Delamination Buckling of Composite Conical Shells Under External Pressure

Abstract

Airframe construction in conical form is the most desired shape of flight hardware due to their low drag profile
and are located at the fore-end region of flight vehicles encountering high drag loads. Owing to their tailoring
capability, materials with orthotropic mechanical properties are preferred choice. Delamination defects formed in
them while manufacturing or when subjected to loads would unfavorably influence the mechanical performance
of the orthotropic airframe. In the current work, FE simulation of delamination which is embedded in orthotropic
cone shaped shells under external pressure load is performed as per the method cited in published literature. A layer wise element based on shell theory has been used and the effect of delamination size and its through the thickness position on the mechanical performance of the cone shaped shell is investigated. Circumferential and rectangular shapes of defects have been simulated. The investigation is performed for metal and composite materials with 3 types of stacking sequences generally used in practical designs. Verification of the procedure is carried out by equating with the procedure cited in published studies on shells of thin orthotropic cylinders. The eigen value of the first mode is taken as the critical buckling factor under external pressure. The buckling factor of the delaminated cone is normalized with the buckling factor of the ideal cone. The normalized buckling factor is showed graphically with the normalised defect size. Global, as well as local buckling and also symmetric as well as asymmetric buckling shapes, are observed in the results of the simulation. Shift from global mode to local mode of buckling is also observed in certain cases. Drastic reduction in buckling capability with the local mode is observed when the defect location is close to the surface and more prominent for an outer surface case.