Mechanical Behavior Of Ceramics Research Articles

Influence of residual stress on the mechanical behavior of ceramics with various quartz sizes

Ceramics are semi vitreous materials that are made of kaolin clay, feldspar and quartz. These materials are fired at a temperature greater than 1000°C. Due to low sinterability during firing, quartz remains embedded in a glassy matrix. During cooling, a mismatch in the thermal expansion coefficient of quartz and its surrounding creates cracks as a result of residual stress. This study therefore explores the effect of quartz particle size on the magnitude of residual stress. The results are later compared with the mechanical behavior of the samples.Test samples were pressed at 40 MPa and then fired at a peak temperature of 1300°C at a rate of 60°C/min. Their microstructure was studied using a scanning electron microscope (SEM). The X-ray diffraction method was used to measure residual stress, calculation was based on [101] and [110] quartz planes. In addition, the measurement of flexural strength and hardness was limited to three point loading and Vickers indentation, respectively.The study revealed that the residual stress on quartz decreases with particle size over a range of 45–200 µm. The decrease was attributed to cracks formed in the microstructure of fired samples. The SEM micrograph of bodies with 45 µm showed a crack free glassy phase. As a result, a high value of flexural strength (33±1 MPa) and hardness (5.8±0.2 GPa) was exhibited by these samples. These results further point out that flexural strength is comparable to ISO 13006 standards of ≥ 35±2 MPa. The samples with 90 µm particle size exhibited strength of 25±1 MPa and hardness of 5.4 ± 0.1 GPa. Due to severe cracks triggered by residual stress effect, samples with 200 µm exhibited strength of 15±1 MPa and hardness of 4.6±0.1 GPa. Therefore, to minimize cracks due to stress effect, quartz size milling of less than 90 µm is encouraged.

Mechanical Behavior of Ceramics and Glass During Specimen Edge Fracture Caused by Rockwell Indentor

Mechanical behavior of ceramics and glass under local loading of specimens by an indentor is studied experimentally by a proposed test procedure. The effect of scratching on fracture resistance is assessed by comparing the test results obtained by two methods – edge fracture under scratching (S+EF method) and without scratching (EF method). Based on the analysis of experimental findings, the fracture mechanism of these brittle materials under such test conditions is discussed.

Multiscale approach to description of deformation and fracture of brittle media with hierarchical porous structure on the basis of movable cellular automaton method

An approach to multiscale description of deformation and fracture of brittle porous materials on the basis of movable cellular automaton method was proposed. The material characterized by pore size distribution function having two maxima was considered. The core of the proposed approach consists in finding the automaton effective response function by means of direct numerical simulation of representative volume of the porous material. A hierarchical two-scale model of mechanical behavior of ceramics under compression and shear loading was developed. Zirconia based ceramics with pore size greater than the average grain size was considered. At the first scale of the model only small pores (corresponding to the first maximum of the pore size distribution function) were taking into account explicitly (by removing automata from the initial structure). The representative volume and effective elastic properties of the porous material at this scale were evaluated. At the second scale of the model, big pores were taking into account explicitly, the parameters of the matrix corresponded to the ones determined at the first scale. Simulation results showed that the proposed multiscale model allows qualitatively and quantitatively correct describing of deformation and fracture of brittle material with hierarchical porous structure.

Instrumented nanoindentation investigation into the mechanical behavior of ceramics at moderately elevated temperatures

Abstract

Influência da expansão por umidade no comportamento mecânico de argilas para uso em blocos de cerâmica vermelha - revisão

O fenômeno da expansão por umidade (EPU) resulta da ação da água e seus vapores causando a expansão dos materiais cerâmicos, podendo provocar danos no material e prejudicar sua vida útil. Na literatura existe muita ênfase nos problemas gerados pela EPU e nas tensões resultantes dessa expansão, porém até o presente não há dados relativos ao comportamento mecânico dos materiais cerâmicos após ação da EPU. Trabalhos recentemente desenvolvidos na UFCG tratam especificamente desse problema em blocos cerâmicos de vedação. Inicialmente verificou-se que, no caso de massas cerâmicas para uso em cerâmica vermelha queimadas em diversas temperaturas na faixa de 700 a 1100 ºC, e com a EPU induzida por imersão, fervura e autoclavagem, a EPU tem correlação com o comportamento mecânico dos corpos queimados, observando-se redução no módulo de ruptura à flexão à medida que a EPU aumenta. Trabalhos desenvolvidos com massas para uso em cerâmica vermelha aditivadas com carbonato de cálcio e carbonato de magnésio e queimadas entre 850 e 1000 ºC, evidenciaram o efeito benéfico do carbonato de cálcio na redução da EPU e aumento da resistência à flexão, sendo observada correlação entre EPU e módulo de ruptura à flexão, mas, no entanto, não foi observada correlação entre a EPU e o módulo quando da utilização do carbonato de magnésio. Pesquisas efetuadas com massas para cerâmica vermelha aditivadas com quartzo fino, visando o desenvolvimento de fases vítreas, não mostraram correlações bem definidas entre EPU e módulo de ruptura, sendo observado que adições de 10 e 20% de quartzo melhoram a resistência mecânica dos corpos cerâmicos após autoclavagem e que a adição de 30% de quartzo reduz seu módulo de ruptura.

