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· The "estimate" of
the theoretical fracture strength is much higher than that measured for real
materials. This indicates that flaws in real materials control the brittle
fracture
process as was suggested by Griffith.
· The concept of equating the work done in brittle fracture to
the total energy of the new surface produced may also be applied in this model.
For
a surface
energy per unit area of S the creation of the crack
increases the total energy by 2S per unit cross sectional area of the sample.
· This energy is provided by
the work done per unit volume in loading the sample to the fracture stress, σF. For a sample of unit volume
with unit cross sectional area, this is just the integral of the stress-distance
curve to sample fracture. Using the sinusoidal approximation for the stress-distance curve:
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