Design Of Ceramic Components Research Articles

Unraveling the oxidation behavior and mechanism of (TiZrTaNbCr)C high-entropy ceramic by introducing Cr3C2

High-entropy carbide ceramic materials exhibited excellent thermal and mechanical properties, making them highly sought after in high-temperature applications. However, the oxidation resistance of high-entropy carbide ceramic needed to be further improved. This work unraveled the oxidation behavior and mechanism of high-entropy carbide ceramic by introducing the Cr3C2. The results indicated that the oxidation rate of (TiZrTaNbCr)C initially decreased with temperature up to 900 °C, followed by an increased with further temperature rise up to 1100 °C. At 800 and 900 °C, the parabolic oxidation rate constants were 0.70 and 0.17 mg2cm−4min−1, respectively. And the minimum thickness of oxidized layer was 60 µm at 900 °C for 120 min. This unusual phenomenon suggested the formation of different oxidation products. Specifically, the CrNbO4 and Nb2Zr6O17 oxide layer were formed at 900 °C, leading to an increased resistance to oxygen diffusion. Subsequently, loose oxidation products of Nb2O5 were formed after 1000 °C, hindering the oxidation resistance. In the current study on oxidation resistance of high entropy carbides, this work showed a competitive performance. Overall, this study illustrated the oxidation mechanism and behavior of (TiZrTaNbCr)C and proposed a new avenue for the design of high-entropy ceramic components.

Finite element analysis of fracture behavior in ceramics: Prediction of strength distribution using microstructural features

AbstractThe estimation of the strength scatter caused by internal defects is necessary in analyzing a reliable design of advanced ceramic components. In this study, we proposed a finite element analysis methodology to predict the stochastic fracture behavior of ceramics based on the microstructural features obtained by the scanning electron microscopy and X‐ray computed tomography. Here, the two‐ and three‐dimensional distribution microstructural data are approximated by various probability density functions and are reflected in the dispersion of parameters of the damage model via a fracture mechanics model. We then applied the proposed method to alumina fine ceramics sintered at three different temperatures, and performed the three‐point bending test. Furthermore, the numerically created Weibull distributions were compared with those obtained experimentally. Our analysis results confirm that the proposed method can reasonably predict the strength scatter in ceramics.

Self-healing by design: universal kinetic model of strength recovery in self-healing ceramics

ABSTRACT We propose a new theoretical kinetic model of strength recovery by oxidation-induced self-healing of surface cracks in composites containing a healing agent (HA). The kinetics is a key parameter in the design of structural components that can self-heal the damage done in service. Based on three-dimensional (3D) observations of crack-gap filling, two crack-gap filling models, i.e., a bridging model and a tip-to-mouth filling model, are incorporated in the proposed kinetic model. These crack-gap filling models account for the microstructural features of the fracture surfaces, crack geometry, and oxidation kinetics of the healing-agent. Hence, the minimum and maximum remaining flaw sizes in the healed crack gaps are estimated for various healing temperatures, times, and oxygen partial pressure conditions. Further, the nonlinear elastic fracture mechanics suitable for small-sized remaining flaws, together with a statistical analysis of the original Weibull-type strength distribution, enables the prediction of upper and lower strength limits of the healed composites. Three sintered alumina matrix composites containing silicon carbide (SiC)-type HAs with various volume fractions and shapes, together with monolithic SiC ceramics, are considered. The strength of the healed-composite predicted by our model agrees well with the experimental values. This theoretical approach can be applied to HAs other than SiC and enables the design of self-healing ceramic components for various applications.

“Toward seashells under stress”: Bioinspired concepts to design tough layered ceramic composites

In this manuscript the potential of building tough, layered ceramic composites with embedded “protective” features has been explored. Novel concepts have been pursued to design ceramics using a non-conventional disposition of “embedded” compressive layers to significantly increase toughness and reduce the scatter in strength. A combination of experiments and modelling has shown the potential of layered architectures in the design of ceramic components with spatially resolved strength and toughness. In addition, texturing of the microstructure in the protective layers has been demonstrated to provide preferential paths for conducting propagating cracks in graceful manner. Recent work has shown that the “flaw tolerance” behaviour of such systems can be enhanced by embedding textured layers holding compressive stresses. Crack arrest and delamination have been observed acting together during the fracture process, which resembles the fracture of nacre. This approach might be further exploited to reduce strength variability and increase toughness in advanced ceramics.

Incorporating Digital Tools with Ceramic Crafting: Design and Fabrication of Light Diffusing Screen Shells

This paper investigates the possibilities which arise by incorporating digital tools into the design and fabrication of ceramic building components. In particular, we present how traditional ceramic crafting fabrication methods could be enriched by using parametric, performative and generative design techniques alongside digital fabrication technologies. Considering the growing importance of ceramic components in architectural construction due to their economic and environmentally friendly properties, this paper highlights the findings of design-led research explorations, demonstrating potential innovative solutions and failures arising through a digitalised ‘file to factory’ design approach.

