9 - Composite patch repair using natural fiber for aerospace applications, sustainable composites for aerospace applications

Abstract

This chapter highlights the advantages of patch repair using natural fiber in order to extend the life of the structurally significant parts of aircraft. Occasionally, fatigue cracks and damage are found to have developed along rivet holes and other highly stressed regions of aircraft. In order to extend the life of these aircraft, repairs should be made to arrest these cracks. Patch repair promotes an innovative repair technique, which can enhance the way in which aircraft are maintained. Such repairs generally have one of three objectives, which are crack enhancement, crack patching, or corrosion repair. Repair of cracked structures may be performed by bonding an external patch to the structure, to either halt or slow the crack growth. Materials that are used to repair the structure must be able to withstand the expected conditions in the damaged area. Natural fiber is one of the materials or composites that have the potential to be used in the composite approach for aircraft parts. Natural fibers offer both cost saving and a reduction in density compared to other fibers. Though the strength of natural fiber is not as great as glass, the specific properties are comparable and can be used as the patching component. Research has been done to examine the suitability of natural fiber kenaf (Hibiscus cannabinus) to be part of the potential material for patching repairs. The results obtained were analyzed in accordance with real applications, and the final properties were determined as to whether it satisfies the requirements for high strength and stiffness, fatigue, environmental durability, formability, and also the long-term durability of the patch. From the experimental results, the compressive strength for a kenaf patch repair panel is almost the same as an undamaged panel and a putty patch repair panel, at 230.08, 230.41, and 230.47GPa, respectively. Meanwhile, the tensile strength for a kenaf patch repair panel is slightly less than an undamaged panel, but higher than a putty patch repair panel, at 725.94, 874.07, and 672.68GPa, respectively. Hence, natural fiber materials have great potential to be used as patch repairs for composite parts. For a damage detection strategy for the repair, the use of piezoelectric (PZT) sensors for structural health monitoring (SHM) systems provided continuous active monitoring on the panels. The specimens with bonded PZT sensors were subjected to mechanical testing. An on-line and active SHM monitoring was carried out during the compression and tensile testing. During this active testing, the specimens showed different wave patterns from the elastic region to the specimen failure. A repaired specimen showed the same signal behavior as the undamaged specimen. This is important, since a new baseline for detecting new damage needs to be established for the new monitoring to take place.