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Composite Structure Repair - Carbon Core (Thermoset Resin) Structure

Composite Structure Repair - Carbon Core (Thermoset Resin) Structure

Composite Structure Repair - Carbon Core (Thermoset Resin) Structure

Dear fellow engineers,

I hope everyone is keeping well and safe. I was recently looking at damage on a carbon core structure where the damage seems to be quite severe and would most likely lie outside of the SRM. Can you suggest a good reference or guide, which shares examples of failures of composite carbon fiber thermosetting structures and suggests industry-wide accepted repair schemes for them?


RE: Composite Structure Repair - Carbon Core (Thermoset Resin) Structure

One place to start is the very same aircraft (assuming this is an aircraft) manufacturer's repair schemes for other damage scenarios that exceeded SRM limits. If any other such repairs have been required in the past, then using that data, though not necessarily yours to use for approval, can be a good guide to see where to go with your own repair. You can't approve a repair by comparison, usually (you have to own the data, both in the sense of rights to data and understanding the method). The benefit of seeing the end result is knowing that you CAN get there, and many of the details of HOW to get there become clearer this way.

The FAA has done plenty research and published guidance to support the certification of composite structural repairs.

Found some:

DOT/FAA/AR-00/46 Repair of Composite Laminates (Office of Aviation Research, Washington, D.C. 20591)
AC 21-26 "Quality Control for the Manufacture of Composite Structures" [6/89]
AC 21-31 "Quality Control for the Manufacture of Non-Metallic Compartment Interior Components" [11/91]
AC 23-15A “Small Airplane Certification Compliance Program” [12/03]
AC 23-20 "Acceptance Guidance on Material Procurement and Process Specifications for Polymer Matrix Composite Systems" [9/03]
AC 25.571-1C “Damage Tolerance and Fatigue Evaluation of Structure” [4/98]
AC 29 MG 8 “Substantiation of Composite Rotorcraft Structure” [4/06]
AC 35.37-1A "Guidance Material for Fatigue Limit Tests and Composite Blade Fatigue Substantiation" [9/01]
AC 145-6 "Repair Stations for Composite and Bonded Aircraft Structure" [11/96]
EUROCAE ED-113 Aircraft Lightning Direct Effects Certification
FAA Technical Report “Aircraft Lightning Protection Handbook” (DOT/FAA/CT- 89/22).
FAA Policy Statement "Static Strength Substantiation of Composite Airplane Structure" [PS-ACE100-2001-006, December 2001]
FAA Policy Statement "Final Policy for Flammability Testing per 14 CFR Part 23, Sections 23.853, 23.855 and 23.1359" [PS-ACE100-2001-002, January 2002]
FAA Policy Statement “Material Qualification and Equivalency for Polymer Matrix Composite Material Systems" [PS-ACE100-2002-006, September 2003]
FAA Policy Statement “Bonded Joints and Structures - Technical Issues and Certification Considerations” [PS-ACE100-2005-10038, September 2005]


RE: Composite Structure Repair - Carbon Core (Thermoset Resin) Structure

Send detailed pictures of the damage to the manufacturer, and ask them for a repair schedule. They will tell you if the damage is repairable or whether you have to buy new components. Remember hidden damage is very hard to detect on carbon composites.

You are judged not by what you know, but by what you can do.

RE: Composite Structure Repair - Carbon Core (Thermoset Resin) Structure

as above … call the OEM. It is highly unlikely IMO that you'll ever be able to substantiate a repair.

the only chance you have is if this is a piece of secondary structure, where of course the consequences of failure are less critical and so the opportunity for "hand waving" presents itself. I'm not saying this is a good course of action, you'll still need an RDA (certification for your repair) and so convince someone else that your "hand waving" is "good enough" … not easy, but possibly not impossible.

can you scrap the part and get a new one ? Probably an OEM repair is the best option ?

another day in paradise, or is paradise one day closer ?

RE: Composite Structure Repair - Carbon Core (Thermoset Resin) Structure

Thanks for all your responses as it gives me a good steer on how to approach this problem!

RE: Composite Structure Repair - Carbon Core (Thermoset Resin) Structure

The source not covered is, talk to the guys in the composite repair shop you use, if they are any good they will most likely have seen something similar before and the repair scheme used.

RE: Composite Structure Repair - Carbon Core (Thermoset Resin) Structure

I'd suggest caution in following that suggestion … the guys doing the work may be able to suggest ways of doing it … certifying that repair is a different matter (if primary structure).

another day in paradise, or is paradise one day closer ?

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