Crack Growth Resistance of Textured Alumina

Abstract

The crack growth resistance of a textured, extruded alumina body was compared with that of an isotropic, isopressed body of similar grain size, density, and chemistry. R-curve levels reflected the preferred orientation; however, R -curve slopes (dK, / d A a ) were the same in all instances, implying a similar crack growth resistive mechanism. Three orthongonal orientations of crack growth in the two structures exhibited similar forms of KIR versus Aa curves, for which a schematic diagram for polycrystalline ceramics is proposed. [

Fracture Toughness of Thin Plates by the Double-Torsion Test Method

“…The good agreement between the C1421 test methods and the DT for all thicknesses of SiC implies that use of appropriate test procedures will ensure good results for flat R-curve materials. The elevated values for the alumina relative to the C1421 values concur with previous long crack values 4,6 from chevron-notch short bar specimens 3 Very large L/W ratios will likely produce large constant K I regions; however, the mass of the test specimen may begin to affect the result. Load point friction needs to be minimized via free bearing balls.…”

“…Alumina is more difficult for such a study because it can exhibit a rising R-curve, stress corrosion, and textural effects. 6 Soda-lime glass, though sensitive to stress corrosion, has a flat R-curve. In addition, its transparency allows easy observation of the crack length.…”

Sintering to Transparency of Polycrystalline Ceramic Materials

“…All RIT values shown so far have been calculated considering texture less materials. However, different routes have shown the possibility to induce some texture in the polycrystalline materials (Salem et al, 1989;Mao et al, 2008;Uchikoshi et al, 2004). Figure 4.7b shows how at two wavelengths, 400 and 700 nm, the RIT increases with increasing texture.…”

Fracture of alumina: an experimental and numerical study

“…by frictional tractions around bridging grains, which produces a strong toughening effect. Although microcracking or damage in the frontal crack tip zone has been reported recently [6], there is no experimental evidence that such a frontal microcrack zone significantly contributes to an increasing crack resistance [7,8]. A microcrack zone, once part of the wake, may, however enhance the frictional tractions because of the dilational strains.…”