best method fod induced hcf executive summary

NORTH ATLANTIC TREATY ORGANISATION

RESEARCH AND TECHNOLOGYORGANISATION

AC/323(AVT-094)TP/68 www.rta.nato.int

RTO TECHNICAL REPORT TR-AVT-094

Best Practices for the Mitigation and Control of Foreign Object Damage-Induced High

Cycle Fatigue in Gas Turbine Engine Compression System Airfoils

(Meilleures pratiques pour l’atténuation et le contrôle de la fatigue mégacyclique résultant des dégâts causés par des corps étrangers dans les turbomoteurs)

Work performed by the

RTO Applied Vehicle Technology Panel (AVT) Task Group-094.

Published June 2005

Official Information No Public Release

NORTH ATLANTIC TREATY ORGANISATION

RESEARCH AND TECHNOLOGYORGANISATION

AC/323(AVT-094)TP/68 www.rta.nato.int

RTO TECHNICAL REPORT TR-AVT-094



(Meilleures pratiques pour l’atténuation et le contrôle de la fatigue mégacyclique résultant des dégâts causés par des corps étrangers dans les turbomoteurs)

Work performed by the

RTO Applied Vehicle Technology Panel (AVT) Task Group-094.

Official Information No Public Release

The Research and Technology Organisation (RTO) of NATO

RTO is the single focus in NATO for Defence Research and Technology activities. Its mission is to conduct and promote co-operative research and information exchange. The objective is to support the development and effective use of national defence research and technology and to meet the military needs of the Alliance, to maintain a technological lead, and to provide advice to NATO and national decision makers. The RTO performs its mission with the support of an extensive network of national experts. It also ensures effective co-ordination with other NATO bodies involved in R&T activities.

RTO reports both to the Military Committee of NATO and to the Conference of National Armament Directors. It comprises a Research and Technology Board (RTB) as the highest level of national representation and the Research and Technology Agency (RTA), a dedicated staff with its headquarters in Neuilly, near Paris, France. In order to facilitate contacts with the military users and other NATO activities, a small part of the RTA staff is located in NATO Headquarters in Brussels. The Brussels staff also co-ordinates RTO’s co-operation with nations in Middle and Eastern Europe, to which RTO attaches particular importance especially as working together in the field of research is one of the more promising areas of co-operation.

The total spectrum of R&T activities is covered by the following 7 bodies: • • • • • • •

AVT Applied Vehicle Technology Panel HFM Human Factors and Medicine Panel IST Information Systems Technology Panel NMSG NATO Modelling and Simulation Group SAS Studies, Analysis and Simulation Panel SCI Systems Concepts and Integration Panel SET Sensors and Electronics Technology Panel

These bodies are made up of national representatives as well as generally recognised ‘world class’ scientists. They also provide a communication link to military users and other NATO bodies. RTO’s scientific and technological work is carried out by Technical Teams, created for specific activities and with a specific duration. Such Technical Teams can organise workshops, symposia, field trials, lecture series and training courses. An important function of these Technical Teams is to ensure the continuity of the expert networks.

RTO builds upon earlier co-operation in defence research and technology as set-up under the Advisory Group for Aerospace Research and Development (AGARD) and the Defence Research Group (DRG). AGARD and the DRG share common roots in that they were both established at the initiative of Dr Theodore von Kármán, a leading aerospace scientist, who early on recognised the importance of scientific support for the Allied Armed Forces. RTO is capitalising on these common roots in order to provide the Alliance and the NATO nations with a strong scientific and technological basis that will guarantee a solid base for the future.

The content of this publication has been reproduced directly from material supplied by RTO or the authors.

Published June 2005

Copyright © RTO/NATO 2005 All Rights Reserved

ISBN 92-837-1148-3

Single copies of this publication or of a part of it may be made for individual use only. The approval of the RTA Information Management Systems Branch is required for more than one copy to be made or an extract included in another publication. Requests to do so should be sent to the address on the back cover.

ii RTO-TR-AVT-094



(RTO-TR-AVT-094)

Executive Summary High Cycle Fatigue (HCF) failures have grown in severity to become a dominant and costly failure mode for gas turbine-based propulsion and power systems. A significant fraction of engine-caused aircraft mishaps are due to HCF but, in addition, a major cost and maintenance penalty is caused by the removal of engines due to foreign object damage (FOD) to the engine compression system airfoils, in order to prevent FOD-induced HCF mishaps. The total HCF impact has therefore been to decrease operational readiness and increase weapon system support costs. The AVT-094 Working Group was chartered to investigate and recommend the best practices for NATO to use in dealing with this FOD-HCF problem.

Effective management of the FOD-induced HCF problem requires a detailed and up-to-date understanding of its impact in the real world of the NATO war fighter. This document therefore highlights the important FOD data that needs to be collected, a task that can be greatly aided through use of a NATO-standard template that has been developed, and which is supported by a developed list of common terminology and a pictorial representative damage guide. Data mining then provides a powerful means of focusing on the most important information in order to take pro-active knowledge-based preventive action. However good FOD prevention procedures are, FOD will still occur. Due to this fact, experimental and numerical simulation, which is discussed in detail, can be used to provide an understanding of how aero gas turbine engine blades will behave following FOD, in order to accurately define safe maintenance procedures and design activity. Blade design is traditionally based on material’s stress allowances and simple excitation avoidance, but this document presents a simple, robust, design methodology that takes in account the interaction between FOD and HCF on new blade designs to help improve their FOD tolerant robustness. In addition to ensuring that the underlying design of components is FOD-tolerant, supplementary treatment of a component’s surface can provide a powerful practical method of reducing the effect of potential FOD. Processes including shot peening, laser shock peening and low plasticity burnishing are explained along with their relative advantages. Finally, foreign objects need to be controlled at their source. This report therefore explains some ways in which FOD prevention should be employed through concentration on tool control methods, hardware accountability, housekeeping procedures, personnel training programs and procedures to be used following the loss of tools and other items.

The benefit of understanding FOD-induced HCF, and mitigating or controlling its occurrence, will be to improve significantly operational gas turbine engine safety and readiness, and reduce its life cycle costs. It is therefore recommended that NATO member Nations use this document and its recommendations to:

1) Examine their FOD data collection, mining and investigation methods and decide where changes could enhance their existing processes.

2) Review their processes for the experimental and numerical simulation of FOD.

3) Review their design practices for the evaluation of FOD/HCF interaction.

