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· With local plastic deformation
the critical crack length is increased and given by: c = (4E{S + P}/2π{1 - ν2}σF2 ~ (2EP/π{1 - ν2}σF2).
· For
this case, taking: 100 < P < 300 J/m2, 0.2 < S <
100 J/m2, gives:
c ~ 9 x 10-6 m = 9,000 nm.
· The critical
crack length increases
linearly as the plastic deformation work in the region of the crack surface
increases.
· Reactive atmospheres
such as OH
or hydrogen
can decrease the surface energy of the crack and reduce the critical
crack length for brittle
fracture.
· When
brittle impurities such as oxides exist on the grain
boundaries of
a ductile polycrystalline material (such as steel), the brittle fracture may
be inter-granular.
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