Conventional and probabilistic fatigue life prediction methodologies relevant to the P-3C aircraft.

162 Pages·2.2 MB·en_US

by  Kousky, Todd R.

NPS ARCHIVE
1997. OS
KOUSKY, T.
NAVAL POSTGRADUATE SCHOOL
Monterey, California
THESIS
CONVENTIONAL AND PROBABILISTIC
FATIGUE LIFE PREDICTION METHODOLOGIES
RELEVANT TO THE P-3C AIRCRAFT
by
Todd R. Kousky
March, 1997
Thesis Advisor: Edward M. Wu
Thesis
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March 1997 Master'sThesis
titleandsubtitle CONVENTIONAL AND PROBABILISTIC FATIGUE LIFE 5. FUNDINGNUMBERS
PREDICTION METHODOLOGIES RELEVANT TO THE P-3C AIRCRAFT N0001996WXCD3YA
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13. ABSTRACT (maximum 200 words)
This thesis investigates conventional and probabilistic methodologies for predicting the fatigue life of critical
components in the P-3C aircraft. A probabilistic damage convolution model was developed with the intent ofproviding
quantitative predictions oflife-variability. Traditional methodologies, which are based nominally on median values, lack
A
the capacity to adequately assess variability. Aluminum 7075-T6 was tested using a fatigue Material Test System.
fatigue database was compiled fromtests conducted atthe Naval Postgraduate School and from literature sources.
14. SUBJECTTERMS 15. NUMBEROF
P-3C Aircraft, Fatigue Life Prediction, Aluminum7075-T6, FatigueDataBase, Probability, Reliability PAGES
159
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Approved for public release; distribution is unlimited
CONVENTIONAL AND PROBABILISTIC
FATIGUE LIFE PREDICTION METHODOLOGIES
RELEVANT TO THE P-3C AIRCRAFT
Todd R. Kousky
Lieutenant, United States Navy
B.S., United States Naval Academy, 1989
Submitted in partial fulfillment ofthe
requirements for the degree of
MASTER OF SCIENCE IN AERONAUTICAL ENGINEERING
from the
NAVAL POSTGRADUATE SCHOOL
March 1997

DUDLEYKNOXLIBRARY
NAVAL POSTGRADUATE SCHOOL
MONTEREY CA 93943-5101
ABSTRACT
This thesis investigates conventional and probabilistic methodologies for predicting
A
the fatigue life of critical components in the P-3C aircraft. probabilistic damage
convolution model was developed with the intent ofproviding quantitative predictions of
life-variability. Traditional methodologies, which are based nominally on median values,
lack the capacity to adequately assess variability. Aluminum 7075-T6 was tested using a
fatigue Material Test System. A fatigue data base was compiled from tests conducted at
the Naval Postgraduate School and from literature sources.
VI
TABLE OF CONTENTS
INTRODUCTION
I. 1
BACKGROUND AND PERSPECTIVE
A.
1
B NPS P-3 LIFE EXTENSION PROGRAM 3
C. SCOPE OF THIS RESEARCH 4
II. CONVENTIONAL FATIGUE LIFE PREDICTION 7
PROBABILISTIC APPROACH TO FATIGUE
III. 13
INTRODUCTION
A. 13
PROBABILITY CONCEPTS
B. 18
WEIBULL DISTRIBUTION
C. 19
MODERN DAMAGE ACCUMULATION METHODOLOGY
IV. 21
A. PROBABILISTIC MODEL 21
B. FLAW DISTRIBUTION 21
C. LIFE DISTRIBUTION 22
D DAMAGE ACCUMULATION VIALIFE CONVOLUTION 23
1. Power Law Damage Function 24
2. Exponential Form Damage Function 26
V. PROBABILISTIC INFORMATION THEORY 27
A. BAYESIAN ANALYSIS 27
B. AN EXAMPLE OF BAYESIAN INFERENCE 27
C. MAXIMUM LIKELIHOOD ESTIMATION 29
D. AN APPLICATION OF MAXIMUM LIKELIHOOD ESTIMATION 31
VI. ALUMINUM 7075-T6 FATIGUE DATA BASE 33
A. INTRODUCTION 33
B. NOTATION AND TERMINOLOGY 34
C. PRELUDE TO APPENDIX A 36
D. PRELUDE TO APPENDIX B 36
E. PRELUDE TO APPENDIX C 37
vn
PRELUDE TO APPENDIX D
F. 37
CONCLUSIONS AND RECOMMENDATIONS
VII. 39
CONCLUSIONS
A. 39
RECOMMENDATIONS
B. 39
LIST OF REFERENCES 41
BIBLIOGRAPHY
45
APPENDIX A. CONSTANT AMPLITUDE, AXIAL FATIGUE 47
APPENDIXB. SPECTRAL, AXIAL FATIGUE 93
APPENDIX C. CONSTANT AMPLITUDE, ROTATIONAL FATIGUE 115
APPENDIXD. SPECTRAL, ROTATIONAL FATIGUE 119
APPENDIXE. SPECIMEN DRAWINGS 125
APPENDIXF. NACA"SAWTOOTH" LOAD SHAPES 141
APPENDIX G. DEVELOPMENT OF GUST AND MANEUVERLOADING
SPECTRA
143
APPENDIXH. ROTATIONAL LOAD SHAPE SPECTRA 145
INITIAL DISTRIBUTION LIST 147
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