Damage mechanisms and fiber orientation effects on the load-bearing capabilities of a NEXTEL/BLACKGLAS low-cost ceramic
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I. INTRODUCTION
MONOLITHIC ceramics have shown great potential for high-temperature structural applications. However, their intrinsic brittle nature, which usually causes catastrophic failures, has hindered their extensive applications.[1] The toughness of these structural ceramics can be improved by introducing continuous ceramic fiber reinforcements into the ceramic matrices to form continuous fiber-reinforced ceramic composites (CFCCs).[2,3] All other intrinsic properties of monolithic ceramics can be retained in CFCCs.[2,3] The enhanced toughness of CFCCs is achieved through certain types of energy-dissipating mechanisms, such as fiber/ matrix interface debonding, fiber pullout, fiber bridging, crack deflection, etc.[2,3,4] As a result of these toughening mechanisms, “graceful failure” characteristics of CFCCs, i.e., elastic-plastic like behaviors, can be expected; also, sufficient warning can be obtained before catastrophic fracture begins.[2–5] The pertinent applications include combustion engines and tailcones for aircraft and aerospace shuttles, hot gas filters, initial walls for power plants and nuclear reactors, etc. Applications of CFCCs will directly benefit the national economy by reducing the weight of components, increasing combustion efficiency through reducing energy consumption, and minimizing downtime for replacing damaged components.[1–5] The national needs for CFCCs are so crucial that in the past few years, several multiyear, multimillion dollar, nationwide research programs have been initiated. The Department of Energy has sponsored a 10-year W. ZHAO, Postdoctoral Research Fellow, is with the Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA 19104-6272. P.K. LIAW, Professor of Excellence, and C.R. BROOKS and C.J. McHARGUE, Professors, are with the Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996-2200. R. BELARDINELLI, Senior Engineer, is with Northrop Grumman Military Aircraft Systems Division, Dallas, TX 75265-5907. D.C. JOY, Distinguished Professor and Distinguished Scientist, University of Tennessee and Oak Ridge National Laboratory, Oak Ridge, TN 37831-6064. This article is based on a presentation made in the Symposium “Mechanisms and Mechanics of Composites Fracture” held October 11–15, 1998, at the TMS Fall Meeting in Rosemont, Illinois, under the auspices of the TMS-SMD/ASM-MSCTS Composite Materials Committee. METALLURGICAL AND MATERIALS TRANSACTIONS A
program on CFCCs,[6] the Defense Advanced Research Projects Agencies has initiated a 3-year program on the lowcost ceramic composites,[7] and the National Science Foundation has granted a 3-year combined research-curriculum development project on ceramic-matrix composites to the University of Tennessee.[8] NEXTEL/BLACKGLAS, a NEXTEL fiber fabric-reinforced BLACKGLAS low-cost ceramic composite, has been drawing great attention in the CFCC community since 1992. The NEXTEL/BLACKGLAS is a polymer-derived siliconoxycarbide glass-ceramic matrix patented
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