Fabrication and axial compressive behavior of composite sandwich cylindrical shells with pyramidal lattice truss

We studied the mechanical response and failure of composite cylindrical shell with pyramidal truss cores under axial compression. We developed interlocking method and a hot press method to manufacture lightweight carbon fiber composite cylindrical shell with pyramidal truss constructions. For interlocking method, Firstly, longitudinal and transverse ribs will be mass produced by 7075 aluminum using wire cutting method. Both Longitudinal and transverse ribs will be assembled together to form core materials using interlocking method. Carbon fiber composite curved face sheets (170^o) for both outer and inner skins of cylindrical shells will be made by hot press method in the curved steel mould. The outer skin of cylindrical shell will be assembled with curved aluminium pyramidal truss cores using J 242-A adhesive bonding, and then, the inner skin of shell will be built from two parts. For hot press method, Single walled cylindrical shells with pyramidal truss cores were made by hot press method firstly and then sandwich-walled cylindrical shells were fabricated by attaching inner carbon fiber-reinforced composite facesheets. In the analytical part of the study, The possible failure modes in axial compression of a composite cylindrical shell with pyramidal truss cores are illustrated in the following: (i) Euler buckling (EB), (ii) Overall buckling (OB), (iii) Local buckling between reinforcements (CB) and (iv) face crushing (CC). The collapse of the cylindrical shell is generally dictated by one of the competing mechanisms that depend on the geometry of the shell and the mechanical properties of the face and core materials. Four different failure modes were considered and theoretical models were presented to estimate the collapse strength associated with each failure mode. In the experimental part of the work, we used the analytical estimates to fabricate sandwich cylindrical shell that would allow probing the several different failure regimes. The measured collapse loads were in reasonable agreement with the analytical predictions.