Effect of Microporosity on Damage Initiation in Ceramic Matrix Composites

2019 ◽  
Author(s):  
Suhasini Gururaja ◽  
Abhilash Nagaraja
Keyword(s):  
Gas Turbines ◽  
Ceramic Matrix Composites ◽  
Local Stress ◽  
Ceramic Matrix ◽  
Matrix Composites ◽  
Damage Initiation ◽  
The Matrix ◽  
Homogenization Approach ◽  
Matrix Porosity ◽  
Monolithic Ceramics

Abstract Ceramic matrix composites (CMC) are a subclass of composite materials consisting of reinforced ceramics. They retain the advantages of ceramics such as lower density and better refractory properties but exhibit better damage tolerance compared to monolithic ceramics. This combination of properties make CMCs an ideal candidate for use in high temperature sections of gas turbines. However, modeling the damage mechanisms in CMCs is complex due to the heterogeneous microstructure and the presence of processing induced defects such as matrix porosity. The effect of matrix pore location and orientation on damage initiation in CMCs is of interest in the present work. CMCs fabricated by various fabrication processes exhibit matrix pores at different length scales. Microporosities exist within fiber bundles in CMCs have a significant effect on microscale damage initiation and forms the focus of the current study. In a previous work by the authors, a two step numerical homogenization approach has been developed to model statistical distribution of matrix pores and to obtain the effective mechanical properties of CMCs in the presence of matrix porosity. A variation of that approach has been adopted to model matrix pores and investigate the severity of pores with respect to their location and orientation. CMC microstructure at the microscale has been modeled as a repeating unit cell (RUC) consisting of fiber, interphase and matrix. Ellipsoidal pores are modeled in the matrix with pore distance from the interphase-matrix interface and pore orientation with respect to the loading direction as parameters. Periodic boundary conditions (PBCs) are specified on the RUC by means of constraint equations. The effect of the pore on the local stress fields and its contribution to matrix damage is studied.

Ceramic Matrix Composites Application in Automotive Gas Turbines

1997 ◽  
Vol 119 (4) ◽  
pp. 790-798 ◽  
Author(s):  
Takao Izumi ◽  
Hiroshi Kaya
Keyword(s):  
Silicon Carbide ◽  
Silicon Nitride ◽  
Gas Turbines ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Screening Tests ◽  
Particle Impact ◽  
Matrix Composites ◽  
Test Pieces ◽  
Monolithic Ceramics

We are conducting the development of ceramic matrix composites (CMC) and components made of CMC for a 100 kW automotive ceramic gas turbine (CGT) as shown in Fig. 1. When compared to monolithic ceramics (MC), CMC that we have developed demonstrate superior strength characteristics in terms of resistance to particle impact and thermal shock. We have conducted evaluation tests on the strength of CMC components in which MC such as silicon nitride and silicon carbide were used as a reference for comparison with CMC in the same testing process as employed for components made of MC such as silicon nitride and silicon carbide. It was confirmed that actual components made of CMC realized approximately the same strength as the test pieces. Furthermore, some CMC components have already passed screening tests that evaluated the strength of the components. It was therefore confirmed that the potential exists for the possibility of testing these components in high-temperature assembly tests and engine tests.

Ceramic Matrix Composites Application in Automotive Gas Turbines

1996 ◽  
Author(s):  
Hiroshi Kaya ◽  
Takao Izumi
Keyword(s):  
Silicon Carbide ◽  
Silicon Nitride ◽  
Gas Turbines ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Screening Tests ◽  
Particle Impact ◽  
Matrix Composites ◽  
Test Pieces ◽  
Monolithic Ceramics

We are conducting the development of ceramic matrix composites (CMC) and components made of CMC for a 100 kW automotive ceramic gas turbine (CGT) as shown in Fig.1. When compared to monolithic ceramics (MC), CMC that we have developed demonstrate superior strength characteristics in terms of resistance to particle impact and thermal shock. We have conducted evaluation tests on the strength of CMC components in which MC such as silicon nitride and silicon carbide were used as a reference for comparison with CMC in the same testing process as employed for components made of MC such as silicon nitride and silicon carbide. It was confirmed that actual components made of CMC realized approximately the same strength as the test pieces. Furthermore, some CMC components have already passed screening tests that evaluated the strength of the components. It was therefore confirmed that the potential exists for the possibility of testing these components in high temperature assembly tests and engine tests.

