non-repairable elements are of complicated construction or comparatively heavy and
their repairs are not feasible on the contrary to irreplaceable repairable elements which
may be subject to repairs from economic or strategic points of view (Fig. 4).
Figure 4. Alterations in functional condition of irreplaceable repairable element
throughout operation period T
Repair ability of such elements may be either envisaged by a designer, or detected
in the course of a system’s operation.
Initial functional condition f
s0
of irreplaceable repairable elements consists of two
components. The first of them is active functional condition fs
A
, enabling the element
to remain in operation prior the repairs. The second represents a passive functional
condition fs
p
, providing for its repairability. Thus,
fs
0
= fs
A
+ fsp,
(4)
Passive functional condition at the initial stage of the element’s operation may be
calculated applying formula (5) below,
2
2
0
0
+
−
=
k
fs
fs
fs
P
, (5)
where k – number of repairs.
Time to expire prior next repairs should be carried on may be calculated applying
the formula (6) below,
1
+
=
k
t
t
o
r
.
(6)
After it is time t
r
the element is reconditioned to the fs
p
value, which may be
expressed as a repair cost. The element’s functional condition for any time may be
calculated applying formula (7) below,
Т
fs
0
fs
T
t
FS
t
s
fs
p
fs
А
fs
р
t
р
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