Additively manufactured biomorphic cellular structures inspired by wood microstructure.

Biological cellular materials are an important area of research in Additive manufacturing due to their intricate lightweight designs and forms with high energy absorption characteristics under compressive loading. In this study, we utilize the capability of Additive Manufacturing (AM) technology, experimental testing, and Finite Element Analysis (FEA) to design and investigate the mechanical behavior and energy absorption capabilities of novel Biomorphic Cellular Structures (BCS) inspired by the microstructure of cedar, oak, and palm wood. A comparative study of the elastic properties of the biomorphic cellular structures is carried out. The deformation and failure modes of the different cells were studied, and their performance was also discussed. Nonlinear finite element numerical simulation conducted has shown high accuracy in the prediction of deformation of the samples manufactured using additive manufacturing. The results show that cedar-bcs provides the best mechanical performance compared to the other two biomorphic cellular structures which could be as a result of its more vertical cell wall orientation, nevertheless, the palm-bcs showed a step-wise deformation and improved collapse stress. The obtained results suggest that the unique opportunities offered by the proposed experimental method, in combination with computational models, could serve to provide novel important information for the rational design of additively manufactured porous biomorphic materials.

Experimental assessment of vehicle performance and injury risk for cutaway buses using tilt table and modified dolly rollover tests.

BACKGROUND: Rollover crashes of buses occur less frequently than do those involving passenger cars; however, they are associated with higher fatality rates. During rollover crashes, a vehicle experiences multidirectional acceleration and multiple impacts, yielding a complex interaction between structural components and its occupants. A better understanding of vehicle and occupant's motion, structural deformation, and vehicle and road interactions are necessary to improve the safety of the occupants during this event. One of the key factors in rollover crashworthiness assessment is to investigate the relationship between the strength of the vehicle's structure and the risk of injury outcomes. However, rollover crashes involving buses have received less research attention than have those involving passenger cars. Experimental studies in bus rollover safety have mainly focused on the structural integrity of the passenger compartment without considering the occupant responses. The main goal of this research is to evaluate the rollover mechanism and associated injury risk during two experimental rollover tests for a paratransit cutaway bus that is commonly used by transit agencies. METHODS: The modified dolly rollover (MDR) and tilt table (TT) tests were conducted using a similar bus and anthropomorphic test device (ATD) configurations. In each test, a 2-point and 3-point belted Hybrid III 50th percent male ATDs were used to quantify the kinematics of the occupants. The deformation index (DI), accelerations and angular velocities of the bus's CG were measured as vehicle responses. The collected data were then calibrated and filtered to assess the effects of the test procedure on kinematic responses of the vehicle and occupants. Next, the effectiveness of the 2-point vs 3-point seatbelt to reduce or prevent the injuries, the vulnerable body regions and corresponded injury risk were evaluated. RESULTS: The residual space remained intact (DI < 1) during both rollover tests, however, the ATD responses were quite different. The results of the injury assessment indicate that the risk of the injuries in the MDR test was significantly higher than the TT test. The highest risk of injuries was identified for the head, neck, and shoulder of 2-point belted ATD during the MDR test. Also, the main source of injuries during the MDR test was partial ejection due to the shattered side window, whereas for the TT test impacts between the ATDs and the side window and/or window frame were the injury causes. From the vehicle point of view, the total energy produced in the MDR was 3.5 times higher than the TT test, but the overall structural deformation in the TT test was higher than MDR test. Overall, the tilt table test provides a more severe scenario compared to the MDR test for the assessment of structural strength. Considering the limited real-world injury data in rollover crashes of buses, the MDR test presented the more realistic occupant responses.