K. Lee’s scientific contributions

The development of aircraft composite propeller blade is necessarily required because recently changing metal propeller to composite propeller is a global tendency due to the improvement of composite manufacture technique and good characteristics of composite materials. The complicated calculation was required at the stress analysis and the design because the aircraft propeller was in curved and twisted structure. Especially, in the case of composite propeller, the analytic method was almost impossible on account of anisotropic material properties. Therefore, the numerical analysis method must be used for the solution of the problem. In this study, structural design and analysis of the propeller blade for turboprop aircraft, which will be a high speed transportation system for the next generation, was performed. The propeller of turboprop shall have high strength to get the thrust to fly at high speed. The high stiffness and strength carbon/epoxy composite material was used for the major structure and skin-spar-foam sandwich structural type was adopted for improvement of lightness. As a design procedure for the present study, firstly the structural design load was estimated through investigation on aerodynamic load and then flanges of spars from major bending loads and the skin from shear loads were preliminarily sized using the netting rule. In order to investigate the structural safety and stability, stress analysis was performed by finite element analysis code MSC. NASTRAN. Finally, it is investigated that designed blade have high efficiency and structural safety to analyze of aerodynamic and structural design results.

This study is focusing on the low velocity impact damage evaluation and the external patch repair techniques of carbon/epoxy UD and fabric laminate adopted developing aircraft. The impact damages of composite laminates of the carbon/epoxy UD and fabric are simulated by the drop-weight type impact test equipment. 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 specimens are compared with the compressive strength test and analysis results of the undamaged specimens and the impact damaged specimens. Finally, through investigation of compressive strengths of the damaged specimens at different environmental conditions, the damage criteria for repairable design of both the impact damaged UD and fabric laminate structure are suggested.