Post Mortem Human Surrogate Research Articles

Effects of acceleration level on lumbar spine injuries in military populations

Background contextClinical studies have indicated that thoracolumbar trauma occurs in the civilian population at its junction. In contrast, injury patterns in military populations indicate a shift to the inferior vertebral levels of the lumbar spine. Controlled studies offering an explanation for such migrations and the associated clinical biomechanics are sparse in literature. PurposeThe goals of this study were to investigate the potential roles of acceleration loading on the production of injuries and their stability characteristics using a human cadaver model for applications to high-speed aircraft ejection and helicopter crashes. Study designBiomechanical laboratory study using unembalmed human cadaver lumbar spinal columns. MethodsThoracolumbar columns from post-mortem human surrogates were procured, x-rays taken, intervertebral joints and bony components evaluated for degeneration, and fixed using polymethylmethacrylate. The inferior end was attached to a platform via a load cell and uniaxial accelerometer. The superior end was attached to the upper metal platform via a semi-circular cylinder. The pre-flexed specimen was preloaded to simulate torso mass. The ends of the platform were connected to the vertical post of a custom-designed drop tower. The specimen was dropped inducing acceleration loading to the column. Axial force and acceleration data were gathered at high sampling rates, filtered, and peak accelerations and inertia-compensated axial forces were obtained during the loading phase. Computed tomography images were used to identify and classify injuries using the three-column concept (stable vs. unstable trauma). ResultsThe mean age, total body mass, and stature of the five healthy degeneration-free specimens were 42 years, 73 kg, and 167 cm. The first two specimens subjected to peak accelerations of approximately 200 m/sec2 were classified as belonging to high-speed aircraft ejection-type and the other three specimens subjected to greater amplitudes (347–549 m/sec2) were classified as belonging to helicopter crash-type loadings. Peak axial forces for all specimens ranged from 4.8 to 7.2 kN. Ejection-type loaded specimens sustained single-level injuries to the L1 vertebra; one injury was stable and the other was unstable. Helicopter crash-type loaded specimens sustained injuries at inferior levels, including bilateral facet dislocation at L4–L5 and L2–L4 compression fractures, and all specimens were considered unstable at least at one spinal level. ConclusionsThese findings suggest that the severity of spinal injuries increase with increasing acceleration levels and, more importantly, injuries shift inferiorly from the thoracolumbar junction to lower lumbar levels. Acknowledging that the geometry and load carrying capacity of vertebral bodies increase in the lower lumbar spine, involvement of inferior levels in trauma sparing the superior segments at greater acceleration inputs agree with military literature of caudal shift in injured levels. The present study offers an experimental explanation for the clinically observed caudal migration of spinal trauma in military populations as applied to high-speed aircraft ejection catapult and helicopter crashes.

Virtual traumatology of pregnant women: The PRegnant car Occupant Model for Impact Simulations (PROMIS)

This study report documents the development of a finite element (FE) model for analyzing trauma in pregnant women involved in road accidents and help the design of a specific safety device. The model is representative of a 50th percentile pregnant woman at 26 weeks of pregnancy in sitting position. To achieve this, the HUMOS 2 model, which has been validated in a wide range of dynamic tests, was scaled to the morphology of a woman in the 50th percentile and coupled with a model of gravid uterus. During scaling, special attention was paid to the pelvic region which is known to differ considerably in morphological terms between men and women. The gravid uterus model includes a placenta, a fetus, uterosacral ligaments and the amniotic fluid by means of fluid structure interaction formulation. The uterus and the female model were coupled using an original method whereby the growth of an uterus was simulated to compress the abdominal organs in a realistic manner. The model was validated based on experimental tests described in the literature. Additional tests based on abdominal loadings with a seatbelt on Post Mortem Human Surrogates (PMHS) coupled to silicone uterus were also performed.Results highlighted the role of the possible interaction of the fetus in the pregnant woman abdominal response. Experimental corridors taking into account the presence of this fetus could therefore be proposed.

