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Delamination is a major problem in multilayer composite structures and may be difficult to detect experimentally using the existing methods. Due to this reason the development of adequate models describing the phenomena arising in the delaminated part of the structure and development of effective methods for delamination detection are very important topics for the engineering practice. In this work a model of layered beam with delamination is developed. It is a variation of the model developed by Wang and Tong . In the present model the possibility of sliding between the sublaminates is taken into account and the additional damping due to delamination is introduced. The model allows the interaction and separation between the crack faces to be considered while the physically impossible interpenetration of the sublaminates is prevented by imposing special constraints. The Timoshenko beam theory is used to describe the beam motion. The beam is discretized in the spatial domain by the finite difference method and the obtained ordinary differential equations in the time domain are solved by an iteration procedure using the so-called Gears method. The model is verified by computation using the ABAQUS finite element code . The beam is modeled by using shell elements and cohesive surfaces are used to model the delamination.
The influence of the parameters of the model on the time history diagrams, Poincar/span> maps of the structure and the damage index based on the Poincarmaps  are studied. A typical disturbance in the Poincarmap of the beam due to the contact interaction between the sublaminates of the beam with delamination is shown on Fig.1.
The possibility of the Poincarmaps based damage index to identify the delamination was tested experimentally on beams having artificially introduced delamination. A high speed camera was used to register the response of the beam subjected to harmonic loading by a shaker. The displacements and velocity were measured in 10 specially marked nodes of the beam. The numerical and experimental results allow us to conclude that the proposed model of delamination is appropriate to describe this phenomenon. The damage index obtained by the time domain response of the beam is quite sensitive to the presence of delamination and it shows precisely the edge of the delamination in the direction of increasing displacements (see Fig. 2).
Fig. 1. Poincarmap of the response of the clamped-clamped beam subjected to harmonic loading at the center of the delaminated area. Black dots- healthy beam; Red dots beam with delamination. Fig. 2. Experimentally obtained damage index for a cantilever beam with delamination