Repair of damage with composites by Vikas Gupta CDLSIET-Panniwala Mota

REPAIR OF DAMAGE REPAIR OF DAMAGE WITH COMPOSITESWITH COMPOSITES

Presented By:

Dr. Vikas GuptaMechanical Engineering Department

Ch. Devi Lal State Institute of Engineering and TechnologyPanniwala Mota, Sirsa-125055, India

Co-Authors

Dr. Prem PrakashEx-Scientist, DRDO, India

Dr. AK SharmaEx-Faculty, BRCMCET, India

CONTENTSCONTENTS

�Introduction

�Metallic vs. Composite Repair

�Methods of Damage Repair

�Facilities Needed for Repair�Facilities Needed for Repair

�Inspection & Testing Equipment

�Conclusion

2Dr. Vikas Gupta, MED, CDLSIET, PW

INTRODUCTIONINTRODUCTION

�Composites provide a very efficient and highly cost-effective method for repair of damage in aircraft structures.

�They have advantage of high specific strength �They have advantage of high specific strength and stiffness as well as ease in handling.

�Improve availability (turn round rate).

�Allow field level repair.


METALLIC vs. COMPOSITE METALLIC vs. COMPOSITE REPAIRREPAIR

Damage repair with metallic reinforce-ment:

�Damage identification.

�Dismantle / Dissemble.�Dismantle / Dissemble.

�Blanking off.

�Regular marking & removal of damaged area, smoothening the edges.


� Preparation of back and flush (reinforcement) plate as per shape and size.

� Picking up the optimum rivet holes.

� Apply leak proofing compound (Thycol).

� Gripping the assembly and complete the riveting by reaction riveting.

� Clean the surroundings.

� Apply protective coatings.

� Assemble the pipe lines etc.


DISADVANTAGES OF METALLIC DISADVANTAGES OF METALLIC REINFORCEMENTREINFORCEMENT

�Introduction of additional fastener holes increases the stress concentration further.

�Drilling in-situ has to be done carefully to avoid �Drilling in-situ has to be done carefully to avoid internal damages (e.g. to hydraulic lines and electrical wiring) which might leave swarf into the structure.


� Poor mechanical fastening may cause fretting damage, thus leading to fatigue cracks or high residual stresses causing stress-corrosion cracking.

� Metallic reinforcements may alter stress distribution significantly causing cracks in distribution significantly causing cracks in the area surrounding the repair.

� High down-time.


ADVANTAGES OF DAMAGE ADVANTAGES OF DAMAGE REPAIR WITH COMPOSITES REPAIR WITH COMPOSITES

�Adhesive bonding provides very efficient load transfer into the patch from the cracked component.

� It produces a sealed interface reducing the � It produces a sealed interface reducing the danger of crevice corrosion and internal leakage (say, from a fuel tank).

�Patch repair has only nominal weight since the composites are very light.


� For example, boron fiber reinforced plastic (with unidirectional fibers) is about six times stiffer than the stainless steel enabling the use of very thin patches.

� The turn round rate of the aircraft is enhanced enormously.enormously.

� Patch repair with composites offers the advantages of high directional stiffness, good resistance to fatigue and corrosion, and excellent formability.


METHODS OF DAMAGE REPAIRMETHODS OF DAMAGE REPAIR

� An ideal repair would restore the structural strength fully without any loss in functional capability and increase in weight of the aircraft.

� A flush patch repair is ideal from aerodynamic considerations. If external patch is unavoidable, a taper ratio of 50:1 is generally used at the outer ends of the bonded patches to ensure minimum ends of the bonded patches to ensure minimum disturbance to the air flow.

� The repair techniques can be broadly divided into two main categories:◦ Non-patch repair (for minor defects)◦ Patch repair (for major damages)


REPAIR TO MINOR DAMAGES / REPAIR TO MINOR DAMAGES / DEFECTSDEFECTS

INJECTION REPAIR

� It involves drilling of some injection and breeder holes up to the depth of the damage.

