Daniel Parent

Crashworthiness analysis of the Placentia, CA rail collision

Abstract The Volpe Center is supporting the Federal Railroad Administration in performing rail passenger equipment crashworthiness research. The overall objective of this research is to develop strategies for improving structural crashworthiness and occupant protection. A field study of passenger train accidents is being conducted to investigate the causal mechanisms of how train occupants are injured during accidents. The investigation of the April 23, 2002 collision in Placentia, CA is being used to develop occupant protection strategies. This process first required the development of two simulation models: a collision dynamics model and an occupant response model. These models suggested that workstation tables brought about fatal thoracic and abdominal injuries in two occupants. Improved crashworthiness performance workstation tables, which limit the abdominal load imparted by the table, are currently under investigation through modelling and full-scale testing with advanced anthropomorphic test devices.

Test system, vehicle and occupant response repeatability evaluation in rollover crash tests: the deceleration rollover sled test

The goal of this study was to evaluate the repeatability afforded by a rollover test system in terms of the test conditions, vehicle and occupant response, and vehicle deformations. Eight full-scale rollover tests were performed using three 2002 Ford Explorer vehicles, instrumented with anthropomorphic test devices and arrays of accelerometers and angular velocity sensors, to examine both intra- and inter-vehicle repeatability in five non-destructive low-speed (LS) and three full-thrown high-speed (HS) rollover crash tests using the deceleration rollover sled method. The cart was accelerated to the target velocity (LS: 19.3 km/h, n = 5; HS: 48.3 km/h, n = 3) and then decelerated (soil trip simulation) to initiate vehicle roll. All five LS and the first two HS tests showed a high degree of repeatability (peak lateral acceleration: 5.3 ± 0.2 g LS and 5.5–6.5 g HS; peak roll rate: 134 ± 12 deg/s LS and 237.3–237.4 deg/s HS; peak curb force: 92.4 ± 2.0 kN LS and 92.6–92.9 kN HS; peak dummy head resultant acceleration: 6 ± 0.2 g LS and 45–56 g HS; peak dummy upper neck axial load: 162 ± 35 N LS and 10.7–13.6 kN HS). However, despite nearly identical deceleration pulses, the third test exhibited significantly different kinematics (237 vs. 250 deg/s, four quarter turns vs. two). These results demonstrate that the test system can generate repeatable test conditions, which result in repeatable vehicle and dummy responses, but that these responses are highly sensitive to variations in the test conditions.

Comprehensive computational rollover sensitivity study, Part 1: influence of vehicle pre-crash parameters on crash kinematics and roof crush

In 2008, fatalities resulting from vehicle rollover events accounted for over one third of all fatalities resulting from motor vehicle crashes. This study describes the initial phase of a detailed computational study aimed at developing causal relationships between crash, occupant, and vehicle parameters and injury outcome using state-of-the-art computational methods. This initial phase examines the sensitivity of vehicle kinematics and structural deformation by isolating the roof-to-ground interaction phase of the rollover event using an LS-DYNA finite element full-vehicle model. Structural deformation is quantified by a measure of the maximum roof intrusion into the occupant space (average = 44 cm, range = 9–66 cm). Roll angle, pitch angle and drop height have a significant effect on structural deformation, while roll rate and yaw angle do not show significant effects. Drop height alone accounts for 70% of the variability in peak roof crush and vertical acceleration, metrics that are related to causal mechanisms for injury.

The Feasibility and Effectiveness of Belt Pretensioning and Load Limiting for Adults in the Rear Seat

The US Fatality Analysis Reporting System (FARS) and State Data System (SDS) for Florida, Pennsylvania and Maryland were utilised to estimate relative fatality rates and injury risk ratios between the front and rear-seat passengers, and a parametric study of rear-seat restraint parameters was performed to assess chest deflection and head excursion trends. The fatality and serious injury risk in frontal crashes is found to be higher for older occupants in rear seats than for those in front seats. In addition, the relative effectiveness of rear seats is lower in newer vehicle models, presumably due to the advances in front-seat restraint technology. The simulations demonstrate that injury risk in the rear seat can be reduced by incorporating front-seat restraint technology (load limiting and pretensioning), even in the absence of an air bag and knee bolster. A force-limiting belt with a pretensioner can maintain or reduce head excursion relative to a standard belt, while reducing thoracic injury risk. In fact, 42 sets of restraint parameters were identified that reduced both head excursion and chest deflection relative to the baseline belt.

