Low Velocity Impact Performance of Delaminated Composite Stiffened Shell

Finite element method is presented to study the low velocity impact response of delaminated composite stiffened shell. An eight noded isoparametric shell element based on first order shear deformation theory along with a three noded isoparametric beam element are employed to model the shell and the stiffener, respectively. The stiffeners are placed along the nodal lines and the properties of the stiffeners at nodes are transferred to the corresponding nodes of the shell considering its curvature and eccentricity. The formulation adopted here employs constraint technique to calculate stiffness matrices of stiffener element placed inside shell element so that there is no further increase in the total number of degrees of freedom due to the stiffener. The modified Hertzian contact law is considered to compute the contact force, while the Newmark's time integration algorithm is used to solve the time dependent equations of both impactor and shell. The multi point constraint algorithm is used to model delamination at desired location of the shell. The compatibility of deformation and equilibrium of stress resultants are ensured at the delamination crack front. The effect of stiffener position, delamination and its location, and impactor's initial velocity on dynamic response of a particular stiffened shell are presented.