23 Application of Causality Model to Propose Maintenance …
329
Fig. 23.3 Example of deterioration process in general corrosion
new deterioration factor, which together with “Insufficient passivation film” causes
“Ion elution.”
In this way, various deterioration processes are represented in a unified way, and
the function that proposes the maintenance action by the part agent is developed.
The deterioration factors and the deterioration mechanisms caused by them are
identified by searching the deterioration mechanism database by operation condition, environmental condition, and the product model assumed. A deterioration factor
should be defined as that occurring when a certain parameter satisfies a certain condition. For example, when the temperature exceeds a certain threshold value, the occurrence of “high temperature” is determined. This threshold is assigned to each input
event when the assumed input satisfies the condition. The determined deterioration
mechanisms are linked to generate a deterioration process. The deterioration factors
determined by the operating and environmental conditions of the user are classified
as an event by the input, the observable deterioration factor, and the unobservable
deterioration factor.
To estimate the failure probability, a causality model is created by assigning a
conditional probability to the created deterioration process (Nagahata et al. 2019).
The conditional probability is the probability of occurrence of a resultant event, and
it varies according to the occurrence of a causal event that is used to estimate the
probability of occurrence of deterioration of a part (the detailed simulation methods
are described in Sect. 23.5).
23.5 Calculation of a Conditional Probability
The procedure of deterioration simulation is shown in Fig. 23.4. The probability of
occurrence for the parameter of the input event of the deterioration process is given
based on the product model, environmental conditions, and operating conditions, and
is defined as a prior probability. To that end, data on the occurrence of input events is
used, if available. If not, an appropriate value is set. Based on this prior probability,
a statistical model using the probability distribution is created.
Figure 23.5 shows how to determine the occurrence of a resultant event. Resultant
events occur when the parameters of an input event satisfy a particular relationship.
For example, in the case of a causal relationship in which “Stress corrosion cracking” arises from “High ion concentration environment” and “High temperature,”
329
Fig. 23.3 Example of deterioration process in general corrosion
new deterioration factor, which together with “Insufficient passivation film” causes
“Ion elution.”
In this way, various deterioration processes are represented in a unified way, and
the function that proposes the maintenance action by the part agent is developed.
The deterioration factors and the deterioration mechanisms caused by them are
identified by searching the deterioration mechanism database by operation condition, environmental condition, and the product model assumed. A deterioration factor
should be defined as that occurring when a certain parameter satisfies a certain condition. For example, when the temperature exceeds a certain threshold value, the occurrence of “high temperature” is determined. This threshold is assigned to each input
event when the assumed input satisfies the condition. The determined deterioration
mechanisms are linked to generate a deterioration process. The deterioration factors
determined by the operating and environmental conditions of the user are classified
as an event by the input, the observable deterioration factor, and the unobservable
deterioration factor.
To estimate the failure probability, a causality model is created by assigning a
conditional probability to the created deterioration process (Nagahata et al. 2019).
The conditional probability is the probability of occurrence of a resultant event, and
it varies according to the occurrence of a causal event that is used to estimate the
probability of occurrence of deterioration of a part (the detailed simulation methods
are described in Sect. 23.5).
23.5 Calculation of a Conditional Probability
The procedure of deterioration simulation is shown in Fig. 23.4. The probability of
occurrence for the parameter of the input event of the deterioration process is given
based on the product model, environmental conditions, and operating conditions, and
is defined as a prior probability. To that end, data on the occurrence of input events is
used, if available. If not, an appropriate value is set. Based on this prior probability,
a statistical model using the probability distribution is created.
Figure 23.5 shows how to determine the occurrence of a resultant event. Resultant
events occur when the parameters of an input event satisfy a particular relationship.
For example, in the case of a causal relationship in which “Stress corrosion cracking” arises from “High ion concentration environment” and “High temperature,”