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The two main motivations for Wayne State University (WSU) and Henry Ford Hospital (HFH) researchers to develop numerical human surrogates are advanced computing technology and a high-speed x-ray imaging device not available just a decade ago. This paper summarizes the capabilities and limitations of detailed component models of the human body, from head to foot, developed at WSU over the last decade (Zhang et al. 2001, Yang et al. 1998, Shah et al. 2001, Iwamoto et al. 2000, Lee et al. 2001 and Beillas et al. 2001). All of these models were validated against global response data obtained from relevant high-speed cadaveric tests. Additionally, some models were also validated against local kinematics of bones or soft tissues obtained using the high-speed x-ray system. All of these models have been scaled to conform to the key dimensions of a 50th percentile male.

The frequency of pelvic fractures is 10%-14% in side impact crashes. In this study, seventeen side impact sled tests were performed using a Heidelberg-type seat fixture. The pelvis along with the rest of the torso impacted a sidewall in these tests. This series of runs provided a good test of injury criteria performance for a variety of impact surfaces. Pelvic injury criteria based on force, acceleration, compression, and the viscous criterion were evaluated. Force was found to be a good criterion according to both the Weibull and Logist analysis. A promising new injury criterion tested was “Average Force” (Favg). It reflects the rate of momentum transfer to the pelvis during a side impact. The slope of the pelvic momentum trace, from 10 to 90% of its peak, is the time rate of change of momentum, and has the dimension of force. In a 32 km/h (20 mph) impact, Favg is 5 kN for a 25% probability of an AIS 2 pelvic injury (maximum likelihood 0.0135).

Seventeen side impact sled tests were performed using a horizontally accelerated sled and a Heidelberg-type seat fixture. In these tests the subject's whole body impacted a sidewall with one of three surface conditions: 1) a flat, rigid side wall, 2) an unpadded side wall with a 6″ pelvic offset, or 3) a flat, padded side wall. Forces, deformations and accelerations of the thorax were measured. VCmax emerged as a good injury criterion in this test series. In the WSU-CDC tests VCmax was 0.86 m/s for the half-chest at 25% probability of AIS 4. In addition, a new criterion we have termed “Average Spine Acceleration” (ASA) performed well. ASA is obtained by integrating the T12-y spinal acceleration to obtain spine velocity. The slope of the spine velocity trace is the Average Spine Acceleration, and reflects the rate of momentum transfer to the body during an impact.

Unembalmed cadavers were exposed to −Gx acceleration while restrained by applying a frontal load to the chest. A pre-deployed non-venting production air cushion mounted on a non-collapsible horizontal steering column provided the distributed load. The sled deceleration pulse was determined from a series of Part 572 dummy runs in which the HIC, chest acceleration and knee loads were at but not in excess of the limits specified in the current FMVSS 208. A total of six cadavers have been tested. In three of the runs, there were severe neck injuries of the type which have not been observed previously in belted tests. They include complete severance of the cord, complete avulsion of the odontoid process, atlanto-occipital separation with ring fracture. This study does not claim to establish the injury potential of air bags but uses the air bag to provide a uniform restraining load to the chest to investigate the mechanism of neck injuries.

The effect of muscular response on occupant dynamics was studied in human volunteers exposed to low level impact acceleration. The study includes identification of muscular response, correlation of electromyographic activity with reaction force, and investigation of the effects of muscular restraint during impact. Human volunteers were subjected to −Gx impact acceleration in a simulated automobile environment while EMG activity of various lower extremity muscles was monitored. The seat and floor pan were supported on load cells which measured all restraining forces. Nine–accelerometer modules and high-speed photography were used to measure kinematics. Identical runs were made with an embalmed cadaver and dummy for comparison. Static EMG and force traces as well as dynamic results for various acceleration levels are presented. Differences between tensed and relaxed states are compared and discussed as to EMG response, force levels, and head kinematics.

