Damage In Ceramic Matrix Composites Research Articles

Ultrasonic Assessment of Interfacial Oxidation Damage in Ceramic Matrix Composites

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.

Errata

Journal of MicroscopyVolume 170, Issue 2 p. 190-190 Free Access Errata First published: May 1993 https://doi.org/10.1111/j.1365-2818.1993.tb03340.xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. References Fullwood, N.J. & Meek, K.M. (1993) A synchrotron X-ray study of the changes occurring in the corneal stroma during processing for electron microscopy. J. Microsc. 169, 53– 60. Powell, K.L., Yeomans, J.A. & Smith, P.A. (1993) Characterization of subsurface damage in ceramic-matrix composites by confocal scanning laser microscopy. J. Microsc. 169, 189– 195. Volume170, Issue2May 1993Pages 190-190 ReferencesRelatedInformation

Continuum modelling of damage in ceramic matrix composites

A continuum model for determining mechanical response of ceramic matrix composites with damage is presented. The mechanisms of damage considered are those observed in unidirectionally fiber-reinforced ceramic matrix composites, viz. matrix cracking, fiber/matrix interfacial slip and fiber/matrix debonding. Four basic configurations of distributed damage at the microscopic level are treated: matrix cracks only, matrix cracks in conjunction with interfacial slip, debonds only and matrix cracks in conjunction with debonds. The elementary damage entities, i.e. cracks, debonds and slipped surfaces, are represented by second-order tensors which are regarded as internal variables. Using a thermodynamics based formulation of constitutive relationships with internal variables, the stress-strain-damage relationships are derived. Specific expressions are given for changes in the engineering elastic moduli in terms of the densities of damage entities for sparsely distributed damage.