Energy Absorption Characteristics And Design Theory Of Novel Tubular Absorbers Subjected To Axial Crushing

As a kind of thin-walled structure with simple form and excellent energy absorption performance,thin-walled tubular energy absorbers subjected to axial crushing are widely used in carriers,such as vehicles,aircrafts and ships.Recently,as the rapid development of land traffic,aerospace and navigation in China,more and more high requirements have been brought forward for the energy absorption behaviors of thin-walled structures.Nowadays,the simple conventional tubular energy absorbers(such as circular tube and square tube)can not meet the demand of practical applications because of the increasing complexity of carriers and their application scenarios.In the present research,the enhancement strategy,initial imperfection strategy and functional gradient strategy are introduced into conventional circular tube,and two novel energy absorbers are proposed,namely foam-filled gradient grooved tube and foam-filled holed tube.The axial energy absorption characteristics of the two above tubular structures are deeply investigated experimentally and numerically,and the theoretical analysis for helping to guiding the engineering design is presented.The main work and conclusions are as follows:(1)Based on the energy absorption mechanism,the grooved tubes are classified into two types: “Type A” grooved tube and “Type B” grooved tube.The functional gradient strategy is introduced into “Type B” grooved tube,and three kinds of gradient grooved tubes are proposed.The effects of width and thickness gradient of thin-walled section on energy absorption characteristics of grooved tube are investigated experimentally,numerically and theoretically.The results show that the introduction of thickness gradient enhances the deformation mode and energy absorption performance more significantly.(2)The approaches to improve the material utilization for grooved tube are put forward,and then the foam filling is introduced to enhance the energy absorption performance and stability of the grooved tube.It can be seen from the experimental results of LY12 aluminum gradient grooved tube that the empty tube with “weak” thick-walled section always generates non-axisymmetric mode with rapture failure,while the non-axisymmetric mode can be transited into axisymmetric mode by filling aluminum foam,and then the energy absorption performance can also be improved.In addition,the results also show that the sufficient thickness of thickwalled section is very important to keep the stability of grooved tube,and reducing the thick-walled section can simultaneously enhance the utilization and energy absorption of grooved tube.It can be seen from the experimental results of 304 stainless steel gradient grooved tube that the tube with “strong” thick-walled section exhibits excellent stability,and introduction of foam filling and thickness gradient configuration both can make the steel tube with “weak” thick-walled section generate more stable deformation mode.Comparisons of experimental results between the aluminum and steel grooved tubes reveals that steel tube is not easy to generate rapture failure and has a relative regular force-displacement curve,while the aluminum tube has higher specific energy absorption and the more obvious interaction between tube wall and foam filler.(3)By taking the plastic hinge curvature into consideration,revised theoretical models of “Type B” grooved tube subjected to axial crushing are established.Compared with the previous theoretical model,the present revised models can greatly improve the accuracy for predictions of effective crushing distance,total energy absorption and mean crushing force.Moreover,a theoretical model of grooved tube subjected to impact loading is further proposed.By taking the inertial and strain rate effects into account,this model can accurately predict the dynamic behaviors of grooved tube subjected to axial impacting.(4)The foam filling is introduced into holed tube,and a novel energy absorber is put forward.The experimental results show that increasing the hole radius and decreasing the distance between adjacent rows may result in unstable deformation modes,while filling aluminum foam into holed tube may make an unstable mode transit into a more stable one,and then enhance the energy absorption performance.In addition,a novel theoretical model for axisymmetric mode of foam-filled holed tube is put forward by taking the eccentricity factor and strain hardening effects into account,and the prediction results of this model are greatly better than that of previous model.The theoretical results indicate that increasing the hole radius,decreasing the wall thickness,improving the plateau stress of foam material and selecting the tube material with obvious strain hardening effect both can enhance the normalize mean crushing force for foam-filled holed tube,while improving the stress ratio is an effective approach to enhance the specific energy absorption for foam-filled holed tube.