含45度斜裂纹圆柱薄壳动态特性试验研究

EXPERIMENTAL STUDY ON VIBRATION CHRARCTERISTICS OF A CYLINDRICAL SHELL WITH A 45circ OBLIQUE CRACK

  • 摘要: 测量了含45度斜裂纹圆柱薄壳的固有频率并拍摄了相应的激光全息振型图. 实验表明斜裂纹比轴向和环向裂纹对壳体动态特性的影响更大,致使振型图发生了严重畸变而显得相当复杂,利用传统思路难以找到裂纹长度对壳体动态特性的影响规律. 为此,把裂纹周围的振动看作为一种独立的局部振动,从而把含斜裂纹壳体的各种复杂振型划分为3类:纯局部振动振型、纯原振动振型、局部振动和原振动耦合振型. 其中前两种振型的固有频率皆随裂纹的加长而降低,但对于耦合振型有时会出现``随裂纹加长频率反而升高的现象'',这是由于把壳体原振动的频率和局部振动的频率相混淆而产生的错觉.

     

    Abstract: The resonant frequencies and corresponding mode shapes ofsteel thin-wall cylinder shell samples each containing an obliquecrack are obtained by a laser holographic interferometry method.It is shown that the oblique cracks have a greateffect upon the vibration characteristics of the shells, with the mode shapes ofthe shell being changed very much and looking very complicated. A kind ofvibration appeared only in the local area round the crack which iscalled the partial vibration by this paper is discovered. The partialvibration, which is responsible for the complicated mode shapes, has resonant frequencies andmodes of vibration of its own. The vibration appeared in the entire shell iscalled the original whole vibration. In a similar way, the original wholevibration has the resonant frequencies and modes of vibration of its own.When the resonant frequencies of the partial vibration close to that of theoriginal whole vibration, the two kinds of vibrations will come together. Sothere are three kinds of vibration mode shapes: pure partial vibration modeshapes, pure original whole vibration mode shapes and the intercouplingvibration mode shapes in which partial vibration and original vibrationinteract with each other. The longer the crack is, the lower the resonantfrequencies of the pure partial vibration and pure original whole vibrationare, but the resonant frequencies of the intercoupling vibrationoccasionallyshows an inverse tendency, which is a phenomenon which may be confusedwith two kinds of the resonant frequencies.

     

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