Stapp car crash journal最新文献

In a previous study (Song et al. 2017), an adjustable generic simplified vehicle buck was developed; eleven PMHS were impacted by the buck representing a SUV, a van and a sedan successively; and biofidelity corridors were established. The objectives of the current study were 1) to develop the computational model of the buck, and 2) to simulate these PMHS tests with the buck model and to assess the biofidelity of the GHBMC 50^th percentile male pedestrian simplified model (GHBMC M50-PS). First, coupon tensile tests and static and dynamic compression tests were performed on the steel tubes representing the bonnet leading edge (BLE), the bumper and the spoiler used in the above PMHS tests. Based on these tests, the computational models of the above components were then developed and validated. Next, the buck model was built with the component models, and used to simulate the PMHS tests with the GHBMC M50-PS model. These simulations allowed to evaluate the biofidelity of the GHBMC M50-PS model in terms of 1) impact forces between the pedestrian and the buck, 2) pedestrian kinematics, and 3) injury outcome resulted. The model well predicted the total longitudinal impact force between the pedestrian and the buck for all three vehicle types, with a total CORA score between 0.72 and 0.78. However, the force distribution across the BLE, bumper and spoiler showed some significant deviations. The kinematic response of the model was rated as fair with a total CORA score ranging between 0.52 and 0.58. It seems necessary to increase the compliance of the GHBMC M50-PS model and its energy dissipation capability in order to achieve a better correlation of its kinematic response. Finally, the model predicted more knee ligament ruptures than observed in the PMHS tests, but less bone fracture of the femur and the fibula.

Thoracic injuries continue to be a major health concern in motor vehicle crashes. Previous thoracic research has focused on 50^th percentile males and utilized scaling techniques to apply results to different demographics. Individual rib testing offers the advantage of capturing demographic differences; however, understanding of rib properties in the context of the intact thorax is lacking. Therefore, the objective of this study was to obtain the data necessary to develop a transfer function between individual rib and thoracic response. A series of non-injurious frontal impacts were conducted on six PMHS, creating a loading environment commensurate to previously published individual rib testing. Each PMHS was tested in four tissue states: intact, intact with upper limbs removed, denuded, and eviscerated. Following eviscerated thoracic testing, eight individual mid-level ribs from each PMHS were removed and loaded to failure. A simplified model in which ribs of each thorax are treated as parallel springs was utilized to evaluate the ability of individual rib response data to predict each subject's eviscerated thoracic response. On average across subjects, denuded thoraces retained 89% and eviscerated thoraces retained 46% of intact force. Similarly, denuded thoraces retained 70% and eviscerated thoraces retained 30% of intact stiffness. The rib model did not adequately predict eviscerated thoracic response but provided a better understanding of the influence of connective tissue on a rib's behavior with-in the thorax. Results of this study could be used in conjunction with the database of individual rib test results to improve thoracic response targets and help assess biofidelity of current anthropomorphic test devices.

The EuroSID-2re (ES-2re) Anthropomorphic Test Device (ATD) commonly known as the crash test dummy is also used in the military domain to assess the risk of injury of armored vehicles occupants from lateral impact. The loading conditions range from low velocity - long duration impacts (4 m/s - 50 ms) similar to the automotive domain, to high velocity - short duration impacts (28 m/s - 3 ms) corresponding to cases where the panel deforms under an explosion. The human shoulder response to lateral impact was investigated at bounds of the loading condition spectrum previously mentioned, and also at intermediate conditions (14 m/s - 9 ms) in previous studies. The aim of the current study is to provide additional insight at the intermediate loading conditions which are not found in the literature. Eight pure lateral shoulder impact tests were performed on Post Mortem Human Subjects (PMHS) using an 8.1 kg rigid impactor at velocities ranging from 3.3 m/s to 8.8 m/s with the duration ranging from 25 ms to 35 ms. The PMHS were instrumented with accelerometers attached to the sternum, and the upper thoracic spine (T1 vertebra). Strain gages were glued onto the right and left clavicles and ribs 2 to 6. The shoulder force was measured at the interface with the impactor and the impact was filmed by high speed cameras (5000 fps) to track the YZ displacements of the impactor, T1 vertebra, and sternum in the laboratory frame. Three shoulders out of the eight sustained AIS 2 injuries which included a clavicle fracture. The impactor forces ranged from 1200 to 4600 N. The PMHS accelerations ranged from 44 to 163 g at the sternum, and from 17 to 60 g at the T1 vertebra. The analysis of the strain gage signals revealed that the clavicle fractures occurred at the beginning of the impact and coincided with a peak force. An estimate of the acromion-to-shoulder compression (Cmax) was computed. It ranged from 0% to 15% for the non-injured shoulders, and from 19% to 28% for the injured shoulders. This new PMHS test series will be used in a future work to develop a shoulder injury criterion for the ES-2re ATD that is relevant for the whole loading conditions spectrum of the military domain.

