Ceramic matrix composites (CMC's) are candidate materials for
high-temperature aerospace applications where high-strength and
low-weight are essential for more efficient engines. One advantage
of fiber-reinforced ceramics over monolithic ceramics is an increase
in fracture toughness because of the presence of unbroken fibers
in the wake of advancing cracks. The unbroken fibers restrict
the crack opening displacements, shield the crack tip, and reduce
the crack driving forces. Extensive experimental studies of various
CMC's have also shown the development of a periodic array of matrix
cracks bridged by unbroken fibers in unidirectional and two-dimensional
woven systems.
Before these ceramic matrix composite systems can be used in actual
engine applications, life-prediction methodologies have to be
established on the basis of these observed failure mechanisms.
Consequently, the NASA Lewis Research Center conducted a study
to determine the stress intensity factor solutions for periodic
arrays of bridged cracks for various crack spacings and crack
lengths. Initially, the stress intensity factor of an array of
unbridged multiple edge cracks was determined under constant global
displacement as well as at a point load along the crack wake.
These solutions are expected to contribute toward the development
of a damage-based life-prediction methodology for CMC engine components.
Ghosn, L.J.; and Worthem, D.W.: Damage Tolerance Based Life Prediction
Methodology in Ceramic Matrix Composites. HITEMP Review 1995,
NASA CP-10178, Vol. III, 1995, pp. 49-1 to 49-12.
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