Influence of porosity on compressive and tensile strength of cement mortar

Calcium phosphate cements for bone substitution: chemistry, handling and mechanical properties.

Mechanical and thermal properties of lime and hemp concrete (“hempcrete”) manufactured by a projection process

Analysis of crack behavior for Ni-based WC composite coatings by laser cladding and crack-free realization

Silicon carbide ceramics with anisotropic pore microstructures pseudomorphous to wood were obtained by liquid Si infiltration of porous carbonized wood templates. Depending on the initial cellular microstructure of the various kinds of wood (ebony, beech, oak, maple, pine, balsa) ceramic materials of different density, pore structure and degree of anisotropy were obtained. Strength and elastic modulus of the pyrolyzed carbon preform and of the final silicon carbide ceramic were measured in different loading directions with respect to the initial cell orientation, e.g. axial, radial and tangential. Generally, the mechanical properties increase with fractional density. Strength and strain-to-failure in axial direction exhibit significantly higher values compared to loading in radial and tangential directions. The orientation dependence of microstructure-property relations may become important for the development of advanced anisotropic light weight structural materials.

Biomorphic cellular silicon carbide ceramics from wood : II. Mechanical properties

A connected-grain model developed earlier to study the modulus of elasticity as a power-law of density was extended to study the dependence of the flexural strength of polycrystalline ceramics on porosity. Relations were derived for specific surface fracture energy, fracture toughness and flexural strength as power laws of (1 −p), wherep is porosity. Model validity was confirmed with data on α-alumina, UO2, Si3N4, and the YBa2Cu3O7−δ superconductor.

Dependence of ceramic fracture properties on porosity

A dependence of Young's modulus of elasticity on open porosity in ceramics is derived from an open-porosity model, which in the literature, is applied to salinity conductivity and fluid permeability in rocks. A random distribution of grain and pore size is assumed. The relation developed,E(p)=E
o(1−"p)m, whereE is the modulus of elasticity of the porous ceramic,E
o is the theoretical elastic modulus,p is the porosity andm is an exponent dependent on the tortuosity of the structure of the ceramic, adequately describes the dependence of the modulus of elasticity on porosity. The model is applied to the experimental data from several ceramics such as alumina, silicon nitride, silicon carbide, uranium oxide, rare-earth oxides, and YBa2Cu3O7−δ superconductor, and the value ofm is obtained for each case. We have shown thatm has a value of nearly 2 for sintered ceramics, unless sintering aids or hot pressing have been used during fabrication of the ceramic. Such additional procedures approximately double the magnitude ofm.

Open pore description of mechanical properties of ceramics

After polycrystalline silicon nitride samples with various α/β phase ratios were fabricated by uniaxial hot-pressing under vacuum, their microstructures, α-to-β transformations, and grain-growth mechanisms were then characterized by electron microscopy. Room-temperature fracture toughness (KIC) increased with increasing β-phase content, and a value of 7.0 ± 0.5 MPa ċ m1/2 was obtained for a sample that contained 60 vol% β phase. The increase in KIC is the result of an increase in elongated-grain fractions with increasing β content, which promotes energy absorption by crack deflection, as well as by grain debonding, pullout, and bridging mechanisms.

Microstructure and room-temperature mechanical properties of Si3N4 with various α/β phase ratios

The effects of unstabilized ZrO2 inclusions on the strength, fracture surface energy and thermal-shock resistance of MgCr2O4 have been evaluated. The fracture surface energy for MgCr2O4-ZrO2 composites was observed to depend on the agglomerate particle size distribution, and volume fraction of the ZrO2 inclusions. Large, nonuniformly distributed ZrO2 inclusions tended to produce a relatively small increase in the fracture surface energy of MgCr2O4. The fracture surface energy increased with increasing ZrO2 content to a maximum value of 24.5J m−2 at 16.5 vol % ZrO2, and decreased as the ZrO2 content increased further. It is proposed that this four-fold increase in fracture surface energy results from the absorption of energy due to microcrack formation in the MgCr2O4 matrix, which results primarily from the tensile stresses due to the tetragonal → monoclinic phase transformation of ZrO2 and the associated volume expansion. The improvement in mechanical properties, specifically the four-fold increase in fracture surface energy, resulted in a substantial increase in thermal-shock resistance of MgCr2O4-ZrO2 composites as indicated by the results of thermal-shock experiments.

J. P. Singh

Papers

Dependence of ceramic fracture properties on porosity

Open pore description of mechanical properties of ceramics

Microstructure and room-temperature mechanical properties of Si3N4 with various α/β phase ratios

Effect of ZrO2 inclusions on fracture properties of MgCr204