Fatigue Crack Growth Failure and Lifing Analyses for Metallic Aircraft Structures and Components

104 Pages·2019·6.58 MB·English

by  Russell Wanhill

SPRINGER BRIEFS IN
APPLIED SCIENCES AND TECHNOLOGY
Russell Wanhill
Simon Barter
Loris Molent
Fatigue Crack
Growth Failure and
Lifing Analyses for
Metallic Aircraft
Structures and
Components
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Russell Wanhill Simon Barter
(cid:129) (cid:129)
Loris Molent
Fatigue Crack Growth Failure
fi
and Li ng Analyses
for Metallic Aircraft
Structures and Components
123
Russell Wanhill Simon Barter
Emmeloord, TheNetherlands Aerospace Division
DSTGroup
LorisMolent Melbourne, Australia
Aerospace Division
DSTGroup
Melbourne, Australia
ISSN 2191-530X ISSN 2191-5318 (electronic)
SpringerBriefs inApplied SciencesandTechnology
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Preface
Thisbookprovidesaconcisediscussionoffatiguecrackgrowth(FCG)failureand
lifing analysis methods for metallic aircraft structures and components. After a
reasonably concise historical review, surveys are made of (i) the importance of
fatigue for aircraft structural failures and the sources of fatigue nucleation and
cracking, (ii) contemporary FCG lifing methods, and (iii) the quantitative fractog-
raphy (QF) required for determining the actual FCG behaviour. These surveys are
followed by the main part of the book, which is a discussion, using case histories,
of the applicabilities of linear elastic fracture mechanics (LEFM) and non-LEFM
methods for analysing service fatigue failures and full- and sub-scale test results.
This discussion is derived primarily from the experiences of the Defence Science
and Technology Group in Melbourne, Australia, and the Netherlands Aerospace
Centre, Marknesse, the Netherlands.
The opinions expressed in this book are those of the authors and do not nec-
essarily represent those of the organisations with which they are, or have been,
associated.
Emmeloord, The Netherlands Russell Wanhill
Melbourne, Australia Simon Barter
Melbourne, Australia Loris Molent
v
Contents
1 Historical Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 FCG Parameters, Concepts and Testing . . . . . . . . . . . . . . . . . . 1
1.2 FCG ‘Laws’ and Models. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2.1 Long Crack Growth ‘Laws’ . . . . . . . . . . . . . . . . . . . . 3
1.2.2 Long Crack Growth Models: LEFM Analyses . . . . . . . 5
1.2.3 Characteristic K Approaches. . . . . . . . . . . . . . . . . . . . 8
1.2.4 The Effective Block Approach (EBA) Framework . . . . 11
1.2.5 Exponential FCG Behaviour . . . . . . . . . . . . . . . . . . . . 13
1.2.5.1 Exponential FCG: Lead Crack Fatigue
Lifing Framework (LCFLF). . . . . . . . . . . . . . 13
1.2.5.2 Exponential FCG: The Cubic Rule . . . . . . . . 17
1.2.5.3 Exponential FCGR . . . . . . . . . . . . . . . . . . . . 18
1.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2 Basic Information for Aircraft FCG Failure and Lifing
Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.1 Importance of Fatigue for Aircraft Structural Failures . . . . . . . . 21
2.2 Fatigue Crack Nucleation, Discontinuities, Early FCG
and Damage Tolerance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.2.1 Fatigue-Nucleating Discontinuities in Aircraft
Structures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.2.2 Early FCG and Damage Tolerance . . . . . . . . . . . . . . . 24
2.3 Summary of FCG Lifing Methods . . . . . . . . . . . . . . . . . . . . . . 26
3 Quantitative Fractography (QF) for FCG Analyses . . . . . . . . . . . . 29
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.2 Fatigue Striation FCG Analyses. . . . . . . . . . . . . . . . . . . . . . . . 29
3.3 Progression Marking FCG Analyses. . . . . . . . . . . . . . . . . . . . . 31
3.4 Fatigue-Nucleating Discontinuities and Equivalent Pre-crack
Sizes (EPS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.4.1 Defining the Initial Crack Sizes for FCG Analyses. . . . 37
vii
viii Contents
3.5 QF Techniques for Fatigue Fracture Surfaces . . . . . . . . . . . . . . 38
3.5.1 Optical Fractography . . . . . . . . . . . . . . . . . . . . . . . . . 40
3.5.2 Electron Fractography and Optical Fractography . . . . . 40
3.6 A Cautionary Note . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
4 Aermacchi MB-326H Wing Spar (1990): Exponential FCG
Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4.2 FCG Analysis for the Failed Spar . . . . . . . . . . . . . . . . . . . . . . 43
4.3 Further Examination of Wing Spars. . . . . . . . . . . . . . . . . . . . . 47
4.3.1 Safe Life Reassessment. . . . . . . . . . . . . . . . . . . . . . . . 47
4.3.2 Fleet Recovery Programme. . . . . . . . . . . . . . . . . . . . . 47
4.4 Lessons Learned. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
5 P&W 125B Engine Bearing (1994): 2-Stage Exponential
FCG Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
5.2 The Failed No. 3 Bearing: Macroscopic and Metallographic
Examination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
5.3 Cage Failure and FCG Analysis. . . . . . . . . . . . . . . . . . . . . . . . 50
5.3.1 Progression Marking QF Analysis. . . . . . . . . . . . . . . . 51
5.4 Interpretation of the Results and Remedial Action . . . . . . . . . . 53
6 EBA Example Lifing Assessment (2004): F/A-18 Horizontal
Stabilator Spindles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
6.2 EBA Validation for the F/A-18 Horizontal Stabilator Spindles . . . 55
6.3 EBA and Total Life Assessment for the F/A-18 Horizontal
Stabilator Spindles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
7 LCFLF Example Lifing Assessment (2004): F/A-18 Vertical
Tail Attachment Stubs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
7.2 The FT46 Stub Flange Crack . . . . . . . . . . . . . . . . . . . . . . . . . 63
7.3 Fractography of the FT46 Stub Flange Crack . . . . . . . . . . . . . . 63
7.4 LCFLF Life Assessment for the FT46 Stub Flange Crack . . . . . 65
8 Cubic Rule Life Prediction Examples . . . . . . . . . . . . . . . . . . . . . . . 67
8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
8.2 McDonnell Douglas F4E Spectrum Coupon Test Data . . . . . . . 68
8.3 Lockheed Martin P3C Spectrum Coupon Test Data . . . . . . . . . 69
8.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
9 Fokker 100 Fuselage Test: Lap Joints Exponential
FCG Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
9.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
9.2 FCG Analysis of the Cracked Lap Splice [71, 72, 95] . . . . . . . 72
Contents ix
10 Sikorsky S-61N Rotor Blade (1974): Exponential FCGR
Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
10.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
10.2 FCG Analysis for the Crashed Helicopter. . . . . . . . . . . . . . . . . 78
10.2.1 Prediction of Detectable FCG Lives . . . . . . . . . . . . . . 79
10.3 Results and Remedial Actions (Lessons Learned) . . . . . . . . . . . 80
11 Westland Lynx Rotor Hub (1998): Progression Marking
LEFM Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
11.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
11.2 Fractography of Early Fatigue Cracking in the M326
‘Yellow’ Arm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
11.2.1 Progression Markings. . . . . . . . . . . . . . . . . . . . . . . . . 84
11.2.2 Detailed Fractography. . . . . . . . . . . . . . . . . . . . . . . . . 85
11.3 Fractography of Early Fatigue Cracking in the M6 Arm
and M326 Specimens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
11.4 FRTB + LEFM Estimations of Damaging Service Fatigue
Stress Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
11.5 Measurements of Service Loads and Fatigue Analysis
by GKNW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
11.6 Causes of Failure and Remedial Action . . . . . . . . . . . . . . . . . . 88
12 Closing Remarks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
References.... .... .... .... ..... .... .... .... .... .... ..... .... 91
Abstract
Thisbookconsidersfatiguecrackgrowth(FCG)failureandlifinganalysismethods
for metallic aircraft structures and components, based on the experiences of the
AustralianDefenceScienceandTechnologyGroupandtheNetherlandsAerospace
Centre. A reasonably concise historical review is followed by surveys of basic
information for aircraft FCG failure analyses and the quantitative fractography
(QF) required for determining the actual FCG behaviour. These surveys are fol-
lowed by a selection of case histories and lifing analyses.
(cid:1) (cid:1) (cid:1)
Keywords Metallic aircraft structures Fatigue crack growth Failure analysis
(cid:1)
Quantitative fractography Lifing of aircraft structures
xi