Bending responses of CFRP thin-walled tubes with different sectional shapes: Experimental, analytical and numerical investigation

Abstract

The stiffness, elastic ultimate load and failure mode of carbon fiber reinforced plastic (CFRP) thin-walled square tube (ST), chamfered square tube (CST) and circular tube (CT) with the same circumference under transverse bending load were compared and analyzed. The load-displacement curves, strain-time curves and video images were recorded throughout the process of quasi-static bending to capture the initiation and propagation of failure. Based on the shear-deformable beam and planar curved rod deformation theory, the analytical models for evaluating the integral stiffness and local stiffness of CFRP thin-walled tube were established respectively. The failure mechanisms of ST, CST and CT were further revealed by developing finite element model. The effects of boundary condition, ply orientation angle, geometric dimension and indenter shape on bending properties of CFRP thin-walled tubes were studied. According to the failure characteristics of CST and CT, the indenters that can increase the contact zone were designed and tested. The complete failure of ST was caused by split cracks extending and web buckling, while that of CT was malposed cracks spreading and wall collapsing. The local stiffness of ST and the integral stiffness of CT were the optimum among three specimens. The elastic ultimate load of CST and CT could be improved by adopting 45° layers and the designed indenters. The boundary condition correction coefficient was calculated and fitted utilizing numerical total stiffness and analytical integral stiffness, contributing to explore the ply orientation angle and geometric dimension design space of CST stiffness parameters.