Effect of Structural Dynamics Characteristics on Damage Tolerance of Crabon Fiber Sandwich Panels

Abstract

The use of composite materials is rapidly growing in the construction of aerospace structures. Most of the aircraft parts made from composite materials, like wing skins, spoilers, fairings, and flight controls, are being used due to their reduced weight as compared to aluminum parts. New generation large commercial aircraft are being designed with all composite fuselage and wing structure. The main advantages of composites over conventional metallic materials are their high strength to weight ratio, corrosion resistance and tailored stiffness. Uni-directional composites have predominant mechanical properties in one direction and vary with the direction relative to the axis of structure. The aero-elastic properties, such as stiffness and dynamic stability, also depend on the stacking sequence of the plies. Fatigue and Damage Tolerance (F&DT) assessment of these advanced composite materials is an emerging field of research. In aircraft structural integrity analysis, the damage tolerance and fatigue life is investigated against a cyclic loading spectrum. The particular spectrum includes the stress/loading levels counted during a flight of certain duration. The occurrences of z-axis load factors ‘Nz’ may include higher gravitational acceleration ‘g’ levels. While maintaining a certain g level occurrence at higher angle of attack, wing structure vibrates with the amplitudes of its natural frequencies. The cyclic stress amplitudes of vibration depend upon the natural frequencies of vibrating structure, i.e. lower frequency gives higher amplitudes and vice versa. These fluctuating load amplitudes are superimposed on the higher ‘g’ level mean loads during fatigue analysis. These additional cycles are very critical in DTA studies.