Stephen Forrest

ACCIDENT RECONSTRUCTION OF ROLLOVERS - A METHODOLOGY

This paper describes a practical methodology and protocol to assist reconstructionists in reconstructing both on-road and off-road rollover accidents. It points to previously published rollover studies relevant to the reconstructionist; presents a methodology and protocol for documenting and analyzing field data, most specifically accident vehicle damage; and, lastly, it reviews various presentation techniques useful for explanation and validation of the reconstructionists conclusions. (A) For the covering abstract see ITRD E106540.

Epoxy Reinforcing for Rollover Safety

Roof intrusion and roof contact injury are common factors in rollovers. Rollover crashes are the most dangerous collision type for light duty vehicles, measured by the ratios of fatal and serious injuries to the number of occupants involved in tow away crashes according to the National Automotive Sampling System. Over half of those sustaining injury with the occurrence of roof intrusion were belted. NHTSA estimates that roof crush intrusion occurs, and potentially contributes to serious or fatal occupant injury, in about 26% of the rollover crashes. Modern automobile vehicles utilize thin sheet metal construction formed into complex sections, which are spotwelded together. During vehicular rollovers, the roof is subjected to multi-directional loading which generally leads to localized buckling in the sheet metal roof pillars and subsequent intrusion into the occupant’s survival space. The utilization of expanding epoxies and rigid polyurethane foams within the sheet metal sections can delay wall buckling through localized confinement. This composite system, sheet metal sections filled with epoxy, demonstrates significant enhancements in peak force and energy absorption under multiple loading conditions. 4-point bending tests on representative vehicle sheet metal sections show a 6-fold increase in peak strength with the composite systems. Inverted drop tests comparisons document the additional survival space retained using the composite sheet metal and epoxy system.Copyright

STRENGTH IMPROVEMENTS TO AUTOMOTIVE ROOF COMPONENTS

Experimental results from three-point bending and axial compression tests of common automotive roof elements are presented in this paper. Modifications of these components were also tested to evaluate the effect of structural reinforcements and void filling. The strength of typical roof structural elements can be significantly improved in both three-point bending and in axial compression through the use of metal reinforcements and void filling. Both void filling and structural reinforcements demonstrated structural advantages in peak load capacities and energy absorption properties. Optimization of the proper void filling density and amount of metal reinforcement is required on an individual design basis to maximize the effectiveness. Both techniques demonstrated an ability to improve upon existing automotive components and repair some of their inherent weaknesses. For the covering abstract of the conference see IRRD E201404.

Acceleration Amplification in Safety Belt Buckle Systems

Multi-planar rollover accidents report belt usage rates that are noted to be significantly lower than that of planar crash modes.1 One explanation for this dramatic difference in reported belt usage in rollovers as compared to planar crashes is that highway patrol officers often conclude that an ejection would not have occurred had the occupant been belted. Restrained occupants can be ejected from the vehicle if the seat belts fail to restrain occupants as a result of belt spool out or buckle unlatching.2,3 Previous studies have documented the susceptibility of certain safety belt buckles to inertially unlatch.4,5,6,7 Under sufficient vertical accelerations, top button safety belt buckles have inertially unlatched in testing which would obviously negate the safety belts ability to restrain the occupant. This study expands on the mechanisms that could lead to inertial release under vertical loading in safety belt buckle systems with stiff attachments to the vehicle floor. An audio transducer was attached to a vehicle floorpan to induce accelerations at variable frequency and amplitude. Accelerations were recorded at the floorpan and safety belt buckle body simultaneously. Accelerations measured at the buckle body were up to 13 times greater than the accelerations measured at the floor pan for frequencies up to 8.5 kHz. The present study provides a first step to better understand the injury biomechanics by quantifying the accelerations at the floor pan and safety belt buckle.Copyright

Quasi-Static and Dynamic Testing as a Basis for Determining Seat Back Strength

The performance of a vehicle’s seat back in rear impact accidents can significantly affect occupant kinematics and the associated injury potential. Efforts to establish seat back performance requirements have generated significant debate between stiff and yielding seats [1]. While this paper will not attempt to resolve that issue, the analysis contained herein will compare various test methods for determining the strength of seat backs. This paper presents two quasi-static test methodologies that can be used to evaluate seat back performance. The first method utilizes the test procedure outlined in Federal Motor Vehicle Safety Standard (FMVSS) 207, Seating Systems, by loading the seat through its upper cross member. The second method utilizes an Anthropometric Test Dummy (ATD) and applies the load to the seat back through the ATD’s lumbar spine; this method is referred to as the Quasistatic Seat Test (QST). Four seat designs were tested utilizing these two quasistatic test methods. The observations and data obtained from these tests are then compared to dynamic test data documented in FMVSS 301, Fuel System Integrity, type rear impact and sled testing.Copyright