Force Corridors of Post Mortem Human Surrogates in Oblique Side Impacts from Sled Tests

To develop region-specific force corridors in side impacts under oblique loadings using post mortem human surrogates (PMHS). Unembalmed PMHS were positioned on a sled. Surrogates contacted a segmented, modular/ scalable load-wall to isolate region-specific forces (shoulder, thorax, abdomen, pelvis). Heights and widths of segmented load-wall plates were adjustable in sagittal and coronal planes to accommodate anthropometry variations. Load cells were used to gather region-specific forces. Tests were conducted at 6.7m/s. Peak forces and times of attainments, and standard corridors (mean±1 SD) are given for the four torso regions and summated forces. The mean age, stature, and total body mass of the five male PMHS were: 56.6±4.4years, 183±3.5cm and 70.6±9.0kg. Peak pelvis forces were the greatest, followed by thorax, abdomen and shoulder. Sequence of times of attainments of peak forces initiating from pelvis increased rostrally to abdomen to thorax and shoulder regions. Corridors were tight in all regions, except shoulder. As previous force corridors were based solely on pure-lateral impacts and region-specific forces were not extracted, the present oblique responses using anthropometry-specific load-wall design can be used to develop injury criteria and evaluate the biofidelity of dummies.

The PROMIS model to highlight the importance of the foetus to the validation of a pregnant woman model

The percentage of trauma during pregnancy related to road accident is between 50% and 75%. This type of trauma can result in premature birth or even foetal loss. To analyse and understand the injury mechanisms in pregnant women involved in a car accident, several studies proposed computational or physical tools to simulate accidents. Specific dummy and numerical models have been proposed and validated using experimental data from post-mortem human surrogate (PMHS) scaled with the equal-stress, equal-velocity scaling method to a pregnant woman. This study proposes to evaluate the reliability of this assumption and its scope.

Finite element analysis of pedestrian lower limb fractures by direct force: The result of being run over or impact?

The elucidation and prediction of the biomechanics of lower limb fractures could serve as a useful tool in forensic practices. Finite element (FE) analysis could potentially help in the understanding of the fracture mechanisms of lower limb fractures frequently caused by car–pedestrian accidents. Our aim was (1) to develop and validate a FE model of the human lower limb, (2) to assess the biomechanics of specific injuries concerning run-over and impact loading conditions, and (3) to reconstruct one real car–pedestrian collision case using the model created in this study. We developed a novel lower limb FE model and simulated three different loading scenarios. The geometry of the model was reconstructed using Mimics 13.0 based on computed tomography (CT) scans from an actual traffic accident. The material properties were based upon a synthesis of data found in published literature. The FE model validation and injury reconstruction were conducted using the LS-DYNA code. The FE model was validated by a comparison of the simulation results of three-point bending, overall lateral impact tests and published postmortem human surrogate (PMHS) results. Simulated loading scenarios of running-over the thigh with a wheel, the impact on the upper leg, and impact on the lower thigh were conducted with velocities of 10m/s, 20m/s, and 40m/s, respectively. We compared the injuries resulting from one actual case with the simulated results in order to explore the possible fracture bio-mechanism. The peak fracture forces, maximum bending moments, and energy lost ratio exhibited no significant differences between the FE simulations and the literature data. Under simulated run-over conditions, the segmental fracture pattern was formed and the femur fracture patterns and mechanisms were consistent with the actual injury features of the case. Our study demonstrated that this simulation method could potentially be effective in identifying forensic cases and exploring of the injury mechanisms of lower limb fractures encountered due to inflicted lesions. This model can also help to distinguish between possible and impossible scenarios.

Determination of peak deflections from human surrogates using chestbands in side impact tests

To understand the biomechanics of the human body in motor vehicle environments, physical models including anthropomorphic test devices (ATD) and biological models (postmortem human surrogates) are used, and sled tests are conducted. Deflection is often used as a biomechanical variable to characterize the effects of impact loading and derive injury criteria. The objective of the present study was to evaluate different techniques and recommend a methodology to determine the peak thorax and abdominal deflections from temporal contours using chestbands in oblique lateral impacts. The side impact ATD WorldSID representing human surrogates was positioned on a seat. The seat was rigidly fixed to the platform of an acceleration sled. The oblique load-wall fixed to the sled consisted of separate and adjustable plates to contact the shoulder, thorax, abdomen, and pelvis. Two 59-gage chestbands were wrapped on the thorax and abdomen. Tests were conducted at low, medium, and high velocities (3.4, 6.7, and 7.5m/s) and three methods, termed the spine-sternum, bilateral, and spine-box, were used to determine the global peak deflection and its angulation. Results indicated that all three methods produced very similar angulations, for all velocity tests, and at both thorax and abdominal regions. However, maximum deflections were the lowest in the spine-sternum, followed by bilateral and spine-box methods, with one exception. Based on the development of deflection contours, locations used in the definitions of the origin, and accuracy in identifying critical locations/points in time-varying contours, results of the present study indicate that the bilateral method is the optimum procedure to determine the oblique peak deflection vector in biomechanical tests.

