本文以有限元素法探討壓電複合樑之自由振動行為，討論壓電致動器之長度、位置和電壓對於複合樑之自然頻率以及振動模態的影響。以勁度效應作為理論基礎，探討壓電致動器對於複合樑結構之勁度所造成的影響，觀察系統自然頻率與振動模態的變化。結果顯示，當壓電致動器放置於系統高彎矩應力處時，其本身質量會造成勁度效應降低，而使得壓電致動器之作用下降。對於包含固定邊界條件之結構而言，壓電致動器之最佳放置位置，除了考慮彎矩應力與剪應力的分布情況外，更必須考量邊界與最大彎矩應力之相對關係。將總長度相同之壓電致動器分為多組，針對不同振動模態，放置於其高剪應力及邊界處，則可提升壓電致動器之效果，並維持振動模態之對稱性。

The effect of piezoelectric actuator on free vibration of composite beam structure was investigated by Finite Element Method. The influence of the length, location and input voltage of piezoelectric actuator on natural frequency and mode shape of composite beam was presented. Stiffening effect was adopted to investigate the variation of the stiffness of composite beam. The results show that the mass of piezoelectric actuators will decrease stiffening effect seriously if they are located on the position within high bending stress. The relationship between boundary and high bending stress area will affects the optimal location of piezoelectric actuator for the structure with clamped boundary. Separate one piezoelectric into several parts and then put them on the high shear stress area of the mode will be able to increase the effect of piezoelectric actuator and remain the symmetry of the mode shape.

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