Assessing Rollover Protection Through the Deformable Occupant Compartment Impact Tester (DOCIT)

Occupant kinematics during rollover or inverted impacts has been the subject of significant research. Controlled experiments have utilized complete vehicles, partial vehicles and seat/restraints systems attached to various platforms. Previous experiments, which included the element of a deforming roof, have required the destruction of a complete vehicle. The Deformable Occupant Compartment Impact Tester (DOCIT) was developed to incorporate functions similar to previously research devices, but has a roof capable of deforming under impact, which can be reset without the destruction of a vehicle. The DOCIT is designed to simulate an occupant compartment including a roof, seat, restraint system in which an Anthropometric Test Device (ATD) is placed and subjected to a repeatable inverted impact environment. Two test series are reviewed, in which baseline tests that based upon real-world rollover accidents are compared with alternate design systems under the same impact environments.Copyright

Failure Analysis and Testing of an Overhead Door Design

Overhead doors see widespread use, primarily in garage door and truck body applications. Although overhead door systems can appear benign to users, there are some types of door system failures that can expose users to potentially injurious hazards. This paper will present the design and operation of an overhead door system in widespread use, the potential hazards of the system, and the possible failure modes of the system. A methodology will be presented that was used to analyze a door system that malfunctioned and resulted in a serious injury to a user. A test matrix which was used to analyze and replicate this malfunction is also presented.Copyright

Heavy Truck Rollover Testing Methods

Rollovers continue to be a major source of heavy truck fatalities when compared to other accident modes. Real world rollover accidents are analyzed and two distinct damage patterns are identified. Damage to heavy truck roofs can occur from lateral loading that transitions to vertical roof loading as the vehicle rolls onto its side and then over onto its roof. A second load path can occur when the vehicle has rolled onto its side and furrows into the ground generating large longitudinal friction forces between the roof and ground. A review of the previous literature and various test methodologies are presented. A sled impact test methodology is presented which allows for structural assessment of a heavy truck cab’s crashworthiness in both of these loading environments. Two test series are presented using the sled impact test methodology in order to analyze real world truck rollovers using varying impact platen and contact angles. The structural deformation and failure patterns were found to be consistent with damage seen in real world accident vehicles. In each case, a second equivalent truck cab was then reinforced and tested under similar conditions to evaluate the energy management and crush resistance of a stronger cab structure. These structural reinforcements demonstrated a substantial reduction in roof crush and protected the survival space of the occupant compartment.Copyright

Designing for Rollover Impacts With Narrow Objects

While some debate has existed in the literature regarding the relationship between roof crush and occupant injury, the United States (U.S.) National Highway Traffic Safety Administration (NHTSA) has identified an increased safety benefit in improving roof strength and has mandated new higher roof crush resistance requirements. Frequently, roof impacts occur in rollover crashes when a vehicle travels off the lanes of the roadway and impacts various types of narrow objects along the roadway edge such as light poles, utility poles and/or trees. A previously reported tilt-test device and methodology is presented along with a new pendulum-test device and methodology, both of which allow for dynamic, repeatable impact evaluation of vehicle roof structures with narrow objects. The data collected includes not only residual crush, but also dynamic vehicle instrumentation and high speed video analysis. Two series of full vehicle tests are reported which represent each of the methodologies. The testing conditions for each series was determined based upon analysis of a real-world narrow object rollover impact. Each testing series allows for analysis of the damage resulting from the narrow object impact to the roof structure for a production vehicle as well as one that has been structurally reinforced. Results demonstrate that the reinforced roof structure significantly reduced the roof deformation compared to that of the production roof structure. The input energy of each test and resulting damage patterns can be used as both a reconstruction tool and structural assessment test.Copyright

Pendulum Animal Impact Testing

When vehicles collide with large animals, such as cattle, moose, elk or horses, the front seat occupants can be seriously or fatally injured; primarily due to roof deformation. In order to protect the front occupants in these accidents, it is necessary to understand the forces and energy involved in the interaction between the animal and the vehicle roof structure. The authors have developed a pendulum test incorporating an animal dummy to generate similar roof deformation to that experienced in real world animal impact accidents. The energy absorbed by the vehicle roof structure in the accident can then be determined by comparing the accident vehicle roof deformation to the pendulum test vehicle roof deformation. Ultimately, alternative roof structural designs are evaluated to demonstrate that a roof can perform well in this type of accident mode and reduce the risk for serious injuries to the occupants.Copyright