scholarly journals Noninteractive Macroscopic Reliability Model for Ceramic Matrix Composites With Orthotropic Material Symmetry

1990 ◽  
Vol 112 (4) ◽  
pp. 507-511 ◽  
Author(s):  
S. F. Duffy ◽  
J. M. Manderscheid
Keyword(s):  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Experimental Program ◽  
Type Model ◽  
Model Parameters ◽  
Reliability Model ◽  
Matrix Composites ◽  
Physical Mechanisms ◽  
Weakest Link ◽  
Monolithic Ceramics

A macroscopic noninteractive reliability model for ceramic matrix composites is presented. The model is multiaxial and applicable to composites that can be characterized as orthotropic. Tensorial invariant theory is used to create an integrity basis with invariants that correspond to physical mechanisms related to fracture. This integrity basis is then used to construct a failure function per unit volume (or area) of material. It is assumed that the overall strength of the composite is governed by weakest link theory. This leads to a Weibull-type model similar in nature to the principle of independent action (PIA) model for isotropic monolithic ceramics. An experimental program to obtain model parameters is briefly discussed. In addition, qualitative features of the model are illustrated by presenting reliability surfaces for various model parameters.

Erosion in Gas-Turbine Grade Ceramic Matrix Composites (CMCs)

2018 ◽  
Author(s):  
N. Kedir ◽  
C. Gong ◽  
L. Sanchez ◽  
M. J. Presby ◽  
S. Kane ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Matrix Composites ◽  
Erosion Behavior ◽  
Image Mapping ◽  
Material Systems ◽  
Multiple Material ◽  
Monolithic Ceramics ◽  
Matrix Hardness

Erosion behavior of a large number of gas-turbine grade ceramic matrix composites (CMCs) was assessed using fine to medium grain garnet erodents at velocities of 200 and 300 m/s at ambient temperature. The CMCs used in the current work were comprised of nine different SiC/SiCs, one SiC/C, one C/SiC, one SiC/MAS, and one oxide/oxide. Erosion damage was quantified with respect to erosion rate and the damage morphology was assessed via SEM and optical microscopy in conjunction with 3-D image mapping. The CMCs response to erosion appeared to be very complicated due to their architectural complexity, multiple material constituents, and presence of pores. Effects of architecture, material constituents, density, matrix hardness, and elastic modulus of the CMCs were taken into account and correlated to overall erosion behavior. The erosion of monolithic ceramics such as silicon carbide and silicon nitrides was also examined to gain a better understanding of the governing damage mechanisms for the CMC material systems used in this work.

scholarly journals Melt Infiltrated Ceramic Matrix Composites for Shrouds and Combustor Liners of Advanced Industrial Gas Turbines

2011 ◽  
Author(s):  
Gregory Corman ◽  
Krishan Luthra ◽  
Jill Jonkowski ◽  
Joseph Mavec ◽  
Paul Bakke ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Matrix Composites ◽  
Industrial Gas Turbines

Micromechanics Approach for the Overall Elastic Properties of Ceramic Matrix Composites Incorporating Defect Structures

2020 ◽  
Author(s):  
Rajesh S. Kumar
Keyword(s):  
Elastic Properties ◽  
Volume Fraction ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Volume Shrinkage ◽  
Matrix Composites ◽  
Defect Structures ◽  
Linear Elastic ◽  
Elastic Tensor ◽  
The Matrix