Fatigue Threshold R‐curves Predict Fatigue Endurance Strength for Self‐Reinforced Silicon Nitride

There is a need for methods that can help predict and avoid fatigue failures of silicon nitride ceramic components. The fatigue threshold R‐curve has been proposed as potential solution to this problem. In this study, the fatigue threshold R‐curve for small, semielliptical surface cracks was calculated for a silicon nitride ceramic using the published bridging stress distribution developed from fatigue threshold tests on macroscopic crack specimens. To test the accuracy of the endurance strengths predicted using the fatigue threshold R‐curve, fatigue tests were conducted using four‐point bend beams of silicon nitride containing semielliptical surface cracks introduced by Knoop indentation. The effectiveness of the methodology was verified; indeed, 77% of the beams tested at stress levels above the predicted endurance strength failed within 107 cycles and 0% of the beams tested below the predicted endurance strength failed within 107 cycles. Furthermore, using the bridging stress distribution, which is thought to be a material property, the need for prohibitively difficult fatigue threshold experiments on small surface cracks is avoided. Accordingly, this methodology is potentially quite practical for use in the engineering design of ceramic mechanical components.

Microstructural effects on the sliding-wear resistance of pressureless liquid-phase-sintered SiC under diesel fuel

Abstract The sliding wear of pressureless liquid-phase-sintered (PLPS) SiC ceramics under diesel fuel lubrication was investigated. It was found that the sliding-wear behaviour under diesel fuel is similar to what is observed under lubrication with the chemically similar paraffin oil: initial mild, plasticity-controlled wear followed by severe, fracture-controlled wear, with a well-defined wear transition. Compared to paraffin oil, however, diesel fuel lubrication decreases the extent of the mild-wear regime and results in damage that is more severe due to its lower viscosity. Also, it was found that the wear resistance under diesel fuel decreases with increasing contact load and sliding speed. Subsequent investigation of the effects of the intergranular phase content, grain size, and grain shape demonstrates nevertheless that the wear performance of PLPS SiC under diesel lubrication can be improved via microstructural control by (i) decreasing the intergranular phase content, and (ii) decreasing the SiC grain size or increasing its aspect ratio. The results of this work are likely to have relevant implications for the design of wear resistant PLPS SiC ceramic components for diesel engines.

A general formulation for strength prediction of advanced ceramics by ball-on-three-balls (B3B)-test with different multiaxial failure criteria

The determination of biaxial strength of ceramics plays a large role in the design of ceramic components. The ball-on-three-balls (B3B)-test is one of the most useful methods for measuring the biaxial strength of ceramics. The strength measured by B3B-test, with any specimen, is dependent on the size of the specimen and loading conditions (type and position of loading); therefore, the strength value, measured with a set of specimens, has to be adjusted by effective volume and/or surface. The standardized strength value obtained from this adjustment can be then used for the design process. Consequently, there is a need for calculating the effective volume/surface of the B3B-test specimens. In this article, general fitting functions are provided for effective volume/surface of B3B-test specimens with different multiaxial criteria, these can be used for all ceramic materials and for various test configurations. Verification of numerical effective volume and effective surface values with experimental measurements show that B3B specimens fail due to surface flaws according to normal stress criterion (NSC).

Simulation of Strength Distribution in Ground Ceramics by Incorporating Residual Stress Effect

Strength of ground ceramics may be affected by residual stress as well as surface flaws induced by grinding. Strength prediction for ground ceramics is convenient for mechanical design of ceramic components. In this article, a numerical procedure based on fracture mechanics was proposed to estimate strength distribution of ground ceramics by considering grinding-induced residual stress. Bending strength and residual stress of ground ceramics were measured for three grinding-conditions. By comparison of simulated results with experimental ones, it was revealed that strength characteristics in experiments were well simulated by using the proposed procedure.

Design of Ceramic Acetabular Components: A Retrospective

Design of Ceramic Acetabular Components: A Retrospective

A New Probabilistic Approach for Accurate Fatigue Data Analysis of Ceramic Materials

Statistical methods for the design of ceramic components for time-dependent failure modes have been developed that can significantly enhance component reliability, reduce baseline data generation costs, and lead to more accurate estimates of slow crack growth (SCG) parameters. These methods are incorporated into the Honeywell Engines & Systems CERAMIC and ERICA computer codes. Use of the codes facilitates generation of material strength parameters and SCG parameters simultaneously, by pooling fast fracture data from specimens that are of different sizes, or stressed by different loading conditions, with data derived from static fatigue experiments. The codes also include approaches to calculation of confidence bounds for the Weibull and SCG parameters of censored data and for the predicted reliability of ceramic components. This paper presents a summary of this new fatigue data analysis technique and an example demonstrating the capabilities of the codes with respect to time-dependent failure modes. This work was sponsored by the U.S. Department of Energy/Oak Ridge National Laboratory (DoE/ORNL) under Contract No. DE-AC05-84OR21400. [S0742-4795(00)02103-7]