Design of Human Surrogates for the Study of Biomechanical Injury: A Review

Human surrogates are representations of living human structures employed to replicate "real-life" injurious scenarios in artificial environments. They are used primarily to evaluate personal protective equipment (PPE) or integrated safety systems (e.g., seat belts) in a wide range of industry sectors (e.g., automotive, military, security service, and sports equipment). Surrogates are commonly considered in five major categories relative to their form and functionality: human volunteers, postmortem human surrogates, animal surrogates, anthropomorphic test devices, and computational models. Each surrogate has its relative merits. Surrogates have been extensively employed in scenarios concerning "life-threatening" impacts (e.g., penetrating bullets or automotive accidents). However, more frequently occurring nonlethal injuries (e.g., fractures, tears, lacerations, contusions) often result in full or partial debilitation in contexts where optimal human performance is crucial (e.g., military, sports). Detailed study of these injuries requires human surrogates with superior biofidelity to those currently available if PPE designs are to improve. The opportunities afforded by new technologies, materials, instrumentation, and processing capabilities should be exploited to develop a new generation of more sophisticated human surrogates. This paper presents a review of the current state of the art in human surrogate construction, highlighting weaknesses and opportunities, to promote research into improved surrogates for PPE development.

A Finite Element Model of the Lower Limb for Simulating Automotive Impacts

A finite element (FE) model of a vehicle occupant's lower limb was developed in this study to improve understanding of injury mechanisms during traffic crashes. The reconstructed geometry of a male volunteer close to the anthropometry of a 50th percentile male was meshed using mostly hexahedral and quadrilateral elements to enhance the computational efficiency of the model. The material and structural properties were selected based on a synthesis of current knowledge of the constitutive models for each tissue. The models of the femur, tibia, and leg were validated against Post-Mortem Human Surrogate (PMHS) data in various loading conditions which generates the bone fractures observed in traffic accidents. The model was then used to investigate the tolerances of femur and tibia under axial compression and bending. It was shown that the bending moment induced by the axial force reduced the bone tolerance significantly more under posterior-anterior (PA) loading than under anterior-posterior (AP) loading. It is believed that the current lower limb models could be used in defining advanced injury criteria of the lower limb and in various applications as an alternative to physical testing, which may require complex setups and high cost.

Response corridors for the medial–lateral compressive stiffness of the human arm: Implications for side impact protection

The biofidelity of side impact anthropomorphic test devices (ATDs) is crucial in order to accurately predict injury risk of human occupants. Although the arm serves as a load path to the thorax, there are currently no biofidelity response requirements for the arm. The purpose of this study was to characterize the compressive stiffness of male and female arms in medial–lateral loading and develop corresponding stiffness response corridors. This was accomplished by performing a series of pendulum tests on 18 isolated post-mortem human surrogate (PMHS) arms, obtained from four male and five female surrogates, at impact velocities of 2m/s and 4m/s. Matched tests were performed on the arm of the SID-IIs ATD for comparison. The arms were oriented vertically with the medial side placed against a rigid wall to simulate loading during a side impact automotive collision. The force versus deflection response data were normalized to that of a 50th percentile male and a 5th percentile female using a new normalizing technique based on initial arm width, and response corridors were developed for each impact velocity. A correlation analysis showed that all non-normalized dependent variables (initial stiffness, secondary stiffness, peak force, and peak deflection) were highly correlated with the initial arm width and initial arm circumference. For both impact velocities the PMHS arms exhibited a considerable amount of deflection under very low force before any substantial increase in force occurred. The compression at which the force began to increase considerably was consistent with the average tolerable medial–lateral arm compression experienced by volunteers. The initial stiffness (K1), secondary stiffness (K2), peak force, and peak deflection were found to significantly increase (p<0.05) with respect to impact velocity for both the non-normalized and normalized PMHS data. Although the response of the SID-IIs arm was similar to that of the female PMHS arms for both impact velocities, the SID-IIs arm did not exhibit a considerable toe region and therefore did not fall within the response corridors for the 5th percentile female. Overall, the results of the current study could lead to improved biofidelity of side impact ATDs by providing valuable data necessary to validate the compressive response of the ATD arm independent of the global ATD thoracic response.

