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Accession Number N20120013871
Title Test Population Selection from Weibull-Based, Monte Carlo Simulations of Fatigue Life.
Publication Date Aug 2012
Media Count 16p
Personal Author B. L. Vlcek E. V. Zaretsky R. C. Hendricks
Abstract Fatigue life is probabilistic and not deterministic. Experimentally establishing the fatigue life of materials, components, and systems is both time consuming and costly. As a result, conclusions regarding fatigue life are often inferred from a statistically insufficient number of physical tests. A proposed methodology for comparing life results as a function of variability due to Weibull parameters, variability between successive trials, and variability due to size of the experimental population is presented. Using Monte Carlo simulation of randomly selected lives from a large Weibull distribution, the variation in the L10 fatigue life of aluminum alloy AL6061 rotating rod fatigue tests was determined as a function of population size. These results were compared to the L10 fatigue lives of small (10 each) populations from AL2024, AL7075 and AL6061. For aluminum alloy AL6061, a simple algebraic relationship was established for the upper and lower L10 fatigue life limits as a function of the number of specimens failed. For most engineering applications where less than 30 percent variability can be tolerated in the maximum and minimum values, at least 30 to 35 test samples are necessary. The variability of test results based on small sample sizes can be greater than actual differences, if any, that exists between materials and can result in erroneous conclusions. The fatigue life of AL2024 is statistically longer than AL6061 and AL7075. However, there is no statistical difference between the fatigue lives of AL6061 and AL7075 even though AL7075 had a fatigue life 30 percent greater than AL6061.
Keywords Aluminum alloys
Fatigue life
Fatigue tests
Metal fatigue
Monte carlo method
Rods
Variability
Weibull density functions

 
Source Agency National Aeronautics and Space Administration
NTIS Subject Category 94 - Industrial & Mechanical Engineering
41G - Quality Control & Reliability
72 - Mathematical Sciences
Corporate Author National Aeronautics and Space Administration, Cleveland, OH. NASA John H. Glenn Research Center at Lewis Field.
Document Type Technical report
Title Note N/A
NTIS Issue Number 1306
Contract Number N/A

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