Despite safety advances, thoracic injuries in motor vehicle crashes remain a significant source of morbidity and mortality, and rib fractures are the most prevalent of thoracic injuries. The objective of this study was to explore sources of variation in rib structural properties in order to identify sources of differential risk of rib fracture between vehicle occupants. A hierarchical model was employed to quantify the effects of demographic differences and rib geometry on structural properties including stiffness, force, displacement, and energy at failure and yield. Three-hundred forty-seven mid-level ribs from 182 individual anatomical donors were dynamically (~2 m/s) tested to failure in a simplified bending scenario mimicking a frontal thoracic impact. Individuals ranged in age from 4 - 108 years (mean 53 ± 23 years) and included 59 females and 123 males of diverse body sizes. Age, sex, body size, aBMD, whole rib geometry and cross-sectional geometry were explored as predictors of rib structural properties. Measures of cross-sectional rib size (Tt.Ar), bone quantity (Ct.Ar), and bone distribution (Z) generally explained more variation than any other predictors, and were further improved when normalized by rib length (e.g., robustness and WBSI). Cortical thickness (Ct.Th) was not found to be a useful predictor. Rib level predictors performed better than individual level predictors. These findings moderately explain differential risk for rib fracture and with additional exploration of the rib's role in thoracic response, may be able contribute to ATD and HBM development and alterations in addition to improvements to thoracic injury criteria and scaling methods.

Relative motion between the brain and skull and brain deformation are biomechanics aspects associated with many types of traumatic brain injury (TBI). Thus far, there is only one experimental endeavor (Hardy et al., 2007) reported brain strain under loading conditions commensurate with levels that were capable of producing injury. Most of the existing finite element (FE) head models are validated against brain-skull relative motion and then used for TBI prediction based on strain metrics. However, the suitability of using a model validated against brain-skull relative motion for strain prediction remains to be determined. To partially address the deficiency of experimental brain deformation data, this study revisits the only existing dynamic experimental brain strain data and updates the original calculations, which reflect incremental strain changes. The brain strain is recomputed by imposing the measured motion of neutral density target (NDT) to the NDT triad model. The revised brain strain and the brain-skull relative motion data are then used to test the hypothesis that an FE head model validated against brainskull relative motion does not guarantee its accuracy in terms of brain strain prediction. To this end, responses of brain strain and brain-skull relative motion of a previously developed FE head model (Kleiven, 2007) are compared with available experimental data. CORrelation and Analysis (CORA) and Normalized Integral Square Error (NISE) are employed to evaluate model validation performance for both brain strain and brain-skull relative motion. Correlation analyses (Pearson coefficient) are conducted between average cluster peak strain and average cluster peak brain-skull relative motion, and also between brain strain validation scores and brain-skull relative motion validation scores. The results show no significant correlations, neither between experimentally acquired peaks nor between computationally determined validation scores. These findings indicate that a head model validated against brain-skull relative motion may not be sufficient to assure its strain prediction accuracy. It is suggested that a FE head model with intended use for strain prediction should be validated against the experimental brain deformation data and not just the brain-skull relative motion.

Statistical methods, using the entire time-history, can be used to assess the impact response of an ATD (Anthropomorphic Test Device) in terms of its repeatability and reproducibility. In general, the methods generate a correlation relationship described as shape, magnitude and phase-difference between two time-histories' in a given set of similar tests: for repeatability the relationship it is for the same ATD, for reproducibility it is for different ATDs of the same design and for biofidelity it is a relationship between ATDs and biomechanical response data from a series of human surrogate impact tests. The method uses the phase relationship to minimize the difference between any two time-histories through an alignment procedure and the magnitude and shape correlations are used to generate a parametric evaluation of the differences between any two time-histories, or set of time-histories. This paper introduces a variance analysis using the entire time history to build additional foundation to the parametric evaluations using the magnitude and shape correlations and how they can be used to define repeatability and reproducibility ratings/criterion. The proposed methodology has been evaluated using two data sets based on HIII 50th dummy's chest acceleration time histories observed in USNCAP tests. The first set consists of five tests from a single Lab. The second set consists of seven tests from labs different from the first set. A time-history parameter, V, (the normalized summation of squared point to point difference between a pair of signals) was introduced and used to perform statistical analysis of Variance (ANOVA) of the reproducibility of the time histories under investigation. In particular, the V-parameter has been analyzed using both ANOVA and T-test approaches. The relationship between the parameter V and the parameters shape correlation and magnitude correlation is derived analytically. Using this relationship, criterions have been defined for reproducibility and/or repeatability with respect to the shape and magnitude correlations metrics. The criterions have been developed using a limited data set and may change as more data becomes available and is analyzed.

