Rectangular plates made of laminated composite material because of the advantageously high strength and stiffness to weight ratio are used frequently as structural component in various branches of engineering, chief of which are aerospace and marine engineering. Design concepts of these plates that lead to the increase in the buckling load can directly lower the structural cost and/or weight. The finite strip method is one of a number of procedures which can be used to solve the buckling problem of plate structures. In the present work the main concern is with the buckling behavior of plates with simply supported ends subjected to uni-axial pure compression loads. The solution is sought by implementing the higher order semi-analytical finite strip method which incorporates additional degrees of freedom for each nodal line by using Reddy's higher order plate theory. Therefore the current method is more universal in dealing with different plate thicknesses. In addition, in this semi-analytical finite strip method, all the displacements are postulated by the appropriate harmonic shape functions in the longitudinal direction and polynomial interpolation functions in the transverse direction. The solution is based on the concept of principle of minimum potential energy and an eigen-value analysis is subsequently carried out. From the presented results it can be concluded that the higher order semi-analytical finite strip method is very reliable for the preliminary design of composite plates especially in the case of buckling analysis of relatively thick plates.
The objective of this research is to evaluate the integrity of a composite bonded joint by simulating Lamb wave propagation using finite element methods. The structure of interest is composed of two stepped carbon fiber reinforced polymer plates bonded together by an adhesive film. Two different bonding conditions are examined for the joint: undamaged and damaged (with disbond). In the finite element model, an antisymmetric guided wave is excited by imposing an out-of-plane displacement on the surfaces and a spatial Fourier transform is performed before and after the bond line for extraction of reflection and transmission coefficients. For validation, experiments are also conducted using two colocalized rectangular piezoceramics for plane wave generation. A 3D laser Doppler vibrometer is employed for noncontact measurement of the in-plane and out-of-plane velocity. The results confirm the reflections from the steps' edges, and it is found that the level of reflection and transmission of the guided wave mode is different for undamaged and damaged joints. The antisymmetric mode in the pulse-echo configuration seems to be an efficient mode and strategy for disbond detection in composite repairs. The results verify that guided wave propagation is very effective for disbond detection in composite bonded joints and scarf repairs.
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