Long-Life Design and Test Technology of Typical Aircraft Structures

160 Pages·2018·7.17 MB·English

by  Jun Liu

Jun Liu · Zhufeng Yue · Xiaoliang Geng
Shifeng Wen · Wuzhu Yan
Long-Life
Design and Test
Technology of
Typical Aircraft
Structures
Long-Life Design and Test Technology of Typical
Aircraft Structures
Jun Liu Zhufeng Yue Xiaoliang Geng
(cid:129) (cid:129)
Shifeng Wen Wuzhu Yan
(cid:129)
Long-Life Design and Test
Technology of Typical
Aircraft Structures
123
Jun Liu ShifengWen
Schoolof Mechanics, Civil Engineering Northwestern Polytechnical University
andArchitecture Xi’an,Shaanxi
Northwestern Polytechnical University China
Xi’an,Shaanxi
China WuzhuYan
Northwestern Polytechnical University
Zhufeng Yue Xi’an,Shaanxi
Northwestern Polytechnical University China
Xi’an,Shaanxi
China
XiaoliangGeng
Northwestern Polytechnical University
Xi’an,Shaanxi
China
ISBN978-981-10-8398-3 ISBN978-981-10-8399-0 (eBook)
https://doi.org/10.1007/978-981-10-8399-0
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Preface
Aviation technology is moving forward at an unprecedented speed. Aircraft
structures tend to be large in scale, complex, lightweight, and sophisticated.
However, the service environment of aircraft structures is getting worse. Its
development increasingly focuses on improving reliability and reducing costs, that
is, improving safety and extending material life under the premise of meeting
structural strength requirements. Structural anti-fatigue design and manufacturing
has become the key issue of aircraft reliability and economy. With the launch of
large passenger aircraft projects and transport aircraft projects in China, typical
structuraldesignsofaircraft,andtheirrelatedtests,haveencounterednewtechnical
problems. Solutions to these key technological issues will be helpful to promote
domestic aircraft design and testing technologies, as well as the comprehensive
performance of aircraft, which has become particularly important.
UnderthesupportofprojectsbytheNationalDefenseScienceandTechnology,
the localization project of materials, the National Natural Science Foundation of
China (50805118, 50375124, and 11102163), the Aviation Science Fund
(2013ZA53010), and the basic research fund of the Northwestern Polytechnical
University (JC20110260), our research group has achieved a lot in in terms of the
exploration and the practice of anti-fatigue design, analysis, and related experi-
mentalverificationoftypicalaircraftstructuresinrecentyears,whichrepresentsthe
basis of this book. The book’s content considers practical engineering issues with
highengineeringapplicationvalues.Partoftheresultsandtechnologieshavebeen
successfully applied to different models of aircrafts in their structural design,
analysis and test. The book is divided into six chapters.
Chapter1introducetheaimandmaincontentofthebook.Chapter2providesan
overviewofthebasicconceptsandknowledgeoftenusedinanti-fatiguedesignand
analysisofaircraftstructures.Chapter3analyzestheeffectofthesurfacequalityof
fastener holes, such as surface defects and processing quality, on fatigue life.
Chapter 4 examines the effects of fatigue resistance techniques, such as cold
expansion, impression, and strengthening by hammering, on the residual stress
distribution and fatigue life of fastening holes. Chapter 5 discusses the effects of
differentparametersofshotpeening,suchasshotmaterials,surfaceroughness,and
v
vi Preface
target properties, on the residual stress field and lifespan of plates. Chapter 6
focuses on three types of typical connections for aircraft: single shear lap joints,
double shear joint and reverse double dog bone joint in terms of nail load and
lifespan assessment. Chapter 7 analyzes fatigue tests and lifespan assessments of
typical wing box structures, and verifies the accuracy of anti-fatigue analysis
technologies used on such structures to determine their anti-fatigue properties.
In the relevant pre-research and project completion process, Dr. Shao Xiaojun,
doctoral students Kang Jianxiong and Yuan Xin, master students Liu Yongjun,
ZhangGang,XuHonglu,WangXiaosen,YangShichao,ZhangZhiguo,andWang
Xing, along with Mr. Yao Shile, Mr. Wei Xiaoming, and Mr. Han Zhe, engineers
from the advanced materials and structural testing center of Northwestern
Polytechnic University, undertook certain tasks. Some parts of the book adopt or
refer to their relevant papers or work reports, and we are exceedingly grateful for
theirhelp.Thisbookhasalsocitedresearchresultsfrombothdomesticandforeign
experts and scholars. However, we may not always indicate original sources and
apologize to the reader when this is the case.
