Repair bonding

One issue with the GBS treatment (and silane-coupling treatments, in general) is that the performance can be highly dependent on processing conditions, especially hydrolysis and drying conditions. Nonetheless, process controls suitable for field application of bonded repair patches are possible. 

Bonded repair sizes, shapes and configurations vary greatly depending on the type of structure and size and location of damage. Typically the damaged area is removed and replacement details of like material and size are prepared to fit. Larger doublers and possibly triplers are installed over the replacement details to hold them in place and transfer load to them. Fig. 23 shows a typical bonded repair for a small damaged area on honeycomb bonded structure. 

The processes used to prepare and bond repair patches are more difficult... 

Most bonded repairs are cured using electric heat blankets and vacuum bags, shot bags or clamps for applying pressure. Programmable heat blanket controllers... 

Tip To avoid tensions in the repair bonding, repair under inflated conditions is recommended. 

The bonded repair can take the form of either an external patch, internal patch or a flush scarf or stepped repair as described in M1L-HDBK-17-3F 3. The internal patch usually is not an option due to accessibility. For simplicity the external lap is commonly used on internal component repairs such as bulkheads and inner skins. To maintain aerodynamic cleanliness and to minimise moment-induced failure modes, however, the flush scarf repair is preferred [1]. Furthermore, on composite control surfaces (flaps, ailerons etc.) which have critical mass balance limitations, the lighter weight flush scarf repair is often the only acceptable means of repair, but a high skill level and longer time is required to prepare the damaged area for repair. 

In summary, bonded repairs are the preferred approach for manufacturing repairs to both honeycomb sandwich and monolithic secondary stmcture. However, for the FAA and European Airworthiness and Safety Administration, the main reason for withholding certification of bonded repairs for primary structure is the lack of certainty over bond quality as it is not possible to assess strength and durability of bonded joints without destructive testing. 

Most repairs are basically designed as a joint to transfer load into and out of a patch. In the case of the bonded repair a simple method of determining the load sharing ratio... 

Baker AA, Jones R. Bonded repair of aircraft structures. Dordrecht Martinus Nijhoff 1998. 

Katnama KB, da Silva LFM, Young TM. Bonded repair of composite aircraft stmctures a review of scientific challenges and opportimities. Prog Aerosp Sci 2013 61 26-42. 

Chiu WK, Galea SC, Koss LL, Rajic N. Damage detection in bonded repairs using piezoceramics. Smart Mater Stmet 2000 9(4) 466—75. http //dx.doi.org/10.1088/0964-1726/9/4/309. 

A A Baker and R Jones, Bonded Repair of Aircraft Structure , Martinus Nijhoff, The Hague, 1988. 

The great diversity of on-site bonding repair situations, timber species and exposure conditions to deal with, structural adhesives and composites available are also a source of problems and challenges. 

Fig. 6.25. Upgrading a timber floor (courtesy Resin Bonded Repairs Ltd).

A. A. Baker and R. Jones, Bonded Repair of Aircraft Structures, Martinus Nijhoff Publishers, 1988. ISBN 90-247-3606-4. 

Temporary repairs on lightly loaded parts are sometimes made by drilling a pattern of holes through the panel at about 50 or 75 mm pitch in all directions, fitting spacers and then bonding and bolting plates on both sides. This may meet an immediate need to keep an aircraft flying, in which case it is justified, but it does mean a more extensive bonded repair at some later date. 

Composite parts Solid composite parts may be repaired by making carefully tapered scarf joints. Hot-bonded repairs are preferred provided that the surface is first adequately dried." Parts made from structural fibres, that is, carbon fibre, Kevlar or boron fibres and some glass-fibre parts require that each repair layer be of the same type as the original, or a direct equivalent, and laid up in the correct orientation. 

Xu Y, Leung C K Y, Tong P, Yi J and Lee S K L (2005), Interfacial debonding detection in bonded repair with a fiber optical interferometric sensor . Compos Sci Technol,... 

A cobalt accelerated, orthophthalic, filled paste for bonding, repair and filling. 

Rider Andrew N., Brack Narelle, and Gopalakrishn J. Surface treatments and adhesives for bonded repairs to high temperature carbon-bismaleimide composite structure. J. Adhes. Set Technol. 26 no. 7 (2012) 911-937. 

Bonded Repairs for Aircraft Structures Martinus NijhofT Publishers (1987)... 

Typical Use Marine. Bonding primed PVC foam and balsa core to Typical Use Automotive - panel bonding. Repairs, e.g. boat hulls. ... 

Vitralit 6164 1 part - base unknown Glass bonding. Repair UV -20/+120 368... 

Fiebig, J. W., Mazza, J. J., McKray, D. B. (2002). An ALC consideration of simple sol-gel preparations for improved durability of field and depot-level bonded repairs. Proceedings of the Aging Aircrcft Conference, 2002, Galaxy Scientific. 

Materials Used for Epoxy-Bonded Repair The epoxy resin used for epoxy-bonded mortar repairs (less than 40 mm depth) should be two component, 100 % solid type, meeting the requirements of specification ASTM C-881 (2010) for type III, grade 2 (medium viscosity), class B or C (depending on the ambient temperature). 

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