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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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today
Today
  • DFDC (Design for a Developing Country)
  • HW November 2
    • detailed design
    • Parts list
    • Trade-off
  • Midterm November 4
  • Factory Visit November 16th
midterm
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)
slide4

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?

what do reliability engineers do
What do Reliability Engineers Do?
  • Implement Reliability Engineering Programs across all functions
    • Engineering
    • Research
    • manufacturing
    • Testing
    • Packaging
    • field service
reliability as a process module
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)
early product failure
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
early product failure1
Early Product Failure
  • Can be catastrophic for human life
    • Challenger, Columbia
    • Titanic
    • DC 10
    • Auto design
    • Aircraft Engine
    • Military equipment
slide9
Reliability as a function of System ComplexityWhy computers made of tubes (or discrete transistors) cannot be made to work
three classifications of reliability failure
Type

Early (infant mortality)

Wearout (physical degradation)

Chance (overstress)

Old Remedy- Repair mentality

Burn-in

Maintenance

In service testing

Three Classifications of Reliability Failure
bathtub curve
Bathtub Curve

Infant

Mortality

Useful life

No memory

No improvement

No wear-out

Random causes

Wear out

Failure Rate

#/million hours

Time

reliability
Reliability

Prob

of dying

in the next

year (deaths/

1000)

Age

From the Statistical Bulletin 79, no 1, Jan-Mar 1998

early failure causes or infant mortality occur at the beginning of life and then disappear
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
chance failures occur throughout the life a product at a constant rate
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
wear out occur late in life and increase with age
Wear-out(Occur late in life and increase with age)
  • Aging
  • degradation in strength
  • Materials Fatigue
  • Creep
  • Corrosion
  • Poor maintenance
  • Developing World Concerns
failure types
Failure Types
  • Catastrophic
  • Degradation
  • Drift
  • Intermittent
failure effects what customer experiences
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
failure modes
Failure Modes
  • Cracking
  • Deformation
  • Wear
  • Corrosion
  • Loosening
  • Leaking
  • Sticking
  • Electrical shorts
  • Electrical opens
  • Oxidation
  • Vibration
  • Fracturing
reliability remedies
Early

Wearout

Chance

Quality manufacture/Robust Design

Physically-based models, preventative maintenance, Robust design (FMEA)

Tight customer linkages, testing, HAST

Reliability Remedies
reliability semi empirical formulae
Reliabilitysemi-empirical formulae

Early failure

=pdf

k

Chance Failure

=constant failure rate

m=MTBF

Wear out

failures vs time as a function of stress
Failures Vs time as a function of Stress

High Stress

Medium Stress

Low Stress

highly accelerated stress testing
Highly Accelerated Stress Testing
  • Test to Failure
  • Fix Failed component
  • Continue to Test
  • Appropriate for developing world?
duane plot reinertson p 237
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

integration into the product development process fmea failure modes and effects analysis
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

risk assessment process
Risk Assessment process

Assess risk

  • Program Risk
  • Market Risk
  • Technology Risk
    • Reliability Risk
  • Systems Integration Risk

Devise mitigation Strategy

Re-assess

fault tree analysis
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

fault tree analysis cont

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

fault tree analysis example
Fault Tree Analysis- example

Example: A solar cell driven LED

reliability management
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
other best practices
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