Ultrasonic Assessment of Interfacial Oxidation Damage in Ceramic Matrix Composites

1993 ◽  
Vol 115 (3) ◽  
pp. 237-243 ◽  
Author(s):  
Y. C. Chu ◽  
S. I. Rokhlin ◽  
G. Y. Baaklini
Keyword(s):  
Elevated Temperatures ◽  
Volume Fraction ◽  
Micromechanical Model ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Fiber Direction ◽  
Matrix Composites ◽  
Fiber Volume ◽  
Ultrasonic Methods ◽  
Oxidation Damage

A new approach to characterizing oxidation damage in ceramic matrix composites using ultrasonic techniques is proposed. In this approach the elastic constants of the composite are determined nondestructively by measuring the angular dependence of both longitudinal and transverse wave velocities. A micromechanical model for composites with anisotropic constituents is used to find the anisotropic properties of an effective fiber which is a combination of the fiber and the interface. Interfacial properties are extracted from the properties of this effective fiber by analyzing the difference between effective and actual fiber properties. Unidirectional [0]28 SiC/Si3N4 composites with 30 percent fiber volume fraction and 30 percent matrix porosity are used. The samples are exposed in a flowing oxygen environment at elevated temperatures, up to 1400°C, for 100 hours and then measured by ultrasonic methods at room temperature. The Young’s modulus in the fiber direction of the sample oxidized at 600° C decreased significantly but it was unchanged for samples oxidized at temperatures above 1200° C. The transverse moduli obtained from ultrasonic measurements decrease continuously up to 1200°C. The shear stiffnesses show behavior similar to the transverse moduli. The effective elastic moduli of the interfacial carbon coating are determined from the experimental data and their change due to thermal oxidation is discussed.

scholarly journals Comparisons of thermomechanical fatigue hysteresis loops of fiber-reinforced ceramic-matrix composites subjected to different phase angles

2018 ◽  
Vol 233 (6) ◽  
pp. 2015-2032 ◽  
Author(s):  
Li Longbiao
Keyword(s):  
Volume Fraction ◽  
Frictional Coefficient ◽  
Hysteresis Loops ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Thermomechanical Fatigue ◽  
Matrix Composites ◽  
Fiber Reinforced ◽  
Fiber Volume ◽  
Phase Angles

In this paper, comparisons of thermomechanical fatigue hysteresis loops of fiber-reinforced ceramic-matrix composites (CMCs) subjected to different phase angles of θ = 0, π/3, π/2, and π have been investigated. The shape, location, and area of fatigue hysteresis loops are affected by the phase angle under the thermomechanical cyclic loading. The effects of fiber volume fraction, fatigue peak stress, matrix crack spacing, interface frictional coefficient, and interface debonded energy on the thermomechanical fatigue hysteresis loops and fiber/matrix interface slip of different phase angles are discussed. The fatigue hysteresis loops of cross-ply CMCs under the phase angles of θ = 0 and π are predicted for different fatigue peak stresses and cycle numbers.

Finite Element Analysis of Interfacial Debonding Damage in Fiber-Reinforced Ceramic Matrix Composites

2007 ◽  
Vol 546-549 ◽  
pp. 1555-1558
Author(s):  
Chun Jun Liu ◽  
Yue Zhang ◽  
Da Hai Zhang ◽  
Zhong Ping Li
Keyword(s):  
Finite Element ◽  
Fiber Volume Fraction ◽  
Volume Fraction ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Interfacial Debonding ◽  
Matrix Composites ◽  
Fiber Reinforced ◽  
Fiber Volume ◽  
Element Analysis

In this paper the composite fracture process has been simulated via the finite element method. A micromechanics model was developed to predict the stress-strain response of a SiO2f/ SiO2 composite explicitly accounting for the local damage mechanisms such as fiber fracture and interfacial debonding. The effects of interfacial strength and fiber volume fraction on the toughness of fiber-reinforced ceramic matrix composites were investigated. The results showed that the composite failure behaviors correlated with the interface strength, which could achieve an optimum value for the elevation of the composite toughness. The increase of fiber volume fraction can make more toughening contributions.

scholarly journals Assessment of Damage in Ceramics and Ceramic Matrix Composites Using Ultrasonic Techniques

