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Domenico Furfari - Bonded Repair for Fuselage Damages - ICAF 2009, Rotterdam, The Netherlands
27-29 May 200925th ICAF Symposium – Rotterdam
Presented by
Domenico FurfariStructure Analysis Stress Methods & TechnologiesResearch & Technologies GroupAIRBUS
Bonded Repair for Fuselage Damages:An Overall Benefit to Commercial Aviation
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Acknowledgements
•N. Ohrloff & T. Beumler – Senior Experts Fatigue & Glare®, Structural Analysis, Airbus for their continuous guide throughout the project;
•A. Woerden – Materials & Corrosion Engineer, Shell Nederland Chemie B.V. major investigator at TU-Delft for this project;
•A. Kwakernaak – Director of the Adhesion Institute at Delft University of Technology, for his technical support throughout the project;
•R. Benedictus – Head of Aerospace Materials Group at Delft University of Technology, for his contribution in preparation of this work.
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Outline
• Introduction and Objectives
• Experimental WorksBonded Repair Manufacturing (“production” and “repair” environment)
Strain Gauge Locations (“Coupon”, “Small”/”Large” flat panels)
Curved Stiffened Panels – panel layout
• Test Results and DiscussionCoupon Specimens – strain survey and fatigue test results
Small Flat Panels – strain survey and fatigue test results
Large Flat Panels – strain survey and fatigue test results
Curved Stiffened Panels – strain survey and fatigue test results
• Conclusions
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Introduction and Objectives• Standard fuselage skin repairs (SRM) can be improved to extend the
inspection threshold and the interval• Fatigue test results of fastened repair solutions reported:
Furfari, D., Meyer, C., Lafly, A.L., Pramono, A., “Advanced Repair Design Principles to Improve Fatigue and Damage Tolerance Behavior of Fastened Repairs”, Proceedings of 24th ICAF Symposium, Naples, Italy, 2007.
• Objectives:F&DT of bonded repairs to aluminum fuselage skin
Influence on F&DT of adhesive types and “environment conditions”:– “’Cold” and “Hot” bonding
– “Production” environment (i.e. grit-blast silane, autoclave)
– “Repair” environment (i.e. SolGel®, vacuum bag and heat blanket)
Fatigue test ranged from coupon levels to curved stiffened panel (representing real aircraft fuselage panel)
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Test Programme Pyramid Approach
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Bonded Repair Manufacturing
• “Production” environment:Surface treatment: solvent cleaning, pickling in tank, phosphoric acid anodizing and cure;Surface pre-treatment:Grit-blast the surface, wet the surface with Silane solution, bonding primer, film adhesive application, autoclave curing;
• “Repair” environment:Surface treatment:solvent cleaning, pickling in tank, phosphoric acid anodizing and cure;Surface pre-treatment:removal of primer layer, SolGel® application, film adhesive, heat blanket, vacuum bag and cure;
Two adhesive systems used: “cold” bonding Vantico® 1590 and “hot bonding Cytec® FM73M.06
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Doubler Repair Manufacturing – “Repair” environment
Mechanically Abrade Surface
Apply SolGel (Bare Surface) Position Adhesive
Position Patch Position Thermocouples Vacuum Bag/Heat Blanket
Cure the Adhesive (front) Cure the Adhesive (back) Finished Panel
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Coupon Specimen Geometry – SG Locations• SGs “back to back” to
investigate the load transfer in different adhesively bonded coupons;
• No difference is expected from different surface pre-treatment;
• No difference is expected from different epoxy adhesives and different cure method used;
• Strains compared with baseline repair coupon at corresponding locations.
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Flat Panels (Small) – SG Locations
• Panel geometry: 1000mm x 500mm x 1.6mm; cut-out 110mm square;
• Strain gauge measurements for stepwise static load increases;
• SGs installed “back to back” for monitoring the secondary bending stresses around the bonded doubler.
