In this era of high capacity passenger aircrafts and high speed military aircrafts, ensuring their airworthiness after its designed life has been an engineering challenge. One of the aspects that includes the airworthiness cetification is the structural integrity. The demand to run aircrafts their designed life pose great engineering challenge.

Repairs and modifications are economic means of improving structural integrity. With the replacement cost skyrocketing, ensuring reliable structural integrity of aging aircrafts has been a topic of paramount interest. Damages in the aircrafts occur mainly due to fatigue, corrosion and accidents. Of these damages those due to fatigue accounts for majority. Damages due to fatigue begin with formation of fine cracks from regions of high stress. These cracks when left unattended can grow at alarmingly fast rates and can cause catastrophic failure. From safety considerations repairs are done to arrest/retard furthur crack growth.

This type of damages are repaired by rivetting a metallic doubler with/without removing the damaged portion. This method has been in use from the time of inception of the aircrafts. Though this method has been standardised, is not very effective for varoius reasons. The prime ones being
1. introduction of fresh sources of stress concentration
2. detection of crack-growth under the doubler becomes difficult
3. causes tremendous amount of stress altercation
4. serious stress-corrosion problems
5. causes addition of weight to weight sensitive structures:aircrafts
6. time consuming causing the aircraft to be heldup in the hanger
7. expensive interms of manhour cost and loss of aircraft.

The best alternative to this is the Bonded composite material patch repair. This necessarily invovles bonding of a composite material patch on the damaged area after a suitable surface treatment.

As a part of my research-work I have arrived at a simple design method to assess the size of the patch once the damage is known. Also In the experimental work we have evaluated the residual strength and fatigue life of the repaired specimens. Presently we are now working on the modelling of the repaired configuration for a full 3D FEA. Encouraging results have been achieved in this directions. At this stage we are on the verge of completion. It may take some time for the full result to be out.

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