Practical Airframe Fatigue and Damage Tolerance - Sigma K

1 Practical Airframe Fatigueand Damage ToleranceL. J. Bent PLEASE USE THE CONTACT FORM ON TO CHECK AVAILABILITY AND PRICING OF THIS BOOK, or EMAIL or TELEPHONE UK (+44) 1292 571 345 PLEASE SEE FOR DETAILS OF Fatigue AND Damage Tolerance TRAINING COURSES THAT ARE OFFERED TESTIMONIALS Practical Airframe Fatigue and Damage Tolerance the course Fantastic course the perfect balance of problems to teaching. The problems at the end really brought it all together. Your thorough knowledge of the subject really showed. Thanks for passing it on. Fiona Scolley, Lead Stress Engineer, Assystem UK Ltd (November 2010) An extremely good course very Practical . Dave Carter, Stress Engineer, Assystem UK Ltd (November 2010) The course covers the fundamentals with detailed illustrations and examples which help to create a solid base to understand the various aspects of crack growth and specific details more easily.

2 I am specifically happy with the simple and easy to understand explanations to various questions raised during the course. Sachin Kumaz Rostogi, Stress Engineer, Goodrich IDC (April 2011) Training instructor has good Practical knowledge and experience. Vimal Kumar Jaiswal, Stress Engineer, Goodrich IDC (April 2011) Personally the course has been very good to consolidate my understanding and experience. I have learnt hand checks and a feel for things which were missing in my bag. Many thanks for a good course. Yogish B. E., Aerospace Engineer, Atkins Aerospace Bangalore (April 2011) Overall very good and very well presented. Scott Ferry, Consultant Engineer, Airframe Designs Ltd (May 2011) Excellent hand-outs and worked examples. Andrew Somers, Stress Engineer, Atkins Aerospace Glasgow (May 2011) F&DT is a difficult subject to pitch right. Les has done this extremely well.

3 Rob Smith, Lead Stress Engineer, Spirit AeroSystems (May 2011) Good knowledge of subject well communicated. Andrew Thomas, Lead Stress Engineer, Spirit AeroSystems (May 2011) Practical Airframe Fatigue and Damage Tolerance the book I have to say I'm very impressed. This should be standard reading for any young engineer like myself .. I'm pleased to see it is full of clear explanations and the calculations are used to provide supporting evidence and reference information. Your service has been excellent and I appreciate it very much Tyrel Beede, Irvine, California See also Practical Airframe Fatigue AND Damage Tolerance by Les Bent Ilustrations by Derek Paul Published by Sigma K Ltd Coylton, Scotland Printed and bound by Antony Rowe Ltd, Eastbourne ISBN 978-0-9565174-0-1 All rights reserved Copyright Sigma K Ltd 2010 No part of the material protected by this copyright notice may be reproduced or utilised or transmitted in any form or by any means, electronic or mechanical, including photocopying , recording or by any information storage and retrieval system without prior written permission from the copyright owner.

4 Ii Chapter 1. Fatigue AND Damage Tolerance Fatigue of aircraft structures 1 The rise and fall of safe life and fail safe 2 Damage Tolerance 6 Damage Tolerance certification regulations 7 Damage tolerant repairs 9 Widespread Fatigue Damage 10 Chapter 2. Fatigue PROCESSES Fatigue crack initiation 13 Effect of stress concentrations on Fatigue crack initiation 19 Fatigue crack propagation 22 Fractography 22 Chapter 3. Fatigue CALCULATIONS Fatigue cycle definitions 25 SN curves and master diagrams 27 Power law factors 28 Form of SN data equations or tabular 30 Effect of tensile strength amongst alloy class 31 Test data 31 Effect of mean stress on Fatigue life 32 Example of a simple Fatigue calculation for a constant amplitude cycle 34 Stress spectra and counting 35 Miner s rule 42 Scatter factors 44 Fatigue calculation programs 45 Strain life Fatigue calculations 47 Some statistical aspects of Fatigue 49 Chapter 4.

