Effect of Crack Velocity on Crack Resistance in Brittle-Matrix Composites

Fast‐ and slow‐fracture studies were conducted on a glass matrix–metal particle composite system, using the appliedmoment double‐cantilever‐beam technique. At 10 vol % metal, the fracture toughness (KIc) was seen to increase 71% over that of the matrix alone, as compared to an increase of only 40% in the stress intensity (KI) for the same system in slow fracture. This difference was corroborated by fracture surface stereology work, which showed 9.6% metal on the fast‐fracture surface as compared to only 5.3% for the slowfracture specimens. This indicates that in slow fracture, the crack “chooses” its path of propagation, thus resulting in a lowering of the expected increase in crack resistance.