Assessment of pedestrian head impact dynamics in small sedan and large SUV collisions

This study compares head impact dynamics between post-mortem human surrogates (PMHS) and the Polar-II pedestrian crash dummy in vehicle–pedestrian impacts with a small sedan and a large sports utility vehicle (SUV). A total of 15 (8 sedan and 7 SUV) full-scale vehicle pedestrian impact tests were performed at 40 km/h. For each vehicle, two (SUV) or three (sedan) PMHS tests and five dummy tests were performed, with three of the dummy tests in the same configuration to show repeatability, and the other two tests utilising slightly different configurations. Head linear and angular kinematics were captured from PMHS and dummy head instrumentation, and dummy upper neck load cell data were used to determine neck forces and calculate head impact forces. Differences in head impact locations, timing and kinematics between the dummy and PMHS were minimised when the dummy was positioned higher above the ground reference level to match the pelvis height of the PMHS. On average, the dummy recorded higher resultant impact forces (2930 N vs. 1862 N) in windshield impacts to the sedan than in hood impacts to the SUV, which resulted in higher 15-ms Head Injury Criteria (HIC15) values and higher peak and averaged angular accelerations. While there are differences in dummy injury risk metrics, both the dummy and PMHS data show that the difference in injury risk metrics predicted by the dummy can be explained by the variation in impact velocity between the sedan (14.1 ± 1.2 m/s) and the SUV (10.7 ± 2.3 m/s), the differences in injury risk predicted by the PMHS are not as clear due to confounding factors. The data and analyses presented in this study also show that neck forces during head impacts contribute a substantial and additive effect to the head impact accelerations (and thus HIC15 values) measured in the dummy, and that for the SUV, neck forces affect head accelerations more than impact forces. Despite analysing only lateral impacts with two vehicle geometries at 40 km/h, this study provides the only comparison of PMHS and dummy pedestrian head impact kinematics data available.

External biofidelity in lateral impact measurement of global and local forces

A study was conducted to develop high-resolution external biofidelity data for the response of post-mortem human surrogates (PMHS) in side-impact loading. This study implemented stationary PMHS (N = 3) impacted by a wall moving at a constant velocity. The wall was subdivided into 15 impact plates, each instrumented to record the normal and shear forces as well as reaction moments about the shear axes. A method to determine the time-history of the centre of pressure (COP) of each load plate was developed and validated in both quasi-static and dynamic loading conditions. A validation test demonstrated that the COP can be predicted to within 1 cm for loads generally achieved by the shoulder and pelvis. The repeatability of COP was very good for the pelvis, where maximum variation was 1.44 cm, but higher for the thorax (3.4 cm) and shoulder (4.1 cm). Patterns of COP motion on the pelvis plate were consistent for all subjects.

Fracture tolerance of the patellofemoral joint in frontal knee impacts of 75 and 35 year-old males

This study investigates the peak force and force at fracture in the patella complex from an axial load similar to that of a knee bolster impact during a frontal automobile collision. A rigid impactor and a 689 kPa padded impactor are used to compare the mechanical behaviour of ‘older’ (mean = 74 years) and ‘younger’ (35 years) post-mortem human surrogate (PMHS) populations. Age-related differences in peak forces and fracture patterns were observed using both impactors, and we hypothesise that the stiffer response of the patella complex in the 74-year-old PHMS group is responsible for these differences. Furthermore, four fracture detection methods (acoustic sensors, strain gauges, piezo-electric sensors and accelerometers) were investigated; the acoustic sensor was found to give the most useful crack detection data. These experimental results can assist numerical modelling and design efforts aimed at reducing the incidence and severity of automotive-related knee injuries.

