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Reliability October 26, 2004

Reliability October 26, 2004. Today. DFDC (Design for a Developing Country) HW November 2 detailed design Parts list Trade-off Midterm November 4 Factory Visit November 16th. Midterm. Presentation Purpose- a midcourse correction less than 15 minutes with 5 minutes discussion

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Reliability October 26, 2004

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  1. ReliabilityOctober 26, 2004

  2. Today • DFDC (Design for a Developing Country) • HW November 2 • detailed design • Parts list • Trade-off • Midterm November 4 • Factory Visit November 16th

  3. Midterm • Presentation Purpose- a midcourse correction • less than 15 minutes with 5 minutes discussion • Approx. 7 power point slides- all should participate in presentation • Show what you have done • Show what you are going to do • Discuss issues, barriers and plans for overcoming (procedural, team, subject matter, etc. • Scored on originality, candor, thoughtfullness, etc. not on total amount accomplished • Schedule today from 1:00 to 4:00 (speaker at 4:00 PM)

  4. ReliabilityThe probability that no (system) failure will occur in a given time intervalA reliable system is one that meets the specifications Do you accept this?

  5. What do Reliability Engineers Do? • Implement Reliability Engineering Programs across all functions • Engineering • Research • manufacturing • Testing • Packaging • field service

  6. Reliability as a Process module INPUT Reliability Assurance Module • Reliability Goals • Schedule time • Budget Dollars • Test Units • Design Data Product Assurance • Internal Methods • Design Rules • Components Testing • Subsystem Testing • Architectural Strategy • Life Testing • Prototype testing • Field Testing • Reliability Predictions (models)

  7. Early product failure • Strongest effect on customer satisfaction • A field day for competitors • The most expensive to repair • Why? • Rings through the entire production system • High volume • Long C/T (cycle time) • Examples from GE (but problem not confined to GE!) • GE Variable Power module for House Air Conditioning • GE Refrigerators • GE Cellular

  8. Early Product Failure • Can be catastrophic for human life • Challenger, Columbia • Titanic • DC 10 • Auto design • Aircraft Engine • Military equipment

  9. Reliability as a function of System ComplexityWhy computers made of tubes (or discrete transistors) cannot be made to work

  10. Type Early (infant mortality) Wearout (physical degradation) Chance (overstress) Old Remedy- Repair mentality Burn-in Maintenance In service testing Three Classifications of Reliability Failure

  11. Bathtub Curve Infant Mortality Useful life No memory No improvement No wear-out Random causes Wear out Failure Rate #/million hours Time

  12. Reliability Prob of dying in the next year (deaths/ 1000) Age From the Statistical Bulletin 79, no 1, Jan-Mar 1998

  13. Early failure causes or infant mortality (Occur at the beginning of life and then disappear) • Manufacturing Escapes • workmanship/handling • process control • materials • contamination • Improper installation

  14. Chance Failures (Occur throughout the life a product at a constant rate) • Insufficient safety factors in design • Higher than expected random loads • Human errors • Misapplication • Developing world concerns

  15. Wear-out(Occur late in life and increase with age) • Aging • degradation in strength • Materials Fatigue • Creep • Corrosion • Poor maintenance • Developing World Concerns

  16. Failure Types • Catastrophic • Degradation • Drift • Intermittent

  17. Failure Effects(What customer experiences) • Noise • Erratic operation • Inoperability • Instability • Intermittent operation • Impaired Control • Impaired operation • Roughness • Excessive effort requirements • Unpleasant or unusual odor • Poor appearance

  18. Failure Modes • Cracking • Deformation • Wear • Corrosion • Loosening • Leaking • Sticking • Electrical shorts • Electrical opens • Oxidation • Vibration • Fracturing

  19. Early Wearout Chance Quality manufacture/Robust Design Physically-based models, preventative maintenance, Robust design (FMEA) Tight customer linkages, testing, HAST Reliability Remedies

  20. Reliabilitysemi-empirical formulae Early failure =pdf k Chance Failure =constant failure rate m=MTBF Wear out

  21. Failures Vs time as a function of Stress High Stress Medium Stress Low Stress

  22. Highly Accelerated Stress Testing • Test to Failure • Fix Failed component • Continue to Test • Appropriate for developing world?

  23. Duane PlotReinertson p 237 Actual Reliability x x x Log Failures per 100 hours x x Required Reliability at Introduction x x x x x x x x x Predicted x Log Cumulative Operating Hours

  24. Integration into the Product Development Process FMEA- Failure Modes and Effects Analysis Customer Requirements Baseline data from Previous Products Brainstorm potential failures Summarize results (FMEA) Use at Design Reviews Update FMEA Baseline data from Previous Products Feed results to Risk Assessment Process Probabilities developed through analysis Develop Failure Compensation Provisions Test Activity Uncovers new Failure modes Failure prob- through test/field data

  25. Risk Assessment process Assess risk • Program Risk • Market Risk • Technology Risk • Reliability Risk • Systems Integration Risk Devise mitigation Strategy Re-assess

  26. Fault Tree analysis Seal Regulator Valve Fails or Valve Fails Open when commanded closed Excessive leakage Regulates High Regulates Low Fails closed when commanded open Fails to meet response time Excessive hysteresis 1 2 3 4 5 or or Excessive port leakage Excessive case leakage Fails to meet response time Fails to meet response time Next Page 6 7 8 9

  27. corosion Armature Contamination or or or Valve orientation Insuff filtering Wire Broken Fault Tree analysis (cont) Valve Fails Open when commanded closed 1 Valve Fails Open when commanded closed or Electrical Failure of Selenoid Mechanical Failure Selenoid Transient electro mechanical force or or Open Circuit Coil short Insulation or wear Material selection Solder Joint Failure Wire Broken seals Material selection

  28. FMEA

  29. FMEA Root Cause Analysis

  30. Fault Tree Analysis- example Example: A solar cell driven LED

  31. Reliability Management • Redundancy • Examples • Computers • memory chips? • Aircraft • What are the problems with this approach • 1. Design inelegance • expensive • heavy • slow • complex • 2. Sub optimization • Can take the eye off the ball of improving component and system reliability by reducing defects • Where should the redundancy be allocated • system • subsystem • board • chip • device • software module • operation

  32. Other “best practices” • Fewer Components • Small Batch Size (why) • Better material selection • Parallel Testing • Starting Earlier • Module to systems test allocation • Predictive (Duane) testing • Look for past experience • emphasize re-use • over-design • e.g. power modules • Best: Understand the physics of the failure and model • e.g. Crack propagation in airframes or nuclear reactors

  33. Other suggestions?

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