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Auto-body's front end structure, such as bumper and crash box, has the vital function of protecting other components from damage during low-velocity collision; moreover, it should accomplish excellent lightweight effect under the insurance of crashworthiness. This article combined the two approaches of lightweight improvement that listed as using structural optimization and replacing original materials with high strength and high mass efficiency materials or employing reinforced materials to conduct the crashworthiness optimization of assembly of bumper, crash box, and front rail. The original materials of bumper, crash box, and front rail were replaced by aluminum alloy 6060, TRIP800, and DP800, respectively. Aluminum foam was filled in bumper to replace the original reinforced plate and also was filled in crash box to increase energy absorption. The comparisons were made between an optimal selection from the multiple materials designs and the single material design. During optimization, crashworthiness criteria were defined as constraint conditions, and response surface surrogate model and genetic algorithm with elite strategy were employed to solve mathematical model of minimum mass. In single material optimization, the result already achieved the energy absorption increased by 10.1%, the peak collision force and the crumple distance decreased by 11.1% and 12.6%, respectively, and the total mass decreased by 11.1%. As for multiple materials optimization, the results obtained further optimal values. It is found that foam-filled bumper can overcome the disadvantage of bumper mid-bending that causes bumper failure of load bearing, and foam filler has the interaction effect with crash box as well, through which it received a significant growth of energy absorption. The application of multiple materials design greatly expands the potential of crashworthiness and lightweight optimization.

Recently, published research indicates that metal/composite hybrid structures, which combine the excellent specific strength and stiffness of composites with the competitive material cost and toughness of metals, have shown superior performance under axial and oblique loadings. Nevertheless, the crushing behaviors under lateral loading are still rarely reported. In this paper, lateral quasi-static planar crushing tests were carried out to investigate the mechanical response and crushing behaviors for aluminum/CFRP hybrid tubes with different configurational schemes (H-I and H-II) by comparing with their counterparts made of singular material (pure aluminum tube and pure CFRP tube). The experimental results indicated that pure aluminum tube showed a stable crushing process and possessed higher EA and SEA compared with CFRP tube. In addition, the EA of H-II hybrid tube was considerably much higher than that of the summation of their constituent components (increased by 110%). The SEA of H-II hybrid tube increased by 90% compared with aluminum tube. In order to further explore the energy-absorbing mechanisms of H-II hybrid tube, the numerical simulations were performed by adopting effective constitutive model and multilayer modeling technique. Based on the developed finite element model, a systematical parametric study was conducted to explore in detail the effects of aluminum wall thickness, the number of CFRP layers, as well as, fiber orientation on the crashworthiness of H-II hybrid tube, and the contribution of different energy-absorbing mechanisms to total energy absorption was quantified. It was found that varying aluminum wall thickness and the number of CFRP layers not only had a great influence on energy absorbed by different mechanism but also was capable to affect lateral stiffness, EA, and SEA of H-II hybrid tube. Finally, the H-II hybrid tube was further optimized by using a discrete optimization method to improve its crashworthiness characteristics, and the results showed that the SEA was improved by 67.9% from the initial design. INDEX TERMS Carbon fiber reinforced plastic (CFRP), hybrid structures, lateral loading, numerical simulation, crashworthiness, lightweight.

This paper presented a numerical analysis of the damping characteristics of truck escape ramps. To explore the procedure of out-of-control trucks running into arrester beds, the discrete element method (DEM) models of both the tire and the truck escape ramp were built. Tire compression tests were conducted on a homemade tire test system, and the results were used to calibrate the parameters of the tire DEM model. A compression machine was used to conduct dynamic compression tests on pebbles obtained from escape ramps, and the results were used to calibrate the parameters of the pebble DEM model. Road tests were then conducted to further validate the simulation method. An adaptive master-slave simulation procedure analysis was utilized in the simulation process. The error of the travel distance between the simulation and test results was 2.95%. The built tire-pebble DEM model was used to perform the simulations of trucks running into truck escape ramps with different truckloads and laying depths. The results of different truckloads indicated that the truck speed was mainly determined by the laying depth at the entrance of the truck escape ramp. With an increase in time, the truckload started to take effect. The results of different laying depths indicated that the truck speed results were approximately constant at the entrance of the truck escape ramp. As the laying depth increased, the truck speed decreased. When the laying depth exceeded approximately 60 cm, the damping properties of the different laying depths were approximately constant. INDEX TERMS Truck escape ramp, damping property, arrester beds, discrete element method (DEM), tire-pebble model, discrete particles.