Reducing Chest Injuries in Automobile Collisions: Rib Fracture Timing and Implications for Thoracic Injury Criteria

The purpose of this study was to quantify the biomechanical response of the human thorax during dynamic shoulder belt loading representative of that seen in a severe automotive collision. Two post-mortem human surrogates (PMHSs) (one male and one female) were instrumented with 26 single-axis strain gages on the ribs, sternum, and clavicle. The thorax of each PMHS was placed on a custom spine support bracket designed to support the thorax on either side of the spinous process, thereby allowing free motion at the costovertebral joints. In addition, the support bracket raised the thorax above the flat base plate, which could otherwise constrain the deformation and motion of the posterior region of the rib cage. The thorax of each PMHS was then loaded using a custom table-top belt loading system that generated thoracic displacement rates representative of a severe automotive collision, 1.3m/s for the male PMHS and 1.0m/s for the female PMHS. The rib fracture timing data, determined by analyzing the strain gage time histories, showed that severe thoracic injury (AIS=3) occurred at 16% chest compression for the male and 12% chest compression for the female. However, these values are well below the current thoracic injury criteria of 29% chest compression for the male and 23% chest compression for the female. This data illustrates that serious thoracic injury (AIS=3) occurs at lower chest compressions than the current ATD thoracic injury criteria. Overall, this study provides critical data that can be used in the design and validation of advanced ATDs and finite element models, as well as the establishment of improved, more stringent thoracic injury criteria.

Assessment and Validation of a Methodology for Measuring Anatomical Kinematics of Restrained Occupants During Motor Vehicle Collisions

Efforts to improve restraint design for human occupant protection require a detailed knowledge of human kinematic response. However, to improve the current understanding of human kinematic response to restraint loading it is necessary to obtain a more detailed knowledge of how structures within the body such as individual ribs and vertebrae move during an impact event. Video-based optoelectronic stereo photogrammetric systems (OSS) have recently been employed for kinematic measurement during simulated vehicle collisions with restrained post mortem human surrogates (PMHS). Application of this methodology requires specialized optical sensor hardware to be surgically attached to anatomical structures of interest such as acromia, ribs orvertebrae. The hardware supports retro reflective spherical targets which are visible to the OSS. The recorded target motions are then transformed to the underlying anatomical structures to quantify the trajectories of individual bone centers throughout the impact event. This study presents the results of seven tests that were conducted to practically assess the efficacy of this emerging methodology for measuring anatomical kinematics during impact loading. The tests used a 16-camera 1000Hz OSS and a single simulated anatomical structure with attached target hardware to quantify the uncertainty in the calculated trajectory of the bone center. Specifically, the tests assessed the intrinsic optical error associated with the OSS, and also evaluated the ability of the rigid body transformation to reproduce a directly measured bone center trajectory. The tests also assessed the effect of compliance in the assumed rigid connection between the visible target hardware and underlying bone on the transformed trajectories. The results demonstrate robust performance of a novel methodology combining state-of-the-art optoelectronic technology, specialized target hardware, and rigid body transformation to obtain kinematic measurements of anatomical structures within the human body which are not visible or accessible for direct measurement during an impact event

Kinematics of the thorax under dynamic belt loading conditions

This research was completed as part of an ongoing effort to characterise human thoracic response to belt loading in a well controlled and repeatable laboratory environment. This paper presents the results of eight tests conducted on three post-mortem human subjects. The sled test environment provides realistic occupant kinematics and restraint interaction in the inertial environment of a vehicle collision, but is too complex for detailed analysis of thoracic deformation under belt loading. To study in more detail the kinematics of the chest when loaded anteriorly by a seat belt, three male post-mortem human surrogates (31-62 years of age) were mounted on a stationary apparatus that supported the spine and shoulder in a configuration comparable to that achieved in a 48 km/h sled test at the time of maximum chest deformation. The belt was positioned across the anterior torso with attachments at D-ring and buckle locations based on the geometry of a mid-sized sedan. The belt was attached to a trolley driven by a hydraulic ram linked to a universal test machine. Ramp experiments were conducted at rates of 0.5 m/s, 0.9 m/s and 1.2 m/s. Average peak sternal displacements ranged from 13% to 23% of chest depth measured at the central sternum. Belt loads and spinal reaction loads were measured along with six degree-of-freedom (DOF) displacement data of the sternum, 4th and 8th ribs anteriorly, 8th and 10th ribs posteriorly, and acromia bilaterally. Three DOF targets were mounted to the distal clavicles, 8th ribs laterally and along the path of the belt. The targets were tracked optically by a high speed 16-camera motion capture system (VICON MX™) in a calibrated space around the torso. Post-test analysis of the target motion included decomposition of the trajectories into Cartesian coordinate displacements with respect to a spine fixed coordinate system. The results showed that the chest deformation closely followed the belt loading regionally with a trough developing where the belt contacted the chest. The anterior rib targets exhibited three-dimensional (3D) translational motion. Displacements in the X direction (anterior-posterior) were the largest, however the Z (vertical) and Y (lateral) displacements comprised nearly 35% and 10% respectively of the total resultant deflection measured at the sternum. Peak posterior deformations were significantly (p < .001) lower than those observed at anterior locations and were below 7 mm except for the final injurious tests in which the peak posterior deformation averaged 13.4 mm (approximately 22% of the average peak anterior ribcage deformation in the injurious tests). Overall, the results provide a detailed 3D mapping of the chest deformation under belt loading, which should be considered in the future development of physical and computational models of the thorax.