DESIGN OF A WORKSTATION TABLE WITH IMPROVED CRASHWORTHINESS PERFORMANCE

Work is currently underway to develop strategies to protect rail passengers seated at workstation tables during a collision or derailment. Investigations have shown that during a collision, these tables can present a hostile secondary impact environment to the occupants. This effort includes the design, fabrication, and testing of an improved workstation table. The key criteria for the design of this table are that it must compartmentalize the occupants and reduce the risk of injury relative to currently installed tables. Strengthening the attachments between the table and the passenger car body will ensure compartmentalization. Employing energy-absorbing mechanisms to limit and distribute the load imparted on the abdomen of the occupant will reduce injury risk. This paper details the design requirements for an improved workstation table, which include service, fabrication, and occupant protection requirements. Service requirements define the geometry of the table, the performance of the table under normal service loads, and the maintenance of the table over the period of installation. Fabrication requirements define the limitations on material usage and construction costs. Occupant protection requirements define the ability of the table to reduce injury risk to the occupants under collision loads. The table must also conform to federal regulations pertaining to interior structures on passenger rail equipment. Four design concepts are evaluated against these design requirements. These concepts present different modes of deformation or displacement that absorb energy during impact. These concepts have been evaluated, and the highest-ranking concept involves a crushable foam or honeycomb table edge attached to a rigid center frame. Preliminary results from a computer simulation demonstrate the effectiveness of this concept in reducing the injury risk to the occupants.Copyright

Two-car impact test of crash energy management passenger rail cars : analysis of occupant protection measurements

As a part of ongoing passenger rail equipment safety research, a full-scale impact test of two cars with energy absorbing end structures was carried out on February 26, 2004. In this test, two coupled cars impacted a rigid barrier at 29 mph. Similar to previous full-scale tests in the series [1,2,3], anthropomorphic test devices (or ATDs) were included on the rail cars to measure the occupant response during the collision. These ATDs were instrumented with accelerometers and load cells to measure the injury risk to the occupants. This paper presents preliminary tests results. Five occupant experiments were included in the two-car test. Three of the experiments were similar to those conducted on the two-car test of conventional equipment that was held on April 4, 2000: forward-facing occupants in inter-city seats, forward-facing occupants in commuter seats, and rear-facing occupants in commuter seats. Two of the experiments examine the interaction of an occupant with a workstation table in a facing-seat configuration. These two tests used experimental ATDs with an increased capacity for recording abdominal impact response. To aid the analysis of this problem, MADYMO computer models were developed for four of the five of the occupant experiments. The models were either modified from earlier simulations, in the case of the commuter seats, or newly developed, in the case of the inter-city seats and table experiment with THOR ATD. The models were validated based on previous tests and/or accident data. Predictions of the ATD response agree closely for the overall kinematics of the ATDs, and for many of the measurements made with the ATDs in the full-scale test.Copyright

Comparison of Hybrid III child test dummies to pediatric PMHS in blunt thoracic impact response.

The limited availability of pediatric biomechanical impact response data presents a significant challenge to the development of child dummies. In the absence of these data, the development of the current generation of child dummies has been driven by scaling of the biomechanical response requirements of the existing adult test dummies. Recently published pediatric blunt thoracic impact response data provide a unique opportunity to evaluate the efficacy of these scaling methodologies. However, the published data include several processing anomalies and nonphysical features. These features are corrected by minimizing instrumentation and processing error to improve the fidelity of the individual force-deflection responses. Using these data, biomechanical impact response corridors are calculated for a 3-year-old child and a 6-year-old child. These calculated corridors differ from both the originally published postmortem human subject (PMHS) corridors and the impact response requirements of the current child dummies. Furthermore, the response of the Hybrid III 3-year-old test dummy in the same impact condition shows a similar deflection but a significantly higher force than the 3-year-old corridor. The response of the Hybrid III 6-year-old dummy, on the other hand, correlates well with the calculated 6-year-old corridor. The newly developed 3-year-old and 6-year-old blunt thoracic impact response corridors can be used to define data-driven impact response requirements as an alternative to scaling-driven requirements.

Biomechanical response targets for physical and computational models of the pediatric trunk.

