Record Details

Record 1 of 1
Probabilistic Analysis for Comparing Fatigue Data Based on Johnson-Weibull Parameters
NTRS Full-Text: Click to View  [PDF Size: 1.2 MB]
Author and Affiliation:
Vlcek, Brian L.(Georgia Southern Univ., Statesboro, GA, United States);
Hendricks, Robert C.(NASA Glenn Research Center, Cleveland, OH, United States);
Zaretsky, Erwin V.(NASA Glenn Research Center, Cleveland, OH, United States)
Abstract: Leonard Johnson published a methodology for establishing the confidence that two populations of data are different. Johnson's methodology is dependent on limited combinations of test parameters (Weibull slope, mean life ratio, and degrees of freedom) and a set of complex mathematical equations. In this report, a simplified algebraic equation for confidence numbers is derived based on the original work of Johnson. The confidence numbers calculated with this equation are compared to those obtained graphically by Johnson. Using the ratios of mean life, the resultant values of confidence numbers at the 99 percent level deviate less than 1 percent from those of Johnson. At a 90 percent confidence level, the calculated values differ between +2 and 4 percent. The simplified equation is used to rank the experimental lives of three aluminum alloys (AL 2024, AL 6061, and AL 7075), each tested at three stress levels in rotating beam fatigue, analyzed using the Johnson- Weibull method, and compared to the ASTM Standard (E739 91) method of comparison. The ASTM Standard did not statistically distinguish between AL 6061 and AL 7075. However, it is possible to rank the fatigue lives of different materials with a reasonable degree of statistical certainty based on combined confidence numbers using the Johnson- Weibull analysis. AL 2024 was found to have the longest fatigue life, followed by AL 7075, and then AL 6061. The ASTM Standard and the Johnson-Weibull analysis result in the same stress-life exponent p for each of the three aluminum alloys at the median, or L(sub 50), lives
Publication Date: Apr 01, 2013
Document ID:
20130014032
(Acquired Jul 24, 2013)
Subject Category: STATISTICS AND PROBABILITY
Report/Patent Number: NASA/TP-2013-217633, E-16056-2
Document Type: Technical Report
Publication Information: (SEE 20070030195)
Meeting Information: International Design Engineering Technical Conferences and Computers and Information in Engineering Conference; 4-7 Sep. 2007; Las Vegas, NV; United States
Meeting Sponsor: American Society of Mechanical Engineers; United States
Contract/Grant/Task Num: WBS 561581.02.07.03
Financial Sponsor: NASA Glenn Research Center; Cleveland, OH, United States
Organization Source: NASA Glenn Research Center; Cleveland, OH, United States
Description: 20p; In English; Original contains black and white illustrations
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: Copyright; Distribution as joint owner in the copyright
NASA Terms: WEIBULL DENSITY FUNCTIONS; FAILURE ANALYSIS; PROBABILITY THEORY; STRESS ANALYSIS; FATIGUE TESTS; FATIGUE LIFE; DEGREES OF FREEDOM; ALUMINUM ALLOYS; EXPONENTS; RANKING; SLOPES
› Back to Top
Facebook icon, External Link to NASA STI page on Facebook Twitter icon, External Link to NASA STI on Twitter YouTube icon, External Link to NASA STI Channel on YouTube RSS icon, External Link to New NASA STI RSS Feed
Find Similar Records
 
NASA Logo, External Link

NASA Official: Gerald Steeman

Sponsored By: NASA Scientific and Technical Information Program

Site Curator: STI Support Services

Last Modified: August 23, 2013

Privacy Policy & Important Notices Disclaimers, Copyright, Terms of Use Freedom of Information Act USA.gov NASA.gov NASA OCIO Free Adobe PDF Reader Free MS Word Viewer