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4) Review their aero-engine manufacture and overhaul techniques for the application of FOD/HCF resistant surface treatments.

5) Examine FOD prevention methods used throughout their industry and government organizations to pick the best.

6) Adopt the Task Group’s definitions for describing blade damage as a NATO standard.

7) Periodically review the definitions, techniques and processes discussed in this report to include application of advancements in relevant technologies, and update documentation as required.

8) Set up a NATO FOD forum at which NATO nations can share FOD statistics and information and solve in-service problems jointly; representatives should be taken from flight safety organisations or other offices with the responsibility for in-service FOD Prevention.

Meilleures pratiques pour l’atténuation et le contrôle de la fatigue mégacyclique résultant des dégâts causés

par des corps étrangers dans les turbomoteurs (RTO-TR-AVT-094)

Synthèse De plus en plus importantes et coûteuses, les pannes dues à la fatigue mégacyclique (HCF) constituent désormais le principal mode de défaillance des turbines à gaz et génératrices. Une partie non négligeable des accidents occasionnés par les moteurs d’avion est imputable à la HCF, mais il faut également tenir compte de l’impact majeur sur les coûts et la maintenance de la dépose des moteurs, suite aux dégâts causés par un corps étranger (FOD) au niveau des aubes du compresseur, dans le but de prévenir des accidents HCF occasionnés par les corps étrangers. Globalement, donc, la HCF a eu pour effet de réduire la disponibilité opérationnelle et d’augmenter les coûts de soutien des systèmes d’armes. Le groupe de travail avait pour mandat d’examiner ce problème FOD/HCF et de faire des recommandations sur les meilleures pratiques à adopter pour le résoudre.

La gestion efficace du problème FOD/HCF requiert des connaissances approfondies et actualisées de son impact sur l’environnement concret du combattant de l’OTAN. Ce document attire donc l’attention sur les données FOD importantes qui doivent être collectées. Cette tâche pourra être considérablement facilitée par la mise en œuvre d’un modèle OTAN normalisé qui a été mis au point et qui est accompagné d’une liste détaillée de terminologie commune, ainsi que d’un guide illustré représentatif des dégâts. Par ailleurs, l’exploration de données représente un outil puissant, permettant de cerner les informations les plus importantes en vue de prendre des actions préventives basées sur la connaissance. Mais, quelque excellentes que soient les procédures de prévention FOD, des dégâts continueront d’être occasionnés. Pour parer à ce problème, la simulation expérimentale numérique, qui est présentée ici dans le détail, peut être exploitée pour représenter le comportement des aubes des turbines à gaz suite à un incident FOD, afin de définir avec précision les procédures de maintenance sans risques, ainsi que le processus de conception. Jusqu’à présent, la conception des aubes a été tributaire des limites de contrainte des matériaux, ainsi que de l’évitement de l’excitation, mais ce document présente une nouvelle méthodologie à la fois simple et étoffée de conception d’aubes de turbines à gaz, qui tient compte des interactions entre FOD et HCF et augmente la robustesse des aubes. Le traitement supplémentaire de la surface d’un composant garantit sa tolérance conceptuelle vis-à-vis des FOD. Il peut également constituer une méthode pratique performante pour l’atténuation des effets des FOD. Les différents procédés, notamment le grenaillage, le nettoyage laser et le polissage à faible plasticité, sont expliqués, ainsi que leurs avantages respectifs. Pour conclure, il a été constaté que les corps étrangers devaient être contrôlés à leur source. Ainsi, ce rapport présente les différentes méthodes de prévention des FOD, y compris les méthodes de contrôle des outils, la responsabilité matérielle, les procédures internes, les programmes de formation personnalisés et les procédures à suivre en cas de pertes d’outils et d’autres objets.

La compréhension du phénomène de FOD résultant de la HCF, ainsi que son atténuation et son contrôle, permettront d’améliorer sensiblement la sécurité et la disponibilité opérationnelles des turbomoteurs et de réduire les coûts globaux de possession. Par conséquent, le groupe de travail recommande aux pays membres de l’OTAN de tirer parti de ce document, ainsi que des recommandations qu’il contient pour :

1) Examiner leurs méthodes de collecte, d’exploration et de dépouillement des données, et définir les changements susceptibles d’améliorer les processus existants.

RTO-TR-AVT-094 v

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2) Faire le point sur leurs processus de simulation FOD numériques et expérimentaux.

3) Examiner leurs pratiques en matière de conception pour l’évaluation des interactions FOD/HCF.

4) Revoir leurs techniques de révision des moteurs d’aéronefs en vue de l’application de traitements de surface résistant aux FOD/HCF.

5) Examiner les méthodes de prévention des FOD mises en œuvre par leurs industriels et leurs organisations gouvernementales afin d’en dégager la meilleure.

6) Adopter les définitions du groupe de travail relatives aux dégâts occasionnés aux aubes, en tant que norme OTAN.

7) Faire le point, de façon périodique, sur les définitions, techniques et processus présentés dans ce rapport, y compris la mise en application d’avancées dans les différentes technologies pertinentes, et la mise à jour de la documentation selon les besoins.

8) Créer un forum OTAN dans le domaine des FOD, où les pays membres pourraient mettre en commun les informations et les statistiques FOD, afin de résoudre conjointement les différents problèmes rencontrés dans la pratique.

Table of Contents

Page

Executive Summary iii

Synthèse v

List of Figures/Tables xiii

Foreword xviii

Task Group Members xix

Report Contributors xxiii

Chapter 1 – Introduction 1-1 1.1 Introduction and Description of the FOD HCF Problem 1-1 1.2 HCF-FOD Interaction 1-5 1.3 FOD Prevention 1-7 1.4 HCF-FOD Design Considerations 1-12 1.5 Chapter Summaries 1-12 1.6 Annex Summaries 1-13 References 1-13

Chapter 2 – FOD Data Mining and Investigation 2-1 2.1 Introduction 2-1 2.2 Data Collection 2-1 2.3 Establishment of Standard Terminology 2-2 2.4 FOD Reporting Template 2-2 2.5 Part 1 – Initial Reporting 2-2

2.5.1 Reporting Station/Organization 2-2 2.5.2 Aircraft Type, Mark and Serial Number 2-2 2.5.3 Engine Type and Mark 2-3 2.5.4 Engine Installed Position 2-3 2.5.5 Engine Serial Number 2-3 2.5.6 Tech Form Serial Number 2-3 2.5.7 Local Serial Number 2-3

