SEDL / STP / STP1231-EB / STP13969S

Using Maximum Likelihood Techniques in Evaluating Fatigue Crack Growth Curves

Cunningham, SE
Senior materials engineer, Structures Technology, and supervisor, Mechanics of Materials, United Technologies Pratt & Whitney, West Palm Beach, FL

Annis, CG
Senior materials engineer, Structures Technology, and supervisor, Mechanics of Materials, United Technologies Pratt & Whitney, West Palm Beach, FL

Pages: 13    Published: Jan 1994

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Abstract

Maximum likelihood is used to develop a quantitative means for defining confidence bounds on single crack growth curves and for comparing more than one crack growth curve. The concept of likelihood is discussed, the technique is applied to the Paris crack growth law, and statistical tests appropriate for pertinent comparative situations are reviewed. Examples of each test are examined, contrasted, and compared, and a practice for engineering comparisons of crack growth rate curves is suggested. Examples using data generated in the Fracture Mechanics Lab at Pratt & Whitney are presented and discussed. These discussions will lead to a final point regarding the role of statistical methods in augmenting engineering judgment and experience.