An Integrated Approach to Identify Thoracic Injuries in Rollover Crashes

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Abstract

The objective of this work is to evaluate thoracic injuries for restrained occupants in far-side rollover and to propose a dynamic rollover test device. Most rollover studies have been driven by litigation and mainly focused on head and spinal injuries, while thoracic injuries, which correspond to one third of belted rollover injuries, have not been fully addressed.

In 2009, the National Highway Traffic Safety Administration (NHTSA) updated the Federal Motor Vehicle Safety Standard (FMVSS) No. 216, which specifies a quasi-static test procedure. The rule was amended to double the strength-to-weight ratio (SWR) requirement from 1.5 to 3.0 on both sides of the vehicle, when tested sequentially. Most vehicles must meet the upgraded requirements by September 1, 2015. Ejection mitigation was addressed by component testing, as mandated in FMVSS No. 226. This regulation is currently being phased in and all manufacturers should fully comply by September 1, 2017. It should be noted that there is no regulation that requires the test of a complete vehicle in a rollover crash.

These federal regulation upgrades will affect the roof strength and ejection mitigation in current and future vehicles. Such changes are expected to reduce roof crush, and (partial/full) ejections, but may not address the vast majority of thoracic injuries.

The focus of this research is first to provide an understanding of the variations of different initial conditions on vehicle damage patterns, especially those that have been associated with thoracic injuries. The vehicle lateral speed, the roll rate, the initial position at roof-to-ground contact (different yaw, pitch, and roll angles), and the vehicle drop height variables were investigated for extended simulation times (2.5 seconds, up to 4 quarter-turn rollover). Subsequently, the Hybrid III 50th percentile male anthropomorphic test device (ATD), which incorporated chest force measurements, was used in the rollover simulations. Finally, the Total Human Model for Safety (THUMS) FE model was used to investigate the potential of using a complex humanlike dummy in rollover simulations.

The simulations showed that vehicle rollover is influenced by many initial condition parameters and vehicle characteristics (roof structure design, shape, and strength). These parameters and characteristics affect the vehicle kinematics and roof deformation during the rollover crash. For some initial conditions, it was found that a vehicle landing on its wheel at the 4th quarter-turn may cause inboard chest injury due to contact with the center console. Additionally, the chest may be dynamically loaded by the seatbelt, seat back and other interior components in the vehicle, sometimes simultaneously, producing highly complex loading.

After reviewing existing quasi-static and dynamic rollover test devices, and assessing full-scale research tests and rollover simulations, a proposed dynamic Guided Rollover Test (GRT) device is presented. The GRT device enables a test vehicle to behave in a fashion similar to a real-life rollover, exposing the (dummy) occupant to realistic kinematics and placing the dummy in the correct location prior to the start of the rollover, loading the roof structure dynamically, and assessing the full- and partial-ejection and injuries (including thoracic injuries) of the occupants. The GRT device subjects vehicles to repeatable initial conditions using a maneuver of a forward motion followed by a gradually increasing curvature sufficient to roll most vehicles. The test vehicle is carried on a cart that follows a guided track, which eliminates the influence of vehicle and road characteristics such as tire properties or road-surface friction during rollover initiation. The vehicle is then subjected to its own roll characteristics that define the dynamics and consequently the roof-to-ground contact.

The use of finite element vehicle and dummy models in the full-scale rollover simulations proved to be valuable in breaking through the stagnation in rollover research. One thoracic injury mode was found and many potential injuries were shown to be possible. Additionally, the proposed rollover test device and all-inclusive rollover rating system would subject vehicles to similar test initial conditions and facilitate dynamic evaluation and comparison.

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