Environmental Engineering Reference
In-Depth Information
c
, m
8.15
Results of calculation of the safe number of loading cycles
for a transverse crack transverse orientation (the ratios of the half
axes of the crack and the number of operating cycles are given in
the brackets): 1) operating mode; 2) hydraulic test.
According to fracture mechanics, unstable (rapid avalanche-like
destruction that cannot be stopped) destruction occurs when the defect
size reaches the critical value. Any defect can be modelled conservatively
by a crack, and any crack can be described by an ellipse with minor
a
and
major
c
semiaxes The higher the pressure and lower the temperature, the
smaller the critical crack size.
A family of cracks is a set of all possible cracks in the structural element
including the orientation and location of this element, size, shape. For this
particular loading the family of cracks can be divided into two parts - the
cracks that do not lead to destruction for the given loading and cracks
that lead to destruction. The boundary between these two sets of cracks is
formed by the critical size cracks. The family of critical size is the set of all
possible critical size cracks classified on the basis of type: the orientation
and location in the given element and shape. Critical size cracks whose
plane passes across the cylindrical part of the pressure vessel or piping,
are referred to transverse (or tangential), if the plane of the crack passes
through the centerline of the pipeline or pressure vessel, then such a crack
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