GLARE teardowns from the MegaLiner Barrel (MLB) fatigue test R.J.H. Wanhill, D.J. Platenkamp, T. Hattenberg A.F. Bosch and P.H. de Haan ICAF 2009, Rotterdam, the Netherlands, May 2009 Nationaal Lucht- en Ruimtevaartlaboratorium – National Aerospace Laboratory NLR
GLARE: Generic illustration of GLAss REinforced aluminium laminate ICAF, Rotterdam, the Netherlands, May 2009 2
GLARE: commercially available examples � All based on aluminium alloy 2024-T3 and high strength S2 silica glass fibres Prepreg lay-up Prepreg Typical applications Type between two layer Al layers thickness Unidirectionally loaded parts with RD-Al* in loading direction 0° / 0° 0.25 mm GLARE 2A (stiffeners) Unidirectionally loaded parts with RD-Al* perpendicular to 90° / 90° 0.25 mm GLARE 2B loading direction (butt straps) Bi-axially loaded parts with ratio 1:1 of principal stresses 0° / 90° 0.25 mm GLARE 3 (fuselage skins, bulkheads) Bi-axially loaded parts with ratio 2:1 of principal stresses with 0° / 90° / 0° 0.375 mm GLARE 4A RD-Al* in main loading direction (fuselage skins) Bi-axially loaded parts with ratio 2:1 of principal stresses with 90° / 0° / 90° 0.375 mm GLARE 4B RD-Al* perpendicular to main loading direction (fuselage skins) 0° / 90° / 90° / 0° 0.5 mm Impact-critical areas (floors and cargo liners) GLARE 5 *RD = Rolling Direction for aluminium layers ICAF, Rotterdam, the Netherlands, May 2009 3
GLARE: standard notation examples GLARE 2B – 7/6 – 0.4 each aluminium layer 0.4 mm thick numbers of aluminium (7) and interleaved prepreg (6) layers type of GLARE, see slide 3 (butt straps) GLARE 4A – 5/4 – 0.4 each aluminium layer 0.4 mm thick numbers of aluminium (5) and interleaved prepreg (4) layers type of GLARE, see slide 3 (fuselage skins) ICAF, Rotterdam, the Netherlands, May 2009 4
General objectives of GLARE teardowns from MLB fatigue test � Verification of teardown capabilities � Crack locations and shapes � Fatigue “initiation” and crack growth behaviour � Provide data to check GLARE crack growth models ICAF, Rotterdam, the Netherlands, May 2009 5
Airbus MLB fatigue test article � 45,402 simulated flights with conservatively high fatigue loads ICAF, Rotterdam, the Netherlands, May 2009 6
“Opened out” MLB view with GLARE teardown locations ICAF, Rotterdam, the Netherlands, May 2009 7
F4 GLARE window area � Skin + one window area doubler: GLARE 3–7/6–0.3/0.4 7 2024-T3 layers ICAF, Rotterdam, the Netherlands, May 2009 8
F4 teardown procedure � NDI fastener holes ● Fastener removal; eddy current rotor inspection ● Window frame removal; eddy current pencil probe inspection of GLARE skin and Al window frame � Optical fractography ● NDI-indicated cracked holes opened up and mapped � Field Emission Gun Scanning Electron Microscope (FEG-SEM) fractography ● Largest fatigue cracks in either window frame and GLARE skin ICAF, Rotterdam, the Netherlands, May 2009 9
F4 largest fatigue crack locations (window C65-C66) GLARE skin aluminium window frame • largest crack(s) 0.91–0.95 mm • largest crack 2.3 mm × 1.7 mm � More crack indications in GLARE, see slide 11 � Most cracks in fastener hole bores rather than countersinks: influence of secondary bending, see slide 12 ICAF, Rotterdam, the Netherlands, May 2009 10
NDI verification and analysis � Fastener hole fatigue cracks Al window frame GLARE skin • Area C64–C65 5 19 • Area C65–C66 3 22 � Statistics for GLARE skin fatigue cracks • 4 false calls for 216 inspected holes • Mean POD curve: - for 90% probability +50% confidence level the detectable crack length is 0.25 mm, i.e. most cracks in GLARE will be detected during complete teardown ICAF, Rotterdam, the Netherlands, May 2009 11
F4 fatigue crack shapes and largest cracks GLARE skin largest “readable” crack: 0.91 mm Al 7175-T73 window frame fretting scar fatigue origin 0.2 mm 0.5 mm ICAF, Rotterdam, the Netherlands, May 2009 12
F4 fractographic analysis (FEG-SEM) � “Readability” of MLB load spectrum (not derived to provide crack growth markers) ● largest window frame crack � Fatigue “initiation” lives and crack growth behaviour ● largest window frame crack ● largest “readable” GLARE skin crack � Comparison of GLARE skin and window frame cracking N.B.: Largest “readable” GLARE crack too small to check GLARE fatigue crack growth models: < 1 mm length, see slide 12 ICAF, Rotterdam, the Netherlands, May 2009 13
