1 Reliability October 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 Reliability The probability that no (system) failure will occur in a given time interval A 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 Reliability Goals Schedule time Budget Dollars Test Units Design Data Reliability Assurance Module Internal Methods Design Rules Components Testing Subsystem Testing Architectural Strategy Life Testing Prototype testing Field Testing Reliability Predictions (models) INPUT Product Assurance

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 Complexity Why computers made of tubes (or discrete transistors) cannot be made to work

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

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 Age Prob of dying in the next year (deaths/ 1000) 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 Reliability Remedies Early Wearout Chance Quality manufacture/Robust Design Physically-based models, preventative maintenance, Robust design (FMEA) Tight customer linkages, testing, HAST

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

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 Plot Reinertson p 237 Log Failures per 100 hours Log Cumulative Operating Hours x x x x x x x x xx xx x x x Actual Reliability Required Reliability at Introduction Predicted

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) Update FMEA Baseline data from Previous Products Feed results to Risk Assessment Process Use at Design Reviews Develop Failure Compensation Provisions Test Activity Uncovers new Failure modes Failure prob- through test/field data Probabilities developed through analysis

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 Valve Fails Open when commanded closed Fails to meet response time Excessive leakage Regulates High Regulates Low Fails closed when commanded open Excessive hysteresis or Excessive port leakage Excessive case leakage Fails to meet response time Fails to meet response time Next Page

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

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?