Reliability Maintainability Engineering An Introduction Robert Brown ITS

Reliability & Maintainability Engineering An Introduction Robert Brown ITS Web Applications Development & Academic Integration Worcester Polytechnic Institute

Reliability / Maintainability *-ability n Reliability – Probability that a device will operate within specifications for the specified duration n Maintainability – Amount of resources required to remove faults – Diagnose-ability – The ability to locate faults – Repair-ability – The ability to remove faults Availability Probability that a device is operationally ready

Why is it important? Reliability & Maintainability Engineering n n Mission Success - The product operates for the duration of the mission Customer Satisfaction – Perceived product quality – Brand loyalty, customer loyalty n n Competitive Products – Market requirements Safety Support Legal & Contractual Requirements Reduce Cost of Ownership – Reduce Product Cost – Warranty reserve cost – Reduce Service Cost – Service delivery cost

Bathtub Curve l Failure Rate Over Time Infancy Steady State Wearout

Bathtub Curve l Failure Rate Over Time Infancy Workmanship Contamination Quality Control Steady State Wearout

Bathtub Curve l Failure Rate Over Time Infancy Steady State Workmanship Random Failures Contamination Overload Quality Control Improper Usage Wearout

Bathtub Curve l Failure Rate Over Time Infancy Steady State Wearout Workmanship Random Failures Thermal Fatigue Contamination Overload Oxidation Quality Control Improper Usage Cracking-Shrinking Friction Wear

Bathtub Curve Failure Rate Over Time l Failure Rate Service Period Warranty Period Time Infancy Steady State Wearout Workmanship Random Failures Thermal Fatigue Contamination Overload Oxidation Quality Control Improper Usage Cracking-Shrinking Friction Wear

Product Life Cycle Activities Reliability & Maintainability Design Develop • Identify • Reliability • market testing requirements • Maintainability • Design for testing • reliability • Develop service • Failure • strategy analysis • Fault insertion • Reliability • predictions Deploy Ongoing Reliability Testing Manage • End of product life planning Engineering • End of changes ECO service life planning Field changes FCO • Logistics strategy Maintenance releases

Reliability Developing reliable products n Develop products specs – Understand market requirements n n Stability – mechanical / electrical Design for operating environment – Design for anticipated load, duty cycle n n n Cooling Reliable materials Reliability prediction program – Modeling, Continuous Improvement n Redundancy - Remove critical paths

Series and Parallel Predicting System Reliability Series Parallel System requires device “A” AND device “B” to operate System requires device “A” OR device “B” to operate RS = R 1 * R 2 * R n RS = 1 – ( 1 - R 1 ) * ( 1 – R N ) 0. 8 0. 9 A B RS = 0. 8 * 0. 9 = 0. 72 0. 8 0. 9 RS = 1 – (1 - 0. 8) * (1 - 0. 9) RS = 0. 98

Complex Configuration Predicting System Reliability System includes series and parallel device configuration 0. 9 B RS = 1 – ( 1 - R 1 ) * ( 1 – R N ) 0. 8 A 0. 8 C 0. 8 0. 98 A BC RBC = 1 – (1 - 0. 8) * (1 - 0. 9) RBC = 0. 98 RS = R 1 * R 2 * R n RS = RA * RBC RS = 0. 8 * 0. 98 = 0. 78

Reliability Metrics Reliability is specified and measured in several ways Failure Rate l § § MTBF or MTTF § § § Reliability % § § Count of failures during a time period. Normally 1 million hours Mean Time Between Failures Mean Time To Fail Stated in hours MTBF = 1 / l Normally MTBF = 1 / l R(p) = e-lt t = Mission time

Calculating System MTBF Example: System with 3 components Component l 30 CPU 20 Power Supply 20 USB 1 MTBF = l Duty Cycle 100 % 20 % Failure Rate l 30 20 4 Total 54 1, 000 = = 18, 518 hrs 54 Note: l per 1 million Hours

Maintainability Time required to remove faults MTTR – Mean Time To Repair n Measured in hours n Major activities n – Diagnoses – Repair n Focus on labor and materials

Diagnose-ability Developing diagnose-able products Quickly and Correctly Locate the Fault n User and service documentation, tools and training Status indicators, error messages and logs. Preserved state indicators accessed by repair depot. Test points Environmental measurements Expert and non-expert end users tools n Remote and On-Site diagnosis n Product labeling and revision management n n n – Flow Charts, Fault Trees, Symptom-Solution Database, Knowledge Base, Diagnostics – Service / Diagnostic / Maintenance Processor

Repair-ability Developing repair-able products Remove the Fault Quick - Effective - Efficient n n n n Service strategy: Repair or replace? Remote and On-site repair? – Firmware, software, micro-code Limit specialized tools Eliminate manual adjustments Hot-Swap Larger, functionally dense sub-assemblies Physical layout – Easy to replace maintenance & less reliable components – Minimal disruption to replace a component

Economics Reliability & Maintainability Population (units) 20, 000 Reliability MTBF Hr 10, 000 Repair cost Duty Cycle 12/24 Day = 50% Annual Operating Hours (12*365*20000) Repair Calls (87600000/MTBF) Service Cost (Calls*Cost) Savings $ 25. 00 50 % 87, 600, 000 8, 760 $ 219, 000

Economics Reliability & Maintainability Population (units) 20, 000 Reliability MTBF Hr 10, 000 15, 000 $ 25. 00 50 % 87, 600, 000 8, 760 5, 840 $ 219, 000 $ 146, 000 Repair cost Duty Cycle 12/24 Day = 50% Annual Operating Hours (12*365*20000) Repair Calls (87600000/MTBF) Service Cost (Calls*Cost) Savings $ 73, 000

Economics Reliability & Maintainability Population (units) 20, 000 Reliability MTBF Hr 10, 000 15, 000 10, 000 $ 25. 00 $ 12. 50 50 % 87, 600, 000 8, 760 5, 840 8, 760 $ 219, 000 $ 146, 000 $ 109, 500 $ 73, 000 $ 109, 500 Repair cost Duty Cycle 12/24 Day = 50% Annual Operating Hours (12*365*20000) Repair Calls (87600000/MTBF) Service Cost (Calls*Cost) Savings

Economics Reliability & Maintainability Population (units) 20, 000 Reliability MTBF Hr 10, 000 15, 000 $ 25. 00 $ 12. 50 50 % 87, 600, 000 8, 760 5, 840 $ 219, 000 $ 146, 000 $ 109, 500 $ 73, 000 $ 109, 500 $ 146, 000 Repair cost Duty Cycle 12/24 Day = 50% Annual Operating Hours (12*365*20000) Repair Calls (87600000/MTBF) Service Cost (Calls*Cost) Savings

Resources n n n Applied Reliability by Dave Trindade IEEE Reliability Society for Automotive Engineers (SAE) Reliability, Maintainability, Supportability Division Reliability and Maintainability Symposium MILL Handbook 217