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Frontal crashes and near-side crashes were compared and found to be significantly different events. In a frontal crash, the energy to be dissipated from the occupant is constant for a given speed. In a side crash, the energy transferred to a struck-side occupant depends highly on his interaction with the door. That difference has important implications on the choice of countermeasures, injury criteria, and subsystem tests. In a frontal crash, chest and abdominal injuries occur in the “second” impact when the occupant, acting like a free-flight mass, strikes the interior. Padding can absorb some of the free-flight energy, reduce the impact force, and provide earlier and longer contact of the occupant with the interior. The earlier contact decreases the differential velocity of the occupant to the interior, and the longer contact allows more time and greater distance to dissipate the kinetic energy.

An analysis of the MVMA-sponsored full scale side impact tests of modified Ford LTDs indicated that the high, nonhuman-like inertia of the dummy chest had profound influence over the dummy responses. In particular, energy absorbing padding was always crushed by the inertial force when the door impacted the dummy. The heavy axial pistons and dampers in the dummy chest, and the variable arm positions further exacerbated poor repeatibility of the chest deflection responses. Although TTI (d), an acceleration based injury criterion, discriminated the presence of padding and was repeatable, it exaggerated the potential benefits of padding in injury mitigation. Analysis of the data also indicated that the structural enhancement performed on the LTDs did not reduce the door intrusion velocity consistently in the tests. Consequently, dummy responses were not influenced by the structural enhancement.

The purpose of this study was to replace the axial deforming elements in the current EUROSID dummy with spring steel ribs and attached damping material to provide improved biofidelity in the lateral chest impact response. This report provides a description of the design, construction, and evaluation of the modified EUROSID chest for injury assessment in side impact crashes. Three spring steel ribs were designed to provide stiffness and deflections of 120 mm when attached to the block on the spine of the EUROSID dummy. Damping material was epoxied to the ribs and the system provided biofidelity in the lateral impact response for blunt impact loading at 4.3 m/s and 6.7 m/s. The new design provides significantly reduced inertia of the near side rib cage, elastic and viscous properties that are representative of the lateral human response and the ability to measure the deflection response of the rib cage for injury assessment with the Viscous response.

The timing of liver laceration in swine during the course of a blunt impact was investigated. The swine were impacted on the upper abdomen by the lower segment of a steering wheel at 6, 9 and 12 m/s. The degree of compression in each impact was controlled independently from 10 to 50%. By varying when “the punch of an impact was pulled,” we reproduced progressive segments of a longer duration blunt impact. Autopsy of the subjects demonstrated that lacerations were initiated after 8 ms of loading at 9 m/s and 6 ms of loading at 12 m/s. The time of injury was concurrent with the time when the Viscous response exceeded a threshold of 1.2 m/s in our specimens. The Viscous injury criterion, defined as the peak Viscous response, was found to be the best predictor of liver laceration. We conclude that the Viscous response relates to the actual etiology of injury, in addition to being an excellent correlative measure.

The discovery of the mechanism of impact-induced soft tissue injury has led to our introduction of a Viscous Injury Criterion, which predicts the severity and the time of occurrence of soft tissue injury induced by impact when other criteria have failed. Human tolerance has been defined by the Viscous response, [VC], a time function generated by the instantaneous product of velocity of deformation [V(t)] and amount of compression [C(t)] of the body. [VC]max = 1.0 m/s corresponds experimentally to a 25% chance of sustaining severe thoracic injury (AIS ≥ 4) in a blunt frontal impact. A similar level of risk for critical abdominal injury (AIS ≥ 5) in a blunt frontal impact is [VC]max = 1.2 m/s. However, human tolerance is defined more completely by the probability function of injury risk versus [VC]max. The Viscous response can be evaluated in the Hybrid III anthropomorphic dummy by a straightforward analysis of the chest deflection data.

The introduction of energy absorbing steering systems has provided a substantial reduction of occupant injury in car crashes. However, the steering system remains the most important source of occupant injury. Injury associated with steering assembly contact is due to high exposure; energy absorbing steering systems reduce the risk of injury for drivers when compared to the injury risk of right front passengers. Our investigation addressed loading of the upper abdominal region by the steering wheel rim using a physiological model for study of soft tissue injury. Injury to the liver was related to the abdominal compression response associated with rim loading. Although liver injury correlated somewhat with peak abdominal compression, a better correlation was found when the rate of compression was also considered. Force limiting by the steering wheel, not by column compression, most strongly influenced the outcome of abdominal injury.

There are currently two accepted criteria for assessment act exposures. Our studies have shown an interaction between the deformation velocity and level of compression during impact, resulting in a greater compression tolerance for low-speed impact than for high-speed loadings. High-speed thoracic impact can cause critical or fatal injury in physiologic experiments before exceeding the acceleration or compression tolerance. The velocity-sensitive tolerance is represented by the maximum product of velocity of deformation and compression, which is derivable from the chest compression response. As the magnitude of this “viscous” response increases, the risk of serious or fatal injury increases. This paper discusses the analysis of available literature and results from our laboratory and demonstrates the need for a viscous tolerance criterion to assess chest impact protection in high-velocity impact.