Design Methodology for Ceramic Structures

1977 ◽  
Vol 99 (4) ◽  
pp. 559-566 ◽  
Author(s):  
G. G. Trantina ◽  
H. G. deLorenzi
Keyword(s):  
Design Methodology ◽  
Subcritical Crack Growth ◽  
Structural Strength ◽  
Ceramic Materials ◽  
Strength Degradation ◽  
Critical Material ◽  
Ceramic Structure ◽  
Single Piece ◽  
Turbine Vane ◽  
Critical Regions

Unique design techniques are required to successfully take advantage of the superior high temperature structural strength of ceramic materials. The design methodology described here combines the results of a finite element stress analysis with a statistical analysis in order to predict the probability of failure of a ceramic structure. The strength degradation of a ceramic material as a result of subcritical crack growth under constant and cyclic loading conditions is incorporated into the methodology. Critical material properties such as strength, Weibull modulus, and the strength degradation exponent are discussed. A tapered disk and a wedge specimen are analyzed. When subjected to thermal shock, these specimens simulate the stresses in critical regions of structures such as the trailing edge of a gas turbine vane. Finally, applications of the design methodology to ceramic transition pieces are discussed where similar probabilities of failure are obtained for single-piece and four-piece designs.

Examination of Fracture Interfaces in Silicon Nitride

1975 ◽  
Vol 33 ◽  
pp. 60-61
Author(s):  
Nancy J. Tighe
Keyword(s):  
Silicon Nitride ◽  
Grain Boundary ◽  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Slow Crack Growth ◽  
Ceramic Materials ◽  
Grain Boundary Sliding ◽  
Boundary Phase ◽  
Turbine Engines ◽  
Boundary Sliding

Silicon nitride is one of the ceramic materials being considered for the components in gas turbine engines which will be exposed to temperatures of 1000 to 1400°C. Test specimens from hot-pressed billets exhibit flexural strengths of approximately 50 MN/m2 at 1000°C. However, the strength degrades rapidly to less than 20 MN/m2 at 1400°C. The strength degradition is attributed to subcritical crack growth phenomena evidenced by a stress rate dependence of the flexural strength and the stress intensity factor. This phenomena is termed slow crack growth and is associated with the onset of plastic deformation at the crack tip. Lange attributed the subcritical crack growth tb a glassy silicate grain boundary phase which decreased in viscosity with increased temperature and permitted a form of grain boundary sliding to occur.

Grinding Mechanisms and Strength Degradation for Ceramics

1989 ◽  
Vol 111 (2) ◽  
pp. 167-174 ◽  
Author(s):  
S. Malkin ◽  
J. E. Ritter
Keyword(s):  
Fracture Mechanics ◽  
Specific Energy ◽  
Ceramic Body ◽  
Ceramic Materials ◽  
Strength Degradation ◽  
Indentation Fracture ◽  
Main Research ◽  
Grinding Conditions ◽  
Workpiece Interaction ◽  
Insight Into

This paper presents a critical review and evaluation of our fundamental knowledge of the grinding mechanisms for ceramic materials and their influence on the finished surface and mechanical properties. Two main research approaches are identified: a “machining” approach and an “indentation fracture mechanics” approach. The machining approach has typically involved measurement of the grinding forces and specific energy coupled with microscopic observations of the surface morphology and grinding detritus. Any proposed mechanisms of abrasive-workpiece interaction must be consistent with the magnitude of the specific energy and its dependence on the grinding conditions. The “indentation fracture mechanics” approach assumes that the damage produced by grinding can be modeled by the idealized flaw system produced by a sharp indentor. Indentation of a ceramic body is considered to involve elastic/plastic deformation with two principal crack systems propagating from the indentation site: lateral cracks which lead to material removal and radial/median cracks which cause strength degradation. Each of these approaches provides important insight into grinding behavior and strength degradation, but each has its shortcomings. Further efforts to develop a fundamental model for grinding of ceramics would benefit from the integration of both of these approaches.

scholarly journals An investigation of strength degradation due to thickness plate reduction on Ferry Ro-Ro Ship’s Hull

