Stability of delaminated composite plates using a higher order theory

A refined higher order shear deformation theory is used to investigate the instability associated with delaminated composite plates subject to dynamic loads. Both transverse shear and rotary inertia effects are taken into account. The theory is capable of modeling the displacement field above and bellow the delamination. All stress free boundary conditions at free surfaces as well as delaminated interfaces are satisfied by this theory. The procedure is implemented using the finite element method. Delamination is modeled as a multi-point constraint using the transformation matrix approach. The natural frequencies are computed and compared with three-dimensional NASTRAN results and available experimental data. The effect of delamination on the critical buckling load and the first two instability regions is investigated for various loading conditions and plate thickness. As expected, the natural frequencies and the critical buckling load of the delaminated plates decrease with increase in delamination length. Increase in delamination length also causes instability regions to be shifted to lower parametric resonance frequencies.