FREE VIBRATIONS OF THROUGH-THICKNESS REINFORCED DELAMINATED BEAMS

Abstract eng:
The dynamic behavior of laminated beam-type structures presenting delaminations is characterized by stiffness degradation, natural frequency shifts and opening modes during vibration. This paper investigates the influence of a through-thickness reinforcement on the natural frequencies of through-width delaminated beam. A model based on the theory of bending of beams is formulated where the reinforcements are modeled as a uniform distribution of linear springs able to react to longitudinal and transversal relative displacements between the surfaces of the delamination. The natural frequencies of a delaminated cantilever beam are predicted for different lengths of the delamination. The effectiveness of the through thickness reinforcement on the natural frequencies is demonstrated through the transition from damaged (unbridged) to intact beam values upon increasing the stiffness of the springs. An application of the model to a typical stitched carbon-epoxy laminate for aeronautical applications shows that low percentages of through-thickness reinforcements can substantially improve the dynamic response of delaminated beams.

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