The completion of this book has also been strongly supported by the National
Defense Science and Industry Bureau, China Aviation Industry Corporation’s
related plants and other units, as well as relevant leadership, engineering, and
technical personnel. We would like to express our sincere appreciation to all
of them.
This book’s content is characterized by systematic, comprehensive, and high
engineering practicality. At the same time, it reflects both domestic and foreign
researchresultsinthisfieldinrecentyearsandassuchcouldbeusedasareference
for relevant professional researchers and engineering and technical personnel.
We warmly welcome your criticism and corrections.
Xi’an, China Jun Liu
Zhufeng Yue
Xiaoliang Geng
Shifeng Wen
Wuzhu Yan
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Outline of Fatigue and Fracture Mechanics . . . . . . . . . . . . . . . . . . . 5
2.1 Basic Conception of Fatigue . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.1 Definition of Fatigue and Its Damage Property . . . . . . . . . 5
2.1.2 Alternating Stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.3 Curve S-N. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1.4 Equal-Life Curve. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1.5 Stress Fatigue and Strain Fatigue . . . . . . . . . . . . . . . . . . . 9
2.1.6 Linear Cumulative Damage Theory . . . . . . . . . . . . . . . . . 10
2.2 The Main Factors that Affect the Structural Fatigue
Performance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2.1 Effects of Load Spectrum. . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2.2 Effects of Stress Concentration. . . . . . . . . . . . . . . . . . . . . 11
2.2.3 Effects of Size. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2.4 Effects of Surface Roughness and Residual Stress . . . . . . . 12
2.3 Mechanism of Fatigue Failure, Crack Propagation,
and Fracture Analysis of Metals . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.3.1 Mechanism of Fatigue Failure . . . . . . . . . . . . . . . . . . . . . 13
2.3.2 Fatigue Crack Propagating Theory . . . . . . . . . . . . . . . . . . 14
2.3.3 Fractographic Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.4 Estimate Methods of Fatigue Life . . . . . . . . . . . . . . . . . . . . . . . . 16
2.4.1 Nominal Stress Approach. . . . . . . . . . . . . . . . . . . . . . . . . 16
2.4.2 Local Stress–Strain Method . . . . . . . . . . . . . . . . . . . . . . . 17
2.4.3 Multiaxial Fatigue Theory . . . . . . . . . . . . . . . . . . . . . . . . 18
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
vii
viii Contents
3 Effect of Surface Quality of Open Holes on Fatigue Life . . . . . . . . . 23
3.1 Effect of the Surface Defects on Fatigue Life of Open Holes . . . . 23
3.1.1 Scratch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.1.2 Cavity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.1.3 Inclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.2 Effect of Manufacturing Quality on Fatigue Performance
of Open Holes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.2.1 Surface Roughness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.2.2 Verticality. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.2.3 Cylindricity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.2.4 Roundness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.2.5 Manufacturing Quality of Fasten Holes and Empirical
Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.3 Effect of Drilling on Fatigue Performance of Open Holes . . . . . . . 50
3.3.1 Specimen Size and Loading . . . . . . . . . . . . . . . . . . . . . . . 51
3.3.2 Fatigue Test Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4 Anti-fatigue Strengthening Technology of Holes. . . . . . . . . . . . . . . . 55
4.1 Effect of Cold Expansion on Fatigue Performance of Open
Holes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.1.1 Direct Mandrel Expansion Process and Its Parameters . . . . 56
4.1.2 Residual Stress Measurements . . . . . . . . . . . . . . . . . . . . . 58
4.1.3 Fatigue Test Results and Fracture Analysis . . . . . . . . . . . . 62
4.1.4 FEM Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
4.2 Effect of Impression on Fatigue Performance of Open Holes. . . . . 66
4.2.1 Impression Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
4.2.2 Influence of Indenter Size on Residual Stress
Distribution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
