Parameters Identification of Flexibly Supported Composite Plate Structures
|關鍵字:||複合材料;彈性常數;識别;自然頻率;composite material;material property;identify;natural frequency|
Due to their high strength/stiffness to weight ratios, the fiber reinforced composite materials have become important in weight-sensitive applications like aeronautical and aerospace industry as well as many other fields of modern technology to fabricate high performance structures. As well known, there are many methods for manufacturing laminated composite components and different manufacturing or curing processes may produce different mechanical properties for the components. And the composite plates in these structures are connected to other members using different joining methods. One popular way to analyze the mechanical behaviors of the composite plates is to consider the plates being supported at the boundary by equivalent elastic restraints. The attainment of the actual behavioral predictions of the flexibly supported composite plates, however, depends on the correctness of the system parameters such as the elastic constants of the plates and the spring constants of the elastic restraints at the plate boundaries. Therefore, the determination of realistic material and spring constants of laminated composite components has become an important topic of research. In this paper several methods are proposed for vibration analysis of elastically restrained rectangular symmetrically laminated composite thin or thick plates and the laminated composite sandwich plates. The methods are constructed based on the Rayleigh-Ritz method in which the deformation characteristic functions are expressed as the Legendre’s orthogonal polynomials. The displacement models of the thin or thick laminated composite plates and laminated sandwich plate are constructed on the basis of the classical laminate plate theory (CLPT) or the first-order shear deformation theory (FSDT) and the layer-wise linear displacement theory, respectively. Extremization of the functional, the total potential energy, with respect to the displacement coefficients leads to the eigenvalue problem. The solution of above equation gives the theoretical natural frequencies of flexibly supported composite plates. The Rayleigh-Ritz method is then used to study the free vibration of different kinds of plates with various supporting conditions such as thin laminated composite plates supported by strip-type elastic pads around the peripheries of the plates with or without center elastic supports, thin plates partially supported by edge elastic restraints, thick laminated composite plates partially supported by edge elastic restraints, and laminated sandwich composite plates supported by strip-type elastic pads around the peripheries of the plates. In this paper, a constrained minimization method is presented for the nondestructive parameters identification of flexibly supported composite plate structures. A frequency discrepancy function is established to measure the sum of the differences between the experimental and theoretical predictions of natural frequencies of the elastically restrained laminated composite plates. The use of a multi-start global minimization method to identify the elastic constants by making the frequency discrepancy function a global minimum, and a design variables normalization technique for expediting the convergence of the search of the global minimum. The accuracy and applications of the proposed method are demonstrated by means of several examples. The present method can be extended without difficultly to the material and spring constants identification of other types of structures.
|Appears in Collections:||Thesis|