Ceramic Stationary Gas Turbine Development Program—Fifth Annual Summary

A program is being performed under the sponsorship of the United States Department of Energy, Office of Industrial Technologies, to improve the performance of stationary gas turbines in cogeneration through the selective replacement of metallic hot section components with ceramic parts. The program focuses on design, fabrication, and testing of ceramic components, generating a materials properties data base, and applying life prediction and nondestructive evaluation (NDE). The development program is being performed by a team led by Solar Turbines Incorporated, and which includes suppliers of ceramic components, U.S. research laboratories, and an industrial cogeneration end user. The Solar Centaur 50S engine was selected for the development program. The program goals included an increase in the turbine rotor inlet temperature (TRIT) from 1010°C (1850°F) to 1121°C (2050°F), accompanied by increases in thermal efficiency and output power. The performance improvements are attributable to the increase in TRIT and the reduction in cooling air requirements for the ceramic parts. The ceramic liners are also expected to lower the emissions of NOx and CO. Under the program uncooled ceramic blades and nozzles have been inserted for currently cooled metal components in the first stage of the gas producer turbine. The louvre-cooled metal combustor liners have been replaced with uncooled continuous-fiber reinforced ceramic composite (CFCC) liners. Modifications have been made to the engine hot section to accommodate the ceramic parts. To date, all first generation designs have been completed. Ceramic components have been fabricated, and are being tested in rigs and in the Centaur 50S engine. Field testing at an industrial co-generation site was started in May, 1997. This paper will provide an update of the development work and details of engine testing of ceramic components under the program.

SPSLIFE: A User-Friendly Approach to the Structural Design and Life Assessment of Ceramic Components

In order to expedite the structural analysis of ceramic components, Sundstrand Power Systems has developed a proprietary computer code called “SPSLIFE,” which can substantially reduce the time spent on the design assessment of ceramic components. The life assessment computations for the various failure modes are performed using the structural analysis and materials files as input data. A number of “menus” are incorporated to request user input data and to guide the user through the problem definition process. The user has the capability to select existing material data files or create new ones. The computational modules are based on the analytical approaches currently used in the industry. The modular construction of the code facilitates making revisions or adding new modules. Graphic display is used to provide a visual summary of the life assessment calculations for the various failure modes. The output files generated provide a detailed review of the results, which is helpful for design optimization. Independently derived component fast fracture and static fatigue survival probabilities using the NASA CARES and CARES/LIFE codes are displayed for reference. The paper provides an application example using a patented design of a ceramic monorotor for the Sundstrand Power Systems TJ-50 small gas turbine engine.

Application of SPSLIFE to Preliminary Design Evaluation and Life Assessment of CSGT Components

The Ceramic Stationary Gas Turbine (CSGT) Program has utilized the SPSLIFE computer code to evaluate the preliminary design of ceramic components. The CSGT program is being performed under the sponsorship of the United States Department of Energy, Office of Industrial Technology, to improve the performance of stationary gas turbines in cogeneration through the selective replacement of hot section components with ceramic parts. Preliminary design evaluation and life assessment results are presented here for the following components: (1) Stage 1 turbine blade, (2) Stage 1 turbine nozzle, and (3) combustor inner liner. From the results of the analysis, recommendations are made for improving the life and reliability of the components. All designs were developed in Phase I (preliminary design) of the CSGT program and will be optimized in Phase II (detail design) of the program.

Reliability evaluation of brittle solids under polyaxial stress states based on maximum energy release rate criterion

In relation to reliability-based design of ceramic components, an investigation is made on evaluation of reliability of brittle solids under polyaxial stress states. Applying the maximum energy release rate criterion to the crack-like flaws in a brittle solid subjected to polyaxial stresses, the probability of failure P f is calculated. As an analytical expression of the maximum energy release rate of a mixed mode crack, G max, a new expression derived by the present author is used. The result is compared with P f calculated by using Lamon's expression of G max.

Computers—the key to reliable ceramic materials and components

Abvanced structural ceramic components are increasingly used in demanding engineering applications. A major impediment to even wider utilization are issues related to reliability and affordability. Exercising greater control over the inherent flaw population in the ceramic component will contribute importantly to resolving these two issues. Computers will play an ever-increasing role in designing to minimize the impact of flaws, in processing to minimize the presence of flaws, and in nondestructive testing (NDT) to assure the absence of critical flaws for reliable, affordable ceramic components. This article reviews the state of the art and/or the potential for the application of computers in the design, fabrication, and inspection of structural ceramic components. A strategy for the integration of design, processing and NDT will be presented.

