Free vibration analysis of rotating pretwisted composite sandwich conical shells with multiple debonding in hygrothermal environment

This paper presents a finite element based method to study the influence of elevated temperature and moisture absorption on the free vibration behavior of rotating pretwisted sandwich conical shells consisting of two composite face-sheets and a synthetic foam core. The sandwich structure is assumed to contain single or multiple debonding present either in the face-sheets or at the interface between the face-sheets and core. The finite element formulation consists of an eight-noded isoparametric shell element having five degrees of freedom at each node. Lagrange's equation is employed to derive the governing equation for free vibration analysis at moderate rotational speeds while the multi-point constraint algorithm is used to model the debonding region present in the composite sandwich shells. Numerical results are presented to depict the effects twist angle, thickness ratio of core to face-sheets, rotational speed and single or multiple debonding on the natural frequency of the composite sandwich conical shells at elevated temperature and moisture concentration.