How to Select the Right ALT Approach
Download as PPT, PDF2 likes811 views
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.
How to Select the Right ALT Approach
- 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 [email protected] // 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
Editor's Notes
- #2: 1