Cyclic Fatigue in Ceramics

Structural ceramics, such as silicon nitride, silicon carbide, alumina and zirconia, are promising instead of metallic materials, for practical applications to various kinds of engineering components, especially for high temperature applications. For example, automotive engine parts, such as turbocharger rotors and swirl chambers, and ball bearing systems have been produced on a commercial basis using these materials for the last ten years. These industrial motivations have promoted extensive progress in the research on evaluation of the strength properties of ceramics. In particular, cyclic fatigue has been investigated as one of the major concerns in the design of reliable ceramic components, and many researchers have been engaged in the field of cyclic fatigue in ceramics. As a result, new aspects such as crack bridging, R-curve behavior, fracture morphology and so forth have been clarified in the last decade. In this volume, the latest topics and experimental techniques in Japan, concerning ceramic fatigue under cyclic loading are provided. Twelve papers address questions concerning ceramic fatigue, and are classified according to subjects in three sections: `Fatigue Behaviour and Crack Growth`, `Fatigue Mechanisms` and `Statistical Properties and Application`. The former two sections are state-of-the-art references for a fundamental understanding of ceramic fatigue, while the third section presents more complicated analytical techniques for statistical treatment and engineering application

Cyclic Fatigue of Ceramics

Cyclic fatigue, and specifically fatigue-crack propagation, in ceramic materials is reviewed both for monolithic and composites systems. In particular, stress/life (S/N) and crack-propagation data are presented for a range of ceramics, including zirconia, alumina, silicon nitride, SiC-whisker-reinforced alumina and a pyrolytic-carbon/graphite laminate. S/N data derived from unnotched specimens often indicate markedly lower lives under tension-compression compared to tension-tension loading; similar to metals, 108-cycle “fatigue limits” generally approach -50% of the tensile strength. Crack-growth results, based on studies on “long” (>3mm) cracks, show fatigue-crack propagation rates to be markedly power-law dependent on the applied stress-intensity range, ΔK, with a threshold, ΔKTH, of the order of -50% of Kc. Conversely, for “small” (<250μm) surface cracks, fatigue-crack growth is seen to occur at ΔK levels some 2 to 3 times smaller than ΔKTH, and to show a negative depen-dency on applied stress intensity. At ambient temperatures, lifetimes are shortened and crack-growth rates are significantly accelerated by cyclic, compared to quasi-static loading, although limited data suggest the reverse to be true at very high temperatures in the creep regime. Such results are discussed in terms of the primary crack-tip shielding (toughening) mechanisms and potential mechanisms of cyclic crack advance. Finally, implications are discussed of long and small crack cyclic fatigue data to life prediction and safetycritical design of ceramic components.

セラミックスの破壊強度データベースと信頼性設計システム

For application of ceramics to mechanical and structural components, a data base system for fracture strength of ceramics was developed. In this data base system, various fracture strength test data of ceramics are compiled with the data of their manufacturing process and the test environment, which are used to retrieve various fracture test data. The fracture strength of ceramics obtained by each test varies usually in spite of being same in material and test environment. For estimating the strength as a material constant independent of each testing method, this system performs a unified analysis for all the fracture strength test data retrieved. This unified analysis method can estimate the material constant expressed by the delayed fracture strength normalized in terms of cummulative effective hold time Nfteff=1sec and effective volume Veff=1mm3.Furthermore, a reliability design system was developed for analyzing the strength reliability of the structural components of ceramics against the actual service loads. It is possible by this system to determine the allowable design stress by applying the normalized strength properties to the probabilistic analysis.This system has a wide applicability in performing the reliability-based design of ceramic structural components as well as in developing ceramic materials.

セラミックス強度の統一的評価の信頼性設計への適用の検討

In order to study the optimizing for reliability-design ceramic components, a unified estimation method based on 3 parameter Weibull statistical analysis was developed by analyzing the fracture strength data obtained from various fracture tests on sintered SiC. The estimated results based on this method were compared with those estimated based on 2 parameter Weibull analysis about fitness for ceramic fracture strength properties. Furthermore special features for application of the unified estimation method to reliability-design were studied by applying it to the design of ceramic components for a gas turbine. The results obtained were as follows:1) The fracture strength of sintered-SiC can be estimated by the unified estimation method based on 3-parameter Weibull statistical analysis considering the lower limit strength.2) As for the normalized strength as a material constant obtained by the unified estimation method, the 3-parameter based estimation method gives a higher value than the 2-parameter based one.3) The unified estimation method based on 3 parameters is realistic for study of allowable stress against extremely low fracture probability in reliability-design.