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Crack Velocity

From World Leader in Underground Blast Design Software

Crack velocities have been measured to be between ranges of 2000 fps - 8000 fps in most instances. From the critical-flaw concept of Griffith, velocity of crack propagation has been found by Mott (1948) to be dependent on the velocity of the longitudinal wave, crack length, and the critical crack size, Co, as determined from Griffith failure theory. Roberts and Wells (1954) evaluated Mott's equations further and determined that the maximum crack velocity that a material can have is approximately .5 the velocity of the shear wave in that specific material. Crack velocity can be expressed in the mathematical form; Cv = f(T,p,E,V,X) where X indicates the residual plastic energy in a specific material type. There is substantial evidence that when cracks attain velocities higher than predicted, approaching .6 that of the velocity of the shear wave, they will tend to curve. At lower velocities cracks will restrict themselves to straight line trajectories. Stresses can be superimposed at the crack tip, thus affecting velocity and trajectory.

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