Experimental Investigation of modal parameters of pre and post impact damaged composite laminates

Abstract

Composite materials are preferred over the traditional engineering materials due to their low density, high strength to weight ratio, have high flexural rigidity, fatigue resistance and excellent damping properties. Damping properties of laminated composites depend on the fiber orientation, stacking sequence, volume fraction etc. Every composite component is subjected to a host of different variety of loads, inducing a wide range of vibrations under different boundary conditions. The damping properties are affected in such conditions. In this paper, the modal properties of a bidirectional GFRP plate having unit aspect ratio are estimated using experimental modal analysis for F-F-F-F and C-F-F-F boundary conditions for pre and post impact damage scenarios. The damping ratio of the specimen for F-F-F-F boundary condition increases after induction of damage. For C-F-F-F boundary condition, however, damping ratio decreases as the mode number increases, reaches a minimum value for fifth mode and increases for higher modes. This particular damping behaviour of the material is very difficult to interpret and the mechanics involved in affecting the damping properties have to be revisited.