Dhafer Marzougui

Development of a Detailed Vehicle Finite Element Model Part I: Methodology

Abstract on September 29, 1993, President Clinton and the Chief Executive Officers of the major domestic automakers (Chrysler Corporation, Ford Motor Company, and General Motors Corporation) announced the formation of the Partnership for a New Generation of Vehicles (PNGV). The long-term goal of PNGV is to develop vehicles that will deliver up to three times todays fuel efficiency (80 miles per gallon or BTU equivalent) and cost no more to own and operate than todays comparable vehicles. At the same time, this new generation of vehicles should maintain the size, utility and performance standards of todays vehicles (i.e., the 1994 Chrysler Concorde, Ford Taurus, and Chevrolet Lumina) and meet all mandated safety and emission requirements [1,2]. As part of the PNGV program, The National Highway Traffic Safety Administration (NHTSA) intends on developing a vehicle finite element model representing each vehicle class and size. These FE models will be used in compatibility studies to ensure that PNGV vehicles meet safety standards and that crashworthiness and crash avoidance attributes are not compromised by their lightweight and use of advanced materials. A detailed finite element model of a 1996 Plymouth Neon was developed at the FHWA/NHTSA National Crash Analysis Center as part of the PNGV program. The Neon represents the sub-compact vehicle class. The three dimensional geometric data of each component was obtained by using a passive digitising arm. The geometric data was imported into a preprocessor for mesh generation, parts connection, and material properties. Tensile testing was conducted on specimen to obtain the material properties of the various sheet metal components. Sheet metal thickness was obtained by using an ultrasonic thickness measurement gauge. The non-linear explicit finite element code LS-DYNA, was used to perform the various simulations. This paper will conclude on the following issues; describing and efficient methodology for reverse engineering vehicles; importance of maintaining geometric accuracy; issues concerning material characterization; significance and necessity of component wise testing.

Crashworthiness Evaluation Using Integrated Vehicle and Occupant Finite Element Models

Abstract Recent development in computer hardware technology and software advancement has made it possible to develop large and detailed finite element models, which include vehicle structures, interior, seats, airbags, and hybrid-III dummies, for crashworthiness evaluation. This paper presents some recent effort of developing an approach for crashworthiness using integrated vehicle structural, interior, occupant, and airbag finite element models. A case study using integrated finite element models of vehicle structure and interior, airbag, seats, and hybrid-III dummy is discussed to demonstrate the potential benefit of the integrated simulation and analysis approach. This new integrated approach will further improve the engineering practice with cost saving in engineering resources and producing more accurate and consistent analysis results.

EVALUATION OF PORTABLE CONCRETE BARRIERS USING FINITE ELEMENT SIMULATION

The use of finite element (FE) simulations in modeling and evaluating roadside hardware has increased significantly in the past few years. Thanks to the remarkable improvements in computer technology and finite element software, the crash behavior of automobiles and roadside hardware objects can be predicted. Finite element simulations were used to evaluate the safety of portable concrete barriers (PCB). The first step was to develop a methodology for creating accurate FE representations of PCBs. This objective was achieved by developing an FE model of an F-shape PCB design and using full-scale crash test data to validate the model. Once the fidelity and accuracy of the modeling methodology had been proved, FE models of two modified PCB designs were created and their safety performance was evaluated. Based on the simulation results, a third design was developed and its performance was analyzed. The safety performance of the three designs was compared.

AN ASSESSMENT OF CONSTITUTIVE MODELS OF CONCRETE IN THE CRASHWORTHINESS SIMULATION OF ROADSIDE SAFETY STRUCTURES

Abstract LS-DYNA, a commercial nonlinear finite element code, is widely used for crashworthiness analysis of roadside safety structures, most of which are made of concrete materials. One of the key ingredients in a successful crashworthiness simulation of roadside safety device is the constitutive model of concrete; a reliable constitutive model should adequately represent the behavior of concrete material under any loading conditions. The performance of the four constitutive (material) models of concrete that are implemented in LS-DYNA code is evaluated first by comparing against a benchmark stress-strain relation obtained from the conventional triaxial tests. Then a vehicle-to-barrier crash test is simulated using the four concrete material models to investigate their prediction of the behavior of concrete barriers subjected to vehicular impact. The findings of the triaxial test and crash test simulations are discussed in this paper along with the pros and cons of the concrete constitutive models.

