This document discusses different approaches to accelerated life testing (ALT). It introduces the thought process for selecting an ALT approach, discusses trade-off decisions, and enables selecting the right approach for a given situation. The key approaches discussed are: real-time testing with no constraints; time compression testing using increased usage cycles; applying an acceleration model relating stress to life; step stress testing; degradation testing; and Weibull success testing. Guiding principles are to respect constraints, use real usage conditions, minimize assumptions, and focus on failure mechanisms.

1. How to Select the
Right ALT Approach
ASQ Silicon Valley
Quality Conference
by
Fred Schenkelberg, CRE, CQE
Senior Reliability Engineer, Ops A La Carte LLC
fms@opsalacarte.com // www.opsalacarte.com // (408) 710-8248

2. Objectives
• Introduce thought process
to select ALT approach
• To discuss trade-off
decisions involved
• To enable you to select
the right ALT approach
for your situation

3. Presenter Biography
Fred Schenkelberg is a Senior Reliability Engineering Consultant at Ops A La
Carte. He is currently working with clients using reliability assessments as a
starting point to develop and execute detailed reliability plans and programs.
Also, he exercises his reliability engineering and statistical knowledge to
design and conduct accelerated life tests.
Fred joined HP in February 1996 in Vancouver, WA. He joined ESTC, Palo Alto,
CA., in January 1998 and co-founded the HP Product Reliability Team. He
was responsible for the community building, consulting and training aspects of
the Product Reliability Program. He was also responsible for research and
development on selected product reliability management topics.
Prior to joining ESTC, he worked as a design for manufacturing engineer on
DeskJet printers. Before HP he worked with Raychem Corporation in various
positions, including research and development of accelerated life testing of
polymer based heating cables.
He has a Bachelors of Science in Physics from the United States Military
Academy and a Masters of Science in Statistics from Stanford University.
Fred is an active member of the RAMS Management Committee and currently
the IEEE Reliability Society Santa Clara Valley Chapter President.

4. • Respect constraints
– Time, expenses, sample size, accuracy
• Use use conditions
– Environment, frequency, loading
• Minimize assumptions
– Statistical, modeling, variability
• Focus on failure mechanisms
– Stress, damage, measurement
Guiding Principles

5. With no constraints
• Build products and deploy,
measure time to failure
for every unit.
– Real time
– Real stresses
– Real variability
– “Customer” defines failure

6. Paperclip Experiment 1
• What is use profile?
• Environment
• Probability of success
• Duration
• Failure definition

7. No Constraints
• Benefits
– Perfect results
– No assumptions
• Problems
– Takes time
– No Sales, or
– Customer risk

8. Time Compression
• Use product more often
– Increase use cycles per day
– Maintain other stresses at use
levels
– Measurement system detects
specific failure
• Assumes specific action leads to
failure
– Wear, fatigue, accumulation
– Must understand or assume failure
mechanism

9. Acceleration Factor (AF)
Time shift
Time shift

10. Paperclip Experiment 2
• Assume clipping
action leads to
eventual failure
• How many cycles?
• What forces, angles?
• How many?

11. Time Compression
• Benefits
– Less time
– May use a sample
– Simple extrapolation
• Problems
– Not suitable for time
dependent failure
mechanisms
– Nor, 24/7 loaded
products

12. Stress to Life Relationship

13. Paperclip Experiment 3
• Assume bend angle is
related to damage
accumulation
• Angles?
• Other variables?

14. Stress to Life Relationship
• Benefits
– Creates AF model
– Product of use specific
• Problems
– 1 or 2 stresses or
failure mechanisms
– Logistically challenging

15. Acceleration Model
• A model exists describing the stress
to life relationship
– Arrhenius, Peck, Coffin-Manson, prior
work
– The failure mechanism,
use profile, and environment
within applicable limits of model
• If failure mechanism doesn’t
change, may use comparative testing
in absence of model, giving up on
accuracy of result.

16. Paperclip Experiment 4
• Assume failure
mechanism is the
same for new product
• Best to run till failure
and conduct detailed
failure analysis

17. Acceleration Model
• Benefits
– Single stress to apply
– Fewer samples
• Problems
– Assumptions
multiplying
– May miss new failure
mechanism

18. ALT w/ AF model
• Peck’s Relationship
• Norris-Landzberg

19. Step Stress
• Variation of acceleration model ALT, with
samples experiencing step increases in
stress
– Quicker than acceleration model method
– May require more samples
– Requires careful control of stress and failure
detection
– Best with accumulated damage failure
mechanisms

20. Degradation
• Useful when performance decays over
time in a measurable way
– Often used with an acceleration model
– Failure is defined by threshold value
– Non destructive measurements permit
repeated measures on samples

21. ALT Limits
• Extrapolation
• Stresses
• Failure Mechanisms

22. Wearout

23. Sample Size

24. Success Testing

25. Weibull Success Testing