� Preheating the repair zone up to 650C.

� With air gun, pumping of resin until excess resin � With air gun, pumping of resin until excess resin flows from the adjacent holes.

� Sealing the holes with protective tape.

� To improve adhesion required pressure is applied.

� Post cure at 1500C.


INJECTION REPAIRINJECTION REPAIR

Resin Injection for Repair of Delaminations


FILLER/POTTING REPAIRFILLER/POTTING REPAIR

Potted Repair of a Damaged Honeycomb


FILLER/POTTING REPAIRFILLER/POTTING REPAIR

� Minor elongations of hole or wear damage may be repaired with a machinable potting compound.

� In a lightly loaded honeycomb panel, potting repair may be used to stabilize the skin and seal the damaged region.

� This repair involves removal of damaged skin and core, and then further undercutting the core to ensure mechanical entrapment of the potting compound.

� The resin in the potting compound is then cured at 150°C.


REPAIR OF MAJOR DAMAGESREPAIR OF MAJOR DAMAGES

Bonded Patch Repair with Shear Stress Distribution


BONDED EXTERNAL PATCH REPAIRBONDED EXTERNAL PATCH REPAIR

External and Flush Patch Repair


BONDED EXTERNAL PATCH REPAIRBONDED EXTERNAL PATCH REPAIR

External Patch Repair with Vacuum Bag


EXTERNAL BOLTED PATCH REPAIREXTERNAL BOLTED PATCH REPAIR

� This method of repair is adopted for damages in thick laminates (8-15mm) where the shear stress requirement exceeds the capability of the adhesive used for patch repair.

� It is also used when complexity of structure or material removal precludes the use of methods described earlier.


Damage repair with metallic reinforcement

External Bolted Patch Repair


�Bolted repair provides a transverse reinforcement with clamping pressure which prevents the spread of delaminations already present.

�The metal patch, nut-plate and fasteners of titanium alloys are preferred as they do of titanium alloys are preferred as they do not show galvanic corrosion.

�They have low thermal expansion.


Flush Patch RepairFlush Patch Repair

Flush Patch Repair with Vacuum Bag


FLUSH PATCH REPAIRFLUSH PATCH REPAIR

�This is a highly efficient method especially suitable for repair of damage in thick laminates. A smooth surface contour is obtained in this method.

�In flush repairs, removal of some �In flush repairs, removal of some undamaged material / portion may also be necessary to form a taper angle of about 18:1. A double scarf may be used instead of a single scarf in order to reduce the taper.


INSPECTION & TESTING INSPECTION & TESTING EQUIPMENTEQUIPMENT

�X-radiography, pulse echo ultrasonics, C-scan ultrasonic devices, environ-mental chamber, eddy current, thermo-graphy and shearography, acoustic emission shearography, acoustic emission and holography test equip-mentetc.


FACILITIES NEEDED FOR FACILITIES NEEDED FOR FIELD/DEPOT LEVEL REPAIRFIELD/DEPOT LEVEL REPAIR

Equipment for mechanical preparation of surface

� Tungsten Carbide tipped tools, end mill cutter, router, shims, sharp knife, grips to peel off plies, drill, grit blasting equipment, peel ply, corrosion drill, grit blasting equipment, peel ply, corrosion inhibiting primer, etchant etc. Basic Repair Materials� Fibers of boron, carbon, glass, graphite,

structural film adhesive (3M’s AF126), Phenolic epoxy, injection adhesive, resins, graphite / epoxy prepregs, storage facilities, potting compounds, glass cloth, Al-honeycomb etc.


CONCLUSIONCONCLUSION

� Very efficient and cost-effective methods are available for repair of damage to aircraft structures using advanced composites. The use of composites is bound to increase in the aircraft in future. It is therefore, advisable to establish field level repair facilities using advanced field level repair facilities using advanced composite materials. Such a facility would enhance the turn round rate of aircraft to a great extent. The existing personnel could be reoriented through short term training courses to undertake repair of damage to aircraft structures using composites.


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