Analysis of bridging Stress Effect of Polycrystlline Aluminas Using Double Cantilever Beam Method

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J. Korean Ceram. Soc. > Volume 33(5); 1996 > Article

Journal of the Korean Ceramic Society 1996;33(5): 602.

Double Cantilever Beam 방법을 이용한 다결정 알루미나의 Bridging 응력효과 해석 III. 다결정 알루미나의 Bridging 응력분포

손기선, 이성학, 백성기

포항공과대학교 항공재료연구센터

Analysis of bridging Stress Effect of Polycrystlline Aluminas Using Double Cantilever Beam Method

ABSTRACT

The purpose of the present study is to investigate the microstructural effect on the R-curve behavior in three aluminas with different grain size distributions by analyzing the bridging stress distribution. The crack opening displacement (COD) according to the distance behind the stationary crack tip was measured using an in situ SEM fracture method. The measured COD values in the fine-grained alumina agreed well with Wiederhorn's sollution while they deviated from Wiederhorn's solution in the two coarse-grained aluminas because of the increase of the crack closure due to the grain interface bridging in the crack wake. A numerical fitting procedure was conducted by the introduction of the power-law relation and the current theoretical model together with the measured COD's in order to obtain the bridging stress distribution. The results indicated that the bridging stress function and the R-curve computed by the current model were consistent with those computed by the power-law relation providing a reliable evidence for the bridging stress analysis of the current model. The strain-softening exponent in the power-law relation n, was calculated to be in the range from 2 to 3 and was closely related to the grain size distribution. Thus it was concluded from the current theoretical model that the grain size distribution affected greatly the bridging stress distribution thereby resulting in the quantitative analysis of microfracture of polycrystalline aluminas through correlating the local-fracture-cont-rolling microstructure.

Key words: R-curve behavior, Bridging stress, Crack opening displacement (COD), in situ SEM fracture method, Strain-softening exponent, Grain size distribution