Transient Behaviour and Impact Induced First-Ply Failure of Delaminated Composite Conical Shells

BackgroundDynamic behaviour of composite materials under impact is a severe concern as it results in premature failure of the structural components. Most of the damages arising due to impact are undetected by visual inspection; therefore prediction of impact response is very crucial.PurposeThe existence of delamination reduces the strength and stiffness of the composite structures and enhances the damage phenomenon. The critical impact velocity at which the first-ply failure (FPF) and the associated transient response is a major engineering concern and needs significant attention.MethodsA finite element method (FEM) based investigation is carried out to analyse the dynamic response of delaminated cantilever composite conical shell impacted centrally at random points by a spherical impactor. An eight-noded isoparametric shell element is used based on Mindlin's shallow shell theory. The indentation laws proposed by Hertz are used to evaluate the contact force, displacement and identification of the failure zones. Newmark's time-integration scheme is used to obtain the dynamic response of the impacted shell. The Tsai-Wu failure criterion which is the most general and consistent criterion for biaxial stresses is used to predict the critical velocity of impact for first-ply failure initiation in composite conical shells.ResultsResults include the effects of different parameters like size and number of delamination, aspect ratio, fibre-orientation angle and impact location on the dynamic behaviour of conical shell at maximum safe impact velocity beyond which first-ply failure will commence.ConclusionsOn increase of the aspect ratio, size and number of delamination, the contact force, shell displacement, impactor displacement and the critical velocity at which the FPF initiates are found to decrease. When the impact location moves from near fixed end to near the free end, the contact force, shell displacement, impactor displacement and impactor velocity decreases.