Energy absorption of braided composite tubes

A model is proposed for simulating the crushing behaviour and predicting the energy absorption characteristics of triaxially braided composite tubes. The crushing model uses the finite element code ABAQUS along with a material module that describes the constitutive behaviour of the braid material. The material module contains a three-dimensional description of the braid geometry, which is used to calculate the effective stiffnesses of a representative volume. The stiffness calculations include the effects of nonlinear shear, damage accumulation, and scissoring and jamming of the braider tows. To facilitate the model development, extensive material tests and tube crushing experiments were performed. Crushing tests were conducted on braided carbon fibre/epoxy-vinyl ester composite tubes with both circular and square cross-sections. All tests were conducted quasi-statically, and plug-type initiators were used to trigger the progressive crushing. Experimental results show that the profile of the load-displacement curve and the overall energy absorption can be significantly affected by the fibre architecture, the cross-sectional shape of the composite tube, and the fillet radius of the plug-type initiator being used. In order to verify the proposed model, simulation results for tubes with various braid angles, being crushed with different initiator plugs, are compared with the experimental data. Predictions from the proposed model correlate well with the test results, and provide useful information about the deformation of the tube and the failure mechanisms occurring as the tube is being crushed.