2.6 Part 2 – When Damage Found 2-3 2.7 Part 3 – Action Taken 2-4 2.8 Part 4 – Operating Factors/Aircraft Movement 2-4 2.9 Part 5 – Circumstances of Ingestion 2-4 2.10 Part 6 – Recent Unusual Circumstances 2-5

2.10.1 Deployments 2-5 2.10.2 Strong Winds 2-5 2.10.3 Airfield Snow/Ice 2-5

RTO-TR-AVT-094 vii

2.10.4 Station Exercises 2-5 2.10.5 Heavy Rain 2-6 2.10.6 Airfield Works 2-6

2.11 Part 7 – FOD Details 2-6 2.12 FOD Investigations 2-6 2.13 Completion of the FOD Investigation 2-9 2.14 Data Mining 2-9 2.15 Non-Engine Investigations 2-10

Appendix 1 – Engine FOD Reporting Template 2-11 Appendix 2 – FOD Occurrence Report 2-13

Chapter 3 – Experimental and Numerical Simulation of FOD 3-1 3.1 Introduction 3-1 3.2 Characterization of Field Experience 3-2

3.2.1 FOD Geometry Distributions 3-7 3.2.2 Microscopic Features of FOD 3-9

3.3 Experimental FOD Simulation 3-11 3.3.1 Impact Simulation 3-12

3.3.1.1 Notch Machining 3-12 3.3.1.2 Shear Chisel, Quasi-Static Impact and Solenoid Gun 3-13 3.3.1.3 Light Gas Gun 3-14

3.3.2 Damage Level 1 3-16 3.3.3 Damage Level 2 3-16 3.3.4 Specimen Design 3-19

3.4 Numerical FOD Simulation 3-24 3.4.1 Detailed Numerical FOD Simulation 3-28

3.5 Post-Impact Life Prediction 3-31 3.5.1 Crack Initiation 3-31 3.5.2 Crack Growth 3-32

3.5.2.1 Calculate Normalized Elastic K for Notch Geometry 3-33 3.5.2.2 Calculate Elastic Kmax and Kmin 3-33 3.5.2.3 Calculate Residual K for Airfoil/Notch Geometry 3-34 3.5.2.4 Calculate K and R-ratio with Residual K 3-34 3.5.2.5 Compare K and R-ratio to Kth Material Capability 3-34 3.5.2.6 Iterate on Stress to Converge on Solution 3-34

3.5.3 Worst Case Notch (WCN) 3-34 3.5.4 WCN Example 3-35

3.6 Conclusion 3-37 References 3-37

Chapter 4 – Method for FOD/HCF Interaction Evaluation 4-1 4.1 Introduction 4-1 4.2 Context 4-2

4.2.1 Material 4-2 4.2.2 Ingestion Mechanisms 4-2

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4.3 Principle of the Method 4-3 4.3.1 Introduction 4-3

4.3.1.1 Current Practices 4-3 4.3.1.2 Main Assumptions Associated to the Method 4-3 4.3.1.3 Limitation of the Method 4-8 4.3.1.4 Alternative Approach to Generate the Goodman-style Diagram 4-9

4.3.2 Effect of FOD on the Blade Dynamic Behaviour 4-10 4.3.2.1 Effect of FOD on the Blade Frequencies 4-10 4.3.2.2 Effect of FOD on the Goodman-style Diagram 4-15 4.3.2.3 Effect of FOD on HCF Margins 4-18 4.3.2.4 Maintenance Books 4-19

4.4 Application Case 4-19 4.4.1 Presentation of the Studied Case 4-19 4.4.2 Effect on Frequencies 4-21 4.4.3 Choice of the Blade Areas 4-23 4.4.4 Computation of the Parameterised Goodman Curves 4-24

4.4.4.1 Limit Goodman Curves for Crack Non-Propagation 4-24 4.4.4.2 Limit Goodman Curve for Crack Propagation 4-25

4.4.5 Maximum Allowable FOD Size on the Blade for Each Mode 4-27 4.4.5.1 In the Case of Criterion 1: Non-Propagation Only 4-27 4.4.5.2 2nd Criterion: Non-Propagation HCF/Propagation LCF 4-30 4.4.5.3 Important Remark 4-33

4.4.6 Maximum FOD Size Allowed on the Airfoil 4-33 4.4.7 Effect of c/a Ratio on the Airfoil Centre 4-34

4.5 Conclusion and Possible Extensions of the Method 4-36 References 4-37

Chapter 5 – FOD/HCF Resistant Surface Treatments 5-1 5.1 Introduction 5-1 5.2 Shot Peening 5-1

5.2.1 Description of the Shot Peening Process 5-1 5.2.2 Increase in Component Fatigue Resistance due to Shot Peening 5-3 5.2.3 Advantages and Disadvantages of Shot Peening 5-4

5.3 Laser Shock Peening 5-5 5.3.1 Description of the Laser Shock Peening Process 5-5 5.3.2 Advantages and Disadvantages of Laser Shock Peening 5-6

5.4 Low Plasticity Burnishing 5-6 5.4.1 Description of the Low Plasticity Burnishing Process 5-6 5.4.2 Increase in Component Fatigue Resistance due to LPB 5-7 5.4.3 Advantages and Disadvantages of the LPB Process 5-10

5.5 Concluding Remark 5-10 References 5-10

Chapter 6 – FOD Prevention 6-1 6.1 Introduction 6-1 6.2 FOD 6-1

RTO-TR-AVT-094 ix

6.3 FOD Prevention Program 6-2 6.3.1 Control and Accountability of Tools and MSP 6-2

6.3.1.1 Tool Control 6-2 6.3.1.2 MSP Control 6-3

6.3.2 Hardware Accountability, Material Handling and Spare Parts Control 6-3 6.3.3 Housekeeping 6-4 6.3.4 Aircraft/Rotorcraft Ground Operations 6-5 6.3.5 Assembly Operations 6-5 6.3.6 Training 6-6 6.3.7 Measurement of FOD Prevention 6-7 6.3.8 Organizational Commitment 6-7 6.3.9 FOD Awareness Point of Contact 6-7

6.4 Lost Tool and Items Procedures 6-8 6.5 Reporting and Investigations of FOD Events 6-9 6.6 FOD Prevention Methods Applied at the Aircraft Design Stage 6-9

