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剪切位移荷载作用下,平面张拉薄膜经历缺陷、临界褶皱和宏观褶皱3种状态。该文依次分别对处于3种状态的薄膜进行自振特性分析,并明确了3种状态的划分原则。计入平面张拉薄膜的微小抗弯刚度,采用ANSYS/LS-DYNA中显式-隐式连续求解的方法对屈曲后薄膜的动力特性进行分析。依据忽略面外变形的理想模型自振特性分析结果,把平面张拉薄膜的振型划分为贯通振型和间断振型,贯通振型又划分为纵向贯通振型和横向贯通振型。研究结果表明:薄膜处于缺陷状态时,面外变形对薄膜自振特性的影响可以完全忽略,受主应力分布的影响,低阶振型中纵向贯通振型更易于出现,纵向贯通振型的波峰或波谷数量随着频率阶数的递增而规律递增。临界褶皱状态,薄膜的各阶频率均随剪切位移的增加而出现大幅波动,面外变形对薄膜振型的影响逐渐增大,横向贯通振型消失,纵向贯通振型的递增规律逐渐破坏;宏观褶皱状态,薄膜的各阶频率趋于稳定,其主应力分布及振型受面外变形的影响显著。
Under the action of shear displacement load, the plane tensioned film experiences three kinds of states: defect, critical fold and macro fold. The paper analyzes the natural vibration characteristics of three kinds of films in turn and clarifies the principle of the three states. The micro-bending stiffness of the plane-tensioned membrane was taken into account. The dynamic characteristics of the post-buckling membrane were analyzed by explicit-implicit continuous solution in ANSYS / LS-DYNA. Based on the analysis of the natural vibration characteristics of the ideal model which ignores the out-of plane deformation, the vibration modes of the plane tensioned membrane are divided into penetrating vibration modes and discontinuous vibration modes. The penetrating vibration modes are also divided into longitudinal penetrating vibration modes and transverse penetrating vibration modes. The results show that the influence of out-of-plane deformation on the self-vibration characteristics of thin films can be completely neglected when the film is in a defect state, and the vertical through-vibration modes are more likely to occur in the low-order modes due to the influence of the main stress distribution. Or the number of troughs increases regularly as the frequency order increases. In the critical wrinkle state, the frequency of each step of the film fluctuates sharply with the increase of shear displacement. The effect of out-of-plane deformation on the film vibration mode gradually increases and the transverse penetration mode disappears. The increasing regularity of the longitudinal through vibration mode gradually deteriorates. In the macroscopic fold state, the frequency of each step of the film tends to be stable, and the distribution of its principal stress and the mode shape are significantly affected by the out-of-plane deformation.