Objectives: This paper quantifies pediatric thoracoabdominal response to belt loading to guide the scaling of existing adult response data and to assess the validity of a juvenile porcine abdominal model for application to the development of physical and computational models of the human child. Methods: Table-top belt-loading experiments were performed on 6, 7, and 15 year-old pediatric post-mortem human subjects (PMHS). Response targets are reported for diagonal belt and distributed loading of the anterior thorax and for horizontal belt loading of the abdomen. Results: The pediatric PMHS exhibited abdominal response similar to the swine, including the degree of rate sensitivity. The thoraces of the PMHS were as stiff as, or slightly more stiff than, published adult corridors. Conclusions: An assessment of age-related changes in thoracic stiffness suggests that the effective stiffness of the chest increases through the fourth decade of life and then decreases, resulting in stiffness values similar for children and elderly adults.

Evaluating Abdominal Injury in Impacts with Workstation Tables

In rail passenger seating arrangements with workstation tables, there is a risk of serious thoracic and abdominal injury. Strategies to mitigate this injury risk are being developed through a cooperative agreement between the U.S. Federal Railroad Administration and the Rail Safety and Standards Board of the United Kingdom. The approach to developing the protection strategies involves collision investigations, computer simulations of the occupant response, and full-scale testing. During the train collision in Placentia, California, on April 23, 2002, many occupants hit workstation tables. The investigation indicated the likely modes of injury caused by the impact, the most traumatic being damage to the liver and spleen. A MADYMO computer simulation was created to estimate the loads and accelerations imparted on the occupants that brought about these injuries. Two experiments were designed and executed on a full-scale impact test with an occupant environment similar to the Placentia collision. These experiments incorporated advanced anthropomorphic test devices (ATDs) with increased abdominal instrumentation. The THOR (test device for human occupant restraint) ATD showed a more humanlike impact response than did the Hybrid III Railway Safety ATD. The full-scale test results are used to refine a MADYMO model of the THOR ATD to evaluate improved workstation tables. The occupant protection strategy that will be developed requires that the table remain rigidly attached to the car body and includes a frangible edge with a force-crush characteristic designed to minimize the abdominal load and compression. MADYMO simulations of this table design show a significantly reduced risk of severe abdominal injury.

DEVELOPMENT OF PERFORMANCE REQUIREMENTS FOR A RAIL PASSENGER WORKSTATION TABLE SAFETY STANDARD

The American Public Transportation Association’s (APTA) Construction and Structural committee, a railroad industry group, with the support of the Federal Railroad Administration (FRA) and the John A. Volpe National Transportation Systems Center (Volpe Center), is creating an industry safety standard for an energy absorbing table. Workstation tables in passenger trains are an increasingly popular seating configuration both in the United States and abroad. Although a well-attached table can provide convenience and compartmentalization for the occupant, there is a risk of abdominal injury during a rail accident. In Fact, there have been several accidents in the United States in which impacts with workstation tables have severely or fatally injured occupants. In 2006, in response to these injuries, an FRA sponsored program developed a prototype table that distributed load over a wider area of the abdomen and absorbed energy during a collision. This table design was tested with specialized anthropomorphic test devices (ATDs) instrumented to measure abdominal impact response and was shown to decrease injury risk compared to a baseline table design. Building on the knowledge gained in the development of the prototype table, the proposed standard requires force to the abdomen be limited while energy is absorbed by the table. Since manufacturers do not have access specialized ATDs, researchers proposed a two part testing requirement. The first part is a quasi-static test which measures the energy absorption capacity of the table with a maximum force level determined from testing with specialized abdominal ATDs. The second part is a sled test with a standard Hybrid III 50th percentile (HIII) ATD to assess compliance with occupant protection standards of compartmentalization and ATD injury assessment reference values (IARVs). This paper discusses the research performed to develop the performance requirement in the draft standard. Current injury measures, originally developed for the automotive industry, were examined to assess their applicability to workstation table impacts. Multiple Mathematical Dynamic Models (MADYMO) model simulations show the estimated injuries during a simulated sled test scenario. Several force-crush parameters were examined, including the initial stiffness of the force-crush curve, the plateau force and the target energy absorbed by the table, to determined the force-crush design characteristics of a table that are likely to reduce injury risk. The results of this study, combined with testing of the current prototype table described in a companion paper [1], led to a draft standard that will greatly improve the safety of workstation tables in passenger rail cars.