Yu Fu

Date of Award

2008

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

Advisor

Zhihe Jin

Second Committee Member

Michael L. Peterson

Third Committee Member

Senthil Vel

Abstract

Ductile particulate reinforced ceramic matrix composites are promising candidates for future aerospace, marine, power industry, and other applications owning to their significantly enhanced fracture resistance compared to the corresponding matrix materials. In this thesis, the residual strength of metal particulate reinforced ceramic-matrix composites with periodically spaced, parallel cracks is studied using a fracture mechanics model. A Fourier transform/integral equation method is used to obtain the stress intensity factor at the tips of the cracks bridged by plastically deformed metal particulates. The crack bridging of metal particulates is described by a bridging law that relates the bridging stress and crack opening. The residual strength of the cracked composites is calculated by a stress intensity factor criterion. Numerical results are presented to illustrate the effects of crack spacing, debonding length of the particulate-matrix interface, and volume fraction of metal particulates on the residual strength behavior of the reinforced ceramic composites with periodically spaced, parallel cracks. It is found that for a given volume fraction of metal particulate and debonding length of the particulate-matrix interface the residual strength increases with decreasing crack spacing. For a given spacing, the residual strength initially decreases dramatically with increasing initial crack length and then becomes flat for long initial cracks. The residual strength becomes insensitive to crack spacing when the initial crack length becomes small. The results also show that the residual strength increases with increasing volume fraction of metal particulates, and decreasing debonding length of the particulate-matrix interface. However, the increase of the volume fraction and the decrease of debonding length for improving the residual strength may be limited because high volume fractions of metal particulates result in extensive microcracking in the ceramic matrix and small debonding lengths lead to a brittle composite. Hence, the volume fraction and the debonding length should be optimized in practical applications.

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