Design Manual for Impact Damage Tolerant Aircraft Structure

232 Pages·2012·12.54 MB·English

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Design Manual for Impact Damg
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AGARD-AG-238
NORTH 4TLANTIC TR!EATY ORGANIZATION
ADVISORY GROUP FOR AERGSPACE 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.
iMow
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;
--
stimulating advances in the aerospace sciences relevant to strengthening the common defencr
-Continuously
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;
assistance to member nations for the purpose of increasing their scientific and technical potential;
-Providing
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 fromt each member nation. The mission of AGARI) is carried out through the Panels which are
composed of experts appointed by the National Delegates, the Consultant and Exchange Programnme 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 fromt material supplied by AGARI) or the author.
Published October 1981
Copyright @ AGARD 1981
All Rights Reserved
ISBiN 92-835-1403-3
Printed by Technical Editing and Reproduction Ltd
Harford House, 7- 9 Charlotte St. London, WIF JHD
PREFACE
Aircraft must maintain structural int~grity relative to many sources of damage such
as, for example, fatigue cracking or corrosion. Military aircraft must also withstand, as far
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 11 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
irformed discussions. This occurred both within the Working Group on Impact Damage
4
Tolerance of Structures and also at the Specialists' Meeting held in Ankara in September
1975 (see AGARD Conference Proceedings CP-l 86). The Panel is therefore deeply indebted
not only to Mr Avery, for his outstanding efforts, targely single-handed, in compiliuig 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.H. RPUR
Chairm~an, Working Group
on Impact Damage Tolerance
of Structures
NT!S c".
lbi
CONTENTS
Page
PREFACE W
AUTHOWS NOTE vii
INTRODUCTION ix
SECTION 1 - DESCRIPTION OP PROIECTILE THREATS I
1.1 MITARY PRO3ECTIES
1.1.1 NmoExplodh ProjKctUl I
1.1.2 EszpIodIng Pr%)@cties 13
1.2 ENGINE DEMIS PRO3ECTrLES is
1.3 REFERENCES AND NILOGRAPHY 23
SECTIO I - ANALYSIS METHOD5 FOR PREDICTING STRUCTURAL RESPONSE TO PRO3ECTILE IMPACT 23
2.0 ANALYSIS METHODS FOR PREDICTING STRUCTURAL RESPONSE TO PRO3ECTILE IMPACT 27
2.0.1 General Approach t Impect Damanp Tolieance 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
2.0.2 Overview of th Stato-of-the-Art in Impact Damifte Tolerance Anulyab Methods 33
2.1 ANALYSIS METHODS FOR BALLISTIC PENETRATION 36
2.1.1 Ballistic Limit Asesment 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 Degration Due to Peetratkio 42
2.2 ANALYSIS METHODS FOR BALLISTIC DAMAGE SIZE AND TYPE 43
2.2.1 Damage Cauaed by Non-Exploding Projectilas 45
2.2.1.1 Non-Exploding Projectiles Impacting Metals 45
2.2.1.1.1 Non-Exploding Projectiles Impacting Metal - Discussion of Parameters
Influencing Damage 43
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 63
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 -
Discu ion of Parameters Influencing Damage 69
2.2.1.2.2 Non-Etploding Penetrators Impacting Graphite/Epoxy - Damage
Size Prediction 77
2.2.2 Damae Camed by H10 Exploive If) Projectiles 79
2.2.2.1 Prediction of Damage Caused by Fragments from HE Projectiles 83
2.2.2.1.1 Characteristics of the Fragment Distributions from HE Projectiles 85
2.2.2.1.2 The BR-2 Comtiater 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 111
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 Flrate Difference Analysis 125
iv
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STTNI
(CONTINUED)
Par
2.2.2.2.3.3 Dynamic Plate Analysis 125
2.2.2.2.3.4 Equivalent Static Load Method of Analysis 125
2.2.2.2.3.3 Critical Impulse Failure Criteria 134
2.2.2.2.3.6 Empirical Failure Criteria for Components 134
2.2.3 IDaage Caued by Enginm De(cid:127)ris Prectla 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 139
2.L4 Hydrodynmnic Ran DImln 140
2.2.4.1 Hydrodynamic Ram Loading and Response 140
2.2.4.2 Hydrodynamic Ram Phenomonology 142
2.2.4.2.1 Shock Waves 142
2.2.4.2.2 Drag Pressure 142
2.2.4.2.3 Fhlud/Structure Interaction 144
2.2.4.2.4 Structural Response and Failure 145
2.2.4.3 Status of Hydrodynamic Ram Analysis 146
2.2.4.3.1 Trajectory and Fluid Pressure Analysis 147
2.2.4.3.2 Fluid/Structure Coupling 151
2.2.4.3.3 Structural Response Analysis 151
2.3 EFFECTS OF CYCLIC LOADING ON PRO3ECMBLE IMPACT DAMAGE 153
2.3.1 Fatigue Crack lInlitlaon 053
2.3.1.1 Crack Initiation From Ballistic Damage 153
2.3.1.2 Crack Initiation In Adjacent Undamaged Structure 153
2.3.2 Fatlgue Crack Growth 153
2.3.2.1 Crack Growth Analysit 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..1 Stilfness Degrplation of Damaged Structural Eleseits 159
2.4.2 Stiffness Degradation of Structural Components 159
2.5 STRENGTH DEGRADATION OF IMPACT DAMAGED STRUCTURE 161
2.5.1 Analysis of Monolithic Panels Contaiulig Impact Duamr 161