6.6.1 Engine Intake Position on the Aircraft 6-9 6.6.2 Engine Intake Duct Shape 6-10 6.6.3 Engine Intake Protection Screen 6-11 6.6.4 Compressor Duct Shape 6-12

References 6-12

Chapter 7 – Conclusions and Recommendations 7-1 7.1 Overall Conclusions 7-1

7.1.1 Introduction 7-1 7.1.2 FOD Data Mining and Investigation 7-1

7.1.2.1 Data Collection 7-1 7.1.2.2 Essential Parameters of Data Collection 7-1 7.1.2.3 FOD Investigations 7-2 7.1.2.4 Data Mining 7-2 7.1.2.5 Opportunities 7-2

7.1.3 Experimental and Numerical Simulation of FOD 7-2 7.1.3.1 Survey and Characterization 7-2 7.1.3.2 Experimental Simulation 7-3 7.1.3.3 Numerical Simulation 7-3 7.1.3.4 Post-Impact Life Prediction 7-4 7.1.3.5 Opportunities 7-4

7.1.4 Method for FOD/HCF Interaction Evaluation 7-4 7.1.4.1 Assumptions 7-5 7.1.4.2 Effect of FOD on Blade Mode Frequencies 7-5 7.1.4.3 Effect of FOD on the Goodman Diagram 7-6 7.1.4.4 Effect of FOD on HCF Margins 7-6 7.1.4.5 Uncertainties 7-6 7.1.4.6 Opportunities 7-7

7.1.5 FOD/HCF Resistant Surface Treatments 7-7 7.1.5.1 Shot Peening 7-7 7.1.5.2 Laser Shock Peening 7-7

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7.1.5.3 Low Plasticity Burnishing 7-8 7.1.5.4 Opportunities 7-8

7.1.6 FOD Prevention 7-8 7.1.6.1 FOD Prevention Program 7-8 7.1.6.2 Lost Tool and Items Procedures 7-9 7.1.6.3 Reporting and Investigations of FOD Events 7-9 7.1.6.4 FOD Prevention Methods Applied at the Aircraft Design Stage 7-9 7.1.6.5 Opportunities 7-9

7.2 Overall Recommendations 7-9 7.2.1 Recommendations Related to AVT-094 TOR 7-9 7.2.2 Complementary Recommendations 7-10

Annex A – FOD Terminology and Acronyms A-1 General Acronyms & Abbreviations A-1 FOD Terminology A-3 References A-7

Annex B – Air, Land, Sea and Space FOD Issues B-1 B.1 Effects of Sand and Dust on Small Gas Turbine Engines B-1

B.1.1 Background B-1 B.1.2 Problems B-2 B.1.3 Engine Protection Systems B-3

B.1.3.1 Inlet Particle Separators (IPS) B-3 B.1.3.2 Erosion-Resistant Coatings B-5

B.1.4 Conclusion B-6 B.2 FOD Avoidance in Industrial Gas Turbines B-7 B.3 Sea-Related FOD Issues B-7 B.4 Space-Related FOD Issues B-8 B.5 Space Debris B-9

Annex C – Engine Blade Damage Definitions C-1

Annex D – Soft-Body FOD Issues D-1 D.1 Bird Strikes D-1 D.2 Bird Strike Prevention D-1 D.3 Management of the Environment D-1 D.4 Bird Dispersal D-1 D.5 Educating the Aircrew D-2 D.6 Bird Strike Reporting D-2 D.7 Examples of Bird Hazard Bulletin D-4 References D-5

Annex E – Additional FOD Reference Materials/Websites E-1

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Annex F – Member Nation Maintenance Personnel F-1

Annex G – Terms of Reference (TOR) G-1 G.1 Origin G-1 G.2 Objectives G-1 G.3 Resources G-2 G.4 Security Classification Level G-3 G.5 Participation by Partner Nations G-3 G.6 Liaison G-3

List of Figures/Tables

Page

Chapter 1 Figure 1: Typical Runway Foreign Object Debris 1-1 Figure 2: Typical Runway Foreign Object Debris, as Picked up by FOD BOSS® System 1-2 Runway Cleaning System Figure 3: US Navy Aircraft Carrier Deck “Non-Skid” Material – Foreign Object Debris 1-3 Source includes Small Shot Peen used to Clean and Repair Flight Deck Figure 4: US Navy Foreign Object Debris – Small Shot Peen used to Clean and Repair 1-3 Flight Deck Figure 5: US Navy Foreign Object Debris Source – Arresting Cable Dragging along 1-4 Flight Deck during Arrested Landings Kicks up Foreign Object Debris from the Deck Surface Figure 6: UK RAF Harrier Crash due to FOD and HCF Interaction 1-4 Figure 7: Compressor Blade Tip Damage due to HCF, and Subsequent Domestic 1-5 Object Damage (DOD) Figure 8: Foreign Object Damaged Fan Blades at Tip with Subsequent HCF Failure 1-6 Figure 9: Simulated FOD on Fan Blade Leading Edge, Near Root 1-6 Figure 10: Close-up of Simulated FOD Notch on Fan Blade Leading Edge 1-7 Figure 11: Runway “FOD-Walk” to remove Foreign Object Debris 1-8 Figure 12: FOD BOSS® and Typical Runway Foreign Object Debris being Picked Up 1-8 Figure 13: Blending Borescope for On-Wing Blade FOD Repair 1-9 Figure 14: Foreign Object Damage to Nacelles and Engine Front Frame Structures due 1-10 to Impact with Ground Equipment Figure 15: Foreign Object Damaged Propeller from In-Flight Impact with another Aircraft 1-10 (USN P3 vs Chinese fighter, over Hainan, China) Figures 16a-b: A Chinese 747 Airliner, whose Destination was Paris, had Landed at Frankfurt 1-11 Germany for an “Unscheduled” Refuelling Stop

Chapter 2 Figure 1: Real FOD Prevention is Achieved through the Answers to the Above Questions 2-6 Figure 2: The Need for an Investigation Check List increases as we move towards the 2-7 Flight Line where the Special Tools and the Expertise of the Personnel become less Figure 3: A Typical FOD Investigation Procedure in the Lab 2-7 Figure 4: SEM Photo of a Damaged Blade (FOD) 2-9

