| This dissertation describes refinements and generalizations to a method (earlier developed by Ayorinde and Gibson, 1993 and 1995) for deriving the elastic constants of composite materials from resonance data obtained from the modal analysis of freely supported thick plates by using the Rayleigh's method with optimal chosen displacement expressions. It had been found that elastic constants identified from different sets of vibration modal data were not equally good. In this work, sensitivity analysis was automatically integrated into the procedure. The flexibility of using diagonally symmetric modes (in the case of isotropic square panels), omitted from previous models for thick plate study, was also provided. The accurate identification of elastic constants, i.e., the longitudinal and transverse Yong's moduli, the in-plane and transverse shear moduli, and especially the Poisson's ratio for the specially orthotropic and transverse isotropic materials, has been one of the most challenging points in this area of research. Attempt was made to refine the search procedure for these values. Example cases included isotropic (aluminum) and orthotropic (graphite/epoxy) composite plates, optimized Rayleigh's three-term displacement representations including those of the diagonal modes for the plates, and an analysis that also incorporated sensitivity analysis of the frequencies to each elastic constant. An effective, inexpensive and nondestructive technique for determining the elastic constants of composites was established based on the results. |
