Design Manual for Impact Damage Tolerant Aircraft Structure

244 Pages·2004·20.57 MB·English

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AGARDographNo.238
Design Manual for Impact Damage
Tolerant Aircraft Structure
NORTH ATLANTIC TREATY ORGANIZATION -
DISTRIBUTION AND AVAILABILITY
ON BACK COVER

AGARD-AG-238
NORTH ATLANTIC TREATY ORGANIZATION
ADVISORY GROUP FOR AEROSPACE RESEARCH AND DEVELOPMENT
(ORGANISATION DU TRAITE DE L'ATLANTIQUE NORD)
AGARDograph No.238
DESIGN MANUAL FOR IMPACT DAMAGE
TOLERANT AIRCRAFT STRUCTURE
by
John G.Avery
Boeing Military Airplane Company
Research and Engineering
P.O.Box 3707, M/S 41-10
Seattle, Washington, USA 98124
This report has been prepared at the request of the Structures and Materials Panel of AGARD.
THE MISSION OF AGARD
The mission of AGARD is to bring together the leading personalities of the NATO nations in the fields of science
and technology relating to aerospace for the following purposes:
— Exchanging of scientific and technical information;
- Continuously stimulating advances in the aerospace sciences relevant to strengthening the common defence
posture;
- Improving the co-operation among member nations in aerospace research and development;
— Providing scientific and technical advice and assistance to the North Atlantic Military Committee in the field
of aerospace research and development;
— Rendering scientific and technical assistance, as requested, to other NATO bodies and to member nations in
connection with research and development problems in the aerospace field;
- Providing assistance to member nations for the purpose of increasing their scientific and technical potential;
- Recommending effective ways for the member nations to use their research and development capabilities for
the common benefit of the NATO community.
The highest authority within AGARD is the National Delegates Board consisting of officially appointed senior
representatives from each member nation. The mission of AGARD is carried out through the Panels which are
composed of experts appointed by the National Delegates, the Consultant and Exchange Programme and the Aerospace
Applications Studies Programme. The results of AGARD work are reported to the member nations and the NATO
Authorities through the AGARD series of publications of which this is one.
Participation in AGARD activities is by invitation only and is normally limited to citizens of the NATO nations.
The content of this publication has been reproduced
directly from material supplied by AGARD or the author.
Published October 1981
Copyright © AGARD 1981
All Rights Reserved
ISBN 92-835-1403-3
I PREFACE
!
• Aircraft must maintain structural integrity relative to many sources of damage such
I as, for example, fatigue cracking or corrosion. Military aircraft must also withstand, as far
j as is practicable, damage inflicted by hostile military weapons. The resistance of the
structure to the impact of projectiles is an important parameter in considerations of
vulnerability. It is necessary to determine the impact failure characteristics of the structure
under load, and its residual strength after damage. The detail design features of the
structure are important in determining the spread of the damage. Where neighbouring
systems or fuel tanks are vulnerable, the degree of penetration of the projectile into the
structure is important. Blast and fragmentation effects must be considered.
This Design Manual has therefore been produced by the Structures and Materials
Panel to aid the designer in making assessments of the tolerance of the structure to various
threats and the probability of the aircraft surviving the impact, completing the mission and
returning safely to base. It describes methods which exist to determine both the damage
resulting from the impact of various types of projectiles and the resulting capabilities of
the damaged structure. It also embraces an analogous problem, arising mainly on transport-
aircraft, of the resistance of the structure to impact of debris from engine disintegration.
The Manual is divided into three Sections, Section I dealing with the projectile threats,
Section II with analysis methods and Section III with design guidelines.
The Structures and Materials Panel was very fortunate from the outset in securing the
services, as Coordinator, Compiler and Editor of the Manual, of Mr John G.Avery of the
Boeing Company, Seattle, who is world renowned as an-expert in the field of impact damage
tolerance of structures. An essential feature of AGARD activities is the pooling of relevant
knowledge with the NATO community aided by the bringing together of specialists for
informed discussions. This occurred both within the Working Group on Impact Damage
Tolerance of Structures and also at the Specialists' Meeting held in Ankara in September
1975 (see AGARD Conference Proceedings CP-186). The Panel is therefore deeply indebted
not only to Mr Avery, for his outstanding efforts, largely single-handed, in compiling this
Manual, but also to all those others who have provided valuable information and
contributions, especially those listed by name in the preliminary pages.
