For a hole of length L (very ellipsoidal), with radius of curvature at the ends, R, the energy of the distorted stress region is . Then . The minimum R is on the level of the atomic size. This means . This is too low. creation of cracks involves surface tension. propagation condition is . Then = griffith crack length. . This means . Surface is actually jagged, increasing the real crack length. =work of fracture which is typically, . Then sometimes, but the crack does not propagate. propagation condition: .

- glass: , then
- steel: , then

There should really be a kinetic term, because the cracks can propagate at the speed of sound.

for you get the griffith crack length.

. Crack can accelerate over time. Stresses tend to be perpendicular to the crack. Instability in crack growth is onset at .

source psfile jl@crush.caltech.edu index