Shear Strength of Titanium Diboride under Shock Wave and Static Compressions

The mechanical behavior of ceramics under high pressures and temperatures is a subject of considerable interest. Since high pressures can be generated under static or dynamic conditions, it is necessary to measure mechanical properties of the materials under both. In the present work, compression and shear strength of titanium diboride measured under plane shock wave compression is revealingly compared with the recent measurement of compression and shear strength of titanium diboride obtained under static high pressures.

Damage, plasticity and failure of ceramics and cementitious composites subjected to multi-axial state of stress

Experimental data on mechanical behavior of ceramics and cementitious composites subjected to triaxial state of stress and verification of the theoretical model capable to describe deformability and fracture of brittle rock-like materials are presented in the paper. To check the validity of the theoretical model the stress–strain curves and stresses at material fracture determined experimentally for brick and mortar were compared with the theoretical predictions. The limit surface at material fracture obtained experimentally from triaxial tests was used in numerical analysis of masonry specimens subjected to compressive loading. These numerical results obtained by employing the Finite Element Method software package Mafem3D were compared with experimental data available in the literature. Fairly good agreement of numerical predictions with experimental results for masonry specimens was observed.

Analysis of the Local Mechanical Behaviour of Ceramics and Composites through Nanoindentation/Scratching and Raman Microspectroscopy

Analysis of the Local Mechanical Behaviour of Ceramics and Composites through Nanoindentation/Scratching and Raman Microspectroscopy

Dependence of the Longitudinal Velocity of Sound in Constructional Ceramic Materials on Pressure and Damage Rate

The effect of porosity and concentration of planar microcracks on the velocity of elastic waves in polycrystalline ceramic materials on the basis of SiC, Al2$O3, B4C, and ZrO2 is numerically studied. The mechanical behavior of ceramics is described using the model of a damaged medium. Various dependences that describe the relationship between the effective moduli of elasticity of the medium material and the relative volume of damages are analyzed as applied to predicting wave dynamics. For porosities up to 20%, a satisfactory prediction of the velocity of longitudinal waves in ceramics is ensured by the use of exponential and linear dependences. Within this range of porosities, the velocity of elastic waves decreases linearly with increasing relative volume of damages. The influence of the pulse amplitude on the velocity of elastic waves is analyzed. It is shown that the velocity of elastic waves in constructional ceramics increases in proportion to pressure up to 5% within the range of pulse amplitudes that do not exceed the Hugoniot limit of elasticity. Numerical values of coefficients in the relation between the velocity of the longitudinal elastic wave and the velocity of material particles are determined for ceramic materials considered. As the Hugoniot limit of elasticity is exceeded, the values of the coefficients decrease by 10–30% for different ceramic materials. The resultant values of the coefficients are in good agreement with experimental data found in the literature.

Bending strength of silica glass

Tensile and bending tests are useful to characterize the mechanical behavior of ceramics. Theoretical comparisons between results of both tests are usually done based on Weibull statistics. In previous experiments on borosilicate glass, no agreement was found between experimental and theoretical values of the ratio of the maximum bending and tensile stresses at 50 percent probability of fracture. In this investigation, additional experiments in bending have been performed, to measure the distribution of fracture initiation points. Good agreement with theory is found. The previous disagreement could be attributed to fatigue effects.