Kinematic Response of the Spine During Simulated Aircraft Ejections

Military aviators are susceptible to spinal injuries during high-speed ejection scenarios. These injuries commonly arise as a result of strains induced by extreme flexion or compression of the spinal column. This study characterizes the vertebral motion of two postmortem human surrogates (PMHS) during a simulated catapult phase of ejection on a horizontal decelerator sled. During testing, the PMHS were restrained supinely to a mock ejection seat and subjected to a horizontal deceleration profile directed along the local z-axis. Two midsized males (175.3 cm, 77.1 kg; 185.4 cm, 72.6 kg) were tested. High-rate motion capture equipment was used to measure the three-dimensional displacement of the head, vertebrae, and pelvis during the ejection event. The two PMHS showed generally similar kinematic motion. Head injury criterion (HIC) results were well below injury threshold levels for both specimens. The specimens both showed compression of the spine, with a reduction in length of 23.9 mm and 45.7 mm. Post-test autopsies revealed fractures in the C5, T1, and L1 vertebrae. This paper provides an analysis of spinal motion during an aircraft ejection.The injuries observed in the test subjects were consistent with those seen in epidemiological studies. Future studies should examine the effects of gender, muscle tensing, out-of-position (of head from neutral position) occupants, and external forces (e.g., windblast) on spinal kinematics during aircraft ejection.

Ejection Injury to the Spine in Small Aviators: Sled Tests of Manikins vs. Post Mortem Specimens

This study presents the results of seven aerospace manikin and three post mortem human surrogate (PMHS) horizontal deceleration sled tests. The objective of this study was to establish a body of baseline data that examines the ability of small (fifth percentile) manikins to predict whole-body kinematics associated with aircraft ejection, and whether currently available head and neck injury criteria are applicable in these situations. Subjects were exposed to a short-duration local z-axis sled pulse while horizontally seated and restrained in an ejection seat. Test subjects included instrumented fifth percentile female and male manikins, and two small (163.8 cm, 48.3 kg; 143.5 cm, 48.6 kg) female and one small (166.2 cm, 54.3 kg) male PMHS. The anterior (local x-axis) translations of the PMHS heads were less than those observed in the manikin tests, but the local z-axis translations of the PMHS heads were greater than those of the manikins. Z-axis translations of the manikins' T1 were generally similar to those of the PMHS T1, but the anterior x-axis translations of T1 were greater in the PMHS. The neck injury criterion (Nij) tended to under-predict observed injury (primarily ruptures of the posterior ligaments at C4-5, T2-3), and the Beam Criterion (BC) tended to over-predict observed injury for small occupants. The USN/USAF neck injury criteria (NIC) performed best in predicting the observed injuries. Present manikin designs do not predict the kinematics of PMHS in ejection tests. Further refinement of existing injury criteria is required to accurately predict location and severity of ejection-induced injuries.

