BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI

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i) costs for penalization regarding the downtime (operational losses,
impact on quality, impact on security and environment).
ii) costs for corrective maintenance:
iii) manpower: direct costs related with the manpower in the event of an
unplanned action;
iv) materials and replacement parts: direct costs related to the consumable
parts and the replacements used in the event of an unplanned action.
In the technical literature (Adolfo, 2007) are presented three basic models
related to the non- reliability cost within the life cycle cost analysis (LCCA):
constant failures rate, deterministic failures rate and Weibull distribution
failures rate. These models include in their evaluation processes the
quantification of the impact that could cause the diverse failure events in the
total costs of a operational asset.
In the followings will be presented the Weibull distribution failure rate
model and its application to the case of the specialized wheeled vehicle systems.
2. Weibull Distribution Failure Rate Model
In terms of cost analysis structure, this model will estimate the nonreliability
cost with failure frequencies calculated from a Weibull distribution
function.
The model proposes the following sequential flow:
1. Identify, for each alternative to evaluate, the main types of failures.
This way for certain equipment there will be f=1… F failure modes.
2. Determine, for each failure mode, the “times to failure” (operational
times). This information will be gathered, based on failure records, databases
and/or experience of the maintenance and operations.
3. Calculate the cost of failures C f (in monetary units/failure). These costs
include replacement of parts, manpower, production loss penalization and
operational impact costs.
4. Determine the frequency of expected failures δ f using the Weibull
distribution function.
Will be used the following notations in Table 1
Variable
ζ
tf
MTBF
Γ
α
β
Table 1
Significance
Frequency of failures
Time between failures
Mean time between failures (inverse of the frequency)
Gamma function
Characteristic life
Shape parameter