Effect of Precrack “Halos” on Fracture Toughness Determined by the Surface Crack in Flexure Method
Effect of Precrack “Halos” on Fracture Toughness Determined by the Surface Crack in Flexure Method
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弯曲法中表面裂纹测定预裂纹“光环”对断裂韧性的影响
DOI：
10.1111/j.1151-2916.1998.tb02620.x
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发表时间：
2005
影响因子：
3.9
通讯作者：
G. Quinn
中科院分区：
文献类型：
--
作者：
J. Swab;G. Quinn
用来测定致密陶瓷断裂韧性的挠曲法中的表面裂纹，需要通过断口检验来测量预裂纹径。在室温条件下，甚至在快速断裂强度或断裂韧性测试过程中，在载荷作用下的较短时间内，裂纹也可能发生稳定的裂纹扩展。在这篇文章中，断口技术被用来表征稳定的裂纹扩展的证据，一个“光环”，在诺普压痕表面裂纹周围。对高纯氧化铝、氮化铝、微晶玻璃和氟化镁断口表面的光学观察表明，每个预裂纹周都存在一个光晕。AlN中的晕只是由于裂纹重定向引起的光学效应，而MgF2中的晕则是由压痕引起的残余应力引发的裂纹扩展。然而，对于Al_2O_3和微晶玻璃来说，环境辅助的缓慢裂纹扩展是产生晕圈的原因。在后两种材料中，必须将这种稳定的裂纹扩展作为临界裂纹尺寸的一部分，以确定适当的断裂韧性。
The surface crack in flexure method, which is used to determine the fracture toughness of dense ceramics, necessitates the measurement of precrack sizes by fractographic examination. Stable crack extension may occur from flaws under ambient, room-temperature conditions, even in the relatively short time under load during fast fracture strength or fracture toughness testing. In this article, fractographic techniques are used to characterize evidence of stable crack extension, a “halo,” around Knoop indentation surface cracks. Optical examination of the fracture surfaces of a high-purity Al2O3, an AlN, a glass-ceramic, and a MgF2 reveal the presence of a halo around the periphery of each precrack. The halo in the AlN is merely an optical effect due to crack reorientation, whereas the halo in the MgF2 is due to indentation-induced residual stresses initiating crack growth. However, for the Al2O3 and the glass-ceramic, environmentally assisted slow crack growth is the cause of the halo. In the latter two materials, this stable crack extension must be included as part of the critical crack size to determine the appropriate fracture toughness.
影响因子：
5.4
作者：
NEWMAN, JC;RAJU, IS
通讯作者：
RAJU, IS