Abstract Initial mechanical behavior of Ceramic Matrix Composites (CMCs) is linear until the proportional limit. This initial behavior is characterized by linear elastic properties, which are anisotropic due to the orientation and arrangement of fibers in the matrix. The linear elastic properties are needed during various phases of analysis and design of CMC components. CMCs are typically made with ceramic unidirectional or woven fiber preforms embedded in a ceramic matrix formed via various processing routes. The matrix processing of interest in this work is that formed via Polymer Impregnation and Pyrolysis (PIP). As this process involves pyrolysis process to convert a pre-ceramic polymer into ceramic, considerable volume shrinkage occurs in the material. This volume shrinkage leads to significant defects in the final material in the forms of porosity of various size, shape, and volume fraction. These defect structures can have a significant impact on the elastic and damage response of the material. In this paper, we develop a new micromechanics modeling framework to study the effects of processing-induced defects on linear elastic response of a PIP-derived CMC. A combination of analytical and computational micromechanics approaches is used to derive the overall elastic tensor of the CMC as a function of the underlying constituents and/or defect structures. It is shown that the volume fraction and aspect ratio of porosity at various length-scales plays an important role in accurate prediction of the elastic tensor. Specifically, it is shown that the through-thickness elastic tensor components cannot be predicted accurately using the micromechanics models unless the effects of defects are considered.

EFFECTS OF AS-RECEIVED DEFECTS ON CERAMIC MATRIX COMPOSITES PROPERTIES USING HIGH- FIDELITY MICROSTRUCTURES WITH PERIODIC BOUNDARY CONDITIONS

2021 ◽  
Author(s):  
KHALED H. KHAFAGY, ◽  
ADITI CHATTOPADHYAY
Keyword(s):  
Boundary Conditions ◽  
Periodic Boundary ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Periodic Boundary Conditions ◽  
Material Behavior ◽  
Recent Effort ◽  
High Fidelity ◽  
Matrix Composites ◽  
Damage Initiation

The presence of microstructural defects in as-received specimens of ceramic matrix composites (CMCs) significantly influences their constitutive response and damage, highlighting the importance of characterization and quantification of these defects for accurate assessment of damage and failure in the service environment. In a recent effort, the authors developed an algorithm to generate stochastic representative volume elements (SRVEs) of Carbon fiber Silicon-Carbide-Nitride matrix (C/SiNC) CMCs based on extensive multiscale material and defect characterization data. This paper implements this algorithm within a commercial finite element solver with periodic boundary conditions (PBCs) for high-fidelity micromechanics analysis and investigation of macroscopic material behavior of C/SiNC composites. Different loading directions are used to predict the global mechanical properties, and the results are in excellent agreement with theoretical (rule of mixture) predictions. Subsequently, the effects of as-received defects on the global and local responses are investigated. The results show that intratow porosity has pronounced degradation effects on the global elastic properties and results in complex stress localization patterns, which can be attributed to potential damage initiation sites.

Micromechanics Approach for the Overall Elastic Properties of Ceramic Matrix Composites Incorporating Defect Structures

2021 ◽  
Author(s):  
Rajesh Kumar
Keyword(s):  
Elastic Properties ◽  
Volume Fraction ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Matrix Composites ◽  
Defect Structures ◽  
Modeling Framework ◽  
Linear Elastic ◽  
Elastic Tensor ◽  
The Matrix

Abstract Initial mechanical behavior of Ceramic Matrix Composites (CMCs) is linear until the proportional limit. This initial behavior is characterized by linear elastic properties, which are anisotropic due to the orientation and arrangement of fibers in the matrix. The linear elastic properties are needed during analysis and design of CMC components. CMCs are made with ceramic unidirectional or woven fiber preforms embedded in a ceramic matrix formed via various processing routes. The matrix processing of interest in this work is the Polymer Impregnation and Pyrolysis (PIP) process. As this process involves pyrolysis to convert a pre-ceramic polymer into ceramic, considerable volume shrinkage occurs in the material. This leads to significant defects in the form of porosity of various size, shape, and volume fraction. These defect structures can have a significant impact on the elastic and damage response of the material. In this paper, we develop a new micromechanics modeling framework to study the effects of processing-induced defects on linear elastic response of a PIP-derived CMC. A combination of analytical and computational micromechanics approaches is used to derive the overall elastic tensor of the CMC as a function of the underlying constituents and/or defect structures. It is shown that the volume fraction and aspect ratio of porosity at various length-scales plays an important role in accurate prediction of the elastic tensor. Specifically, it is shown that the through-thickness elastic tensor components cannot be predicted accurately using the micromechanics models unless the effects of defects are considered.

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