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Curved Stiffened Panels – Panel Layout
• 1 Rosette; 15 X-Y and 76 single strain gauges
Driv
en R
ivet
Bas
elin
eSu
ppor
t Dou
bler
Hot
Bon
ding
Full
Load
Tra
nsfe
r
Rep
air C
orne
rs
Driv
en R
ivet
Bas
elin
eSu
ppor
t Dou
bler
Hot
Bon
ding
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Coupon Specimens
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Strain Survey – Coupon Specimens
Strain
Rem
ote
appl
ied
stre
ss
Hot bonded re pa ir
Cold bonded repa ir
Ba s e line re pa ir
SG1 (full symbol)SG5 (empty symbol)
Strain
Rem
ote
appl
ied
stre
ss
Hot bonded repa irCold bonde d repa irBas e line re pa ir
SG4 (full symbol)SG8 (empty symbol)
There is hardly any influence between the two adhesive systems;The secondary bending in both skin plates as well as in the doubler is significantly higher than in the base line riveted coupon;This shows that the epoxy adhesive connection is stiffer than fastened connection.
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0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0
76
57
47,5
σ am
plitu
de (
MPa
)
Fatigue Life Factor (normalized to riveted reference) ..
Riveted Reference, Al-AlHi-Lok,IFHi-Lok & Shim,IFHi-Lok,FP,CW,IFHi-Lok,CW,IFPAA,BR127,Gritblast-Silane,HB,RPAA,BR127,HB,PCAA,BR127,CB,PCAA,BR127,HB,RCAA,BR127,CB,RCAA,BR127,HB,P
IF=interference fit, FP=flap peening, CW=cold working, HB=hot bonded, CB=cold bonded, P=production, R=repair
Fatigue Life Factors – Coupon Specimens
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Test Results – Failure Modes
• Majority of specimens failed in skin plates (desired failure mode).
• Failure in doubler occurred only for 1 sample.
• Specimens with lives comparable to baseline showed adhesive / cohesive failure. Those specimens were manufactured following “repair procedure”.
“Skin failure” at the doubler run-out “Doubler failure” at the skin run-out
“Bond line failure”
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Small Flat Panels
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Strain Survey – Secondary Bending
7
6
Strain
Rem
ote
appl
ied
load
Scotch-Brite, Sol-Gel, Al Doubler
Grit blast, Silane, Glare Doubler
Baseline repair
SG6 (full symbol)SG7 (empty symbol)
15
16
Strain
Rem
ote
appl
ied
load
Scotch-Brite, Sol-Gel, Al DoublerGrit blast, Silane, Glare DoublerBaseline repair
SG15,SG16
SG15 (full symbol)SG16 (empty symbol)
10
9
Strain
Rem
ote
appl
ied
load
Scotch-Brite, Sol-Gel, Al DoublerGrit blast, Silane, Glare DoublerBaseline repair
SG9 (full symbol)SG10 (empty symbol)
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Text Matrix – Small Flat Panels
8 panels total
Production in TUD
Testing in Delft (500 kN machine)
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0,0 0,5 1,0 1,5 2,0 2,5 3,0
40,5
45
54
63
σ am
plitu
de (
MPa
)
Fatigue Life Factor (normalized to Baseline) ..
Riveted Reference, Al-AlHi-Lok,FP, IF, Al-AlHi-Lok,IF, Al-GlHi-Lok,FP, IF, Al-GlHi-Lok,IF, SD, Al-Al-AlScotch-Brite/SolGel,HB, R, Al-AlGritblast/Silane,HB, R, Al-Al taperedGritblast/Silane,HB, R, Al-GlScotch-Brite/SolGel,HB, R, Al-AlScotch-Brite/SolGel, HB, R, Al-Al
RUN OUT
IF=interference fit, FP=flap peening, SD=Support Doubler, HB=hot bonded, R=repair
Fatigue Test Results (Small Flat Panels)
Fatigue Life Factor (normalized to the riveted reference)
Concave (hollow doubler side)Concave but edge tapered
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Test Results – Failure Mode
• All specimens failed in skin plates (desired failure mode).• Anticipated initiation at doubler run-out near doubler corner fillet.• No cohesive or adhesive failures AT ALL.
