Progressive tearing failure in pultruded composite material tubes

Progressive tearing failure has been identified as an important damage mechanism in single-cell, thin-walled, rectangular pultruded composite material tubes subjected to transverse (bending) loads. This progressive failure occurs along the corners of the tube at the junction between the cell walls and propagates in a stable fashion as the transverse load is increased. This allows the tube to undergo large global flexural deformation as well as local cell wall deformation needed to develop membrane response before ultimate failure. The response enhances load-carrying capacity in the tube and provides energy absorption during the failure. A numerical method has been developed to model the crack propagation along the corners of the tube using an energy criterion. The energy release rate for the mixed-mode crack propagation corresponding to the progressive tearing failure has been determined for pultruded composite material tubes that were tested in a previously reported experimental study. Effects of different tube configurations, geometries, and end-supports on the energy absorption are reported. It was found that substantial energy can be dissipated by the progressive tearing failure of the tube if appropriate axial restraint is provided at the ends of the tube.