Effect of Microstructure on Measurements of Fracture Energy of Al₂O₃

Abstract

Alumina specimens were fabricated under a wide range of conditions using cold-pressing and sintering techniques. Fracture energies were measured by an analytical technique (notched beam) and by the Tattersall-Tappin method. Problems in using the latter method are discussed. The effects of porosity, pore distribution, and grain size on fracture energy sore evaluated. Connected porosity has a deleterious effect on fracture energy. A grain-size effect dominates in dense material; the fracture energy decreases with increasing grain size.

Fracture behaviour of microcrack-free alumina–aluminium titanate ceramics with second phase nanoparticles at alumina grain boundaries

“…51 In those coarsegrained aluminas the main toughening mechanisms identified, crack bridging and crack branching, 52 were related to extensive grain boundary microcracking, at the expense of lower strength values ( ∼ =300 MPa, 25% inferior to strength for fine-grained alumina). 53 The same drawback strength-microcracking occurs in the composites studied here, that present lower strengths than the previously studied composite material (28-36% lower, Table 1).…”

Porous Yttrium Aluminum Garnet Fiber Coatings for Oxide Composites

“…I T HAS been well-documented that increasing the porosity of a ceramic decreases its mechanical properties. [1][2][3][4][5][6][7][8][9] This concept has been used to weaken matrixes of oxide composites to the extent that a fiber coating is not needed to protect the fibers from matrix cracks. 10 -14 In such composites, the matrix contributes little to the strength of the composite; its function is mainly to hold the fibers in place and prevent matrix cracks from developing enough energy to be able to penetrate the fibers.…”

Processing and Properties of ZrO2‐Containing Reaction‐Bonded Aluminum Oxide with High Initial Aluminum Contents

“…It is surmised that the slight variation in the ZrO 2 content among the samples 16.9–17.8 vol% may have contributed to the differences 21,22 . In addition, the lower elastic modulus and increase in porosity may have allowed for the generation of higher stresses in the AZ3 matrix, which could have induced a marginal contribution from transformation toughening 23 . In fact, there was a corresponding slight increase in fracture toughness with increasing aluminum content (3.1 to 3.5 to 3.6 MPa·m 1/2 ), which correlated to the differences in the biaxial fracture strengths.…”

“…21,22 In addition, the lower elastic modulus and increase in porosity may have allowed for the generation of higher stresses in the AZ3 matrix, which could have induced a marginal contribution from transformation toughening. 23 In fact, there was a corresponding slight increase in fracture toughness with increasing aluminum content (3.1 to 3.5 to 3.6 MPa Á m 1/2 ), which correlated to the differences in the biaxial fracture strengths. This change in toughness certainly supports this hypothesis; however, no systematic study was conducted to determine how much, if any, t-ZrO 2 transformed during mechanical testing.…”