Kennerly Digges

Side impact injury risk for belted far side passenger vehicle occupants

In a side impact, the occupants on both the struck, or near side, of the vehicle and the occupants on the opposite, or far side, of the vehicle are at risk of injury. Since model year 1997, all passenger cars in the U.S. have been required to comply with FMVSS No. 214, a safety standard that mandates a minimum level of side crash protection for near side occupants. No such federal safety standard exists for far side occupants. The mechanism of far side injury is believed to be quite different than the injury mechanism for near side injury. Far side impact protection may require the development of different countermeasures than those which are effective for near side impact protection. This paper evaluates the risk of side crash injury for far side occupants as a basis for developing far side impact injury countermeasures. Based on the analysis of NASS/CDS 1993-2002, this study examines the injury outcome of over 4500 car, light truck, and van occupants subjected to far side impact. The analysis was restricted to 3-point belted occupants. The paper evaluates the risk of far side impact injury as a function of struck body type, collision partner, delta-V, crash direction (PDOF), occupant compartment intrusion, and injury contact source. Injury risk is evaluated using the maximum injury severity for each occupant, by injury severity for each body region, and by Harm, a social cost measure.

Occult abdominal injuries to airbag-protected crash victims: a challenge to trauma systems.

A multidisciplinary, automobile crash investigation team at the University of Miami School of Medicine, William Lehman Injury Research Center of Jackson Memorial Hospital/Ryder Trauma Center in Miami, Florida, is conducting a detailed medical and engineering study. The focus is restrained (seatbelts, airbag, or both) occupants involved in frontal crashes who have been severely injured. More than 60 crashes have been included in the study to date. Analysis of the initial data supports the general conclusion that restraint systems are working to reduce many of the head and chest injuries suffered by unrestrained occupants. However, abdominal injuries among airbag-protected occupants still occur. Some are found among occupants who appeared uninjured at the scene. Case examples are provided to illustrate abdominal injuries associated with airbag-protected crashes. The challenges of recognizing injuries to airbag-protected occupants are discussed. To assist in recognizing the extent of injuries to occupants protected by airbags, it is suggested that evidence from the crash scene be used in the triage decision. For the abdominal injury cases observed in this study, deformation of the steering system was the vehicle characteristic most frequently observed. The presence of steering wheel deformation is an indicator of increased likelihood of internal injury. This may justify transporting the victim to a trauma center for a closer examination for abdominal injuries.

Computer modeling and validation of a hybrid III dummy for crashworthiness simulation

A finite element model of the Hybrid III crash test dummy is developed for computer crash simulations. A description of the major components of the Hybrid III dummy and their finite element representations are given. The results of testing procedures required by the Code of Federal Regulations on the physical dummy are also presented and compared with results obtained from the computer model. The reasonable accuracy obtained from the model makes it useful for crashworthiness simulations when combined with other vehicle and restraint system models.

Blunt trauma and acute aortic syndrome: a three-layer finite-element model of the aortic wall

OBJECTIVE The exact process by which blunt trauma to the aorta produces a typical characteristic lesion set of primary, transverse, intimal injury remains unknown. The likely cause is a combination of intraluminal hypertension and mechanical deformation. We set about creating a three-layer finite-element model of the aorta. We hypothesised that deformation of the aorta through tension, torsion and bending would have differential effects on the constitutive layers of the aorta and this differential stress strain pattern would help to explain the mechanism of this injury. METHODS A finite-element model of the aorta was created with three distinct layers representing tunica intima, media and adventitia. A rubble-like material model in the commercial dynamic finite-element package LS-DYNA was adopted. Numerical methods for considering the interaction between aortic tissue (solid) and blood (fluid) were defined using arbitrary Lagrangian Eulerian methods. Simulations of mechanical deformation including tension, torsion and bending were applied with loading set at 1m/s and intraluminal blood pressure rising from 86.6mmHg to 146mmHg. The simulations were run until material failure. The role of blood within these simulations was explored. RESULT Our initial simulations confirmed the functionality of the three-layer finite-element model of the aorta with behaviour as expected from previously published experimentation. The addition of mechanical loading through torsion, tension and bending resulted in failure of the aorta at significantly lower mean blood pressures than without. Temporal and spatial aspects of failure were distinct for each method of loading. Bending resulted in rapid primary adventitial failure while tension and torsion resulted in a relatively delayed primary intimal failure. Blood flow altered the stress strain characteristics within the model. CONCLUSIONS This work confirms the feasibility of using a three-layer FE model of the aorta. Our data suggest that the relative contribution of intraluminal hypertension to BTAR is lower in the presence of complex loading by tension, torsion and bending. In addition, failure of the aorta is load dependent with bending causing a relatively early primary adventitial failure, while tension and torsion result in a relatively delayed primary intimal failure.

Research programs in crash-induced fire safety

The research reported in this paper is a follow-on to a five year research program conducted by General Motors in accordance with an administrative Settlement Agreement reached with the US Department of Transportation. This paper is the third in a series of technical papers intended to disseminate the results of the ongoing research [Digges 2003 and 2004]. This paper summarizes progress in several of the projects. A statistical analysis of FARS and NASS/CDS indicates that frontal collisions are the most common in both fatal and non-fatal crashes with fires. NASS/CDS indicates that most major and minor fires originate under the hood. Fire rates in FARS are higher in rollovers than in planar crashes, and most rollover fires in NASS/CDS originate under the hood. An experimental study of the fuel containment technology in rollover crashes found that some current vehicle models are designed to prevent fuel tank leakage in rollovers, even when the fuel lines and hoses are severed (one at a time). An experimental under hood fire suppression system was tested and showed promise. Conductivity measurements of various engine compartment fluids indicates that these fluids are not sufficiently conductive to cause an ignition risk by inducing arc-tracking in 42 volt electrical systems.