N.F.HARPUR
Chairman, Working Group
on Impact Damage Tolerance
of Structures
CONTENTS
Page
PREFACE m
AUTHOR'S NOTE v"
INTRODUCTION ix
SECTION I - DESCRIPTION OF PROJECTILE THREATS 1
1.1 MILITARY PROJECTILES 1
1.1.1 Non-Exploding Projectiles 1
1.1.2 Exploding Projectiles 13
la ENGINE DEBRIS PROJECTILES 18
1.3 REFERENCES AND BIBLIOGRAPHY 23
SECTION D - ANALYSIS METHODS FOR PREDICTING STRUCTURAL RESPONSE TO PROJECTILE IMPACT 25
2.0 ANALYSIS METHODS FOR PREDICTING STRUCTURAL RESPONSE TO PROJECTILE IMPACT 27
2.0.1 General Approach to Impact Damage Tolerance Analysis 27
2.0.1.1 Factors Determining the Structural Capability of Projectile Damaged Structure 28
2.0.1.2 Incorporation of Probalistic Events 28
2.0£ Overview of the State-of-the-Art in Impact Damage Tolerance Analysis Methods 33
2.1 ANALYSIS METHODS FOR BALLISTIC PENETRATION 36
2.1.1 Ballistic Limit Assessment 36
2.1.1.1 Ballistic Limit Assessment for Metallic Structure 37
2.1.1.2 Ballistic Limit Assessment for Fiber Composite Structure 41
2.1.2 Projectile Degradation Due to Penetration 42
2O. ANALYSIS METHODS FOR BALLISTIC DAMAGE SIZE AND TYPE «
2.2.1 Damage Caused by Non-Exploding Projectiles . "5
2.2.1.1 Non-Exploding Projectiles Impacting Metals *5
2.2.1.1.1 Non-Exploding Projectiles Impacting Metal - Discussion of Parameters
Influencing Damage *5
2.2.1.1.2 Non-Exploding Projectiles Impacting Metals - 'Damage Size
Prediction 52
2.2.1.1.3 Non-Exploding Penetrators Impacting Metals - Damage
Type Prediction 65
2.2.1.1.4 Non-Exploding Penetrators Impacting Metals - Damage Orientation
Prediction 65
2.2.1.2 Non-Exploding Projectiles Impacting Fiber Composites 69
2.2.1.2.1 Non-Exploding Projectiles Impacting Fiber Composites -
Discussion of Parameters Influencing Damage 69
2.2.1.2.2 Non-Exploding Penetrators Impacting Graphite/Epoxy - Damage
Size Prediction 77
2.2.2 Damage Caused by High Explosive (HE) Projectiles 79
2.2.2.1 Prediction of Damage Caused by Fragments from HE Projectiles 85
2.2.2.1.1 Characteristics of the Fragment Distributions from HE Projectiles 85
2.2.2.1.2 The BR-2 Computer Code for Predicting Fragment Damage 92
2.2.2.2 Predicting Damage Caused by Blast from HE Projectiles 102
2.2.2.2.1 Dynamic Pressure Loadings Induced by HE Projectiles 103
2.2.2.2.1.1 Shock Overpressure 103
2.2.2.2.1.2 Confined Gas Pressure 108
2.2.2.2.2 Fundamental Aspects of the Response of Structure to Blast Pressure
Loadings HI
2.2.2.2.3 Analysis Methods for Predicting Structural Response 113
2.2.2.2.3.1 Finite Element Analysis 113
2.2.2.2.3.2 Firute Difference Analysis 125
CONTENTS
(CONTINUED)
Page
2.2.2.2.3.3 Dynamic Plate Analysis 125
2.2.2.2.3.4 Equivalent Static Load Method of Analysis 125
2.2.2^2.3.5 Critical Impulse Failure Criteria 134
2.2.2.2.3.6 Empirical Failure Criteria for Components 134
2.2.3 Damage Caused by Engine Debris Projectiles 136
2.2.3.1 Description of Engine Debris Projectiles 136
2.2.3.2 Encounter Parameters 139
2.2.3.3 Typical Terminal Effects j
39
2.2.4 Hydrodynamic Ram Damage 140
2.2.4.1 Hydrodynamic Ram Loadings and Response 140
2.2.4.2 Hydrodynamic Ram Phenomenology 142
2.2.4.2.1 Shockwaves 142
2.2.4.2.2 Drag Pressure 142
2.2.4.2.3 Fluid/Structure Interaction 144
I 2.2.4.2.4 Structural Response and Failure 145
j 2.2.4.3 Status of Hydrodynamic Ram Analysis 146
i 2.2.4.3.1 Trajectory and Fluid Pressure Analysis 147
