Natural frequencies of laminates during its progressive failure are investigated using finite element method. The finite element formulation is based on seven degrees of freedom displacement field, deduced for an orthotropic material. Free vibration analysis is carried out during ply-by-ply failure for a laminate subjected to uniformly distributed load. The variation of fundamental frequency with material and geometric properties is also presented. This study illustrates the effect of ply failure on the natural frequencies of a laminate. The prediction of failed ply and failure mode is accomplished via. Hashin failure criterion. Ply-discount material degradation model is adopted to modify the elastic constants of the failed ply. The effect of fibre orientation, failure mode and failed-ply on natural frequencies is highlighted in this paper. Jacobi iterative method is used to evaluate the natural frequencies of laminate. For the analysis, a computer code is written using FORTRAN based on the finite element formulation.

采用有限元方法研究了层合板在渐进破坏过程中的固有频率。有限元公式基于为正交异性材料推导出的七个自由度位移场。对于承受均匀分布载荷的层压板，在逐层破坏期间进行自由振动分析。还介绍了基频随材料和几何特性的变化。这项研究说明了层板破坏对层压板固有频率的影响。失效层的预测和失效模式通过来完成。Hashin破坏准则。采用层折材料退化模型来修改失效层的弹性常数。本文重点介绍了纤维取向，失效模式和失效层对固有频率的影响。Jacobi迭代法用于评估层压板的固有频率。为了进行分析，使用FORTRAN基于有限元公式编写了计算机代码。