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 17t,
2.5.1.2 Modified Fracture Mechanics 173
2.5.1.2.1 Effective Critical Stress Intensity Factor for Projectile Damage 178
2.5.1.2.2 Additioril Residual Strength Pred:ction Techniques for Fiber
Composites 184
2.5.1.3 Dynamic Effects Associated With Strength DeV.Tadation 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 Impa:t I(cid:127)muae 195
2.5.2.1 Analytical Approach 195
2.5.2.2 Finite Element Analysis 197
2.5.2.3 Engineering Analysis Method 200
v
CONTENTS
(CONCLUDED)
Page
2.5.3 AWAY& M Mv1 1i-EfmmSUmVnttm wr Ca(cid:127) ft Im#=pat Dsainq 201
2.5.3.1 Finite Element Analysis Techniques for Damaged Structure 201
2.5.3.2 Application of Finite Element Techniquws to Damaged Structure 203
2.6 REFERENCES 211
SECTION 11- DESIGN GUIDELIMES 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 Desig Methidolop Overvew 220
3.1.i.i 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 2'
3.1.2 Design Methadolo Elements 224
3.1.2.1 Structural Survivability Assessment 224
3.1.2.2 Design Threat Definition 224
3.1.2.3 Mission Definition 224
3.1.2.4 Threat Encounter Definition 224
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 Iripact 226
3.1.2.8 Cyclic Loading After Impact 226
3.1.2.9 Rigidity and Stiffness After Impact 226
3.2 DESIGN TECHI-QUES FOR ACHIEVING IMPACT DAMAGE TOLERANCE 226
; Vi
AUtHK)OR'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 mantescripts and submitted review comments. Mr. 0. 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. 3. 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 !I.
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 Boelng, whose early wo.,k 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. Ratwark, and their
coworkers at Northop Corporation, 3. R. Yamane and 3. Brass, provided valuabie source material for portions of the
Manual, as did the work of E. A. Lundstrom of Naval Wea,'ons 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. 0. Fearnow of AFWAL. The technical -ommunications 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.
3oh G. Aveýýal2
Mahat , St v abi lit y/V uihnera ;y
Ree=chi a i~neering (
',~~~ MUlotllly Airplane Coml y
Seattle, W Ington 98124
vi-
INTRODUCTION
Aircraft must maintain structural integri ty relative to many types of damaging mechanisms including for example,
fatigue, non-detectable initial defects and in-flight damage such as that inflicted by military weapons or by debris
from disintegration of an englne. While the design methodology for some of these is well established within the
structural design disciplines, that for in-flight damage has not been widely distributed to designers.
The resistance of the structure to the impact of projectiles is an important parameter in consideration of the
vulnerability of military aircraft. Information on this subject Is contained in AGARD Advisory Report AR-47
"Physical Vulnerability of Aircraft". However there is a need for considerable augmentation of this information,
extending the scope to include design methodology. The Structures and Materials Panel of AGARD, recognizing this
need, corn missioned the preparation of this Design Manual.
The overall objective of the Manual is to inform designers of thi general character of projectile threats and available
analysis methods for predicting damage and strength degradation, and io outline a methodology for incorpo×rating
p. jectile damage tolerance into the structural design of aircraft. Toward this end, the Manual contains three major
sections;
Section I Description of Projectile Threats
Section u Analysis Methods for Predicting Structural Response to Projectile
Impact
Section NI Design Guidelines for Impact Damage Tolerance
Section I describes projectile types, important encounter parameters, and typical terminal effects, written primarily
for the aircraft designer rather than the vulnerability or weapons effects specialist. The intent is to provide a very
general overview useful to an individual having little familiarity with projectiles aad their effects. Vulnerability and
weapons effects specialists have more specific and often classified dota, and should be consulted as required in design
applications.
Section II presents analysis methods and data available for predicting the response of metal and fiber composite
structure to projoctile impact. The analysis methods discussed are applicable to impacts by small arms projectiles,
missile warhead fragments, and the fragmentation and blast effects of high-explosive projectiles. The responses
addressed Include penetration capability, damage size and type, strength and stiffness degradation of damaged
structure, and internal load redistribution.
Section III summarizes a design methodology for Implementing projectile damage tolerance within structural design
disciplines, developing methods and requirements within a format that is compatible with existing damage tolerance
procedures.
amUIN i- Aa uw-NOt nILu
ix
SECTION I
DESCRIPTION OF PROJECTILE THREATS