MLB load spectrum “readability” at F4 location: window frame crack � Repeated blocks of 2150 simulated flights � 8 basic flight types C C B C � Identifiable patterns due to peak loads in severest flights A (A, B, C ) � Conclusion: good “readability” ICAF, Rotterdam, the Netherlands, May 2009 14
Fractographic analysis of largest window frame crack � Fretting scar at fatigue origin � Persistent retardation beginning explains effectively zero at a*=0.6 mm could be due to “initiation” life and the termination of the well-known indication of an initial crack size “short crack effect” ICAF, Rotterdam, the Netherlands, May 2009 15
Fractographic analysis of largest readable GLARE aluminium layer crack � Back-extrapolation of � da/dN “plateaux”: GLARE at a versus N unfeasible about 50% of plateau for window frame crack ICAF, Rotterdam, the Netherlands, May 2009 16
F4 GLARE window area summary � Complete teardown enabled NDI detection of 0.25 mm cracks in GLARE with 90% probability and 50% confidence � Crack shapes and distributions in window frames and GLARE skin indicate local secondary bending � Fractographic “readability” of MLB fatigue load spectrum was excellent for largest window frame crack ● Fatigue “initiation” life ~ 0, owing to fretting between fastener and hole � Fractographic “readability” was less for largest GLARE crack, owing to much lower growth rates ICAF, Rotterdam, the Netherlands, May 2009 17
F7 GLARE door beam area (detail) failure location of rectangular sample � Beam: GLARE 3–9/8–0.4 skin + seven doublers 34 2024-T3 layers ICAF, Rotterdam, the Netherlands, May 2009 18
F7 teardown procedure � NDI fastener holes (Airbus Deutschland) ● fastener removal; eddy current rotor inspection ● largest crack indication 7 mm, at fastener hole 33 � Rectangular sample removed and pulled to failure (see also slide 18) ● breaking load exceeded Limit Load requirement � Optical and FEG-SEM examination ● fractography of fastener hole 33 failure ● fastener hole bores 31–35 ICAF, Rotterdam, the Netherlands, May 2009 19
F7 fastener hole 33 optical fractography largest fatigue crack 6.55 mm � Crack shapes show influence of secondary bending owing to pressurization-induced bulging of door cut-out area ICAF, Rotterdam, the Netherlands, May 2009 20
F7 fastener hole 33 fractographic analysis (FEG-SEM): I � Uniformly spaced fatigue striations � Conclusion: predominance of pressurization loads at F7 location: but see slide 22 for minor influence of severe simulated flights 2 μ m ● crack length 6.55 mm ICAF, Rotterdam, the Netherlands, May 2009 21
F7 fastener hole 33 fractographic analysis (FEG-SEM): II � Comparison of crack growth � Poor hole quality explains rates for the F4 and F7 locations. effectively zero “initiation” Note effectively constant da/dN life: corrected trend line for door beam crack. This is compensates for minor encouraging for GLARE crack influence of severe simulated growth models flights ICAF, Rotterdam, the Netherlands, May 2009 22
F7 fasteners hole bores: fatigue and hole quality: hole 34 severe cracking ● glass fibre layers starting to protrude and crack 500 μ m 500 μ m less severe cracking ● fatigue crack “initiation” often at aluminium layer corners ● occasional heavy scoring on aluminium surfaces leading to crack “initiation” away from 200 μ m 200 μ m corners ICAF, Rotterdam, the Netherlands, May 2009 23
F7 GLARE door beam area summary � Breaking load of rectangular sample > Limit Load despite fatigue cracks at several fastener holes � Largest crack NDI-indication, 7 mm, close to actual crack length, 6.55 mm � Fractographic “readability” excellent for largest crack ● Fatigue “initiation” life ~ 0, owing to poor hole quality ● Effectively constant fatigue crack growth rate ICAF, Rotterdam, the Netherlands, May 2009 24
F6 GLARE stringer coupling area (schematic) � Stringer coupling: 3 thicknesses of GLARE 2A–2/1–0.3 2 2024-T3 layers ICAF, Rotterdam, the Netherlands, May 2009 25
F6 teardown procedure: NDI only � Fastener removal and complete disassembly � Eddy current rotor inspection of fastener holes for skins, butt strap, stringers and stringer couplings � Eddy current pencil probe inspection of fastener hole faying surfaces (not possible for aluminium skin/stringer faying surfaces because adhesively bonded as well as mechanically fastened) ICAF, Rotterdam, the Netherlands, May 2009 26
F6 NDI-indicated crack classification � Many crack indications for GLARE components, but all < 4.5 mm � Aluminium stringers had longer cracks ICAF, Rotterdam, the Netherlands, May 2009 27
Recommend
More recommend