Chapter 3 Figure 1: Comparison of Impact Surfaces on Simulated Airfoil Leading Edges from 3-1 1 mm Glass Spheres at a Velocity of 300 m/s Figure 2: Percentage of FOD Located along the Span Relative to the Blade Tip 3-2

RTO-TR-AVT-094 xiii

Figure 3: Histogram and Cumulative Distribution Function for FOD Depth 3-3 Figure 4: Examples of Severely Damaged Blades 3-4 Figure 5: 0.059-inch Dent with No Cracking in Leading Edge of 2nd Stage Fan Blade 3-4 Figure 6: 0.028-inch Tear in 2nd Stage Fan Blade 3-5 Figure 7: Two Notches in Leading Edge of 2nd Stage Fan Blade 3-5 Figure 8: 0.090-inch Deep Notch in Leading Edge of 2nd Stage Blade 3-6 Figure 9: FOD Impact Site on Pegasus Fan Blade 3-6 Figures 10a-d: Damage to RB199 Fan Blades 3-7 Figure 11: Distribution of Service-induced FOD from Two Different Surveys 3-8 Figure 12: Distribution of FOD Notch Root Radii 3-8 Figure 13: Histogram and Cumulative Distribution Function for FOD Notch kt 3-9 Figure 14: Micrograph Showing FOD Site with Non-Propagating Crack 3-9 Figure 15: Illustration of Typical FOD Impact Angles in Modern Gas Turbine Engines 3-10 Figure 16: Path of Projectile and Viewing Angles 3-11 Figure 17: Micrograph of a Machined Notch in a Simulated Airfoil 3-12 Figure 18: Solenoid Gun Indentation Set Up 3-13 Figure 19: Indentation from Solenoid Gun 3-14 Figure 20: Typical Light Gas Gun 3-15 Figure 21: Level 1 Repeat Shots 3-16 Figure 22: Level 3 Repeat Shots 3-16 Figure 23: Level 2 Front Surface 3-17 Figure 24: Simulated FOD Using Light Gas Gun Impact 3-18 Figure 25: Shear Band Pattern beneath Impact Crater 3-18 Figure 26: Edge of Ballistic Damage on Plate 3-19 Figure 27: Typical Fan Blade 3-20 Figure 28: Normalized Stress Distribution across Typical Fan Blade 3-21 Figure 29: Stress Distribution across Section A-A 3-21 Figure 30: Diagram of Simulated Leading Edge Specimen 3-22 Figure 31: Comparison of Calculated Blade and Specimen Stresses 3-22 Figure 32: Overview of Diamond Cross-Section Tension (DCT) Specimen 3-23 Figure 33: Representative Mesh for Sharp Edged Specimen Impact 3-25 Figure 34: Mesh Geometries used in Mesh Refinement Study 3-26 Figure 35: Comparison of Various Mesh Refinements to Experimental Damage 3-27 Figure 36: Comparison of Residual Stress Fields for Different Impact Angles 3-28 Figure 37: Shear Crack Running Ahead of Projectile, Damage Intensity Contours 3-30 Figure 38: Application of Equivalent Stress Parameter to Data with Different Stress Ratios 3-31 Figure 39: Equivalent Stress for a Given Notch Depth on Ballistically Impacted Winged 3-32 Specimens Figure 40: Kitagawa-Takahashi Diagram 3-33

xiv RTO-TR-AVT-094

Figure 41: Worst Case Notch Model Predicting Crack Initiation, Growth and Arrest 3-35 Figure 42: Prediction of Experimental vs. Predicted Threshold Stress using the 3-35 WCN Model

Table 1: Level 1 Summary of Shots 3-16 Table 2: Level 2 Summary of Shots 3-17

Chapter 4 Figure 1: Paris-type Law 4-4 Figure 2: Way to take into account Dynamic Cycles 4-5 Figure 3: Goodman-style Diagram for Non-Propagation 4-6 Figure 4: Non-Propagation Criteria as a Function of the Load Ratio 4-7 Figure 5: Evolution of the First Criterion to the Second Criterion 4-8 Figure 6: Example of a Goodman-style Diagram 4-9 Figure 7: Effect of the FOD Size on the Frequency Shift 4-11 Figure 8: Campbell Diagram of a Military HP Compressor Blade 4-12 Figure 9: Mesh Modification to Model the Local Loss of Stiffness 4-13 Figure 10: Mistuned Forced Response of an Industrial Bladed Disk 4-14 Figure 11: Amplification as a Function of Mistuning Standard Deviation 4-15 Figure 12: Example of Zone Choice: LE – Airfoil Centre – TE 4-15 Figure 13: Example of Crack Shape (2D Approaches) 4-16 Figure 14: Determination of the Limit Coupled Steady/Dynamic Stresses 4-17 Figure 15: Plot a Goodman-style Diagram Curve for One Given Damage Type and Size 4-17 Figure 16: Parameterised Goodman-style Diagram in Function of the Damage Size 4-18 Figure 17: Evaluation of the Maximum Allowable FOD Size for One Element of the FEM 4-18 Figure 18: View of the Studied HP Compressor Blade 4-19 Figure 19: Static Stresses Repartition on the Blade 4-20 Figure 20: Dynamic Stresses Repartition on the Blade for Mode 1F 4-20 Figure 21: Dynamic Stresses Repartition on the Blade for Mode 1T 4-20 Figure 22: Dynamic Stresses Repartition on the Blade for Mode 2S1 4-21 Figure 23: FOD in the Dynamically Most Loaded Area for Mode 1F 4-22 Figure 24: FOD in the Dynamically Most Loaded Area for Mode 1T 4-22 Figure 25: FOD in the Dynamically Most Loaded Area for Mode 2S1 4-23 Figure 26: Areas of the Blade and Associated Damage 4-23 Figure 27: Parameterised Goodman Curves (Non-Propagation) – Leading and Trailing Edge 4-24 Figure 28: Parameterised Goodman Curves (Non-Propagation) – Airfoil Centre 4-25 Figure 29: Parameterised Goodman Curves (Propagation) – Leading/Trailing Edge 4-26 Figure 30: Parameterised Goodman Curves (Propagation) – Airfoil Centre 4-26 Figure 31: Maximum Allowable FOD Size on the Suction Side for Mode 1F 4-27 Figure 32: Maximum Allowable FOD Size on the Suction Side for Mode 1T 4-28

