Fracture Toughness of Carbon-Carbon Composites

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Abstract
The fracture toughnesses of two carbon-carbon composites and ATJ-S graphite were determined from the load-deflection responses of single- edge-notched specimens subjected to three-point bending. The resistance to crack initiation in the presence of a pre-existing flaw (machined notch) was examined using the linear elastic fracture mechanics parameters of critical stress intensity factor Kc, and critical strain energy release rate Gc. The resistance of the materials to both crack initiation and propagation was determined using the work-of-fracture parameter γ F. Both the fracture toughnesses and the failure modes (delamination or crack propagation colinear with the notch) were found to be strongly dependent on material characteristics.