Deformation and strength of engineering ceramics and single crystals

A comparative investigation has been performed of the laws of deformation and strength of engineering silicon nitride-, alumina, and zirconia-based ceramics, as well as zirconia crystals. The specimens were tested in four-point bending in air over a temperature range from ambient to 1400 °C. The materials' mechanical behaviour was analyzed by load versus deflection diagrams (deformation diagrams). It has been found that above the brittle-to-ductile transition temperature, T BD, for the ceramics studied it is possible to choose such combinations of temperature and deformation rate, which would ensure the same path of deformation diagrams, i.e. equivalent influence of those two parameters on the mechanical behaviour of ceramics is observed. The mechanism of inelastic deformation of the ceramics studied is shown to be associated with the development of two processes: viscous flow of the grain boundary phase and crack propagation to a critical size, with one of them prevailing at different load levels. In contrast to ceramics, the strength of zirconia crystals remained practically unchanged (partially-stabilized crystals) up to 1400 °C or even increased (fully-stabilized crystals). For all the crystals, static elasticity moduli were independent of the number of repeated-static loading cycles at high temperatures (their values remained constant), while for ceramics a reduction was observed. Partially-stabilized zirconia crystals, as compared to other investigated materials, exhibited practically no creep up to 1400 °C at loads close to limiting ones. This allows them to be considered as a promising engineering material for high-temperature application.

Strength, fracture toughness, and acoustic emission of ceramics based on partially stabilized zirconium dioxide

A study is made of the mechanical behavior of ceramics based on ZrO2: a ceramic partially stabilized with MgO and a tetragonal polycrystalline ceramic with an addition of Y2O3. It is shown that the Y2O3-stabilized ceramic is linearly elastic, is characterized by a plane R-curve, and exhibits the fracture barrier effect. The ceramic with MgO is inelastic, has an increasing R-curve, and does not exhibit the fracture barrier effect. Data is obtained on acoustic emission in a study of the ceramics, the sources of the emissions being both microscopic and macroscopic defects.

Mechanical behavior of ceramics not following Hooke's law

The new characteristics of mechanical behavior, i.e., the degree of brittleness and the comparative brittleness, proposed previously by the author can be used efficiently in analysis of the results of strength tests on ceramics and other low-formability materials during mechanical and thermal loading. From the group of the low-formability materials it is convenient to separate the relatively brittle materials (materials not following Hooke's law) whose mechanical behavior differs greatly not only from the ductile but also brittle materials (materials which follow Hooke's law). This must be taken into account both in the course of investigations and in using the experimental results in practice.

Predicting the mechanical behavior of ceramics and refractories from their typical brittleness values

It is shown that the brittleness values can be used to predict the features of the mechanical behavior of materials during static and thermal loadings at different temperatures. In this case, for an approximate evaluation of such features it is possible to use data from the determination of deformation diagrams at room temperature, made on a single specimen, which is particularly valuable in research studies connected with the creation of new types of ceramics and refractories.

Ceramics and Ceramic Composites: Opportunities and Cooperative Research Modes

AbstractCeramics and ceramic composites are a rapidly evolving category of materials capable of being tailored to have unique combinations of electrical, optical, mechanical, and chemical properties that make them essential and irreplacable in many engineering applications. Conventional ceramics have both enabled and enhanced many important aspects of our modern technological society; the next generation of ceramics will play a further enabling role for still higher performance devices.A briefing panel of the National Academies of Science and Engineering recently identified four areas into which promising research areas for advanced ceramics can be grouped: 1.New thin films and layer structures with improved properties.2.Exploration of completely new, multicomponent ceramic crystal structures and composites.3.The mechanical behavior of ceramics and tough composites.4.Ceramic processing of large parts and assemblies.Three mechanisms for achieving critical mass in ceramics research were recommended: 1.University/industry programs.2.A summer institute.3.A large interdisciplinary center.

Cambridge Solid State Science Series: Mechanical Behaviour of Ceramics

R W Davidge 1979 London: Cambridge University Press viii + 165 pp price £15 This very welcome addition to the CSSS series must be the best survey of the basis of the mechanical behaviour of ceramic materials currently available and is clearly and lucidly written. Covering the entire spectrum of behaviour from fundamentals of crack behaviour to the increasingly important topic of lifetime prediction for engineering components, the concise and wellreferenced text retains and stimulates the reader's interest throughout, though perhaps some of the topics could have been dealt with more thoroughly (e.g. the development of microstructure and the fracture mechanics of thermal shock).

Mechanical properties of ceramics

Mechanical Behaviour of Ceramics. By R. W. Davidge. Pp. 165. (Cambridge University Press: Cambridge, 1979.) £15.