The armies of the North Atlantic Treaty Organization need a shoulder injury criterion for the EuroSID-2re dummy that must be reliable over a large range of loading conditions, from high velocity, short duration impacts (28 m/s - 3 ms) to low velocity long, duration impacts (4 m/s - 50 ms). In the literature, the human shoulder response to lateral impact was investigated at bounds of the loading condition spectrum as previously mentioned. For the low velocities, the injuries were mainly clavicle fractures and the maximum compression between the acromion and the sternum (Cmax) was proposed as an injury criterion. For the high velocities, the typical injury was humerus fractures, including a crushed humeral head. The present study investigates the human shoulder response at an intermediate loading condition (14 m/s - 9 ms). Six lateral shoulder impact tests have been performed with three Post Mortem Human Subjects using a rigid impactor. The duration of the impact was controlled by means of an aluminum honeycomb that decelerated the impactor during the impact. The shoulder external deflection (impactor-to-sternum) ranged between 40 to 64 mm and the applied forces ranged from 4.3 kN to 8 kN. Four shoulders out of six sustained AIS2 injuries. Two acromio-clavicular joint dislocations, one clavicle fracture, and one scapula fracture were observed. Though the shoulder force responses were closer to those induced by the high velocity, short duration impacts, the injury patterns resembled those observed for low velocity, long duration loading conditions. Furthermore, the estimated acromion-to-sternum deflection values were not inconsistent with the prediction of the shoulder injury risk curve of the literature. Despite the relatively high-velocity impact (14.3 m/s), the shoulder injury mechanism appeared to be similar to those observed in the automotive field.

This study aims to provide a set of reference post-mortem human subject tests which can be used, with easily reproducible test conditions, for developing and/or validating pedestrian dummies and computational human body models against a road vehicle. An adjustable generic buck was first developed to represent vehicle front-ends. It was composed of four components: two steel cylindrical tubes screwed on rigid supports in V-form represent the bumper and spoiler respectively, a quarter of a steel cylindrical tube represents the bonnet leading edge, and a steel plate represents the bonnet. These components were positioned differently to represent three types of vehicle profile: a sedan, a SUV and a van. Eleven post-mortem human subjects were then impacted laterally in a mid-gait stance by the bucks at 40 km/h: three tests with the sedan, five with the SUV, and three with the van. Kinematics of the subjects were recorded via high speed videos, impact forces between the subjects and the bucks were measured via load cells behind each tube, femur and tibia deformation and fractures were monitored via gauges on these bones. Based on these tests, biofidelity corridors were established in terms of: 1) displacement time history and trajectory of the head, shoulder, T1, T4, T12, sacrum, knee and ankle, 2) impact forces between the subjects and the buck. Injury outcome was established for each PMHS via autopsy. Simplicity of its geometry and use of standard steel tubes and plates for the buck will make it easy to perform future, new post-mortem human subject tests in the same conditions, or to assess dummies or computational human body models using these reference tests.

This study aims to clarify the relation between axonal deformation and the onset of axonal injury. Firstly, to examine the influence of strain rate on the threshold for axonal injury, cultured neurons were subjected to 12 types of stretching (strains were 0.10, 0.15, and 0.20 and strain rates were 10, 30, 50, and 70 s^-1). The formation of axonal swellings and bulbs increased significantly at strain rates of 50 and 30 s^-1 with strains of 0.15 and 0.20, respectively, even though those formations did not depend on strain rates in cultures exposed to a strain of 0.10. Then, to examine the influence of the strain along an axon on axonal injury, swellings were measured at every axonal angle in the stretching direction. The axons that were parallel to stretching direction were injured the most. Finally, we proposed an experimental model that subjected an axon to more accurate strain. This model observed the process of axonal injury formation by detecting the same neuron before and after stretching. These results suggest that the strain-rate dependency of axonal tolerance is induced by a higher magnitude of loading strain and an experiment focusing on axonal strain is required for obtaining more detailed injury criteria for an axon.

Recent epidemiology studies have reported increase in lumbar spine injuries in frontal crashes. Whole human body finite element models (FEHBM) are frequently used to delineate mechanisms of such injuries. However, the accuracy of these models in mimicking the response of human spine relies on the characterization data of the spine model. The current study set out to generate characterization data that can be input to FEHBM lumbar spine, to obtain biofidelic responses from the models. Twenty-five lumbar functional spinal units were tested under compressive loading. A hydraulic testing machine was used to load the superior ends of the specimens. A 75N load was placed on the superior PMMA to remove the laxity in the joint and mimic the physiological load. There were three loading sequences, namely, preconditioning, 0.5 m/s (non-injurious) and 1.0 m/s (failure). Forces and displacements were collected using six-axis load cell and VICON targets. In addition, acoustic signals were collected to identify the times of failures. Finally, response corridors were generated for the two speeds. To demonstrate the corridors, GHBMC FE model was simulated in frontal impact condition with the default and updated lumbar stiffness. Bi-linear trend was observed in the force versus displacement plots. In the 0.5 m/s tests, mean toe- and linear-region stiffnesses were 0.96±0.37 and 2.44±0.92 kN/mm. In 1.0 m/s tests, the toe and linear-region stiffnesses were 1.13±0.56 and 4.6±2.5 kN/mm. Lumbar joints demonstrated 2.5 times higher stiffness in the linear-region when the loading rate was increased by 0.5 m/s.