Analysis of Force Mitigation by Boots in Axial Impacts using a Lower Leg Finite Element Model.

Lower extremity injuries caused by floor plate impacts through the axis of the lower leg are a major source of injury and disability for civilian and military vehicle occupants. A collection of PMHS pendulum impacts was revisited to obtain data for paired booted/unbooted test on the same leg. Five sets of paired pendulum impacts (10 experiments in total) were found using four lower legs from two PMHS. The PMHS size and age was representative of an average young adult male. In these tests, a PMHS leg was impacted by a 3.4 or 5.8 kg pendulum with an initial velocity of 5, 7, or 10 m/s (42-288 J). A matching LS-DYNA finite element model was developed to replicate the experiments and provide additional energy, strain, and stress data. Simulation results matched the PMHS data using peak values and CORA curve correlations. Experimental forces ranged between 1.9 and 12.1 kN experimentally and 2.0 and 11.7 kN in simulation. Combat boot usage reduced the peak force by 36% experimentally (32% in simulation) by compressing the sole and insole with similar mitigations for calcaneus strain. The simulated Von Mises stress contours showed the boot both mitigating and shifting stress concentrations from the calcaneus in unbooted impacts to the talus-tibia joint in the booted impacts, which may explain why some previous studies have observed shifts to tibia injuries with boot or padding usage.

A novel bridge wire model of blast traumatic brain injury - biomed 2013.

Research into the mechanics of blast-induced traumatic brain injury requires a device capable of reproducing pressures of the same magnitude and time scale as a blast wave. A blast simulator based on the exploding bridge wire mechanism was created with these capabilities. Peak blast pressures in the range of 5 – 29 psi were generated with a positive phase duration less than 20 µs. A series of experiments using 0.008 inch diameter wires (10-20 psi) were used to demonstrate the ability of the blast simulator to injure in vitro primary brain cell cultures at 1, 24, and 48 hours following blast. Blast exposure caused a rapid loss of cells which was significant over controls. Propidium iodide uptake indicated limited injury to cellular membranes but the cytoskeletal structure showed signs of degeneration 1 hour following blast. These results indicate that the bridge wire blast simulator can serve as a suitable in vitro model of blast injury.

Vibrational frequency response to impact loading of skull models.

More than 73% of soldiers returning from duty are injured by explosive devices. The shock waves generated are believed to cause injury via intracranial pressure and skull flexure. Prior modal analyses of spherical shells as skull substitutes using analytical solutions to the wave equation indicate the impact point and opposite side as areas of intense bending. In this study, finite element models extend modal analyses and applied impulse scenarios for a variety of altered spherical geometries. Holes of differing sizes, the direction of impact, and the presence of water inside were considered. The finite element model matched the analytical modal frequencies within 4%. The discrete modal frequencies are lost as the geometry deviates from the ideal sphere. The frequency response to impact was complex with many participating modal frequencies. The deformation near holes increased as the hole increased in size. Impacts in line with holes increased the minimum to maximum spread by 30% whereas angled impacts caused more pronounced motion near holes. Filling the sphere interior with liquid diverted some load from the shell and decreased the maximum deflections by 80%. Avenues of further research focused on more accurate geometries are discussed.

Evaluation of the Accuracy of NASS/CDS Delta-V Estimates from the Enhanced WinSmash Algorithm.

