Analytical solutions for predicting in-plane strain and interlaminar shear stress of ultra-thin-walled lenticular collapsible composite tube in fold deformation

The paper deals with the analytical solutions on geometrical and mechanical properties of ultra-thin-walled lenticular collapsible composite tube (LCCT) in fold deformation for understanding the phenomenon of actual fold deformation and for improving the structural behaviours in engineering application. The LCCT in fold deformation was idealized as the curved thin-walled beam with a biaxisymmetrical lenticular cross-section described by concave and convex tangential circular arcs and with a longitudinal path depicted by using multinomial shape function. New geometrical equations were established for predicting the in-plane strain of the LCCT in fold deformation (consisting of flattening and curling deformation modes) based on apt geometrical approximations and deformation assumptions, and analytical solution was derived for calculating the interlaminar shear stress on the bonding interface of the LCCT by means of equilibrium equation and linear-elastic constitutive equation founded on micromechanics. In order to validate the model, experiments were performed to determine respectively the load-displacement and in-plane strains of the ultra-thin-walled LCCT in the flattening and curling deformation modes and the comparison between the theoretical predictions and the experiments was conducted. It is shown that the predictions from the new models correlate well with the experiments within small deflection range. These efforts are argued to be successful in predicting the fold deformation of ultra-thin-walled LCCT, but limited to small deflection range only.