The thermal decomposition process of calcite particles (0.45–3.60mm average diameter), made up of porous agglomerates of very small CaCO3 microcrystals, was studied in the 975–1216K temperature ...range. The experiments were carried out under isothermal conditions in air atmosphere, in CO2 atmosphere, as well as in a gas stream comprising different concentrations of air and CO2.
An equation is proposed that relates the calcite conversion degree to both reaction time and operating conditions. The equation satisfactorily fits to the experimental results obtained in the entire tested range of particle sizes and temperatures in all the studied carbon dioxide concentrations.
Most industrial porcelain tiles suffer changes in their curvature after firing: such process is known as delayed curvature. One of the hypotheses used to explain this phenomenon is based on the ...relaxation of residual stresses by creep. In this study two types of industrial glazed porcelain tiles have been studied. One of them displayed delayed curvature after firing, whereas the other one presented a stable curvature. The main objective was to determine if the delayed curvatures were caused by the residual stresses generated during rapid industrial cooling. Both types of existing residual stresses (thermal stresses, caused by thermal gradients inside the tile during cooling, and body–glaze fit stresses, due to the thermal expansion mismatch between body and glaze) were measured, as well as related samples properties (elastic modulus, creep behaviour, thermal expansion). The results demonstrated that the residual stresses are not the main cause of the delayed curvature phenomenon.
This paper presents a comparative study of three- and four-point bending tests and diametral compression (DC) tests, used to measure the mechanical strength of green pressed compacts. The study has ...been conducted on pressed ceramic test pieces, formed at different pressing conditions. It was found that Weibull statistics largely explained the differences in the results of the three-point and four-point bending tests. However, Weibull statistics could not explain the much lower mechanical strength obtained with the diametral compression tests. The study establishes a correlation between the bending and DC tests; however, this correlation depends on moisture content, which is directly related to the plasticity of the piece. This finding confirms that the types of mechanical tests studied do not have the same sensitivity to the factors that lead to fracture. The differences in mechanical strength between the bending and DC tests were explained using a suitable fracture criterion (based on maximum strain) and plastic deformation.
The aim of this work is to clarify the influence of quartz inclusions added to a vitreous matrix on the macroscopic fracture toughness (KIC). We use numerical simulations to model a silicate-based ...ceramic material as a heterogeneous region composed of an isotropic brittle matrix and a distribution of embedded quartz inclusions. Using the material point method (MPM), we present a two-dimensional study, that albeit an approximation, sheds light on the role of the material composition in the fracture behavior observed in these ceramic materials. The value of KIC is calculated from the maximum strength obtained via computational analysis of a single-edge-notch tension specimen. The model test allows us to study in detail the effects occurring in a region close to the main notch. Additionally, to validate and understand our numerical findings, we fabricated and characterized experimentally a representative set of specimens with the same features as the numerical ones. We focus our attention on the effect of both the size and volume fraction of the dispersed phase, as well as the initial state of microcracking of the material and its influence on the macroscopic mechanical performance. The simulations have shown the decisive role played simultaneously by the volume fraction and typical size of the inclusions that are cracked during the cooling process.
We report a comparison between experimental evidences and simulation results of the micro cracking in ceramic materials provoked by the cooling process. The solid model and the fracture process are ...carried out using the Material Point Method. This model, where cracks may initiate and propagate, consists of a quartz particle embedded in a glassy phase. We focus our interest on the key role of the particle morphology on the micro fracture patterns.
► We model fracture of quartz particle in ceramic material by fast cooling. ► Shape of inclusions defines fracture pattern. ► Rounded shapes generate hoop cracks in matrix-quartz interface. ► Elongated shapes generate multiple transversal inner cracks perpendicular to the largest dimension. ► Irregular particles fail in sharp regions like corners.
Inappropriate mechanical properties of spray-dried powder compacts lead to significant green product losses, entailing considerable costs in ceramic tile manufacture as well as serious environmental ...problems. In addition, green strength can be indicative of how well a ceramic processing system is working.
In this study, granules were prepared by spray drying a red clay slurry used in floor tile manufacture. The resulting granules were characterised and their porosity, morphology, and mechanical behaviour were determined.
The study analyses the fracture properties of green ceramic materials using Linear Elastic Fracture Mechanics (LEFM), which has been widely used for fired materials, but whose application to green compacts has drawn much less attention. Two types of tests for determining fracture parameters (fracture toughness, fracture energy, and crack size) in green materials are also critically examined. Finally, the fracture parameters have been correlated to the microstructural characteristics of the compacts, in particular to granule size and the topography of the fracture.
On 25 January 2016, an earthquake of magnitude Mw=6.4 occurred at the southern part of the Alboran Sea, between southern Spain and northern Morocco. This shock was preceded by a foreshock (Mw=5.1) ...and followed by a long aftershock sequence. Focal mechanism of main shock has been estimated from slip inversion of body waves at teleseismic distances. Solution corresponds to left-lateral strike-slip motion, showing a complex bilateral rupture, formed by two sub-events, with most energy propagating along a plane oriented N30°E plane dipping to the NW. Relocation of larger events of the aftershock series, show two alignments of epicentres in NE-SW and NNE-SSW direction that intersect at the epicentre of the main shock. We have estimated the focal mechanisms of the largest aftershocks from moment tensor inversion at regional distances. We have obtained two families of focal mechanisms corresponding to strike slip for the NNE-SSW alignment and thrusting motion for the NE-SW alignment. Among the faults present in the area the Al Idrisi fault (or fault zone) may be a good candidate for the source of this earthquake. The study of Coulomb Failure Stress shows that it is possible that the 2016 earthquake was triggered by the previous nearby earthquakes of 1994 (Mw=5.8) and 2004 (Mw=6.3). The possible seismic reactivation of the central part of the Ibero-Maghrebian region is an open question, but it is clear that the occurrence of the 2016 earthquake confirms that from 1994 the seismicity of central part of IMR is increasing and that focal mechanism of largest earthquakes in this central part correspond to complex ruptures (or zone of fault).
•Relocation of largest aftershocks show two alignment of epicentres in NE-SW and NNW-SSW direction.•Two families of focal mechanism corresponding to strike-slip and thrusting motion.•The Al Idrisi fault may be a good candidate for the source of this shock.•The CFS shows a possible trigger effect of the 1994 and 2004 earthquakes on the 2016 shock.
The upgrade and enhancement of sea level networks worldwide for integration in sea level hazard warning systems have significantly increased the possibilities for measuring and analyzing high ...frequency sea level oscillations, with typical periods ranging from a few minutes to a few hours. Many tide gauges now afford 1 min or more frequent sampling and have shown such events to be a common occurrence. Their origins and spatial distribution are diverse and must be well understood in order to correctly design and interpret, for example, the automatic detection algorithms used by tsunami warning centers. Two events recorded recently in European Atlantic waters are analyzed here: possible wave-induced “seiches” that occurred along the North coast of Spain during the storms of January and February of 2014, and oscillations detected after an earthquake in the mid-Atlantic the 13th of February of 2015. The former caused significant flooding in towns and villages and a huge increase in wave-induced coastal damage that was reported in the media for weeks. The second was a smaller signal present in several tide gauges along the Atlantic coast that, that coincided with the occurrence of this earthquake, leading to a debate on the potential detection of a very small tsunami and how it might yield significant information for tsunami wave modelers and for the development of tsunami detection software. These kinds of events inform us about the limitations of automatic algorithms for tsunami warning and help to improve the information provided to tsunami warning centers, whilst also emphasizing the importance of other forcings in generating extreme sea levels and their associated potential for causing damage to infrastructure.
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