Abstract
Increase in has been fracture toughness due to crack deflection has been evaluated by theoretical calculation assuming mixed mode fracture (mode I+mode II+mode III) for a deflecting crack under the stress condition of mode I. Decrease in energy release rate occuring by the crack deflection was estimated from the stress intensity factors (K values) of an elliptical crack subjected to the mixed loads of tensile and shear stress (mode I+mode II+mode III).
The toughening effect was discussed on the volume fraction, aspect ratio, radius of rod-like grains in the bulk materials and Poisson's ratio of the bulk materials. The results obtained are as follows.
(1) The fracture toughness increases, due to crack deflection, by an amount of 90% of the fracture toughness attained by the crack with no-deflection.
(2) The contribution of aspect ratio to the fracture toughness is significant up to 5 in its aspect ratio, and becomes constant at about 10.
(3) The contribution of volume fraction to the fracture toughness is significant up to 10 vol%.
(4) The fracture toughness is almost constant irrespective of the radius of rod-like grains.
(5) The increase of fracture toughness has a tendency of inversely proportional to Poison's ratio.
