Tailoring the crash response of cylindrical crash-boxes via novel lateral thickness gradation scheme

The present study examines the crashworthiness behaviour of circular crash-boxes featuring a lateral thickness gradient. Two distinct design strategies are employed to achieve a lateral thickness gradient in circular crash-boxes with the locations and magnitudes of minimum and maximum thickness are varied. All the crash-boxes are fabricated through a sequence of machining processes from a uniform-thickness circular pipe. The axial quasi-static collapse behaviour of graded circular tubes is compared experimentally and numerically with that of a uniform-thickness circular tube having an equivalent mass. Lateral thickness gradient circular tubes are found to be superior to equivalent circular tubes with uniform thickness in terms of crashworthiness. The thickness ratio ‘TR’, which is the ratio of minimum thickness to maximum thickness for a tube (Tmin/Tmax), governs their energy absorption characteristics. The effect of TR on the axial quasi-static performance of graded circular crash-boxes is further studied numerically. In this parametric numerical study, the values of TR are varied from 1 to 0.2 for 1 mm, 1.5 mm, and 2 mm effective thickness under the same mass condition. There exists a threshold value of TR for each effective thickness at which graded circular tubes perform better than the corresponding uniform-thickness tubes. Finally, multi-objective optimisation is carried out using NSGA-II to determine the dimensions of the graded circular tube with better crashworthiness. The optimised circular tube with a lateral gradient thickness absorbs about 27% more energy per unit of its mass. This study highlights the effect of redistribution of mass in the circular crash-box on its crashworthiness.