The uniaxial compressive creep experiment allows identification of which mechanism controls creep and to predict material lifetime under high temperature and low stress service conditions. Firstly, we detail a measurement apparatus developed in our laboratory to measure compressive creep for metals and ceramics, focusing on some important features to produce reliable measurements. Then we describe a protocol to analyze data in order to limit misinterpretation. Multi-stress and multi-temperature tests, particularly useful to determine stress exponent and activation energy, are described highlighting their advantages compared to single-dwell tests. Results obtained from a zircon-based ceramic refractory are used to discuss experimental uncertainties, accuracy and precision associated with creep rate, and creep parameters. Some consideration to decide testing conditions and parameters for different ceramic and metallic materials are also summarized. (C) 2017 Elsevier Ltd. All rights reserved.

The feasibility of producing high‐hardness ceramic sandwich structures, with compressive residual stresses in the faces, was evaluated in this study. The faces were originally chosen to be SiAlON with an SiC core. To produce structures that did not crack during processing, however, it was necessary to hybridize the faces by adding SiC particles to the SiAlON. This modification resulted in a composite face that reduced the thermal expansion mismatch with the core. The residual stresses in the face were measured with an indentation technique and these values agreed well with those measured by X‐ray diffraction and calculated from the theory using experimental values.

The compaction and fracture of brittle spherical particles in a cylindrical vessel were experimentally and numerically studied in the context of the American Petroleum Institute Recommended Practice 60 for proppants used in the hydraulic fracturing of oil and gas wells. Because pressures within the cylindrical vessel could not be directly measured, strain was experimentally determined via gauges along the outside surface. In addition, an epoxy resin was also injected at various loading stages to "freeze" the damage states for analysis. In addition, acoustic emissions were monitored in situ to determine damage signatures that could be correlated with the frozen test and strain measurement data. Experimental results were then compared to finite element simulations by using an assumed double-exponential pressure distribution applied to the inner face of the vessel. The results indicated that the assumed pressure distribution adequately described the loading state within the cylinder and revealed apparent stratification of damaged proppants near the top and bottom of the container. In addition, the damaged proppants and acoustic emission signatures showed that the damage increases progressively with the loading in distinct stages characterized by fracture and subsequent stress redistribution.

Microstructural evolution of silicon nitride (Si3N4) and SiAlON materials and its influence on creep resistance is reviewed. Grain size, grain morphology, and the ratio of α‐ to β‐phase grains play a part in resistance to creep. The glassy, intergranular phase typically has the strongest influence on creep. Creep data are usually obtained using uniaxial tensile or compressive tests, where creep in tension is controlled by cavitation and grain boundary sliding controls creep in compression. The impression creep methodology is also reviewed. An additional creep mechanism, dilation of the SiAlON grain structure, was found to be active in impression creep.

The composition and lattice parameters of several Yb‐SiAlON materials are reported. Electron microprobe analysis was used to measure the compositions of each phase, as this technique avoided the peak overlap problems encountered when using energy‐dispersive spectroscopy. A refined set of equations relating the composition of Yb‐α‐SiAlON to its lattice parameters is presented. The amount of oxygen substitution (n value) in α‐SiAlON has an effect on lattice parameters that is almost as strong as the amount of Al and Yb substitution (m value). The α‐SiAlON phase stability region is shown to extend much closer to the Si3N4‐4/3(AlN:Al2O3) line than reported previously.

Contact damage behavior of microstructurally tailored Yb-SiAlON ceramics under a spherical indenter was examined. Environmental scanning electron microscopy and optical microscopy were used to characterize the Hertzian contact damage. Four different microstructures with different alpha-SiAlON contents and grain morphology were evaluated for initiation of ring cracking. Onset of cracking was interrogated using acoustic emission spectroscopy and correlated to elastic failure models. Results indicated that a finer grain size distribution lead to a higher characteristic strength. From this study it was concluded that a fine grain size distribution is needed for high Hertzian contact strength.

The validity of diametral compression as an effective means of determining the tensile strength of spherical ceramic bodies has often been questioned. In this paper, a comprehensive review of the original work, as well as alternative studies that suggest shortcomings of the original method, is made. For comparative purposes, data recently collected via diametral compression on aluminosilicate aggregates is presented in the context of these latter works and compared with the original methodology. Overall, results indicate that the diametral compression test can indeed provide an accurate measure of tensile strength when several important test criteria are met.

Commercial aluminosilicate aggregates derived from kaolinite and bauxite were evaluated for various physical and mechanical properties. Suites of thermal treatments based on known phase relationships were performed, resulting in significant modification of microstructural and crystalline phase evolution. These structural changes were evaluated and rationalized via scanning electron microscopy and X‐ray diffraction, respectively. Subsequent measurement of mechanical strengths by diametral compression and density by gas pycnometry indicated increases in overall strengths (up to 24%) at a comparable densities (approximately 2.8 g/cm3) in kaolinite‐derived aggregates. Results of this study are being used to drive processing modifications to achieve higher specific strength in aluminosilicate‐derived aggregates.

The effect of tin on the properties of soda-lime-silica glass was examined in glasses doped with 0.2–3.0 mol% SnO2. Trends in the properties are consistent with an increase in the network connectivity with increasing tin concentration. The difference in the thermo-elastic properties of the tin doped glasses suggests the creation of residual stresses in the near surface region of float glass, resulting from the tin concentration gradient during cooling. Two-point fiber bend tests were conducted to determine the effect of tin on the stress corrosion susceptibility of tin doped sodalime-silica glasses. The results showed the stress corrosion exponent for the tin-doped glasses to be a weak positive function of tin concentration.

The effect of tin-oxide on the physical properties of soda-lime–silica glasses was investigated. Glasses containing tin-oxide concentrations ranging from 0 to 3mol% were synthesized in the laboratory. In some of the glasses, an attempt was made to control the ratio of Sn2+ to Sn4+ present in the glass. Dilatometry, beam-bending viscosity, and sonic resonance experiments were performed on the glasses to determine the role of tin on the thermal expansion, glass transition temperature, dilatometric softening temperature, annealing temperature, strain temperature, and elastic modulus of the glass. Mössbauer spectroscopy was used to determine the presence and relative amount of Sn2+ and Sn4+ in the glasses. The data suggest that the substitution of relatively small amounts of tin for a modifier species in the glass composition results in an increase in the network connectivity. In addition, the results suggest that this increase in network connectivity is more apparent in glasses containing higher relative amounts of Sn4+ compared to Sn2+.