Crack‐Interface Grain Bridging as a Fracture Resistance I, Mechanism in Ceramics: I, Experimental Study on Alumina
Crack‐Interface Grain Bridging as a Fracture Resistance I, Mechanism in Ceramics: I, Experimental Study on Alumina
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DOI：
10.1111/j.1151-2916.1987.tb04982.x
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发表时间：
1987-04
影响因子：
3.9
通讯作者：
P. Swanson;C. J. Fairbanks;B. Lawn;Y. Mai;B. Hockey
中科院分区：
文献类型：
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作者：
P. Swanson;C. J. Fairbanks;B. Lawn;Y. Mai;B. Hockey
直接的微观证据支持在单相陶瓷的R-曲线行为的解释，在新形成的裂纹界面的晶粒局部化桥接。对粗晶氧化铝的锥形悬臂梁和压痕弯曲试样的裂纹扩展进行了原位观察。观察到的断裂是高度稳定的，典型的材料具有强烈增加的电阻特性，但在微观结构水平上是不连续的。与这种不连续性相关联的是在桥接颗粒周围的表面断裂迹线中出现重叠段;这种“活性位点”沿迹线沿着的平均间距约为2至5个颗粒直径。这些部分与试样表面下的主裂纹连接，并随着断裂的进行继续向桥断裂方向发展。桥保持活跃在大的距离，100晶粒直径或更多的顺序，后面的裂纹尖端。扫描电子显微镜的一些桥接网站表明，二次（界面相邻）微裂缝和摩擦牵引力的桥梁分离过程中的重要因素。寻求证据，但没有发现，一些更流行的替代模型的增韧，特别是前端区微裂纹和裂纹尖端/内应力的相互作用。这表明裂纹界面桥接机制可能是非相变陶瓷中的普遍现象。
Direct microscopic evidence is presented in support of an explanation of R-curve behavior in monophase ceramics by grain-localized bridging across the newly formed crack interface. In situ observations are made of crack growth in tapered cantilever beam and indented flexure specimens of a coarsegrained alumina. The fractures are observed to be highly stable, typical of a material with a strongly increasing resistance characteristic, but are discontinuous at the microstructural level. Associated with this discontinuity is the appearance of overlapping segments in the surface fracture trace around bridging grains; the mean spacing of such “activity sites” along the trace is about 2 to 5 grain diameters. These segments link up with the primary crack beneath the specimen surface, and continue to evolve toward rupture of the bridge as fracture proceeds. The bridges remain active at large distances, of order 100 grain diameters or more, behind the crack tip. Scanning electron microscopy of some of the bridging sites demonstrates that secondary (interface-adjacent) microfracture and frictional tractions are important elements in the bridge separation process. Evidence is sought, but none found, for some of the more popular alternative models of toughening, notably frontal-zone microcracking and cracktip/internal-stress interaction. It is suggested that the crackinterface bridging mechanism may be a general phenomenon in nontransforming ceramics.