some toughness reinforced ceramic-based composites )polycrystalline aluimina containing a few vol% stainless-steel particles, β-spodumene glass ceramics containing 30.vol% Ni or Co metal, and silicon nitride ceramics reinforced with 20 vol% silicon carbide whisker , etc.) were prepared. We tried to clarify the toughening mechanism by 1) Spectroscopic techniques at micro scale, 2) R-curve evaluation, and 3) Crack profile observation. The R-curve behavior and crack opening displacement (COD) profiles for those composites were evaluated and mechanism for fracture resistance was examined. Those composites showed remarkable R-curve behavior within short crack extension of 1 mm. The results were discussed, associated with microstructural features and fracture surface geometry of those composites. For COD profile observation in glass or ceramic single crystals, the interaction between fracture surfaces was not observed. In the COD profiles of toughness reinforced ceramic-based composites on the other hand, the experimental value was lower than the theoretical one (Irwin parabola) near the crack tip, resulting in the enhancement of the fracture surface interaction. Especially, it was obvious that external stress shielding effects acted more strongly near the crack tip in highly toughened composite. The increase in matrix grain size and addition of metal powder or whisker were found to enhance the interaction between fracture surfaces. The relationship between the applied stress intensity and the stress intensity at the tip of crack as a function of K(appl)/K(tip) indicate that the agents for reinforcement acted as elastic bridging elements in the toughness reinforced ceramic-based composites. The size of bridging zone in COD profile for each specimen was clarified to correspond to that of rising extension in R-curve characteristics.