Session 4.3: Reliability Editing

Session 4.3 Outline

• 4.3.1: Introduction to Item Reliability
• 4.3.2: Access Reliability Editor
• 4.3.3: Edit Item Reliability — Exponential Distribution
• 4.3.4: Edit Item Reliability — Weibull Distribution
• 4.3.5: Edit Failure Mode Ratios
• 4.3.6: Failure Paths Metrics

Discussion 4.3.1: Introduction to Item Reliability

• Entering Reliability Data into components & parts determines their Probability of Failure, P(f)
• Item reliability is taken into account in the RBD model to calculate subsystem & system reliability
• Aggregation of P(f) determines Reliability of RBD Groups

Exercise 4.3.2: Accessing Reliability Editor

To access the Reliability Editor:

1. Select Analyses > Criticality & Reliability Editor from the main menu
2. In the Item/Failure Selection section select Reliability from the drop down menu and select the Control Unit component from the tree

Discussion 4.3.3: Edit Item Reliability — Exponential Distribution

General Reliability section contains reliability fields used to capture:

• Duration of Operation
• Mean Time to Repair (MTTR)
• Failure Distribution Type: Exponential or Weibull
• Delay Time
• Turn Around Time
• Spares on Hand

Exercise 4.3.3: Edit Item Reliability — Exponential Distribution

To edit reliability values from the Reliability editor:

1. Select the Control Unit component from the Item/Failure Selection tree
2. For the General Reliability section, edit/confirm the following:
   • Duration of Operation: ~91.09 Hours (from Mission Group)
   • Mean Time To Repair: 3 Hours
   • Failure Distribution Type: Exponential
   • Delay Time: 3 Hours
   • Turnaround Time: 5 Hours
   • Spares on Hand: 2
3. For the Exponential Section:
   • Mean Time To Failure: 8,000 Hours
   • Part Failure Rate: 125.00 (1.25E+02)

Note: Part Failure Rate and MTTF are dynamically linked values (Inversely Proportional).

4. Expand the Control Unit component & Failure Diagram in the Item/Failure Selection Tree
5. Select the Faults below to set their individual Failure Mode Ratio (FMR):
   • Dielectric strength decreased: 0.60
   • Electrical potential decreased: 0.10
   • Open circuit: 0.15
   • Property mismatch: 0.15

Exercise 4.3.4: Edit Item Reliability — Weibull Distribution

1. Select the Air Filter component from the Item / Failure Selection Tree
2. For the General Reliability section, edit/confirm:
   • Duration of Operation: ~91.09 Hours (taken from Mission Profile)
   • Mean Time To Repair: 5 Hours
   • Failure Distribution Type: Weibull
   • Delay Time: 5 hours
   • Turn Around Time: 12 Hours
   • Spares on Hand: 0
3. For the Weibull section, enter or verify:
   • Slope: 3
   • Characteristic Life: 10000 Hours

Discussion 4.3.5: Edit Failure Mode Ratios

MIL-STD-1629A: Failure Mode Ratios represent probabilities that an item will fail in the identified failure mode with respect to other failures.

Failure Mode Ratio is applied in MADE in two areas:

• Failure Mode Responses (e.g. High/Low)
• Faults

Note: Failure Path Metrics can be minimized.

Which Failure Mode Ratios (FMR) should be used?

Use Failure Mode Response FMR when:

• Physics of Failure is not known
• There are no failure concepts in the Failure Diagram (except for Failure Mode)
• Failure Diagram Override is applied

Use Fault FMR when:

• Physics of Failure is understood (i.e. Fault-level information)
• Failure Trees are present: Cause → Mechanism → Fault → Failure Mode

FMR is used in the following analysis outputs:

• Criticality Analysis (FMECA)
• Relative Probability of Failure Causes (Classic RCM)

Exercise 4.3.5: Edit Failure Mode Ratios

1. Expand the Air Filter component & Failure Diagram in the Item/Failure Selection tree
2. Select the Faults below to set their individual Failure Mode Ratio (FMR):
   • Blocked: 0.50
   • Contaminated: 0.20
   • Outgrowths: 0.10
   • Perforated: 0.20

Discussion 4.3.6: Failure Paths Metrics

• Concepts and connections from the Failure Diagram are used to derive the failure paths.
• The Failure Paths Metrics table presents these paths together with their corresponding reliability metrics.

Session 4.3 Summary

• 4.3.1: Introduction to Item Reliability
• 4.3.2: Access Reliability Editor
• 4.3.3: Edit Item Reliability — Exponential Distribution
• 4.3.4: Edit Item Reliability — Weibull Distribution
• 4.3.5: Edit Failure Mode Ratios
• 4.3.6: Failure Paths Metrics