Effect of Thermoelastic Anisotropy on theR‐curve Behavior of Monolithic Alumina

Publisher Website
Google Scholar
Abstract
The postfracture tensile (PFT) test has previously been used to evaluate the wake stresses of both cubic and noncubic monolithic ceramics at room temperature. The present study applies this procedure to the evaluation of the characteristic stress–crack face separation relationships for alumina at temperatures ranging from room temperature through 600°C, which is slightly below the softening temperature for the glassy grain boundai y phase. For comparison with the PFT behaviors,R‐curves are obtained throughout this range of temperatures using a short double cantilever beam geometry. The average residual stresses arising from thermal expansion anisotropy diminish with increasing temperature, causing two effects evidenced by a general downward shift of the characteristic PFT stress–displacement curves. The resulting lower peak stresses and smaller limiting crack opening displacements (COD) manifest through a decrease of the COD–grain size ratio criteria for bridging. Also, the residual stresses contribute to a significant fraction of large grains fracturing transgrarularly. This fraction is modified somewhat by test temperatures of 800°C and above; however, no detectable change can be claimed for the present results, which are limited to 600°C.