Matrix cracking in brittle-matrix composites with tailored interfaces

Conference · Sun Oct 01 04:00:00 EDT 1995

OSTI ID:100562

Danchaivijit, S; Chao, L Y; Shetty, D K ^[1]

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1. Univ. of Utah, Salt Lake City, UT (United States). Dept. of Materials Science and Engineering

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 x 25 x 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 filament-bridged 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 (K{sub cm}), the interfacial sliding friction stress ({tau}) and the residual stress in the matrix ({sigma}{sub m}{sup I}). 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. Tests on specimens without the deliberately introduced cracks indicated a matrix-cracking stress significantly higher than the steady-state stress.

• DOE Contract Number: FG02-87ER45312
• OSTI ID: 100562
• Report Number(s): CONF-941144--; ISBN 1-55899-266-9
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM OXIDES
ALUMINIUM SILICATES
CALCIUM SILICATES
COMPOSITE MATERIALS
CORRELATIONS
CRACKS
EPOXIDES
FRACTURE MECHANICS
FRACTURE PROPERTIES
INTERFACES
MATHEMATICAL MODELS
POISSON RATIO
RESIDUAL STRESSES
SAMPLE PREPARATION
SILICON CARBIDES
SLIDING FRICTION
STRESS INTENSITY FACTORS
STRESSES
TENSILE PROPERTIES
YOUNG MODULUS