Probabilistic Damage Tolerance Method for Metallic Aerospace

134 Pages·2012·3.85 MB·English

WRDC-TR-89-3093
PROBABILISTIC DAMAGE TOLERANCE METHOD
FOR METALLIC AEROSPACE STRUCTURE
M1argery E. Artley
Structural Integrity Branch
Structural Division
LC)
N
3eptember 1989
U
Si nal Report for Period July 1984 - February 1989
Approved for Public Release; Distribution Unlimited
DTIC
ELECTE
f
NOV2 9 1989
SEUD
FLIGHT DYNAMICS LABORATORY
WRIGHT RESEARCH AND DEVELOPMENT CENTER
AIR FORCE SYSTEMS COMMAND
WRIGHT-PATTERSON AIR FORCE BASE, OHIO 45433-6553
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for kARGERY-E. ARTLEY ___r.,-vv 1 ,.f.(cid:127) Torh Mnr
Project Engineer Fatigue, Fracture & Reliability Gp
Structural Integrity Branch
FOR THE COKLWANTER
JA S L. RUDD, Chie f
S(cid:127)uctural Integrity Branch
Structures Division
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1 1. TITLE (Include Security Classification)
Probabilistic Damage Tolerance Methous for Metallic Aerospace Structures
1. MPEaRrgSOeNryA L EA.U TAHORtJeS)y
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16. SUPPLEMENTARY NOTATION
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FIELD GROUP SUB-GROUP )-iProbabilisticM ethods, Damage Tolerance, Metallic Structure
13 "T3'
12 03 ---
19. ABSTRACT (Continue on reverse if necessary and identify by block number)
ABSTRACT
Damage tolerance analysis, based on fracture mechanics, is an important tool for ensuring
ctnahanaesat eulysrs.esa ,ef se tbTyufho et ro ppf murforelpbitogaaslhebl tiic loi ofs sfti ttchrau iiscrmf treudatrhmiaosleds sse .cr othamatvTpieoor nanebd neiteitssni, o ntaoap blplfalyosie,er mdd tuhtoloena steedU a.mSpa.a nrgoaeAlb yiatsrob elsiFel oirsaractrnieecc e dd daemaatmeangraamegl ey itsnotiiolsse ltreiiacrnna ncilecnime ited
philosophy for slow crack growth and fail safe components. A survey of the literature
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in crack growth rate, and the probability of crack detection.
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19. Continued
A probabilistic damage tolerance analysis was performed with a deterministic crack growth
rate and then a stochastic crack growth rate, based on a probabilistic durability
method. Examples of slow crack growth and fail safe structures are presented.
As an example of a slow crack growth component, a lug from an aircraft subjected
to an 80-flight fightei/trainer wing lower surface spectrum was selected. A
stiffened panel from a lower wing skin of a tanker was selected as an example of
a fail-safe component. Crack arrest in the panel, followed by catastrophic failure
of the stiffener was considered as the failure mechanism.
The model formulated here can be used to decide on the frequency and quality cf
the inspection of a component needed to keep the probability of failure at acceptable
levels. Results of this study can serve as bases for decision making for inspection
maintenance and fleet management.
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PROBABILISTIC DAMAGE TOLERANCE METHODS FOR
METALLIC AEROSPACE STRUCTURES
Margery E. Artley
B.S.C.E. 1975, Purdue University,
West Lafayette, IN 47907
M.S.C.E. 1976, Purdue University
West Lafayette, IN 47907
A Dissertation submitted to
The Faculty of
The Scnool of Engineering and Applied Science of
The George Washington University in partial
satisfaction of the requirements for
the degree of Doctor of Science
February 20, 1989
Dissertation directed by
Jann-Nan Yang, Sc.D.
Professor of Engineering and Applied Science
SI
iii
Dedicated to
My Parents, Tom and Eleancr
i
iv
ACKNOWLEDGEMENT
The author wishes to express her great appreciation to
Professor J.N. Yang, dissertation research director, for his
valuable guidance, insightful suggestions, and needed
encouragement.