RTO-TR-AVT-094 xv

Figure 33: Maximum Allowable FOD Size on the Suction Side for Mode 2S1 4-28 Figure 34: Maximum Allowable FOD Size on the Pressure Side for Mode 1F 4-29 Figure 35: Maximum Allowable FOD Size on the Pressure Side for Mode 1T 4-29 Figure 36: Maximum Allowable FOD Size on the Pressure Side for Mode 2S1 4-30 Figure 37: Maximum Allowable FOD Size on the Suction Side for Mode 1F 4-30 Figure 38: Maximum Allowable FOD Size on the Suction Side for Mode 1T 4-31 Figure 39: Maximum Allowable FOD Size on the Suction Side for Mode 2S1 4-31 Figure 40: Maximum Allowable FOD Size on the Pressure Side for Mode 1F 4-32 Figure 41: Maximum Allowable FOD Size on the Pressure Side for Mode 1T 4-32 Figure 42: Maximum Allowable FOD Size on the Pressure Side for Mode 2S1 4-33 Figure 43: Maximum Allowable FOD on the Airfoil 4-34 Figure 44: Maximum Allowable FOD Size (Parameter c) on the Airfoil 4-35 Figure 45: Maximum Allowable FOD Size – c/a=10 for Type B Damage (Airfoil Centre) 4-36

Chapter 5 Figure 1: Residual Stresses Generated by Shot Peening in a Nickel Plate 5-2 Figure 2: Residual Stress Profile after Shot Peening 5-3 Figure 3: The Effect of Shot Peening on the Endurance Limit of 7075 Alloy, after Peyre 5-3 Figure 4: Improvement in Fatigue Properties of Notched and Shot Peened Specimens 5-4 made out of 7075 Aluminium Alloy Figure 5: Schematic Representation of Laser Shock Peening Process 5-5 Figure 6: Representative Residual Stress Profile for Ti-6Al-4V showing the Depth of 5-6 Beneficial Compressive Residual Surface Stress created by LSP Figure 7: Low Plasticity Burnishing Process 5-7 Figure 8: Comparison of Residual Stresses Created by Shot Peening, LSP and LPB for 5-7 IN718 Material Figure 9: Effect of Shot Peening and LPB on Fatigue for Ti-6Al-4V 5-8 Figure 10: Residual Stress Distribution for Deep Rolled (DR) and Laser Shock Peened 5-9 Ti-6Al-4V Specimens Figure 11: Stress-Life Plots for Untreated and Deep Rolled Ti-6Al-4V Specimens at Two 5-9 Temperatures Figure 12: Comparison of Fatigue Lives for Deep Rolled and Laser Shock Peened 5-10 Specimens in Two Temperatures and for Two Stress Levels

Chapter 6 Figure 1: Top-Mounted Engine Intakes on A-10 Aircraft 6-9 Figure 2: F-16, Showing Engine Intake in Front of Nose Wheel 6-10 Figure 3: Chinook Helicopter with IPSs 6-10 Figure 4: Ovalized Intake on Boeing 737 Aircraft 6-11 Figure 5: Example of a Protection Screen on the A109 Helicopter 6-11 Figure 6: Permanent Protection Screen on Kamov Ka-52 6-11

xvi RTO-TR-AVT-094

RTO-TR-AVT-094 xvii

Figure 7: Removable Screens used on Su-27 Aircraft 6-12 Figure 8: Duct Shape to Reduce a Danger of FOD 6-12

Annex B Figure 1: Helicopter in Sand/Dust Environment B-1 Figure 2: Tank in Sand/Dust Environment B-2 Figure 3: Eroded Centrifugal and Axial Compressors B-2 Figure 4: Vortex Tube Separator B-3 Figure 5: Vortex Tube Pack B-3 Figure 6: T700 Vaned Separator B-4 Figure 7: T800 Vaneless Separator B-4 Figure 8: Results of US Navy Sand Ingestion Test on T64 Engine B-6 Figure 9: Industrial Gas Turbine Engine B-7 Figure 10: Turbine Engine Powered Ship Applications B-8 Figure 11: Water-Induced FOD on Rocket Combustion Chamber Injector B-8 Figure 12: Flux (per year) of Debris and Meteorites per Diameter for a 940 km Altitude B-9 Figure 13: Repartition of Objects around the Earth B-10 Figure 14: Example of Impact on the Solar Panel of Hubble Telescope B-11 Figure 15: Picture of LDEF (Long Duration Exposure Facility) B-12

Annex C Figure 1: Example of a Burred Blade C-1 Figure 2: Example of a Chipped Blade C-1 Figure 3: Example of a Cracked Blade C-2 Figure 4: Example of Curled Blades C-2 Figure 5: Example of a Dented Blade C-3 Figure 6: Example of Blades with Deposits C-3 Figure 7: Example of a Distorted Blade C-4 Figure 8: Example of a Gouged Blade C-4 Figure 9: Example of a Nicked Blade C-5 Figure 10: Example of a Blade with a Piece Out C-5 Figure 11: Example of a Pitted Blade C-6 Figure 12: Example of a Torn Blade C-6

Annex D Figure 1: Bird Hazard Bulletin D-4

Foreword Fatigue is a type of failure that occurs in components subjected to repeated loading. Fatigue failure can occur through crack initiation and growth, void coalescence or a combination of the two. High Cycle Fatigue (HCF) refers generally to those failures that occur due to lower levels of cyclic loading at typically higher frequency. HCF has been identified as a major maintenance problem in fielded gas turbine engines and a primary concern for future engines. Low Cycle Fatigue (LCF) refers to fatigue failures that occur due to relatively high levels of loading. Depending on the material and component, HCF typically begins at between 105 and 107 cycles.

HCF failures can result from vibration, forced response, unsteady aerodynamic loads, or other fluctuating loads. Gas turbine engine rotor blades and stator vanes are subject to all of these types of loads and are particularly vulnerable to HCF failures. HCF failures have grown in severity to become a dominant and costly failure mode for gas turbine-based propulsion and power systems. A significant fraction of engine-caused aircraft mishaps are due to HCF, but a cost and maintenance penalty is caused by the removal of engines due to foreign object damage (FOD) to the engine compression system airfoils, to prevent FOD-induced HCF mishaps. FOD-induced HCF has caused a significant increase in the financial burden of NATO military forces due to loss of aircraft and large increases in maintenance and logistics workload for all types of gas turbine engine-powered vehicles and systems that operate on land, sea, space or air. The total HCF impact has been to decrease operational readiness and increase weapon system support costs.