5 Fatigue OF JOINTS Introduction 53 Stress concentration factors in joints 54 Stress concentrations in the bearing mode 57 Stress concentrations in the clamped and mixed modes 61 Secondary bending effects 65 Fretting 67 Failure locations under Fatigue 68 Analysis of multiple row fastened joints 69 SN data for multiple row attachment joints 79 Lugs 85 Interference fit 91 iii Cold working 92 Burr marks and scratches 95 Fatigue of bolts 96 Fatigue of bonded joints 97 Chapter 5. CRACKS UNDER STRESS Fracture mechanics 102 Historical development 103 The effect of a crack in a stress field 107 Crack tip stress intensity factor 111 Fracture toughness 111 Crack growth 114 Crack growth programs 117 Threshold, closure and short crack behaviour 123 Crack growth retardation 127 Chapter 6. STRESS INTENSITY FACTORS Centre cracked panel 130 Edge crack 132 Surface flaws 134 Small cracks at holes 136 Through cracks at holes 146 Stress gradients 147 Thickness changes 153 Crack tip bulging in fuselages 154 Compounding methods 160 Cracks in stiffened panels 165 Development of crack shape 178 Finite element and boundary element methods 179 Multiple site Damage 179 Chapter 7.

6 RESIDUAL STRENGTH Nett section yield 181 Critical fracture toughness 185 Plastic zone size 186 R-curves 189 Residual strength of stiffened panels 196 Chapter 8. LOAD AND SPECTRUM DERIVATION Loading spectra 200 Cumulative frequency (exceedence) diagrams 202 iv Flight profiles 208 Gust and manoeuvre spectra 210 Ground spectra 225 Fatigue calculation using a cumulative frequency diagram 229 Fatigue calculation using a defined time sequence 236 Undercarriage loading 238 Omission of load levels during testing 239 Standard loading spectra 240 Chapter 9. Damage DEFINITION AND INSPECTION Identification of Principal Structural Elements and Structurally Significant Items 241 Fatigue stresses and Damage mapping 242 Static stress levels 244 Geometry and stress concentrations 245 In-service data 248 Test data 249 Material properties 250 Areas prone to accidental Damage 250 Initial Damage assumptions 250 Detectable Damage pre- and post-MSG3 252 Non-destructive testing (NDT) 258 The non-destructive testing manual 260 Eddy current testing (ET) 260 Magnetic testing (MT)/Magnetic Particle Inspection (MPI) 261 Penetrant testing (PT)/Penetrant Flaw Detection (PFD) 262 Radiographic testing (RT) 262 Ultrasonic testing (UT) 263 The interface between the Stress Office and NDT 264 Chapter 10.

7 CERTIFICATION CALCULATIONS Overview of calculation process 265 Report layout 271 Assemble background data 271 Load path, expected Damage progression and detectable Damage 272 Limit load and test/in-service factors 272 Fatigue loads 272 Stress intensity factor calculation 273 Critical crack length 273 Threshold calculation 273 Repeat inspection period calculation 274 Single load path structure 277 Multiple load path structure CASE 1: SD item intact until PD item failure 278 Multiple load path structure CASE 2: PD item fails before SD item 280 v Multiple load path structure CASE 3: SD item fails before PD item 282 Reporting and summary sheets 284 General considerations 284 Chapter 11. Damage Tolerance OF TYPICAL STRUCTURE Lugs 287 Spanwise/chordwise wing joints 303 Spar joints 313 Fuselage lap/butt joints 317 Fittings 321 Stiffened panels 323 Wing/empennage cut outs and holes 332 Spars 335 Fuselage cut-outs and holes 341 Stringer run outs 345 Ribs 347 Fuselage pressure bulkheads 349 Chapter 12.

