James R. Bolton

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.

Load path distribution within the pelvic structure under lateral loading

Lateral loading of the pelvis occurs for both vehicle occupants struck during side impacts as well as pedestrians. This research investigated the load distribution through the anterior (i.e. pubic symphysis) and posterior (i.e. sacrum) aspects of the pelvis for both acetabular and iliac loading. Sixteen male post-mortem human surrogate pelves were tested in quasi-static (n = 4) anddynamic (n = 12) conditions. On the basis of finite element model simulations of a pedestrian being struck at 40 km/hr, a velocity profile for the dynamic tests was prescribed that began at rest (v = 0 m/s) and then achieved apeak velocity of the struck pelvis moving relative to the midline at 4.5 m/s. The average anterior load at fracture from a high − rate acetabulumimp act was 1911 ± 929 N compared to the posterior load averaging 1022 ± 630 N. The average anterior load at fracture from a high − rate iliumimpact was 418 ± 388 N compared to the posterior load averaging 3107 ± 1473 N.

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.

Deployment of Air Bags into the Thorax of an Out-of-Position Dummy

The air bag has proven effective in reducing fatalities in frontal crashes with estimated decreases ranging from 11% to 30% depending on the size of the vehicle. At the same time, some air bag designs have caused fatalities when front-seat passengers have been in close proximity to the deploying air bag. The objective of this study was to develop an accurate and repeatable out-of-position test fixture to study the deployment of air bags into out-of-position occupants. Tests were performed with a fifth percentile female Hybrid III dummy and studied air bag loading on the thorax using draft ISO-2 out-of-position occupant positioning. All tests were performed in one of four nominal positions with respect to the steering wheel plane using a production depowered air bag from the current automobile fleet. Dummy positioning on the test fixture was found to be repeatable to within 0.3 cm on all axes. This variation was within the dimensional similarity of the two available fifth percentile female Hybrid III dummies. A large variation in occupant response was found with a very small change in effective distance from the sternum to the air bag module. Nearly 50% variation in peak chest center-of-gravity resultant acceleration was found when moving from the sternum pressed on the air bag module to the sternum effectively being 2 cm from the module. In addition, large variations in occupant response were found with vertical and horizontal displacements of the occupant with respect to the air bag module center. Also, a qualitative change in air bag deployment was found on changing the horizontal position by 4 cm to the left. These variations have significant implications for expected response from in-vehicle out-of-position dummy tests.

A method for the experimental investigation of acceleration as a mechanism of aortic injury

Rupture of the thoracic aorta is a leading cause of rapid fatality in automobile crashes, but the mechanism of this injury remains unknown. One commonly postulated mechanism is a differential motion of the aortic arch relative to the heart and its neighboring vessels caused by high-magnitude acceleration of the thorax. Recent Indy car crash data show, however, that humans can withstand accelerations exceeding 100 g with no injury to the thoracic vasculature. This paper presents a method to investigate the efficacy of acceleration as an aortic injury mechanism using high-acceleration, low chest deflection sled tests. The repeatability and predictability of the test method was evaluated using two Hybrid III tests and two tests with cadaver subjects. The cadaver tests resulted in sustained mid-spine accelerations of up to 80 g for 20 ms with peak mid-spine accelerations of up to 175 g, and maximum chest deflections lower than 11% of the total chest depth. Transient increases in intra-aortic pressure up to 177 kPa were measured. No macroscopic injuries to the thoracic aorta resulted from these tests. The method employed proved consistent and repeatable. This method may be appropriate for future investigation of the efficacy of acceleration as a predictor of aortic injury.

Comparison and evaluation of contemporary restraint systems in the driver and front-passenger environments

Abstract Restrained driver and passenger kinematics and injury outcome in frontal collisions are compared using US fatality field data and post-mortem human surrogate sled tests. The fatality data indicate that a frontal airbag may provide greater benefit for a passenger than for a driver. The thoracic injuries sustained by passenger-side surrogates restrained by a force-limited, pre-tensioned belt and airbag are evaluated, and kinematics are compared with driver-side subjects exposed to a similar impact. Driver and passenger kinematic differences are identified and the implications are discussed with respect to the injury-predictive ability of existing thoracic injury criteria. The chest acceleration of the passenger-side subjects exhibited a bimodal profile with an initial (and global) maximum before the subject loaded the airbag. A second acceleration peak occurred as the subject loaded both the belt and the airbag. A similarly restrained driver-side subject loaded the belt and airbag concurrently at the time of peak chest acceleration and therefore did not exhibit this biomodal chest acceleration. While the injury-causing or injury-mitigating significance of this bimodal response is not known, its significance with respect to thoracic injury prediction is discussed.

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.