2021 ◽  
Vol 921 (1) ◽  
pp. 012053
Author(s):  
A M Nugraha A ◽  
M U Pawara ◽  
A Ardianti ◽  
F Mahmuddin
Keyword(s):  
Structural Strength ◽  
Plate Thickness ◽  
Strength Degradation ◽  
Element Analysis ◽  
Allowable Limit ◽  
Strength Performance ◽  
Dimensional Changes ◽  
Longitudinal Response ◽  
Package Program ◽  
Shell Plate

Abstract Old ships will experience a degradation of the structural strength after receiving repeated loads. Decreased strength performance is also caused by structure shape and structural dimensions changes. In steel ships, Dimensional changes will be discovered when the ship is docked, because the material undergo corrosion causing in thinning the shell plate. In this study, a thickness reduction of the shell plate has been simulated to determine the longitudinal response of the ship’s structure. A Finite element analysis of ferry Ro-Ro ship’s hull was carried out using ANSYS package program. The simulation was carried out to exceed the allowable limit for reducing the thickness plate by the Indonesian Classification Bureau (BKI), which is 20% of the initial plate thickness. Based on simulation result, it was found that an increase of stress at each variation of the reduction in hull plate thickness in hogging and sagging conditions.

Small ozone generator fabricated from low-temperature co-fired ceramics

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Kostja Makarovič ◽  
Darko Belavič ◽  
Barbara Malič ◽  
Andreja Benčan ◽  
Franci Kovač ◽  
...  
Keyword(s):  
Low Temperature ◽  
Electric Discharge ◽  
Applied Voltage ◽  
Design Methodology ◽  
Oxygen Flow ◽  
Ozone Generator ◽  
Ceramic Structure ◽  
Content Type ◽  
Buried Channels

Purpose The purpose of this study is the design, fabrication and evaluation of a miniature ozone generator using the principle of electric discharge are presented. Design/methodology/approach The device was fabricated using a low-temperature co-fired ceramics (LTCC) technology, by which a multilayered ceramic structure with integrated electrodes, buried channels and cavities in micro and millimeter scales was realized. Findings The developed ozone generator with the dimensions of 63.6 × 41.8 × 1.3 mm produces approximately 1 vol. % of ozone in oxygen flow of 15 ml/min, at an applied voltage of 7 kV. Originality/value A miniature ozone generator, manufactured in LTCC technology, produces high amount of ozone and more than it is described in the available references or in datasheets of commercial devices of similar size.

scholarly journals Probabilistic LCF Risk Evaluation of a Turbine Vane by Combined Size Effect and Notch Support Modeling

2017 ◽  
Author(s):  
Lucas Mäde ◽  
Hanno Gottschalk ◽  
Sebastian Schmitz ◽  
Tilmann Beck ◽  
Georg Rollmann
Keyword(s):  
Size Effect ◽  
Risk Evaluation ◽  
Low Cycle Fatigue ◽  
Combined Model ◽  
Sharp Stress ◽  
Standard Specimens ◽  
Turbine Vane ◽  
Turbine Design ◽  
Critical Regions ◽  
Life Predictions

A probabilistic risk assessment for low cycle fatigue (LCF) based on the so-called size effect has been applied on gas-turbine design in recent years. In contrast, notch support modeling for LCF which intends to consider the change in stress below the surface of critical LCF regions is known and applied for decades. Turbomachinery components often show sharp stress gradients and very localized critical regions for LCF crack initiations so that a life prediction should also consider notch and size effects. The basic concept of a combined probabilistic model that includes both, size effect and notch support, is presented. In many cases it can improve LCF life predictions significantly, in particular compared to E-N curve predictions of standard specimens where no notch support and size effect is considered. Here, an application of such a combined model is shown for a turbine vane.

