An investigation of tensile behavior of CMC's at room and elevated temperatures.
Item
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Title
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An investigation of tensile behavior of CMC's at room and elevated temperatures.
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Identifier
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AAI9530937
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identifier
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9530937
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Creator
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Zhang, Shaojin.
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Contributor
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Adviser: Feridun Delale
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Date
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1995
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Language
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English
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Publisher
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City University of New York.
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Subject
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Engineering, Mechanical | Engineering, Materials Science
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Abstract
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Tensile behavior has been widely recognized as one of the most important properties for ceramic matrix composites. In this study, the tensile failure mechanisms of ceramic matrix composites were investigated experimentally and analytically.;First, unidirectional Nicalon/CAS II tensile specimens with fiber volume fractions of 30% and 40% were tested at room as well as elevated temperatures. All tests exhibited a non-linear stress-strain behavior. Using an innovative in-situ testing technique (1), damages to the specimens at different temperatures and at different loading levels were identified and correlated with the failure behavior of the composites. Matrix crack density was introduced and used to characterize the damage behavior of the composite. The effects of fiber volume fraction and temperature on the failure behavior were also studied. Matrix crack initiation stress showed an increase with increasing fiber volume fraction. However, temperature effect was found not quite significant within the temperature range tested (from room temperature to 700{dollar}\sp\circ{dollar}C). Specimen size effect was noted and discussed.;Then, two analytical models, one using the singular integral equation technique and the other using finite element method were developed. Both models assume that the composite consists of equally spaced fiber strips in a matrix material and the actual problems were simplified as two dimensional. In the singular integral equation model, a variety of single row H-shaped crack geometries were used to study the singular behavior at the crack tips. In the finite element model, a multiple row H-shaped crack geometry was adopted to simulate the non-linear stress strain behavior. The stress intensity factors and strain energy release rates were calculated for various crack geometries and used to explain the failure behavior of the composite. The results from the singular integral equation formulation predict that once the matrix cracks are formed, they will propagate to the fiber/matrix interface. This behavior conforms with the observed behavior. The results from the finite element model compared well with the experimental results.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
