Environmental Engineering Reference
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τ, years
a)
b)
7. 1 9
Variation of the probability of nucleation of a fatigue crack in
the dished end of the PRZ (a) and graphical determination of the
optimum frequency of inspection and reconditioning operations
on the dished end of the PRZ (b).
The above example with the PRZ is interesting for two reasons. First,
the analysis was carried out within the concept of complex inspection. The
conditions for optimum inspection of not only defects but also other
parameters that determine the condition and reliability of the PRZ were
determined. Secondly, it is shown that flaw inspection can be optimised not
only for residual defects but also in the risk of crack nucleation directly
during operation.
7.4.7 Optimisation norms for defects during operation
(probabilistic approach)
In section 7.4.2 it was shown that the norms of defects based on fracture
mechanics methods are optimum. It was assumed that the strength margins
used in the calculations were selected by the optimum procedure. In reality,
the safety margins used in practice are evidently close to optimum (because
they reflect a large amount of experience in strength calculations in various
areas of technology), yet they may differ from the optimum values in one
direction or another.
The laws of probability in flaw inspection and analysis of the strength
can also be used to explore and define the optimum safety margins in
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