8 Damage Tolerance OF REPAIRS Introduction 352 AC 120-93 and the three stage repair approval process 353 Considerations before metal is cut 355 Stop drilling 358 Use and abuse of power laws 361 Oversizing and bushing holes 365 Oversizing and spotfacing holes 372 Cold working of holes 374 Blend repairs to skin and flange elements 375 Repair doublers 380 Inspection requirements 387 Repair doubler proximity 390 Widespread Fatigue Damage and repair doublers 393 Availability of data 393 REFERENCES 401 SUBJECT INDEX 409 INDEX409 Practical Airframe Fatigue and Damage Tolerance Index Note: Figures are indicated (in this index) by italic page numbers, Tables by emboldened numbers, and footnotes by suffix n . Abbreviations used in index: PD = primary Damage ; SD = secondary Damage ; SIF = stress intensity factor; SSI = structurally significant item 1 g on the ground (1 GOG) stress 210 2024-T3 material 35, 43, 80, 189 2024-T4 material 358 2024-T351 material 291 AC 120-93 repair approval process 353 5 access rating [in detectable crack calculations] 257 accidental Damage , areas prone to 250, 290 adhesively bonded joints see bonded joints adhesives high-temperature curing compared with cold bonding 65 and stress concentrations at knife edged fastener holes 64 5, 317 AFGROW material data 291 output file for example 298 SIF solution 295, 296 Ageing Aircraft Working Group (AAWG), Final Report 12, 51 Air Transport Association (ATA)

9 , guidance document on NDT instruction 259 Airbus UK 286 aircraft maintenance planning, updates 354 aircraft mass ratio 212 Aloha B737 accident 10, 12, 65, 317 alternating stress 26 relationship to proof stress 31 AMC 20-20 10, 353 angularity [between bolt head and retaining nut] 96, 97 arrest of crack 196 7, 326, 327 Avro 688 Tudor 2, 3 axial scratches, Fatigue life affected by 95 BAe ATP wing and fuselage 248 BAe Jetstream 9 BAE SYSTEMS formation of 286 P621 computer program 235 banked turn manoeuvre 212 13 basic detectable crack length 255 factors affecting 256 7 Basquin exponent/relationship 29, 48, 49 beachmarks 23 bearing mode of load transfer and clamping mode 62 4 effect of load transfer on Fatigue life 58, 59 stress concentrations in 56, 57 61 bearing stress in joints 57, 384, 385 in lugs 295, 302 bending stress distribution, in spar 339 beta ( ) 111 centre cracks 130 1, 193 corner cracks at holes 136, 138 edge cracks 133 surface flaws 134 biaxial loading, at crack tip 108 blend repairs 375 80 reinforcement for 378, 380 1 blunting of crack 325 body-centred cubic (bcc)

10 Crystal structure 13, 14 Boeing 707 4, 5, 5, 6 Boeing 737 10, 65 Boeing fastener flexibility formula 71, 72 Boeing Fatigue methods 244 bolt bending 96, 379 bolted joints 62 bolts cocking of 96, 97 Fatigue of 96 bonded butt joints, Fatigue of 100, 101 bonded joints debonding and failure of 10, 65, 317 Fatigue of 97 101 load extension curve 175 bonded lap joints, Fatigue of 100, 100 boundaries 160, 246 boundary element method, SIFs determined using 179 Bowie factor 136, 137, 368, 369 braking loads 238 break out of cracks 308 9, 312 & n, 322 break through of cracks 309 British Aerospace plc 286 see also BAE SYSTEMS brittle fracture 110, 112 bulging factors 154 7 comparison of various factors 157, 158 9 burr marks, Fatigue life affected by 95 bushing of oversized hole 356, 365 72 410 Practical Airframe Fatigue AND Damage Tolerance butt joints 53, 54 Fatigue of 100, 101 butt strap 306, 307 castellations in ribs 347 9 centre crack in panel offset crack 146, 308 SIF for 130 2, 193, 194 certification calculations background data for 271 2 critical crack size calculations 273 Fatigue loads 272 3 general considerations 284 5 hand calculations for checking 285 inspection threshold calculations 273 4 limit loads defined 272 load path type defined 272 material data for 272 multiple load path structure 267 70 overview of process 265 70 repeat inspection interval calculations 274 83 report compilation 284 report layout 271 re-run after repairs 395 SIF calculations 273 single load path structure 265 7 summary sheet(s)