I 2.2.4.3.2 Fluid/Structure Coupling 151
j 2.2.4.3.3 Structural Response Analysis 151
I 2.3 EFFECTS OF CYCLIC LOADING ON PROJECTILE IMPACT DAMAGE 153
j 2.3.1 Fatigue Crack Initiation 153
2.3.1.1 Crack Initiation From Ballistic Damage 153
2.3.1.2 Crack Initiation In Adjacent Undamaged Structure 153
I 2.3.2 Fatigue Crack Growth 153
2.3.2.1 Crack Growth Analysis for Metallic Structure 154
2.3.2.2 Damage Extension Analysis for Fiber Composite Structure 157
\ 2.4 STIFFNESS DEGRADATION OF IMPACT DAMAGED STRUCTURE 159
2.4.1 Stiffness Degradation of Damaged Structural Elements 159
2.4.2 Stiffness Degradation of Structural Components 159
i 2.5 STRENGTH DEGRADATION OF IMPACT DAMAGED STRUCTURE 161
I
! 2.5.1 Analysis of Monolithic Panels Containing Impact Damage 161
I 2.5.1.1 Conventional Fracture Mechanics Applied to Ballistic Damage 163
: 2.5.1.1.1 Effect of Damage Geometry 164
2.5.1.1.2 Effect of Damage Spacing-Multiple Impact Damage 169
• 2.5.1.1.3 Additional Factors Influencing Tensile Fracture 174
, 2.5.1.2 Modified Fracture Mechanics 178
' 2.5.1.2.1 Effective Critical Stress Intensity Factor for Projectile Damage 178
! 2.5.1.2.2 Additional Residual Strength Prediction Techniques for Fiber
j Composites 184
2.5.1.3 Dynamic Effects Associated With Strength Degradation 189
2.5.1.3.1 Effect of Applied Tensile Load 189
2.5.1.3.2 Dynamic Stress Intensity Factors 192
2.5.1.4 Effect of Combined Stress 193
; 2.5.2 Analysis of Multiple Load Path Panels Containing Impact Damage 195
', 2.5.2.1 Analytical Approach 195
2.5.2.2 Finite Element Analysis 197
2.5.2.3 Engineering Analysis Method 200
CONTENTS
(CONCLUDED)
Page
2.53 Analysis of Multi-Element Structure Containing Impact Damage 201
2.5.3.1 Finite Element Analysis Techniques for Damaged Structure 2°1
2.5.3.2 Application of Finite Element Techniques to Damaged Structure 203
2.6 REFERENCES 211
SECTION ID- DESIGN GUIDELINES FOR IMPACT DAMAGE TOLERANCE 217
3.0 DESIGN GUIDELINES FOR IMPACT DAMAGE TOLERANCE 219
3.1 DESIGN METHODOLOGY FOR ACHIEVING IMPACT DAMAGE TOLERANCE 220
3.1.1 Design Methodology Overview 220
3.1.1.1 Determination of Structural Requirements 220
3.1.1.2 Determination of the Capability of Damaged Structure 222
3.1.1.3 Structural Survivability Assessment 223
3.1.2 Design Methodology Elements 224
3.1.2.1 Structural Survivability Assessment 22*
3.1.2.2 Design Threat Definition 224
3.1.2.3 Mission Definition 22*
3.1.2.4 Threat Encounter Definition 22*
3.1.2.5 Critical Structure Identification 225
3.1.2.6 Damage Size Determination 225
3.1.2.7 Residual Strength 225
3.1.2.7.1 Strength Requirements At Impact 226
3.1.2.7.2 Strength Requirements After Impact 22$
3.1.2.8 Cyclic Loading After Impact 226
3.1.2.9 Rigidity and Stiffness After Impact 226
3.2 DESIGN TECHNIQUES FOR ACHIEVING IMPACT DAMAGE TOLERANCE 226
AUTHOR'S NOTE
This Design Manual was prepared as the primary task of the Impact Damage Tolerance Working Group formulated by
the Structures and Materials Panel, with N. F. Harpur of British Aerospace serving as the originator and guiding light
of the effort. The objective of the Manual is to describe a methodology for incorporating projectile impact damage
tolerance into structural design, with the aim of improving inherent Survivability. The scope of the work includes
military projectiles and engine debris.
