Study On Deformation Damage Identification Of Composite Structures Based On Modal Flexibility Curvature Matrix

Composite materials are widely used in aviation, aerospace and other fields. In the structure of composite materials, the matrix cracking and delamination are the main forms of damage, and damage does not appear on the outside surface of the structure, so it’s not easy to be observed. Therefore, it is very important to study the method of detecting the delamination damage of composite materials. Composite delamination will lead to changes of the material stiffness and flexibility matrix, changes of modal flexibility curvature based on model is an efficient detection method. The main contents of this paper are as follows:(1) Flexibility matrix of composite components were established based on vibration theory, take the shape of component into account, we found suitable method to calculate flexibility curvature matrix separately. The corresponding flexibility curvature matrix is applied to the different structures of the composite delaminated damage detection. The research shows that this method can be used to identify the location and size of the delaminated damage of the composite structures.(2) While considering the size, position and layer, lossess and delaminated composite beams are produced respectively. The modal vibration mode and the natural frequency of the structure were obtained by experimental method; The finite element software ANSYS were used to establish the model of the composite material which is corresponding to the experimental modal, and the modal parameters are obtained. After analysisng the experimental and simulation data we obtained the modal flexibility curvature matrix. Comparative study found that either single or multiple delaminated damage, the damage identification index, flexibility curvature matrix FDM can be used to accurately determine the size and location of the injury.(3) The finite element software ANSYS was used to establish the composite laminates and cylinders with single and multiple delaminated damage. The modal shift values and natural frequency data obtained by finite element analysis are substituted into the modal flexibility matrix formula, and finally we obtained the flexibility value of each node in composite laminates and cylinders. For the laminate, the vertical flexibility curvature matrix FC are considered as the damage identification index, the results show that the larger the area of the delamination, the more obvious the mutation of FC. For multiple damages, it was also detected that the mutation value of FC in the boundary layer is obviously higher than the middle layer regardless of damage size that is similar to single damage. For the laminated cylinders, the circumferential flexibility curvature matrix Fd and axial flexibility curvature FC were obtained by differentiating the flexibility curvature matrix twice circumferentially and axially respectively. Analysis results show that, the circumferential and axial flexibility curvature can accurately identify single and multiple delaminations. And relatively speaking, the mutation of the axial flexibility curvature FC at delaminated location is far greater than circumferential flexibility curvature Fd, so FC is easier to judge delaminations. But due to itself small mutation at the fixed end boundary, when damage occurs near the fixed end along axis direction, the axial flexibility curvature FC may cause misjudgment, in this case, we should use circumferential flexibility curvature Fd to identify damages.