항공기 복합재 구조의 저속 충격 손상 평가 및 유지 보수 기법 연구

Abstract

Recently, most aircraft structures use increasingly composite materials to reduce their weights. In Korea, the KPP, which is a small scale piston propeller general aviation aircraft, has been developed to establish a domestic certificate infrastructure and system through the BASA(Bilateral Aviation Safety Agreement) program by KAI(Korea Aerospace Industries, Ltd.) and KC-100 PMO(Project Managing Office). This KC-100 aircraft adopted the whole composite structure concept for an environmental friendly aircraft through low fuel consumption due to structure weight reduction as well as for a competitive aircraft market. However the carbon/epoxy composite structure, which is mainly used for this aircraft, is very weak against impact damage. Especially, the low velocity impact damage rather than the high velocity impact damage cannot be easily found during visual inspections. Thus the low speed impact damage of the composite structure has become an important issue in composite structure design. Because the composite not only is weak to external impact damage but also has a different repair method from existing metallic materials, the repair method for the impact damage of composite structure is very important for certification of developing aircraft. This work is focusing on the low velocity impact damage evaluation and the external patch repair techniques of the aircraft composite structure. The damage criteria are classified into five categories depending on the severity of damages for the damage tolerance design. The first category is the barely visible impact damage(BVID), and the second category is the visible impact damage(VID). Repair should be carried out from the second category. Thus the definition of the criteria for the VID category is important in structure design. In order to define the VID energy, this study produces impact damages with different impact energies in low velocity impact range, examines the visual finding possibility, and analyzes the decreasing tendency of compressive strength. The damaged specimens are repaired using the external patch repair method after removing the damaged area. The compressive strength test and analysis results of the repaired impact damaged specimens are compared with the compressive strength test and analysis results of the undamaged specimens and the impact damaged specimens. Finally, the strength recovery capability after repairing is investigated.