HCF is not unique to military products. The HCF problem affects products for the civil market, and HCF technologies are being widely researched by a number of universities, companies and nations for application to a broad spectrum of propulsion and power generation systems, and this effort needs to be assessed and evaluated.

HCF failures in military applications are generally the most difficult to understand and prevent. In the air, the military pilot is free to employ unrestricted flight tactics throughout the aircraft’s certified flight envelope. Many such tactics give rise to distorted engine inlet flow and pressure pulses that can cause component HCF failures. Further compounding the “air” HCF problem, but also encompassing “land”, “sea”, and “space” operational HCF problems, are operators’ constant throttle motion that gives rise to repeated high mechanical stress and vibration. The HCF problem is made worse by the ever-present risk of FOD to system components, which limits their structural integrity, and in turn, lessens the design’s resistance to HCF.

The benefit in understanding FOD-induced HCF, and mitigating or controlling its occurrence, will be to significantly improve the operational safety, readiness, and life cycle cost of the air-, sea-, space- and ground-based gas turbine engines of NATO nations.

As stated in the Terms of Reference (TOR, ref. Annex G), the purpose of this report is to provide a common understanding for the mitigation and control of FOD-induced HCF in gas turbine engine compression system airfoils, including providing advice to NATO nations on how best to focus their efforts to monitor and mitigate these problems. Although the current task is related to compressor airfoils, it should be noted that HCF is not exclusive to these components. HCF in other engine components introduces additional issues (e.g., forced response, mistuning, lack of adequate damping, operating temperature, oxidation, corrosion, coating integrity, single crystal orientation, etc.) which have not been covered in this document.

xviii RTO-TR-AVT-094

Task Group Members

CHAIRMEN

CHAIR Richard J Hill Sr Prog Mgr, Engineering Div Universal Technologies Corp 1270 North Fairfield Rd. Dayton, OH 45432-2600 UNITED STATES

Phone: +1 937 426-2808 x286 Fax: +1 937 426-7753

e-mail: [email protected]

CO-CHAIR Flt Lt John Franklin PSG-FLPT, L Block RAF Wyton Huntingdon Cambridgeshire, PE28 2EA UNITED KINGDOM

Phone: +44 1480 52451 x6393 Fax: +44 1480 446565


NATION LEAD MEMBERS

BELGIUM Dr Patrick Hendrick Applied Mechanics Dept. Royal Military Academy of Belgium Renaissance Avenue 30 1000 Brussels

Phone: +32 2 737 65 56 Fax: +32 2 737 65 47


CANADA Dr Wieslaw Beres Institute for Aerospace Research National Research Council Canada 1500 Montreal Road, Building M-7 Ottawa, Ontario, K1A 0R6

Phone: +1 613 993-0033 Fax: +1 613 990-7444


FRANCE Eric Seinturier SNECMA Moteurs Design Method Department Division Mecanique – Batiment 7D Site de Villaroche – BP 42 77552 Moissy-Cramayel Cedex

Phone: +33 1 60 59 82 44 Fax: +33 1 60 59 80 25


GERMANY Dr Joerg Frischbier MTU Aero Engines GmbH Dept. TPMS PO Box 50 06 40 Dachauer Str. 665 80976 Muenchen

Phone: +49 89 1489 4758 Fax: +49 89 1489 6261


RTO-TR-AVT-094 xix

mailto:[email protected]






GREECE Capt Eftychios Kleinakis H.A.F. Centre of Applied Technology Terma Mikras Asias str 165 62 GLYFADA Athens

Phone: +30 210 8934122 Fax: +30 210 9621333

e-mail: [email protected], or [email protected]

THE NETHERLANDS Gerrit Kool Voorsterweg 31 8316 PR Marknesse P.O. Box 153 8300 AD Emmeloord

Phone: +31 527 24 8290/8286 Fax: +31 527 24 8210


UNITED STATES Daniel Thomson ASC/LP 2145 Monahan Way Wright-Patterson AFB OH 45433-7017

Phone: +1 937 255-4056 x3254 Fax: +1 937 255-2660


MEMBERS

UNITED KINGDOM Sqn Ldr Hugh Graham L Block RAF Wyton Huntingdon Cambridgeshire, PE28 2EA Now Retired

UNITED KINGDOM Prof George Harrison QinetiQ Ively Road Farnborough Hampshire, GU14 0LX

Phone: +44 1252 397286 Fax: +44 1252 397298


UNITED KINGDOM Ian Stewart Rolls-Royce plc PO Box 31 Derby DE24 8BJ

Phone: +44 1332 249332 Fax: +44 1332 245672


UNITED STATES Sqn Ldr Richard Wade AFRL/PRTA 1950 Fifth Street, Bldg. 18 Wright-Patterson AFB OH 45433-7251

Phone: +1 937 255-2734 Fax: +1 937 255-0082


xx RTO-TR-AVT-094




UNITED STATES Dr Jeff Calcaterra AFRL/MLLM 2230 10th Street, Suite 1 Wright-Patterson AFB OH 45433-7817

Phone: +1 937 255-1360 Fax: +1 937 656-4840


UNITED STATES Charles Gorton Head, Propulsion Technology Office (AIR-4.4T)Naval Air Systems Command 22195 Elmer Road (Unit 4) Patuxent River, MD 20670-1534

Phone: +1 301 757-0450 Fax: +1 301 757-0534


UNITED STATES Sandra Hoff Deputy Commander Aviation Applied Technology Directorate US Army AMCOM, Building 401 Lee Blvd Fort Eustis, VA 23604-5577

Phone: +1 757 878-3507 Fax: +1 757 878-1323


UNITED STATES Glen Lazalier AEDC/SVT/TA0 877 Avenue E Arnold AFB TN 37389-5051

Phone: +1 931 454-5367 Fax: +1 931 454-5026


UNITED STATES John Warren Propulsion Structural Integrity & Life Management (AIR-4.4.7.2) Naval Air Systems Command 22195 Elmer Road (Unit 4) Patuxent River, MD 20670-1534

Phone: +1 301 757-0466 Fax: +1 301 757-0562


OBSERVERS

THE NETHERLANDS Dr Henk Kolkman Senior Materials Engineer National Aerospace Laboratory (NLR) Voorserweg 31, 8316 PR Marknesse P.O. Box 153, 8300 AD Emmeloord