Viscoelastic Response of the Thorax under Dynamic Belt Loading

Objective: Three postmortem human surrogates (PMHS) were positioned and rigidly mounted through the spine to a tabletop test fixture for the purpose of characterizing thoracic response to diagonal belt loading with well-defined boundary conditions. Methods: These PMHS were mounted to a stationary apparatus that supported the spine and shoulders in a configuration comparable to that seen in a 48 km/h automobile sled test at the time of maximum chest deformation. A belt restraint was positioned across the anterior torso with attachments at D-ring and buckle locations based on the geometry of a mid-sized sedan. The belt was attached to a trolley driven by a hydraulic ram linked to a universal test machine. Ramp and hold experiments were conducted at rates of 0.5, 0.9, and 1.2 m/s and hold times of 60 s. Ramp-hold displacement waveforms of up to 20 percent of the chest depth were applied to the chest while the resulting belt loads and spinal reaction loads were recorded. These data were used to identify parameters in a seven-parameter thoracic structural model mathematically analogous to a viscoelastic material model. A final test with 40 percent deflection was performed at the completion of the loading sequence. Results: Model fits to ramps of different magnitudes indicated that the assumption of temporal linearity was reasonable over the range of inputs in this study. In agreement with previous studies, the spatial (force-deflection) response was only slightly nonlinear, indicating that a fully linear model would be reasonable up to the deflection levels used here. Conclusions: Pronounced variability in the instantaneous elastic behavior was observed among the three test subjects, whereas the relaxation behavior exhibited less variability.

Pedestrian kinematic response to mid-sized vehicle impact

This study examines how pedestrian anthropometry affects response kinematics when pedestrians are struck by an automobile. Seven post-mortem human surrogates were tested under identical conditions in full-scale vehicle-pedestrian impact experiments using a mid-sized sedan. The ability of a geometric scaling technique to predict the response of a mid-sized pedestrian from the responses of pedestrians of other statures was evaluated. Pedestrian kinematic response to sedan impacts was shown to be sensitive to the pelvis and hood interaction, which was largely determined by the height of the pelvis relative to the hood leading edge. The scaling method was shown to be not sufficient to predict mid-sized pedestrian response in impacts with the test vehicle used in this study.

Whole-body kinematic and dynamic response of restrained PMHS in frontal sled tests.

The literature contains a wide range of response data describing the biomechanics of isolated body regions. Current data for the validation of frontal anthropomorphic test devices and human body computational models lack, however, a detailed description of the whole-body response to loading with contemporary restraints in automobile crashes. This study presents data from 14 frontal sled tests describing the physical response of postmortem human surrogates (PMHS) in the following frontal crash environments: A) (5 tests) driver position, force-limited 3-point belt plus airbag restraint (FLB+AB), 48 km/h deltaV. B) (3 tests) passenger position, FLB+AB restraint, 48 km/h deltaV. C) (3 tests) passenger position, standard (not force-limited) 3-point belt plus air bag restraint (SB+AB), 48 km/h deltaV. D) (3 tests) passenger position, standard 3-point belt restraint (SB), 29 km/h deltaV. Reported data include x-axis and z-axis (SAE occupant reference frame) accelerations of the head, spine (upper, middle, and lower), and pelvis; rate of angular rotation of the head about y-axis; displacements of the head, upper spine, pelvis and knee relative to the vehicle buck; and deformation contours of the upper and lower chest. A variety of kinematic trends are identified across the different test conditions, including a decrease in head and thorax excursion and a change in the nature of the excursion in the driver position compared to the passenger position. Despite this increase in forward excursion when compared to the driver's side FLB+AB tests, the passenger's side FLB+AB tests resulted in greater peak thoracic (T8) x-axis accelerations (passenger's side -29 g; driver's side -22 g;) and comparable maximum chest deflection (passenger's side - 23+/-3.1% of the undeformed chest depth; driver's side - 23+/-5.6%; ). In the 48 km/h passenger's side tests, the head excursion associated with the force-limiting belt system was approximately 15% greater than that for a standard belt system in tests that were otherwise identical. This was accompanied by a decrease in chest deflection of approximately 20% with the force-limiting system. Despite the decrease in test speed, the 29 km/h passenger's side tests with standard (not force-limiting) 3-point belt restraints resulted in maximum chest deflection (16+/-5.6% average) comparable to that observed in the 48 km/h, FLB+AB, driver's side tests (21+/-3.1% average). Finally, forward head excursion was slightly higher in the 29 km/h passenger's side tests (33+/-1.1 cm average) than in the 48 km/h driver's side tests (27+/-3.7 cm average), and was lower than that in the 48 km/h FLB+AB (58+/-4.4 cm average) and SB+AB (46+/-2.1 cm average) passenger's side tests.