Formation of Ceramic Crock Structure Made of Technogenic Raw Materials with Vanadium Component

2015 ◽  
Vol 756 ◽  
pp. 250-256 ◽  
Author(s):  
Andrey Stolboushkin ◽  
Alexey Fomin ◽  
Oxana Stolboushkina
Keyword(s):  
Iron Ore ◽  
Raw Materials ◽  
Pore Space ◽  
Ceramic Materials ◽  
New Mineral ◽  
Ceramic Structure ◽  
Porous Texture ◽  
Mineral Phases ◽  
Technogenic Raw Materials ◽  
Sintering Processes

The present study provides chemical, granulometric and mineral compounds of raw materials of ceramic charge. The ceramic materials structure made of slimy part of iron ore wastes with corrective additions has been observed by the SEM, petrographic methods and spectral analysis. The introduction of corrective additions leads to formation of crock with evident glass ceramic structure describable by porous texture. Pore space is completely or partially filled with cryptocrystalline substance. It has been determined vanadium component intensifies sintering processes during the firing and leads to formation of new mineral phases. This increases the strength of ceramics.

scholarly journals Investigation of the structure glass-ceramic materials according to data of IR spectroscopy

2021 ◽  
pp. 71-78
Author(s):  
О.V. Savvova ◽  
◽  
O.I. Fesenko ◽  
G.K. Voronov ◽  
V.D. Tymofieiev ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Ir Spectroscopy ◽  
Glass Ceramic ◽  
Ceramic Materials ◽  
Aluminosilicate Glass ◽  
Structural Elements ◽  
Ceramic Structure ◽  
Glass Ceramic Materials ◽  
Temperature Heat Treatment ◽  
Cordierite Structure

The efficiency of the use of IR spectroscopy in studying the structure of magnesium-aluminosilicate glass-ceramic materials was analyzed. It was established that the formation of the structure of these glass-ceramic materials during the heat treatment is associated with a distortion of the cordierite structure. The presence of solid solutions, high and low cordierite in the structure of the materials under study was detected according to the systems of bands F2, E2, C2 and D2, depending on the temperature of their heat treatment. The mechanism of phase formation in magnesium-aluminosilicate glass-ceramic materials has been determined, which consists in the formation of future crystals of -cordierite and spinel at the initial stages of nucleation, and crystals of -cordierite and mullite at the stage of crystallization. Formation of a finely dispersed glass-ceramic structure with a predominant content of -cordierite or mullite under conditions of low-temperature heat treatment is a decisive factor in ensuring high thermal and mechanical properties of glass-ceramic materials. This allows them to be used as structural elements of devices and equipment under thermal and mechanical loads.

Subcritical Crack Growth of Dental Ceramic Materials

2005 ◽  
pp. 122-125 ◽  
Author(s):  
Rudolf Marx ◽  
Joachim Tinschert ◽  
Horst Fischer
Keyword(s):  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Ceramic Materials ◽  
Dental Ceramic

Residual Lifetime Determination of Low Temperature Co-Fired Ceramics

2016 ◽  
Vol 713 ◽  
pp. 266-269
Author(s):  
Zdeněk Majer ◽  
Kateřina Štegnerová ◽  
Pavel Hutař ◽  
Martin Pletz ◽  
Raul Bermejo ◽  
...  
Keyword(s):  
Low Temperature ◽  
Residual Stresses ◽  
Crack Propagation ◽  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Particulate Composite ◽  
Ceramic Materials ◽  
Ceramic Composites ◽  
Residual Lifetime ◽  
Density Factor

The effect of subcritical crack growth is nowadays intensively studied mainly in relation to the strength of ceramic materials. The main aim of the contribution is to describe behavior of micro-crack propagating in the Low Temperature Co-fired Ceramics (LTCC) under subcritical crack growth (SCCG) conditions. The micro-crack behavior is significantly influenced by residual stresses developed in the LTCC due to different coefficients of thermal expansion of individual components. Two-dimensional numerical model was developed to simulate micro-crack propagation through the composite. The micro-crack propagation direction was determined using Sih’s criterion based on the strain energy density factor and the micro-crack path was obtained. The residual lifetime of the specific ceramic particulate composite (LTCC) was estimated on the basis of experimental data. The paper contributes to a better understanding of micro-crack propagation in particulate ceramic composites in the field of residual stresses.

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