Dynamic instability of delaminated composite plates subjected to in-plane harmonic loading

Abstract

Composite materials are increasingly used in aerospace, naval and high performance civil engineering structures high-strength-to weight, stiffness-to-weight ratio, corrosion resistance, and longer fatigue life and stealth characteristics. Structural elements subjected to in-plane periodic forces may lead to parametric resonance due to certain combinations of the values of load parameters. The instability may occur below the critical load of the structure under compressive loads over wide ranges of excitation frequencies. Several means of combating resonance such as damping and vibration isolation may be inadequate and sometimes dangerous with reverse results. The present work deals with the study of the parametric instability characteristics of delaminated cross ply composite plates subjected to periodic in-plane load. A first order shear deformation theory based on finite element model is developed for studying the instability region of mid plane delaminated composite plate.The boundaries of instability regions are obtained by using the Bolotin’s method and are represented in the non dimensional load amplitudeexcitation frequency plane. A detailed parametric investigation is carried out to study the influence of delamination area, number of layers, and degree of orthotropy, aspect ratio and static in plane load on the dynamic stability characteristics of delaminated cross ply plates. As expected, the natural frequencies and the critical buckling load of the plates decrease with increase in delamination size. Increase in delamination size also causes dynamic instability regions to be shifted to lower excitation frequencies.