Airbag and facebag benefits and costs

There is debate about the appropriate design of supplementary airbags for passenger car occupants with high levels of seatbelt use. A theoretical analysis was performed to demonstrate the likely costs and benefits of U.S. fullsize driver airbags and the smaller European-style facebag. This study, undertaken for the Federal Office of Road Safety in Australia, builds upon previous work in this area. Benefits were determined using Harm Reductions for front-seat occupants involved in frontal crashes. A sensitivity analysis was undertaken for different benefit scenarios for the facebag, given the lack of available performance data. Likely costs of the components were derived from information provided by the local automobile manufacturers, part suppliers, and vehicle importers, with adjustments made for fitting to Australian vehicles. The results demonstrate the advantage of fullsize airbags over facebags, even when seatbelt wearing rates are high.

Effect of increase in weight and stiffness of vehicles on the safety of rear seat occupants

In this study, full-scale finite element (FE) simulations have been performed to identify factors affecting the protection of rear seat occupants. An FE model based on the 2001 Ford Taurus was used and coupled with a Hybrid III 5th percentile female dummy model in the rear seat of the vehicle. The dummy model was restrained using a three-point belt system. The effects of changes in the vehicle design, including changes in vehicle weight and stiffness, on injury readings of the rear seat dummy, including head injury criterion (HIC), chest acceleration and Nij, were evaluated. The simulation results were first validated against available test data for a Ford Taurus vehicle and later used for the analysis. The analysis showed that an increase in the stiffness of the vehicle can significantly increase rear seat dummy injury measures. It was shown, for example, that the HIC15 of a rear seat dummy can increase from 478 to 755 between two vehicles with an increase in stiffness from 1000 to 1557 N/mm.

HEART INJURIES AMONG RESTRAINED OCCUPANTS IN FRONTAL CRASHES

The William Lehman Injury Research Center has conducted multi-disciplinary investigations of one hundred seventy-eight crashes involving adult occupants protected by safety belts and air bags. When used in conjunction with National Accident Sampling System/Crashworthiness Data System (NASS/CDS) they provide insight into the most severe injuries suffered by restrained occupants in frontal crashes. Heart injuries are rare, but when they occur they are usually life threatening. NASS/CDS shows that heart injuries comprise about 0.2% of the injuries in frontal tow-away crashes, In the NHTSA file of Special Crash Investigations (SCI) of air bag cases, heart injuries are reported in 1% of the occupants over 15 years of age. Twenty-five percent of the fatally injured occupants had heart injuries and 83% of those with heart injury died. In the Lehman Center cases, heart injuries are present in 5.1% of the cases. Forty percent of the fatally injured had heart injury, and 78% of the victims with heart injury died. This paper suggests two additional triage criteria, based on observations from multi-disciplinary studies. These include: (1) passengers in 2-point belts and crashes of 25 mph or higher, with the lap belt unfastened or with the seat full forward; (2) drivers in crash conditions which delay the air bag deployment or permit the driver to be close to the air bag at deployment. (A) For the covering abstract see IRRD 893297.

Severe Head and Neck Injuries in NASS Rear Impacts

This paper examines the characteristics of rear impact crashes. General information about rear impact collisions is derived from recent data from the National Automotive Sampling System, General Estimates System (NASS/GES) and Fatality Analysis Reporting System (FARS) as reported in the annual National Highway Traffic Safety Administration (NHTSA) Traffic Safety Facts. Additional details about the frequency, severity, type, and cause of injuries to front seat outboard occupants is analyzed using the National Automotive Sampling System, Crashworthiness Data System (NASS/CDS) data from 1997 to 2005. Serious head and neck injuries are focused on for further analysis. Specific cases from the CDS database that meet this classification are examined. Federal Motor Vehicle Safety Standard (FMVSS) 301-R test data is used to analyze occupant, seat, and vehicle kinematics in single impact rear collisions and to look at the occupant rebound velocity. The 301-R analysis found the forward velocity of the dummys head after rebound was as high at 6 m/sec. Analysis of NASS cases of vehicle-to-vehicle rear crashes found numerous contacts with frontal components even in the absence of a frontal crash. However, the most severe and frequent injuries were attributed to the seat back and head restraint. Severe injuries were observed in seats with and without deformation.

Application of Load Cell Barrier Data to Assess Vehicle Crash Performance and Compatibility

The National Highway Traffic Safety Administration routinely measures the force exerted on the barrier in crash tests. Thirty-six load cells on the face of the rigid barrier measure the force. This study examines the load cell barrier data collected during recent years of testing to determine how it can be used to assess vehicle structural crash characteristics and vehicle compatibility in car-to-car crashes. To illustrate the value of the data, the load cell measurements for a sport utility vehicle are compared with a small car. The proposed aggressiveness metrics for frontal crash modes are the force at 250 mm of crush, the linear stiffness at various levels of crush, and the height of the center of force at 250 mm of crush. For front-to-side vehicle crashes, some additional metrics are proposed. The force distribution when the loading is sufficient to cause intrusion of the side door is proposed as the basis for a metric. A high percentage of force on the lowest rows is indicative of sill loading, which should be favorable. A high percentage of force on the highest rows of load cells is indicative of intrusion in the region of the occupants thorax, which should be unfavorable. The presence of loading in the upper row of load cells at any time during the crash is indicative of a high hood, which could be the source of head impacts.