On energy absorption of functionally graded tubes under transverse loading

As a relatively new configuration with higher efficiency of material utilization, functionally graded thickness (FGT) structure has become more and more attractive. In order to understand transverse load bearing behaviors, three circular FGT tubes with different linear thickness gradients from one end to its nearest indenter are investigated through three-point and four-point bending tests in this study. A series of loading conditions, namely different loading offset for three-point bending and different loading span for four-point bending tests, are considered to explore the energy absorption characteristics of the FGT tubes. The experimental deformation modes and force-displacement curves of FGT tubes are first compared with corresponding uniform thickness (UT) tubes. Second, the finite element (FE) models of circular FGT tubes are established for comparisons with the experimental tests. Third, a dimensionless analysis is conducted to compare the deflections in the three-point and four-point bending tests of the circular FGT tubes with different thickness gradient. It is shown that the FGT tubes have more regions to participate in deformation than the UT counterparts to bear the transverse loads. Based on the validated FE models, a parametric study is finally carried out to explore the influence of thickness gradient or thickness difference on the three-point and four-point bending behaviors of the FGT tubes in comparison with the same mass UT counterparts. The results show that a proper selection of thickness gradient can effectively enhance the energy absorption of tubal structures under transverse loading, exhibiting that the FGT tubes are considerably more advantageous over the uniform tubes.