4.2.3 Influence of Different Factors on Residual Stress
of Impression-Reinforced Holes . . . . . . . . . . . . . . . . . . . . 70
4.2.4 Fatigue Test of Three-Hole Sample Impressed. . . . . . . . . . 74
4.3 Effect of Hammering on Fatigue Performance of Open Hole. . . . . 76
4.3.1 Hammering and Fatigue Testing. . . . . . . . . . . . . . . . . . . . 76
4.3.2 Finite Element Analysis of Hammering. . . . . . . . . . . . . . . 78
4.3.3 Fracture Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
5 Shot Peening Strengthening Technology . . . . . . . . . . . . . . . . . . . . . . 85
5.1 Mechanism of Shot Peening and Status of Art . . . . . . . . . . . . . . . 85
5.2 Effect of Shot Materials on Fatigue Performance . . . . . . . . . . . . . 87
5.2.1 Fatigue Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
5.2.2 Comparative Analysis of Fatigue Test Data. . . . . . . . . . . . 87
Contents ix
5.2.3 Fatigue Fracture Analysis. . . . . . . . . . . . . . . . . . . . . . . . . 90
5.2.4 Numerical Simulation of Shot Peening with
Different Shot Materials. . . . . . . . . . . . . . . . . . . . . . . . . . 92
5.3 Effect of Surface Roughness on Residual Stress Field
of Shot Peening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
5.3.1 Finite Element Model . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
5.3.2 Residual Stress Distribution . . . . . . . . . . . . . . . . . . . . . . . 97
5.3.3 Effect of Surface Roughness on Residual Stress
of Shot Peening. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
5.3.4 Influence of Shot Size on Residual Stress
Considering Surface Roughness . . . . . . . . . . . . . . . . . . . . 99
5.3.5 The Effect of Shot Peening Velocity on Residual
Stress Considering Surface Roughness . . . . . . . . . . . . . . . 101
5.4 Effect of Mechanical Properties of Target Materials on Shot
Peening Energy Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
5.4.1 Conversion Between Kinetic Energy and Deformation
Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
5.4.2 Finite Element Model . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
5.4.3 Model Verification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
5.4.4 Effect of Young’s Modulus of Target . . . . . . . . . . . . . . . . 106
5.4.5 Effect of Target Yield Strength. . . . . . . . . . . . . . . . . . . . . 108
5.4.6 Effect of Strain Hardening Rate . . . . . . . . . . . . . . . . . . . . 108
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
6 Anti-fatigue Design and Analysis of Joints . . . . . . . . . . . . . . . . . . . . 113
6.1 Single Shear Lap Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
6.1.1 Fatigue Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
6.1.2 Analysis of Hole Stress . . . . . . . . . . . . . . . . . . . . . . . . . . 121
6.2 Double Shear and Interference Fit Joints . . . . . . . . . . . . . . . . . . . 123
6.2.1 Effect of Interference on Pin Load . . . . . . . . . . . . . . . . . . 123
6.2.2 Fatigue Test and Analysis . . . . . . . . . . . . . . . . . . . . . . . . 127
6.3 Reverse Double Dogbone Joints . . . . . . . . . . . . . . . . . . . . . . . . . 131
6.3.1 Nail Load Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
6.3.2 Fatigue Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
6.3.3 Maximum Principal Stress Analysis . . . . . . . . . . . . . . . . . 136
6.4 Application of Multi-axis Fatigue Theory on Fatigue
Life Prediction of Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
6.4.1 Life Prediction of Aluminum Alloy Reverse Double
Dogbone Joints Specimen . . . . . . . . . . . . . . . . . . . . . . . . 138
6.4.2 Estimation of Life of Single Shear Lap Joints . . . . . . . . . . 139
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
x Contents
7 Fatigue Test and Analysis of Box Section . . . . . . . . . . . . . . . . . . . . . 143
7.1 Box Section Fatigue Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
7.1.1 Specimen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
7.1.2 Loading Method and Test Results. . . . . . . . . . . . . . . . . . . 145
7.2 Box Section Life Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
7.2.1 Box Section Model and Results . . . . . . . . . . . . . . . . . . . . 147
7.2.2 Shape and Size of Initial Defects . . . . . . . . . . . . . . . . . . . 148
7.2.3 Fatigue Crack Propagation Analysis Program . . . . . . . . . . 149
7.2.4 Evaluation Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153