“Skin failure” at the doubler run-out “Skin failure” at the doubler run-out
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Large Flat Panels
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Strain Survey at the Baseline Repair
• An increase of stress was monitored at the by-pass position;• Lowest stress at the repair doubler.
60
65
70
75
80
85
90
95
100
105
110
Strain Gauge Location
Stra
in G
auge
Rea
ding
(MPa
) SG1/2 (stress)SG5/6 (stress)SG7/8 (stress)SG9/10 (stress)SG11/12 (stress)SG13/14 (stress)
SG1/2
SG5/6 SG7/8 SG9/10 SG11/12
SG13/14
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Stresses at the Bonded Repair Solution
• By-pass stress comparable to far field stress;• Highest stress at the skin of the doubler corner.
60
65
70
75
80
85
90
95
100
105
110
Strain Gauge Location
Stra
in G
auge
Rea
ding
(MPa
) SG1/2 (stress)SG5/6 (stress)SG7/8 (stress)SG9/10 (stress)SG11/12 (stress)SG13/14 (stress)
SG1/2
SG5/6 SG7/8 SG9/10
SG11/12
SG13/14
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Fatigue Test Results
BL BL+FP SD Hi-Lok CB DR
Fatig
ue L
ife
Crack started from corner cut-out and stopped at first rivet;
No further crack detected; test suspended.R
UN
OU
T
Bon
ding
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Fatigue Test Results (Large Flat Panel)
• Failure Mode: Fatigue Crack in the Skin at the Corner Doubler• Similar Failure mode for all Small Flat Panels
Back View Front View
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Curved Stiffened Panels
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Fatigue Test Results (Curved Stiffened Panels)
• The applied fatigue loading was internal pressure (+10% increased ΔP) and longitudinal loading, simulating a similar in service conditions of an aircraft fuselage;
• In both curve panels no fatigue crack was detected in the bonded repair after a number of cycles correspondent to more than 2 times the fatigue life of the first fatigue crack detected in the baseline repair.
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Tear Down Inspection (Curved Stiffened Panels)
• No major debonding areas;• Small debonding at the frame
to skin attachment;• Adhesive not uniformly
distributed but no influence on fatigue.
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Conclusions• Coupon Specimens:
The hot bonded repairs increase the fatigue life more up to more than 4.5 times in respect to the baseline repair;
• Small Flat Panels:The bonded small flat panel solutions showed the amount of improvement of factor 2 or more, compared to the baseline solution;
• Large Flat Panels:The fatigue life improvement in this case has shown an improvement of more than 2 times the baseline repair;The benefit in fatigue life achievable with the coupon specimens cannot be obtained because of the different load transfer conditions between coupon specimens and the other specimen geometry;
• Curved Stiffened Panels:In both curve panels no fatigue crack was detected in the bonded repairafter a number of cycles correspondent to more than 2 times the fatigue life of the first fatigue crack detected in the baseline repair.
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Future Work Ongoing investigations
Bonded repair on thin shells, e.g. GLARE4A-2/1-.4
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Future Work – Shear Compression Test NLR
Shear fatigue buckling investigation with bonded repair patch(Dutch/Airbus Cooperation)• Tests at RT, elevated temperature
and negative temperature• Supported by FE
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Failure mode (static): failure of bondline
Load-displacements non-repaired / repaired
0
25
50
75
100
125
150
175
200
0 10 20 30 40Verschiebung s [mm]
Dru
ckkr
aft F
[kN
]
Repariertes Hautfeld Unrepariertes Hautfeld
(1) buckl. onset
(2) fatigue load
(3) failure(1)
(2)
(3)
Future Work – Shear Load Displacement
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