Performance Evaluation of Low-Tension Three-Strand Cable Median Barriers

The primary purpose of longitudinal safety barriers, such as cable barriers, is to contain or redirect errant vehicles that depart the roadway and thereby keep them from entering opposing travel lanes or encountering terrain features and roadside objects that may cause severe impacts. In this study, finite element analysis, vehicle dynamics analysis, and full-scale crash testing were performed to study the effects of sloped terrain on the safety performance of cable median barriers. A detailed finite element model of a three-strand cable barrier was developed and validated against a previously conducted full-scale crash test. The full-scale crash test and simulation were set up for an impact of the cable barrier with a 2,000-kg (4,400-lb) pickup truck at an angle of 25° and an initial velocity of 100 km/h (62 mph). This setup is in accordance with NCHRP Report 350 guidelines for Test Level 3 safety performance. With this model, computer simulations were performed to assess the performance of the barrier under different impact scenarios and with different terrain profiles. Vehicle dynamics analyses were also conducted to compute the trajectory and dynamics of the vehicle as it crossed the sloped terrain and struck the cable median barrier. On completion of the computer simulation analyses, full-scale crash testing was performed to validate the results.

Development and validation of a vehicle suspension finite element model for use in crash simulations

Abstract Finite element models, based on a Chevrolet C2500 pickup truck vehicle, were developed at the FHWA/NHTSA National Crash Analysis Center (NCAC). These models have been used by several transportation safety researchers to analyze vehicle safety issues as well as to evaluate and improve roadside hardware. Over the past few years, modifications and more details have been incorporated in the models to add capabilities of these models to be used in different impact scenarios. In this study, a detailed suspension model has been added to the C2500 pickup truck model. Pendulum tests have been conducted at The Federal Highway (FHWA) Federal Outdoor Impact Laboratory (FOIL) and used in the validation of the suspension model. The focus in this study was on the rear suspension system of the vehicle. Simulations were conducted and the results are compared to the pendulum tests in terms of deformation, displacement and acceleration at various locations. To ensure the accuracy of the newly upgraded vehicle model, previously conducted full-scale crash tests were simulated and the results from these simulations were analyzed and compared to the tests.

Validation of a Single Unit Truck Model for Roadside Hardware Impact

The objective of this research is to validate the Finite Element (FE) model of a Ford F800 Single Unit Truck (SUT). The FE model of the SUT was developed at the FHWA/NHTSA National Crash Analysis Centre (NCAC) at the George Washington University (GWU). In this study, the characteristics of the SUT model were investigated and several modifications were incorporated in the model to accurately simulate its interaction with roadside safety hardware. A full-scale crash test of the Ford F800 SUT impacting an F-shape Portable Concrete Barrier (PCB) was conducted at The Federal HighWay Administrations (FHWA) Federal Outdoor Impact Laboratory (FOIL) and used in the validation. The response of any vehicle impacting a PCB is primarily governed by the mass and suspension characteristics of the vehicle. Detailed methods for modelling the trucks suspension components are discussed.

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.

Guidance for the Selection, Use, and Maintenance of Cable Barrier Systems

This report provides guidance for the selection, use, and maintenance of cable barrier systems. While cable barrier systems have been in use for more than 70 years, their use has been on the rise and is expected to continue in the future. The increase in use of cable barrier systems has been attributed to the success rate in keeping vehicles from crossing the median, reducing roadway departures, and decreasing impact severity. Due to advancements in cable barrier system technology, installation and repair costs are lower and cable barrier use has increased in varying roadway environments. Safety studies, although limited, have shown that cable barriers help reduce those median cross-over collisions that lead to some of the most severe head-on type crashes. This document will be of particular interest to design, maintenance, traffic, and safety engineering professionals.

IMPROVED TRUCK MODEL FOR ROADSIDE SAFETY SIMULATIONS: PART I--STRUCTURAL MODELING

Computer simulation is now a mainstream tool for design and analysis of roadside hardware. For the past several years, researchers at the National Crash Analysis Center, Worcester Polytechnic Institute, and the University of Nebraska–Lincoln have been improving various features of a 2000-kg pickup truck model, the most widely used vehicle model for roadside safety simulation. Many modeling techniques have been learned, and an improved model has been developed that should aid analysts at other locations who are performing similar simulations. The various effects and difficulties of “reducing” a finite element model to decrease computational costs are examined, including the elimination of initial penetrations, free-edge tangling, snagging, and “shooting nodes.” The elective refinement of mesh density, the elimination of manipulated material densities to achieve desired masses, the improvement of connections between components, and the inclusion of all significant parts to improve accuracy are analyzed. The significance of not oversimplifying critical components is emphasized, as well as the importance of realistic model behavior. Evolutionary changes to vehicle models are required as more information is obtained about modeling and truck behavior in roadside safety applications. Different research groups will have different modeling approaches, but by sharing the details of those approaches and by sharing models, the collective capabilities in roadside safety simulation will improve, ultimately resulting in better roadside hardware. The models described are thought to be a tremendous improvement over previous-generation models of the reduced pickup truck.