Nabih E. Bedewi

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.

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.

EVALUATION OF CAR-TO-CAR FRONTAL OFFSET IMPACT FINITE ELEMENT MODELS USING FULL SCALE CRASH DATA

This paper describes the results of a study conducted to evaluate the performance and accuracy of a medium size sedan finite element model (FEM) for off-set car-to-car impacts. This model was originally developed for front impact. The model does not include side structure compliance. Two tests conducted by the National Highway Traffic Safety Administration (NHTSA) are used for evaluation of the simulations. The overall results indicate that the simulations appear to be consistent with the crash test data. Problems associated with the use of node constraints, lack of side structure model fidelity, and the different integration time marching are identified. Solutions for the problems are proposed. (A) For the covering abstract of the conference see IRRD 875833.

Dynamics modeling of robotic manipulators using an artificial neural network

Dynamics modeling is important for the design, analysis, simulation, and control of robotic and other computer-controlled mechanical systems. The complete dynamic modeling of such systems involves the computationally intensive solution of a set of non-linear, coupled differential equations. Artificial neural networks are well suited for this application due to their ability to represent complex functions and, potentially, to operate in real time. The application of an artificial neural network to dynamics modeling of robotic systems is investigated. The Cerebellar Model Arithmetic Computer (CMAC) is employed. A hybrid implementation of CMAC is proposed to allow use of the model for either simulation or control of robotic manipulators. The success of the simulated results and the accuracy of the generated outputs after a few training cycles demonstrate great promise for further development of the method and its implementation in control systems.

Sign Support Height Analysis Using Finite Element Simulation

Abstract Finite element (FE) computer simulation has been proven to be an essential tool for evaluating crashworthiness and safety performance of automobiles, roadside hardware appurtenances, as well as several other engineering structures. Its use has increased dramatically thanks to remarkable improvements in computer technology and finite element codes. In this study finite element simulation is used to analyse the safety performance of roadside sign support systems. Specifically, the study focuses on determining the effect of sign height on the amount of intrusion into the occupant compartment. The sign support system that is investigated in this study is the 4lb/ft U-post. FE models of 5ft (1.5m) and 7ft (2.1m) height signs were created and impacted with a set of vehicle models at different impact speeds. Five vehicle models were employed in the study: Chevrolet C2500 pickup, Geo Metro, Ford Taurus, Plymouth Neon, and Dodge Caravan. Three impact speeds were analysed: 20, 40, and 60mph (32, 64, and 96km/h). A total of 18 simulations were performed and the results were compared to evaluate intrusion of the signs into the occupant compartment. The simulation results were verified by conducting a full-scale test of the worst-case scenario, a Geo Metro into the U-post at 60 mph.

Effect of Occupant Position and Air Bag Inflation Parameters on Driver Injury Measures

This paper investigates the effects of driver airbag inflation characteristics, airbag relative position, airbag to dummy relative velocity, and steering column characteristics using a finite element model (FEM) of a vehicle, airbag, and Hybrid III 50% male dummy. Simulation is conducted in a static test environment using a validated FEM. Several static simulation tests are performed where the airbag modules position is mounted in a rigid steering wheel and the vertical and horizontal distances are varied relative to the dummy. Three vertical alignments are used: one position corresponds to the head centered on module, another position corresponds to the neck centered on module, and the third position centers the chest on the module. Horizontal alignments vary from 0 mm to 50 mm to 100 mm. All of these tests are simulated using a typical pre-1998 type inflation curve. Simulation tests are repeated using two other airbag inflation curves. One curve is a simple 75% reduction of baseline and another has a shorter but wider and more delayed peak. Results indicate the benefit of keeping a minimum distance of 50 mm between airbag and dummy. Results also indicate benefits of less aggressive inflation. A milder inflation curve that supplies the same amount of energy but takes longer to peak may also result in reduced inflation induced injuries. (A) For the covering abstract of the conference see IRRD 492347.

Finite element modelling of anthropomorphic test devices for vehicle crashworthiness evaluation

Abstract This research focuses on the development and implementation of a methodology for creating highly accurate occupant finite element models. This study concentrates on a 50th Percentile Anthropomorphic crash Test Dummy (ATD) Finite Element (FE) model with application in vehicle crashworthiness evaluation. An extensive review of currently available FEM models of the Hybrid Ill 50th percentile dummy revealed the need for a more extensive model of ATDs. Currently available models contain upwards of 20,000 elements but do not include each components full geometry. This research has spawned a model that is composed of 45.000 elements, and includes all parts of an actual Hybrid 111 ATD in acute detail. A method for creating dummy finite element models is presented. This methodology is based on the premise that the model must be based on the fundamentals of mechanics, focusing directly on component geometry and material mechanical properties. Furthermore, the model should be created and validated at the component level and then integrated and re-evaluated at a system level to ensure accuracy. All parts of an existing Hybrid III ATD are incorporated in their original manufacturer intended form and function. This paper will focus on the method, which has been developed and employed to create a Hybrid III ATD finite element model. Discussion of the relevant issues and pitfalls in modeling an occupant for use in impact simulation will be highlighted. This modeling was done with several fundamentals in mind: First the resulting FEM must accurately represent an actual ATD in mass, inertia, and material properties. Secondly, special attention must be paid to the need for this model to be integrated into existing and future models of vehicle occupant compartments. Finally, the methodology must be logical and easy to follow in order to reduce error in implementation.

CHEST INJURY RISKS TO DRIVERS FOR ALTERNATIVE AIR BAG INFLATION RATES

While the present air bag systems have been shown to be highly effective in high severity crashes, undesirable side effects have been reported in some low severity events. The inflation rate of the airbag during deployment has been cited as a factor which induces injuries. A rapid airbag deployment rate is advantageous to provide protection to occupants in severe crashes. On the other hand, airbag aggressivity associated with the high inflation rate can increase injuries in the lower severity crashes. The injury producing forces from the airbag increase as the occupant position becomes closer to the bag at the time of deployment. This paper describes the results of an analytical study to evaluate chest injury measures for reduced inflation rates of a Taurus type air bag in a variety of crash modes. A detailed nonlinear finite element model of an unfolding airbag and a 50th percentila male Hybrid III dummy are used in conjunction with a test buck to simulate frontal crashes. The model is calibrated for a 30 mph crash, and then used to evaluate the effects of chest loading for other crash modes and air bag flow rates. Different acceleration time histories are introduced to model high speed (35 mph) crashes and low speed (16 mph) pole impacts. (A) For the covering abstract see IRRD 893297.