As its title implies, the Design Manual is intended for structural designers and technologists having little prior
knowledge of projectile impact phenomena and weapon effects. An early goal was to avoid the necessity of security
classification, as it was felt that this would restrict its accessibility to designers. As a result, the data presented is
limited in scope. Within this context, the user should regard the Manual as a guide in defining methods and
identifying the type of data required for impact damage tolerant design, rather than as a source of data pertaining to
the nature and effects of specific threats.
The Manual was prepared in three sections using information available to the author, most of it developed under the
sponsorship of the U.S. Department of Defense. Each section was separately submitted for public release approval
and distributed to Working Group members for technical review. This process began in 1977, and has only recently
been concluded following fairly major revisions undertaken in 1980 to satisfy release requirements.
Mr. Keith I. Collier, Deputy Director of the Flight Dynamics Laboratory, AFWAL, coordinated the final release
activity and deserves special thanks for his interest and effort.
The author would like to thank all those who read the manuscripts and submitted review comments. Mr. D. W. Voyls
of AFWAL spent many hours reviewing the entire Manual and the implementation of his suggestions has made a
significant contribution in content and releasability. Mr. K. T. Shaw of the RAE provided detailed commentary which
resulted in substantial improvements to Section I. Special thanks is also extended to Messrs. J. Olsen, C. Wallace,
and L. Kelly of AFWAL, and W. Kirkby and R. Anstee from the Structures Department of the RAE. Because of the
urgencies of the printing schedules, some excellent recommendations for improvement could not be implemented,
including the reduction of duplication between Sections I and II.
With regard to preparing the Manual, I would like to acknowledge the contributions of Mr. T. R. Porter of the Boeing
Military Airplane Company. Much of the format, content, and philosophy of the Manual remains from his prior
efforts. The same comments apply to Mr. R. 3. Bristow, also of Boeing, whose early work established the approach
used for later developments in ballistic damage prediction and residual strength assessment. Ms. S. 3. Bradley, again
of Boeing, has been instrumental in preparing the Manual from all standpoints, including technical contributions,
editing, formatting and reviewing. The notable work of Messrs. M. 3. Jacobson and M. M. Ratwani, and their
coworkers at Northrop Corporation, 3. R. Yamane and 3. Brass, provided valuable source material for portions of the
Manual, as did the work of E. A. Lundstrom of Naval Weapons Center, D. McCarthy of Rolls-Royce, and P. C. Huang
of NSWC. Several researchers were particularly supportive of the activity, including 3. Massmann of IABG,
D. F. Haskell of BRL, and R. W. Lauzze and D. O. Fearnow of AFWAL. The technical communications contributed by
Mr. Massmann were of great value to the effort. Considerable information presented in the Manual was developed
under contractual programs managed by A. 3. Holten formerly of AFWAL, and Drs. A. Somoroff and D. Mulville of
Naval Air Systems Command. Special appreciation is extended to the Boeing Military Airplane Company, particularly
Mr. D. E. Strand, for supportive interest in the activity.
3ohn G. Ave/y / 8/1/81 /
Manager, SUrvtfability/Vulnerabifrty
Research and /Engineering U
Boeing Military Airplane Company
Seattle, Washington 98124
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