Energy absorption of braided composite tubes

In this investigation, a model was developed for simulating the crushing behavior and predicting the energy absorption characteristics of braided composite tubes. The crushing model uses the finite element code ABAQUS along with a material module that describes the constitutive behavior 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. A stiffness reduction scheme, based on the predicted failure mode, is used to account for tow and resin failure throughout the representative volume. Scissoring of the braider tows results in an increase in the overall effective compliance until jamming occurs. To facilitate the model development, extensive coupon tests and tube crushing experiments were conducted.; Coupon tests were conducted on braided flat plaques to help characterize the damage mechanisms occurring and to obtain the initial stiffnesses for verifying the proposed model. The braided flat plaques were made using 80k Akzo Nobel Fortafil carbon fiber tows for both the axial and braider tows, and Hetron 922 epoxy-vinyl ester resin for the matrix.; Crushing tests were conducted on braided carbon fiber/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. The braided tubes were made using 80k Akzo Nobel Fortafil carbon fiber tows for the axial tows, 12k Hercules Grafil 34-700 carbon fiber tows for the braider tows, and Hetron 922 epoxy-vinyl ester resin for the matrix. The energy absorption characteristics are significantly affected by the fiber architecture of the tube and the fillet radius of the initiator plug.; 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 tubes and the failure mechanisms occurring as the tubes are being crushed.