A Long List of Reasons to Perform an ALT and The Selection of Applied Stresses



A Long List of Reasons to Perform an ALT:

A. Confirm a minimum life estimate or time to first failure of a large population.

B. Look at variability or robustness of the manufacturing process.

C. Determine whether screening will be required for production to meet customer requirements or market goals.

D. Look at the impact of various customer environments, such as duty cycle, on the performance or ultimate life of a system.

E. Determine if customer rough handling, customer abuse or customer misuse is a significant factor in the expected life of a product in the field.

F. Identify the impact of software redundancy to hardware and hardware redundancy to the proper and continuous system operation.

G. Determine if little-used, emergency or “one-shot products” will operate properly when called upon to do so. This is especially true of warning systems or emergency systems such as fire alarms or extinguishers.

H. Show that no dangerous situations exist for a product. This covers all aspects of liability, hardware and software warnings and system safe operating conditions and fail-safe modes.

I. Estimate the acceleration factor for a component or system with respect to a specific set of customer stresses.

J. Demonstrate successful customer operation and maintenance across the many divergent customer environments and customer use conditions.


The Selection of Applied Stresses:

A) Select standard environmental stresses, including items such as high temperature, low temperature, random vibration, dust or humidity.

B) Select cyclic stress conditions, such as temperature cycling, humidity cycling, stress cycling or sine wave vibration.

C) Select stresses that are frequently called out in the Military Standards and have been found useful to demonstrate conformance to stringent military customer environments.

D) Select stresses based upon tradition for the market or business. These may be unique to an industry or situation.

E) Select stresses based upon the expected customer environment or industry. This includes consideration of worst-case customers, abusive customers and customer who fail to perform suggested maintenance.

F) Select stresses based upon known or anticipated failure modes or physics of failure for critical components or system functions. Such stresses are thought to dominate the operation of a system

G) Select stresses based upon customer safety or liability considerations.

H) Select stresses based upon long term degradation modes such as corrosion or material degradation.


Published in Practical Weibull Analysis Techniques – Fifth Edition by James A. McLinn Published by  The Reliability Division of ASQ – January 2010 ISBN 0277-9633 (available as free download for ASQ Reliability Division Members)

Picture © B. Poncelet https://bennyponcelet.wordpress.com


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