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Matrix Cracking In Brittle-Matrix Composites with Tailored Interfaces

Published online by Cambridge University Press:  15 February 2011

Sawai Danchaivijit ,
L-Y. Chao  and
D. K. Shetfty
Sawai Danchaivijit
Affiliation:
University of Utah, Department of Materials Science and Engineering, Salt Lake City, Utah 84112
L-Y. Chao
Affiliation:
University of Utah, Department of Materials Science and Engineering, Salt Lake City, Utah 84112
D. K. Shetfty
Affiliation:
University of Utah, Department of Materials Science and Engineering, Salt Lake City, Utah 84112
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Abstract

Matrix cracking from controlled through cracks with bridging filaments was studied in a model unidirectional composite of SiC filaments in an epoxy-bonded alumina matrix. An unbonded, frictional interface was produced by moderating the curing shrinkage of the epoxy with the alumina filler and coating the filaments with a releasing agent. Uniaxial tension test specimens (2.5 × 25 × 125 mm) with filament-bridged through cracks were fabricated by a novel two-step casting technique involving casting, precracking and joining of cracked and uncracked sections. Distinct matrix-cracking stresses, corresponding to the extension of the filamentbridged cracks, were measured in uniaxial tension tests using a high-sensitivity extensometer. The crack-length dependence of the matrix-cracking stress was found to be in good agreement with the prediction of a fracture-mechanics analysis that employed a new crack-closure force - crack-opening displacement relation in the calculation of the stress intensity for fiber-bridged cracks. The prediction was based on independent experimental measurements of the matrix fracture toughness (Kcm), the interfacial sliding friction stress (τ) and the residual stress in the matrix (σmI). The matrix-cracking stress for crack lengths (2a) greater than 3 mm was independent of the crack length and agreed with the prediction of the steady-state theory of Budiansky, Hutchinson and Evans[2]. Tests on specimens without the deliberately introduced cracks indicated a matrix-cracking stress significantly higher than the steady-state stress.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 365: Symposium M – Ceramic Matrix Composites–Advanced High-Temperature Structural Materials , 1994 , 251
Copyright
Copyright © Materials Research Society 1995

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References

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