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Journal Article

Rollover Dynamics: An Exploration of the Fundamentals

Research focusing on automotive rollovers has garnered a great deal of attention in recent years. Substantial effort has been directed toward the evaluation of rollover resistance. Issues related to crashworthiness, such as roof strength and restraint performance, have also received a great deal of attention. Much less research effort has been directed toward a more detailed study of the rollover dynamics from point-of-trip to point-of-rest. The reconstruction of rollover crashes often requires a thorough examination of the events taking place between point-of-trip and point-of-rest. Increasing demands are placed on reconstructionists to provide greater levels of detail regarding the roll sequence. Examples include, but are not limited to, roll rates at the quarter-roll level, CG trajectory (horizontal and vertical), roll angle at impact, and ground contact velocity. Often the detail that can be provided in a rollover reconstruction is limited by a lack of physical evidence.
Journal Article

Measurement and Modeling of Rollover Airborne Trajectories

Much has been written about reconstruction techniques and testing methods concerning vehicle rollovers. To date, most of the literature describes rollovers as one-dimensional events. Rollovers account for a disproportionate fraction of serious injuries and fatalities among all motor vehicle accidents. The three-dimensional nature of rollover sequences in which a rolling vehicle experiences multiple ground contacts contributes to the environment where such injuries occur. An analytical technique is developed to model the airborne segments of a rollover sequence as a parabolic path of the vehicle center of gravity. A formulation for the center of gravity descent from maximum elevation to full ground contact is developed. This formulation contains variables that may be readily determined from a thorough reconstruction. Ultimately, this formulation will also provide a vertical ground impact velocity at contact.
Technical Paper

Determination and Mechanisms of Motor Vehicle Structural Restitution from Crash Test Data

The coefficient of restitution is an indicator of the elasticity of a collision. Restitution, or elastic rebound of a deformed surface, contributes to the change in velocity of collision partners, a common measure of injury severity in automobile collisions. Because of the complex nature of collisions between motor vehicles, the characterization of the expected magnitude of the coefficient in such collisions lacks detail and mechanisms influencing its value are not well understood. Using crash test data from the National Highway Traffic Safety Administration (NHTSA), this study investigates the expected magnitude of the coefficient of restitution and mechanisms influencing restitution in automobile collisions. Both vehicle-to-barrier and vehicle-to-vehicle tests are considered for all types of collisions. The influence of a variety of collision and vehicle parameters on restitution is also explored.
Technical Paper

A Repeated-Crash Test Technique for Assessment of Structural Impact Behavior

An economical alternative technique is presented for obtaining vehicle frontal crush characteristics from a series of repeated low speed barrier crashes. Results were analyzed using a technique of linear correlation of residual crush depth with a defined crush energy parameter. The data compared closely with crashes reported in the literature, and suggested that the structure exhibits only a slight strain rate sensitivity. Crush energy is shown to correlate well with dynamic crush depth. Relations among dynamic and residual crush and recovery distance are reported, Velocity restitution is shown to be about constant at 15% over the impact velocity range employed. A force-deflection relation based on the offset force linear harmonic oscillator theory is suggested, shown to agree quite well with data. Repeated crash testing can be an effective method to obtain information needed for development of analytical and predictive tools useful in design and reconstruction.
Technical Paper

A Technical Review of Automotive Racing Fuels

Automobile racing engine performance has historically progressed with and aided the development of automotive technology. Racing engine performance has been improved in various applications with specialized liquid fuels, such as nitroparaffins, alcohol (methanol) and certain hydrocarbons used in racing gasolines. This paper presents physical and thermodynamic properties of commonly used racing fuels and selected additives, including nitrous oxide and hydrazine. Improving the antiknock properties of gasoline for racing purposes is also discussed. Engine operating characteristics and power output for each fuel are discussed in terms of appropriate fuel properties and engine parameters such as air/fuel ratio and compression ratio. Combustion of various fuels is discussed along with the effect of dissociation and heat loss on performance. Some experimental performance data are presented, and theoretical and practical considerations which effect fuel utilization are also discussed.
Journal Article

Rollover Crash Tests on Dirt: An Examination of Rollover Dynamics

Most rollover literature is statistical in nature, focuses on reconstructed field data and experiences, or utilizes a very broad pool of dissimilar test data. When test data is presented, nearly all of it involves hard surface rollover tests performed at speeds near 30 mph, with a mix of passenger cars, sport utility vehicles and minivans. Five full-scale dolly rollover tests on dirt of production sport utility vehicles (SUV) and multi-purpose vehicles (MPV) were performed with similar input parameters. The similarities included Federal Motor Vehicle Safety Standard (FMVSS) 208 rollover dolly initiated events, level dirt rollover surfaces, and initiation speeds over 40 mph. All tests were recorded with multiple high-speed and real-time cameras. Additionally, some of the tests included detailed documentation of the rollover surface and the resulting evidence and debris patterns, as well as onboard angular rate sensing instrumentation.
Technical Paper

Friction Applications in Accident Reconstruction

The determination of appropriate friction coefficient values is an important aspect of accident reconstruction. Tire-roadway friction values are highly dependent on a variety of physical factors. Factors such as tire design, side force limitations, road surface wetness, vehicle speed, and load shifting require understanding if useful reconstruction calculations are to be made. Tabulated experimental friction coefficient data are available, and may be improved upon in many situations by simple testing procedures. This paper presents a technical review of basic concepts and principles of friction as they apply to accident reconstruction and automobile safety. A brief review of test measurement methods is also presented, together with simple methods of friction measurement to obtain more precise values in many situations. This paper also recommends coefficient values for reconstruction applications other than tire- roadway forces.