Repair of metall structure with composite patches

Transcription

1 Repair of metall structure with composite patches Background Design philosophy and materials Processes Testing and evaluation Applications Conclusion 1 2 1

2 3 Repair of metall structure with composite patches This work has been financed by FMV, the Swedish Defence Administration. The aim is to get knowledge and understanding of the method and give practical guidelines to conduct composite patch repairs on metal structures. 4

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4 Restore strength and stiffness Reduce stress intensity Stiffen 7 Requirements on composite patch repair method. An adhesive bonding alternative to welding and riveting General method for a range of structure and materials. Method for field repair No dip method for surface treatment Reliable and repeatable Cost effective Minimized stress concentrations Environmentally friendly 8

5 Crack patch philosophy Restore strength and stiffness Reduce stress intensity Stiffen 9 Design philosophy and materials 10

6 Fundamentals for composite repair of metal structure Stiffness and strength of patch and adhesive Adhesion Long term environmental resistance 11 Design of process 12

7 Materials Fibre composites Carbon / epoxy Boron / epoxy (Glass / epoxy) Metal Aluminium Steel Titanium (Magnesium) Laminated metallic materials GLARE Aluminium-Fibreglass/Epoxy ARALL Aluminium-Aramide/Epoxy Adhesive Film Paste Primer Silane Epoxy/Phenolic with StrontiumChromate 13 Shear strength vs temperature for different epoxy adhesives Skjuvhållfasthet [Mpa] Temperatur [C ] 14

8 Fibres for crack patching 15 FE Analysis of strength and stiffness Strength Stiffness Thermal stresses New stress concentrations 16

9 Patch geometry Stiffness matching E p x T p ~ (1 to 2) x E x t Thermal matching α p ~ α Taper 1/18 Width > 1,2 x Crack length Major stiffness transverse to crack Taper~18 x t p E p, t p, α p E, t, α 17 Processes 18

10 Process Cleaning Abrasion Surface geometry Inspection of surface (Water break test) Drying Grit blasting Priming Patch fabrication Bonding Post control 19 Cleaning Cleaning using water and industrial detergent (Second cleaning with solvent (MEK)) Scrubbing with ScotchBrite Water break test 20

11 Water break test Indicate ability to wet the surface Show contamination 21 Grit blasting 22

12 Surface structure Abraded and grit blast aluminium surface 23 Application of primer Epoxy/Phenolic with StrontiumChromate Toxic Limited use Needs accurate application Very good environmental resistance Silane Low toxicity 99% distilled water Simple application Limited experience 24

13 Patch preparation and bonding 25 Bonded patch 26

14 Testing Quality and process control Estimate lifetime 27 Testing and qualification of method and operator Boeing wedge test Fracture surface examination Lap shear strength test Ultrasonic testing Coin tapping Micro Calorimetry to verify galvanic corrosion 28

15 Boeing Wedge Test (BWT) ASTM D mm 3,2 mm 19 mm Separator film Trim 25,4mm Adhesive Boeing wedge test (BWT) - ASTM D3762, test of adhesive joint in 50ºC, %RH Requirements Initial crack < 40mm Crack propagation after 24 h testing < 5 mm Crack propagation after 48 h testing < 6.5 mm 20 test coupons (4 panels) shall pass the test to secure the method 29 Boeing Wedge Test (BWT) Measure Initial crack 24 h ageing 48 h ageing Test environment 50ºC % RH 30

16 Visual results from BWT. BWT +50 C at 95%RH 70,00 65,00 60,00 55,00 Crack lenght 50,00 45,00 40,00 35,00 30,00 25, hours 31 Crack length with silane or BR127 primer 60,0 50,0 40,0 Crack length [mm] 30,0 BR127 JB82,311,312 BR127 JB264,314,315 BR Silane ,0 10,0 0, hours 32

17 Crack propagation with silane or BR127 primer Crack propagation 18,0 16,0 14,0 Crack propagation [mm] 12,0 10,0 8,0 6,0 BR127 JB82,311,312 BR127 JB264,314,315 BR Silane ,0 2,0 0, hours 33 Quality assurance by ultrasonic inspection 4 defects φ12 mm and φ6 mm 34

18 Ultrasonic resonance SonicBondmaster and XY-scanner 35 Galvanic corrosion Galvanic corrosion occur when: Galvanic potential between the materials Electrolyte is present Electric conduction between the materials 36

19 Test of galvanic corrosion using micro-calorimetry 37 Applications 38

20 C-130 Hercules fleet-wide application of composite patches on the C- 130 and C-141 metallic wings, making it possible to keep the aircraft flying when riveted repairs would have been ineffective, or possibly even harmful Dr. John Hart-Smith, McDonnel-Douglas Corporation 39 Wing spar SAAB 105 / SK 60 40

21 Wing leading edge SAAB 37 Viggen 41 Tripod leg RB56 42

22 HKP 4 Ramp Plate aft body 43 Ship deck Strain gauge 2 Strain gauge 1 (fore) 44

23 Wind mill for SAAB 37 Viggen 45 Wing spar for SAAB 37 Viggen 46

24 Conclusion Reliable and repeatable process for crack patching available Silane treatment have successfully replaced Epoxy / Phenolic / StrontiumChromate Primer Significant defects detected with NDT-methods for process and in-service control Cost effective Patch repair allows extended service life Environmentally friendly process Technology can be applied to high performance bonding 47 Mats Eklund Chelton Applied Composites AB +46 (0) mats.eklund@acab.se 48