Effect of Residual Stress Due to Knoop Indentation on Subcritical Crack Growth Behavior in Ceramics

Abstract

The application of indentation technique to the evaluation of elevated temperature subcritical crack growth (SCG) behavior of ceramics is examined in detail, with particular emphasis on the effect of residual stress. A bending strength test is made to characterize the residual stress field around indentation. Then, the SCG velocity, v, is measured as a function of stress intensity, K₁, with the extension of indentation flaws placed on the tensile surface of specimens in 3—point bending. An obvious deviation exists between the K1∼v curves obtained by considering or neglecting the residual stress effects due to indentation. So a residual stress term is suggested to be incorporated into the calculation of stress intensity for indentation flaw in order to establish a precise K₁∼ v curve. With a further discussion on the earlier period of extension of indentation flaws, it is shown that the stress intensity at crack tip exhibits a decreasing tendency and a characteristic stress is proposed to differentiate the mechanisms for the delayed failure of ceramics at elevated temperatures.

This paper is done under the cooperative research contract with Hitachi Chemical Co., Ltd.