Dynamic characteristics and buckling strength of composite-repaired aluminum plates

Abstract

A dynamic finite-element model of a cracked aluminum plate repaired with a composite laminate is presented and the influence of cracks and debond of the repair laminate on the static strength and dynamic characteristics of the repaired structure are investigated. NASTRAN is used to develop a refined two-dimensional finite-element model that accounts for cracks in the aluminum plate, the debond of the repair laminate from the aluminum plate, and transverse shear deformations. The transverse shear effects are accounted for by using an energy-equivalent first-order shear-deformation theory derived from a new layerwise higher-order model of transverse shear deformations. Normal mode analysis shows that debond of the patch significantly reduces natural frequencies and changes the mode shapes of only the higher modes. Frequency response analysis shows that the debond of the patch causes a large change in the magnitudes and shapes of frequency response functions (FRFs) near the patch in the direction of the excitation. Moreover, linear buckling analysis shows that debond reduces the buckling load and may change the buckling mode shape. However, the critical size of debond that reduces the buckling load to a certain percentage of the healthy case is boundary-condition-dependent. Transverse shear deformations also reduce the natural frequencies, move the FRFs to the low-frequency range, and reduce the buckling loads, but they have no significant influence on mode shapes and the shape of the FRFs. This damage characterization study provides information useful for the design of composite repair patches and the development of health-monitoring systems using FRFs.