Spinal kinematics of the living human volunteers undergoing -Gx impact acceleration are described along with the experimental procedures followed to acquire such data. There were 4 male and 3 female volunteers who were subjected to impacts in the tensed and relaxed mode from 2 - 8 g, in 1-g increments. Their lower extremities were tightly clamped to the impact seat and the pelvis was restrained by a lapbelt. The biodynamic response of the living spine is quite similar to that of the cadaveric spine, particularly in terms of T1 displacement, acceleration at T1 and flexural resistance. Female volunteers tend to withdraw from the test program at lower g-levels than males due to transient neck pain.

A six-axis femoral load cell was designed, fabricated, calibrated and tested in an ATD upper leg. It has linear characteristics with adequate output and dynamic response. Its output compared well with that of load cells mounted behind a knee bolster which was impacted by an ATD instrumented with this load cell. Although the axial load was found to be well below the present limit of FMVSS208, the bending moments were found to be high. A conservative tolerance limit for axial load should be considered and cadaver data are required.

Previous work on biodynamic response to whole-body +Gz (caudocephalad) acceleration gave ample evidence of facet loads in intact cadaveric spines. The computation of facet loads was based on an assumption that the total spine load was proportional to the measured seat pan load. In this study, the aim is to investigate the magnitude of the facet load during static and dynamic loading of an exised spinal segment. The applied loads resulted in a close simulation of those experienced by the intervertebral disc during whole-body impacts. An intervertebral load cell was used as the controlling mechanism in the duplication of the whole-body run in a testing machine. During these tests, both the total spine load and the intervertebral load were measured and thus the facet load was determined without relying on any assumptions.

A series of 10 full-scale experimental simulations of pedestrian-vehicle impact was carried out using cadavers and a 95th percentile anthropomorphic dummy. The test subjects were impacted laterally and frontally at 24, 32 and 40 km/h (15, 20 and 24 mph). Each subject was extensively instrumented with miniature accelerometers, up to a maximum of 53 transducers. The nine-accelerometer scheme was used to measure angular acceleration of body segments from which it was possible to compute the head injury criterion (HIC) for cadaver head impact. A full-size Chevrolet was used as the impacting vehicle. The impact event was three-dimensional in nature during which the body segments executed complex motions. Dummy impacts were more repeatable than cadaver impacts but the response of these test subjects were quite different. The HIC was higher for head-hood impact than for head-ground impact in two of the cases analyzed.

A biodynamic model of the spine simulated the action of spinal musculature on the head, vertebral bodies and pelvis in the midsagittal plane. Muscle was treated as a force generator whose contractile force was dependant on muscle stretch, stretch rate and neural delay time. Eight model runs were conducted with and without muscle, simulating +Gz and -Gx impact acceleration. The model predicted that spinal musculature was incapable of affecting overall spinal column kinematics. However, as a result of muscle contraction, significantly higher local axial forces were predicted in the discs and facets than were predicted when muscle was absent.

A review of the existing mathematical models of a car occupant in a rear-end crash reveals that existing models inadequately describe the kinematics of the occupant and cannot demonstrate the injury mechanisms involved. Most models concentrate on head and neck motion and have neglected to study the interaction of the occupant with the seat back, seat cushion, and restraint systems. Major deficiencies are the inability to simulate the torso sliding up the seat back and the absence of the thoracic and lumbar spine as deformable, load transmitting members. The paper shows the results of a 78 degree-of-freedom model of the spine, head, and pelvis which has already been validated in +Gz and -Gx acceleration directions. It considers automotive-type restraint systems, seat back, and seat cushions, and the torso is free to slide up the seat back.

The biodynamic response of cadaver torsos subjected to -Gx impact acceleration is discussed in this paper, with particular emphasis on the response of the vertebral column. The existence of an axial force along the spine and its manifestation as a load on the seat pan are reported. Spinal curvature appears to be an important factor in the generation of this spine load. In anthropometric dummies, the spine load does not exist. Details of the testing and results are given, and the development of a mathematical model is shown.