BEng MSc CEng MIMechE. Cascade Aerospace

Transcription

1 The Meaning of Life Jamie Johnson BEng MSc CEng MIMechE C-130 Program Director Cascade Aerospace

2 Scope Concept of fatigue Regulations & fatigue management Usage monitoring Fatigue testing Damage patterns Options

3 Structural Fatigue Degradation of strength & stiffness of a structure as a result of repeated application of loads during in-service operations

4 Fatigue Due to load cycles rather than steady state loads Rate of load application not important Damaging loads can be much less than static limit loads Fatigue damage is cumulative

5 Fatigue Damaged item may retain original static strength until: Local stress concentration causes crack to grow rapidly Crack causes significant loss in area

6 Fatigue Fatigue exhibits scatter Failure of a given component under a given load will not always occur at the same time Distribution tends to be Log Normal

7 Fatigue Local Cracks Single cracks appearing at areas of local stress concentration Behaviour can be observed from test or predicted analytically ll If crack location is known then it can be inspected for [or part replaced] Effect on structural integrity can be analysed

8 Fatigue Widespread Fatigue Damage (WFD) Multiple cracks appearing at numerous locations Behaviour can be observed in tests, but is almost impossible to predict analytically Cracks can interact such that small flaws can become critical rapidly Effect on structural integrity can be equally difficult to predict

9 Regulations & Fatigue Management Regulations applied to prevent local cracks becoming critical & to retire aircraft before the occurrence of WFD Fatigue Management policies generally based on Full Scale Test (FST)

10 Regulations & Fatigue Management Safe Life based on retiring aircraft/components before a significant probability of WFD exists Valid up to 1/3 Test Life

11 Regulations & Fatigue Management Damage Tolerance: an inspection-based method of finding cracks before they become critical Initial Inspection based on half the time for initial flaw (a i ) to grow to critical crack length (a CR ) Repeat Inspection based on half Initial or half the time for a detectable crack k( (a NDI ) to become critical i (whichever is least)

12 Regulations & Fatigue Management

13 Regulations & Fatigue Management

14 Regulations & Fatigue Management

15 FAA Limits AD Centre Wing Inspection 40K AFH repeat 10K AFH Rule $ WFD LOV 50K AFH/20K Cycles

16 Military Usage Mission by Mission; Usage is defined in Equivalent Baseline Hours (EBH) EBH = Airframe Hours (AFH) x Severity Factor (SF) Flight by Flight

17 Usage; Flight by Flight Measured Flight Data Crack Growth Algorithm Inspections

18 Usage; Mission by Mission Sample Flight Data Define Mission Profiles Define Mission Mix Single Mission Usage Mixed Usage Baseline Mission Crack Growth SEVERITY FACTOR Baseline Crack Growth Inspections

19 Usage Severity Factor dependant on; Take Off Weight Altitude GAG Cycles (Mission Length) [Airspeed] [Environment] [Manoeuvre]

20 Usage Mission Type Utilization AFH Severity EBH % Factor Long Range Logistics 50 8, ,000 Short Range Logistics 25 4, ,000 Long Range Tactical ca , ,000 Short Range Tactical , ,000 Total , ,000

21 Usage LM/USAF Baseline becoming C-130 standard SB Wing Operational Usage & Service Life Assessment Full LM Usage Assessment (or DaDTA)

22 USAF Wing Durability Test Conducted by Lockheed Martin on behalf of USAF: Tip to tip B/E/H center wing H84 outer wing USAF spectrum

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24 Economic Life As aircraft ages more cracks are likely to occur: More inspections More rectification Higher costs Lower availability

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27 Options Inspect Rework Refurbish Replace

28 Inspections Aim to detect smallest flaw possible; in order to gain largest interval Best techniques are most intrusive Practical limitations on how many repeat inspections can be carried out LoV provides backstop

29 Rework Rework or replace elements where localized cracking is known to occur: Reduces future inspection and maintenance burden Reduces probability of major repairs Increases availability Does NOT increase Service Life Improvement factors not recognized by all certification agencies

30 WASP Wing Availability & Sustainment Program (WASP) SB82-771: recommends rainbow fitting replacement at or before 25,000 EBH

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32 Refurbish Replace all fatigue-prone structure (up to 90%) Assembly techniques and processes are critical Final product has to certified and given Service Life NRE is significant; low volume costs will approach or exceed replacement assemblies or aircraft

33 Replace New center wings in production Incremental design improvement incorporated Extended Service Life wing Installation process and equipment defined Reduced NRE OEM-certified product Used aircraft and structural assemblies readily available

34 Replace

35 Case Study Lower Fwd dspar Cap Splice Tee Engine Mount Truss Lower Cap AL Web VIEW LOOKING AFT - LH CWS L Steel Web CWS L

36 Summary Structural Fatigue principle driver of Service of Life Usage Evaluation critical for comparison Rework activities preventative measure against significant repairs

37 Questions?