In order to optimize the crashworthy characteristic of energy-absorbing structures,the surrogate models of specific energy absorption(SEA)and ratio of SEA to initial peak force(REAF)with respect to the design parameters were respectively constructed based on surrogate model optimization methods(polynomial response surface method(PRSM)and Kriging method(KM)).Firstly,the sample data were prepared through the design of experiment(DOE).Then,the test data models were set up based on the theory of surrogate model,and the data samples were trained to obtain the response relationship between the SEA & REAF and design parameters.At last,the structure optimal parameters were obtained by visual analysis and genetic algorithm(GA).The results indicate that the KM,where the local interpolation method is used in Gauss correlation function,has the highest fitting accuracy and the structure optimal parameters are obtained as: the SEA of 29.8558 kJ/kg(corresponding to a=70 mm and t= 3.5 mm)and REAF of 0.2896(corresponding to a=70 mm and t=1.9615 mm).The basis function of the quartic PRSM with higher order than that of the quadratic PRSM,and the mutual influence of the design variables are considered,so the fitting accuracy of the quartic PRSM is higher than that of the quadratic PRSM.
In order to reduce casualties and property losses in a collision accident, thin-walled structure has been extensively used as energy absorber in crashworthiness design of train. With the help of energy absorber, collision kinetic energy can be controllably dissipated by the plastic deformation of structures. A new kind of multi-cell thin-walled structure called as bitubular polygonal tubes with internal walls(BPTIW) was constructed. The crashworthiness characteristics of BPTIWs were investigated by LS-DYNA. It can be found that the BPTIW with 12 sides has the most excellent crashworthiness characteristics. Therefore, based on response surface method(RSM) and multiobjective particle optimization(MOPSO) algorithm, the BPTIW with 12 sides was selected to optimize the dimensions of cross-sectional configuration under different constraints of energy absorption(EA) and crushing peak force(CPF). The results show that the optimal designs of BPTIW12 under different constraints present excellent crashworthiness characteristics and can be used in the practical engineering.
In order to investigate the energy absorption characteristics of multi-cell polygonal tubes with different cross-sectional configurations,firstly,the theoretical formulae of the mean crushing force under axial load for four multi-cell polygonal tubes were derived by combining the Super Folding Element theory with Zhang’s research results.These formulae can be used to validate the numerical model and quickly evaluate the energy absorption ability of multi-cell polygonal tubes.Furthermore,a comparative study on the energy absorption performance of eight multi-cell polygonal tubes under axial and oblique loads was conducted.The results show that all tubes have a stable mixed deformation mode under axial load.The multi-cell decagon tube has better energy-absorption ability compared with other tubes.Whenθis less than 10°,all the tubes maintain a stable deformation mode,and the multi-cell decagon tube also has the biggest crushing force efficiency and specific energy absorption among these eight tubes;meanwhile compared with the results atθ=0°,the specific energy absorption of all tubes decreases by about 8%-21%,while the crushing force efficiency increases by 20%-56%.However,at large angles 20°and 30°,all of the tubes collapse in bending modes and lose their effectiveness at energy absorption.
A numerical study of bitubular tubes with diaphragms compared with single and bitubular tubes subjected to dynamic axial impact force was presented. At first, the energy absorption response of the composite structure under axial loading was analyzed by finite element simulation. The results show that the efficiency of energy absorption can be improved by introducing diaphragms to the double-walled columns. Then, the effect of the amount and location of diaphragms, the shape and the size of the inner tubes, and the thickness of the composite structures were also studied numerically. The collision performance of the composite structure is affected by the deformation of diaphragms, as well as the interaction of outer and inner tube. The non-uniform distribution of diaphragms can improve the energy absorption efficiency of structures for a constant number of diaphragms. The specific energy absorption of the hexagonal inner tube is the highest, followed by the circular, octagonal and square ones.
