is the energy required for plastic deformation per unit area of crack.
In most metals y
p
is greater than γ.
6.4 Fracture toughness
Fracture
toughness
can be defined as being a measure of the resistance of a
material to fracture, i.e. a measure of the ability of a material to resist crack
propagation.
One measure of the fracture toughness of
a
material is the
elastic strain energy
release
rate (G) at the tip of a crack. When the rate of release of elastic strain
energy at the tip of a crack reaches a high enough value then the crack
propagates. This critical value is given the symbol G
c
. Thus in
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