1994 ◽  
Author(s):  
S. K. Rokhlin ◽  
Y. C. Chu ◽  
G. Y. Baaklini
Keyword(s):  
Thermal Shock ◽  
Elastic Constants ◽  
Elevated Temperatures ◽  
Elastic Anisotropy ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Matrix Composites ◽  
Ultrasonic Methods ◽  
Ultrasonic Measurements ◽  
Ultrasonic Techniques

This paper addresses the application of ultrasonic methods to damage assessment in ceramics and ceramic matrix composites. It focuses on damage caused by thermal shock and oxidation at elevated temperatures. The damage-induced changes in elastic constants and elastic anisotropy are determined by measuring the velocities of ultrasonic waves in different propagation directions within the sample. Thermal shock damage measurement is performed in ceramic samples of reaction bonded silicon nitride (RBSN) and aluminum oxide. Thermal shock treatment from different temperatures up to 1000°C is applied to produce the microcracks. Both surface and bulk ultrasonic wave methods are used to correlate the change of elastic constants to microstructural degradation and to determine the change in elastic anisotropy induced by microcrack damage. Oxidation damage is studied in silicon carbide fiber/reaction bonded silicon nitride matrix (SCS-6/RBSN) composites. The oxidation is done by exposing the samples in a flowing oxygen environment at elevated temperatures, up to 1400°C, for 100 hours. Significant changes of ultrasonic velocities were observed for composites before and after oxidation. The elastic constants of the composites were determined from the measured velocity data. The Young’s modulus in the fiber direction as obtained from ultrasonic measurements decreases significantly at 600°C but retains its original value at temperatures above 1200°C. This agrees well with the results of destructive tests by other authors. The transverse longitudinal and shear moduli obtained from ultrasonic measurements decrease continually until 1200°C. The results of this work show that the damage-induced anisotropy in both ceramics and ceramic matrix composites can be determined successfully by ultrasonic methods. This suggests the possibility of assessing damage severity using ultrasonic techniques.

scholarly journals Assessment of Damage in Ceramics and Ceramic Matrix Composites Using Ultrasonic Techniques

1995 ◽  
Vol 117 (3) ◽  
pp. 417-423 ◽  
Author(s):  
S. I. Rokhlin ◽  
Y. C. Chu ◽  
G. Y. Baaklini
Keyword(s):  
Thermal Shock ◽  
Elastic Constants ◽  
Elevated Temperatures ◽  
Elastic Anisotropy ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Matrix Composites ◽  
Ultrasonic Methods ◽  
Ultrasonic Measurements ◽  
Ultrasonic Techniques

This paper addresses the application of ultrasonic methods to damage assessment in ceramics and ceramic matrix composites. It focuses on damage caused by thermal shock and oxidation at elevated temperatures. The damage-induced changes in elastic constants and elastic anisotropy are determined by measuring the velocities of ultrasonic waves in different propagation directions within the sample. Thermal shock damage measurement is performed in ceramic samples of reaction bonded silicon nitride (RBSN) and aluminum oxide. Thermal shock treatment from different temperatures up to 1000°C is applied to produce the microcracks. Both surface and bulk ultrasonic wave methods are used to correlate the change of elastic constants to microstructural degradation and to determine the change in elastic anisotropy induced by microcrack damage. Oxidation damage is studied in silicon carbide fiber/reaction bonded silicon nitride matrix (SCS-6/RBSN) composites. The oxidation is done by exposing the samples in a flowing oxygen environment at elevated temperatures, up to 1400°C, for 100 hours. Significant changes of ultrasonic velocities were observed for composites before and after oxidation. The elastic constants of the composites were determined from the measured velocity data. The Young’s modulus in the fiber direction as obtained from ultrasonic measurements decrases significantly at 600°C but retains its original value at temperatures above 1200°C. This agrees well with the results of destructive tests by other authors. The transverse longitudinal and shear moduli obtained from ultrasonic measurements decrease continually until 1200°C. The results of this work show that the damage-induced anisotropy in both ceramics and ceramic matrix composites can be determined successfully by ultrasonic methods. This suggests the possibility of assessing damage severity using ultrasonic techniques.

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.

Sign in / Sign up

Export Citation Format

Share Document