The author is sincerely grateful to Dr. Frank D. Adams
of the Air Force Wright Aeronautical Laboratories for his
constant encouragemeiit and gentle prodding. Thanks also to
Dr. George P. Sendeckyj, AFWAL/FIBEC, for his helpful
suggestions and invaluable discussion.
The author is also grateful to the faculty of the
School. of Engineering and Applied Science of the George
Washington University for providing the fundamental
engineering and mathematical tools necessary to perform this
study.
And finally, the author is 'Indebted to the U.S. Air
Force Wright Aeronautical Laboratories, Flight Dynamics
Laboratory, Wright-Patterson AFB, OH, for funding this
program of study under the Long-Term, Full-Time Training
program and the structural integrity in-house work unit No.
2307N124.
TABLE OF CONTENTS
Page
ABSTRACT .................. ....................... ii
ACKNOWLEDGEMENTS .................. ................... v
LIST OF TABLES .............. .................... ix
LIST OF FIGURES ................. ................... x
Chapter
I INTRODUCTION
1.1 Objectives and Scope .......... ............ 1-1
1.2 Overview of Damage Tolerance Philosophy -
II BACKGROUND
2.1 Initial Fatigue Quality ..... .......... 2-1
2.1.1 The Equivalent Initial Flaw Size
Distribution ..... ........... 2-1
2.1.2 Time-to-Crack-Initiation
Distribution ..... ........... 2-3
2.2 Stochastic Crack Growth Model .. ....... 2-5
2.3 Probability of Detection .... .......... 2-11
2.4 Probabilistic Life Prediction .. ....... 2-13
III ANALYTICAL FORMULATION OF PROBABILISTIC APPROACH TO
LIFE PREDICTION
3.1 Deterministic Crack Growth Approach . ... 3-1
3.1.1 Analytical Crack Growth Approach 3-1
3.1.1.1 No Inspection .. ....... 3-2
3.1.1.2 One or Multiple Inspections. 3-4
3.1.2 Master Curve Approach .......... .. 3-9
3.1.2.1 No Inspection .. ....... 3-12
vi
3.1.2.2 One or Multiple Inspections. 3-12
3.2 Stochastic Crack Growth Approach ........ .. 3-18
3.2.1 Analytical Crack Growth Approach . . 3-19
3.2.1.1 No Inspection .. ....... .. 3-20
3.1.1.2 One or Multiple Inspections. 3-22
IV EXAMPLES CF iICCHASTIC LIFE PREDICTION
4.0 Introduction ....... ............... .. 4-1
4.1 Lug Example ........ ................ .. 4-1
4.1.1 Deterministic Crack Growth Approach 4-9
4.1.2 Stochastic Crack Growth Approach . . 4-10
4.2 Stiffened Panel Example .... .......... 4-20
4.2.1 Slcw Crack Growth Approach ..... .. 4-36
4.2.1.1 Deterministic Crack Growth
Approach .... .......... .. 4-36
4.2.1.2 Stochastic Crack Growth
Approach .... .......... .. 4-42
4.2.2 Crack Arrest Approach .......... ... 4-47
4.2.2.1 Deterministic Crack Growth
Approach .... .......... .. 4-48
4.2.2.1.1 General Master Curve
Approach ......... .. 4-48
4.2.2.1.2 Special Case, Q(a)=1 4-48
4 2.2.2 Stochastic Crack Growth
Approach ... .......... .. 4-53
4.2.2.2.1 General Master Curve
Approach ......... .. 4-53
4.2.2.2.2 Special Case, P(a)h1 4-55
4.3 Concl ns . 4-59
V CONCLUSIONS AND RECOMMENDATIONS
5.1 Summary . . ................... 5-1
5.2 Conclusions ........... ................ 5-4
5.3 Recommendations for Future Research . . .. 5-5
VI REFERENCES ..................................... 6-1
AI Appendix ....................................... A-i