Rising Crack-Growth-Resistance (R-Curve) Behavior of Toughened Alumina and Silicon Nitride
Rising Crack-Growth-Resistance (R-Curve) Behavior of Toughened Alumina and Silicon Nitride
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DOI：
10.1111/j.1151-2916.1991.tb06812.x
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发表时间：
1991-10
影响因子：
3.9
通讯作者：
N. Ramachandran;D. Shetty
中科院分区：
文献类型：
--
作者：
N. Ramachandran;D. Shetty
通过直接测量与维氏压痕缺陷相关的裂纹长度来评估烧结/HIPed SiC（晶须）增强氧化铝和烧结氮化硅的r曲线。基于(a)初始（缩进）裂纹长度，(b)增加远场载荷时裂纹的平衡增长，以及(c)不稳定断裂对应的裂纹长度的断裂韧性测量显示了两种材料的明确的r曲线趋势。断裂力学分析采用了压头-材料常数，该常数是通过残余驱动力的物理模型和自由表面修正因子独立估计的，该因子考虑了裂纹的大小和形状对应力强度的影响。结果表明，基于裂纹长度测量的r曲线估计具有固有的优点，即不像传统的基于强度的分析那样假定裂纹长度与断裂韧性的依赖关系。SiC（晶须）增强氧化铝的断裂韧性与基于部分脱粘晶须的裂纹桥接增韧模型的预测一致。
R-curves for a sinter/HIPed SiC(whisker)-reinforced alumina and a sintered silicon nitride were assessed by direct measurements of lengths of cracks associated with Vickers indentation flaws. The fracture toughness measurements based on (a) initial (as-indented) crack lengths, (b) equilibrium growth of cracks during increasing far-field loading, and (c) crack lengths corresponding to unstable fracture showed definitive trends of R-curves for both materials. The fracture mechanics analyses employed an indenter-material constant that was independently estimated using a physical model for the residual driving force and a free surface correction factor that accounted for the effects of size and shape of the cracks on stress intensity. It is shown that R-curve estimations based on crack length measurements have the intrinsic advantage that crack length dependence of fracture toughness is not assumed a priori as is done in conventional analysis based on strength. The measured fracture toughness of SiC(whisker)-reinforced alumina was in agreement with the prediction of a toughening model based on crack bridging by partially debonded whiskers.