One of the most crucial functionalities of load-bearing biological materials such as shell and bone is to protect their interior organs from damage and fracture arising from external dynamic impacts. However, how this class of materials effectively damp stress waves traveling through their structure is still largely unknown. With a self-similar hierarchical model, a theoretical approach was established to investigate the damping properties of load-bearing biological materials in relation to the biopolymer viscous characteristics, the loading frequency, the geometrical parameters of reinforcements, as well as the hierarchy number. It was found that the damping behavior originates from the viscous characteristics of the organic (biopolymer) constituents and is greatly tuned and enhanced by the staggered and hierarchical organization of the organic and inorganic constituents. For verification purpose, numerical experiments via finite-element method (FEM) have also been conducted and shown results consistent with the theoretical predictions. Furthermore, the results suggest that for the self-similar hierarchical design, there is an optimal aspect ratio of reinforcements for a specific loading frequency and a peak loading frequency for a specific aspect ratio of reinforcements, at which the damping capacity of the composite is maximized. Our findings not only add valuable insights into the stress wave damping mechanisms of load-bearing biological materials, but also provide useful guidelines for designing bioinspired synthetic composites for protective applications.

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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.

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