The National Automotive Sampling System / Crashworthiness Data System (NASS/CDS) uses the WinSmash program to reconstruct changes in vehicle velocity for real world crashes. Vehicle change in velocity, or delta-V, is a measure of crash severity and a predictor of injury risk. Earlier studies have demonstrated that WinSmash 2.42 underestimated the delta-V by 23% on average with the use of categorical stiffness values for vehicles identified as a source of error. An enhanced version of WinSmash, WinSmash 2008, was developed to employ vehicle specific stiffness values whenever possible. A total of 478 General Motors vehicles equipped with event data recorders (EDRs) and involved in real-world crashes were collected from years 2000 - 2008 of the NASS/CDS database and the delta-V was computed using the enhanced WinSmash. All vehicles were involved in frontal impacts. The enhanced reconstruction algorithm reduced the underestimation of delta-V from 23% to 13% on average for all vehicles. Delta-V estimates for cars only were greatly improved but still understated by 16% on average. Less than 5% error in delta-V was observed for pickup trucks and utility vehicles. The amount of structural overlap for the vehicle and investigator confidence in the reconstruction continued to have an effect on accuracy. No difference in average delta-V was observed when using either updated categorical stiffness values or vehicle specific stiffness values. The changes in WinSmash delta-Vs have important policy implications for NHTSA as the NASS/CDS delta-Vs are the basis for traffic and safety regulations as well as the speeds for vehicular crash testing and costs/benefits analyses.

Influence of the missing vehicle and cdc only delta-v reconstruction algorithms for prediction of occupant injury risk - biomed 2009.

Delta-V, the change in velocity of a vehicle, is a widely used predictor of occupant injury in vehicle collisions. In real worldv crashes, delta-V is commonly estimated from measurements of vehicle deformation using absorbed energy based methods. The accuracy of these estimates is highly dependent on the availability of deformation measurements for both vehicles involved in a crash. Specialized algorithms have been developed for those cases in which complete information is not available from a crash (e.g. the missing vehicle algorithm) or has been estimated (e.g. the collision deformation classification, or CDC only algorithm). The objectives of this study are to evaluate (1) the accuracy of the missing vehicle and CDC only algorithms and (2) the influence of these algorithms upon estimates of occupant injury risk. The approach is to develop and critically evaluate occupant injury risk curves using the standard, missing, and CDC only reconstruction algorithms for 1899 real vehicles extracted from the National Automotive Sampling System / Crash Data System for 2006.

NASS/CDS delta-V estimates: the influence of enhancements to the WinSmash crash reconstruction code.

The change in velocity (delta-V) crash severity metric in the NASS/CDS (National Automotive Sampling System / Crashworthiness Data System) is computed using the WinSmash crash reconstruction code. Beginning in 2008, NASS/CDS investigators have started to use an enhanced version of WinSmash, WinSmash 2008, which features a comprehensive vehicle specific library for over 5000 vehicle make-model-year combinations and updated categorical stiffness values. The use of WinSmash 2008 is expected to greatly improve delta-V estimates. However, there is concern that this may result in a step change in the NASS/CDS delta-V estimates, making it difficult to compare NASS/CDS 2008 with earlier years. A total of 1,808 collisions were recomputed using data from NASS/CDS 2007. The new version of WinSmash shows improved accuracy, but still underpredicts delta-V. The use of WinSmash 2008 increased the delta-V by 7.9% or 1.9 kph on average. The changes in delta-V were not evenly distributed. Delta-V increases were larger for side impacts (8.3%) than for back impacts (5.3%). The calculation type had little effect on the delta-V changes. For vehicles, pickup trucks showed a small increase (3.3%) and utility vehicles increased the most (9.6%). This jump in delta-V may prevent the data from NASS/CDS 2008 and later from being readily aggregated with previous years.

Numerical simulation of a cellular-level experiment to induce traumatic injury to neurons.

Previous research has developed a pneumatically driven device for delivering a controlled mechanical insult to cultured neurons. The neuronal cell culture was injured by applying a transient air pulse to a culture well fitted with a highly elastic Silastic culture well bottom. In response to the pressure pulse, he Silastic culture well bottom deformed, stretched the attached cell culture, and resulted in observable cell injuries and death. The goal of this paper was to computationally model the spatial distribution of membrane strain, stress, and strain rate to which these cultures were subjected. The simulation results, using a finite element model of the culture well membrane, compared well with the results from the original experiments. When peak air pressure was varied from 69 kPa to 345 kPa (10 to 50 psig), numerical simulations showed that the corresponding membrane strains varied from 20 to 95% and the stress response varied from 0.5 to 1.2 MPa.