A combined analytical and computational approach to the structural behavior of composite tubes

In this paper, we touch on the mechanical behavior of casing-infill composite tubes, as potential new lightweight structural elements. The axial and the torsional behavior of composite tubes of circular cross-section, comprising a casing and an infill, is addressed analytically, to develop physical insight into the mechanical interactions between these two components, in the linear range. The influence of the material parameters of the infill, relative to those of the casing, and of geometry - such as the ratio of wall-thickness to diameter of the casing - on the structural stiffness and capacity of the composite are revealed and presented in a novel graphical form. It is shown that significantly improved overall stiffness and capacity at yield can be obtained by bonding a moderately softer, but highly auxetic, infill to the casing, which highlights the need to develop new lightweight auxetic materials, without compromising their stiffness. These predictions are verified in torsion and confirmed in bending by means of suitable computational models based on the finite element method.