Phone: +31 527 24 82 84 Fax: +31 527 24 82 10


UNITED KINGDOM Sqn Ldr Liz Downey PSG Futures, L Block RAF Wyton Huntingdon Cambridgeshire, PE28 2EA

Phone: +44 1480 52451 x8412 Fax: +44 1480 446565


RTO-TR-AVT-094 xxi




xxii RTO-TR-AVT-094

UNITED KINGDOM Paul Tranter QinetiQ Ively Road Farnborough Hampshire, GU14 0LX

Phone: +44 1252 39 7288 Fax: +44 1252 39 7298


UNITED STATES Dr Dennis Corbly GE Aircraft Engines Mail Stop A413 1 Neumann Way Cincinnati, OH 45215-6301

Phone: +1 513 243-5832 Fax: +1 513 243-8091


UNITED STATES Bob Morris Pratt & Whitney Mail Stop 163/07 400 Main Street East Hartford, CT 06108

Phone: +1 860 565-8653 Fax: +1 860 565-5494


UNITED STATES Vince Spanel ASC/ENFP 2530 Loop Drive West Bldg. 560 Wright-Patterson AFB, OH 45433

Phone: +1 937 255-8604 Fax: +1 937 656-4546


Report Contributors Chair:

Richard Hill – UTC (USA)

Co-Chair:

John Franklin – PSG, RAF Wyton (UK)

Secretary:

Charles Gorton – NAVAIR (USA)

Editor:

Richard Wade – AFRL, WPAFB (UK)

Lead Authors:

Chapter 1: John Warren – NAVAIR (USA)

Chapter 2: John Franklin – PSG, RAF Wyton (UK)

Chapter 3: Jeff Calcaterra – AFRL, WPAFB (USA)

Chapter 4: Eric Seinturier – SNECMA (FR)

Chapter 5: Wieslaw Beres – NRC (CA)

Chapter 6: Wieslaw Beres – NRC (CA)

Chapter 7: Richard Wade – AFRL, WPAFB (UK)

Annex A: Charles Gorton – NAVAIR (USA)

Annex B: John Warren – NAVAIR (USA)

Annex C: John Franklin – PSG, RAF Wyton (UK)

Annex D: Wieslaw Beres – NRC (CA)

Annex E: John Warren – NAVAIR (USA)

Annex F: John Warren – NAVAIR (USA)

Annex G: John Warren – NAVAIR (USA)

Specialists:

Fernand Alby – French Space Agency (FR)

Dennis Corbly – GE Aircraft Engines (USA)

Liz Downey – PSG, RAF Wyton (UK)

Chris Eady – PSG, RAF Wyton (UK)

Joerg Frischbier – MTU (GE)

Hugh Graham – PSG, RAF Wyton (UK)

RTO-TR-AVT-094 xxiii

xxiv RTO-TR-AVT-094

Specialists (cont’d):

George Harrison – QinetiQ (UK)

Patrick Hendrick – RMA (BE)

Sandra Hoff – US Army AMCOM (USA)

Eftychios Kleinakis – HAF (GR)

Henk Kolkman – NLR (NE)

Gerrit Kool – (NE)

Glen Lazalier – AEDC (USA)

Bob Morris – Pratt & Whitney (USA)

John Schofield – Rolls-Royce (UK)

Vince Spanel – ASC/ENFP, WPAFB (USA)

Ian Stewart – Rolls-Royce (UK)

Daniel Thomson – ASC/LP, WPAFB (USA)

Paul Tranter – QinetiQ (UK)

REPORT DOCUMENTATION PAGE

1. Recipient’s Reference 2. Originator’s References 3. Further Reference 4. Security Classificationof Document

RTO-TR-AVT-094 AC/323(AVT-094)TP/68

ISBN 92-837-1148-3 UNCLASSIFIED/ UNLIMITED

5. Originator Research and Technology Organisation North Atlantic Treaty Organisation BP 25, F-92201 Neuilly-sur-Seine Cedex, France

6. Title Best Practices for the Mitigation and Control of Foreign Object Damage-Induced High Cycle Fatigue in Gas Turbine Engine Compression System Airfoils

7. Presented at/Sponsored by

The RTO Applied Vehicle Technology Panel (AVT) Task Group-094.

8. Author(s)/Editor(s) 9. Date

Multiple June 2005

10. Author’s/Editor’s Address 11. Pages

Multiple 212

12. Distribution Statement

There are no restrictions on the distribution of this document. Information about the availability of this and other RTO unclassified publications is given on the back cover.

13. Keywords/Descriptors Aircraft maintenance Blade design Compressor blades Cyclic loads Damage Damage assessment Data acquisition Data bases

Data management Data mining Failure analysis Fatigue (materials) Fatigue life Foreign bodies Foreign Object Damage (FOD) Gas turbine engines

Hardening (materials) HCF (High Cycle Fatigue) Jet engine inlets Mathematical prediction Mechanical properties Shot peening Software development Standardization

14. Abstract

High Cycle Fatigue (HCF) failures are a dominant and costly failure mode for gas turbine-engines. Foreign Object Damage is one of the major contributing factors necessitating preventive engine repair to avoid consecutive HCF mishaps, causing operational readiness decrease and weapon system support costs increase. Best practices for NATO to deal with this FOD-HCF problem were developed as follows: Definition of FOD-HFC Issues; FOD Data Investigation; FOD Experimental and numerical Simulation; Method for FOD/HCF Interaction Evaluation; FOD/HCF Resistant Surface Treatments; and FOD Prevention.

This is supplemented by overviews on: FOD Terminology and Acronyms; Air, Land, Sea and Space FOD Issues; Engine Blade Damage Definitions; Soft-Body FOD Issues; Additional FOD Reference Materials/Websites; and Annex F – Member Nation Maintenance Personnel.

Some highlights are: a NATO-standard template which has been created supported by a developed list of common terminology and a pictorial representative damage guide. Safe maintenance procedures and design activity were defined. Blade design, traditionally based on material’s stress allowances and simple excitation avoidance, was improved by a simple and robust design methodology including the interaction between FOD and HCF on new blade designs. Effects of supplementary treatment of a component’s surface for reducing the effect of potential FOD. Some ways of FOD prevention following maintenance mishaps such as loss of tools or material are discussed. It is recommended that NATO member Nations use this document and its recommendations to analyse and improve their practice. Setting up a NATO FOD forum is recommended.

RTO-TR-AVT-094

RTO-TR-AVT-094

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