National Crash Analysis Center Research Articles

Feature-aware reconstruction of trimmed splines using Ricci flow with metric optimization

The lack of a compelling tool to automatically or semi-automatically create analysis-suitable spline spaces hampers the progress of the isogeometric framework. In this work, we review current techniques to analyze so-called “trimmed” CAD models and present a new approach, based on surface Ricci flow with metric optimization, that can be used for rebuilding trimmed CAD objects. The method is both theoretically grounded and suitable for use on real engineering objects. We demonstrate its efficacy by rebuilding both the US Army’s DEVCOM Generic Hull vehicle and the chassis of the National Crash Analysis Center’s 1996 Dodge Neon into sets of watertight splines. These reconstructed splines are used in isogeometric analysis on model parts and in performing hybrid finite element/isogeometric crash analysis for the Neon vehicle.

Reconstruction finite element model of cars

The experimental method used in a frontal crash of cars costs much time and expense. Therefore, numerical simulation in crashworthiness is widely applied in the world. The completed car models contain a lot of parts which provided complicated structure, especially the rear of car models do not contribute to behavior of frontal crash which usually evaluates injuries of pedestrian or motorcyclist. In order to save time and resources, a simplification of the car models for research simulations is essential with the goal of reducing approximately 50% of car model elements and nodes. This study aims to construct the finite element models of front structures of vehicle based on the original finite element models. Those new car models must be maintained important values such as mass and center of gravity position. By using condition boundaries, inertia moment is kept unchanged on new model. The original car models, which are provided by the National Crash Analysis Center (NCAC), validated by using results from experimental crash tests. The modified (simplistic) vehicle FE models are validated by comparing simulation results with experimental data and simulation results of the original vehicle finite element models. LS-Dyna software provides convenient tools and very strong to modify finite element model. There are six car models reconstructed in this research, including 1 Pick-up, 2 SUV and 3 Sedan. Because car models were not the main object to evaluate in a crash, energy and behavior of frontal part have the most important role. As a result, six simplified car models gave reasonable outcomes and reduced significantly the number of nodes and elements. Therefore, the simulation time is also reduced a lot. Simplified car models can be applied to the upcoming frontal simulations.

Modelling and Simulation of Crash Tests on Curved Barriers Taking into Account Vehicle Speed Limits

The reliable speed of a vehicle, assigned to a given road arc, is not usually taken into account in simulation of crash tests on road safety barriers located on horizontal concave arcs with small radii (20−200 m). In this work, the numerical modelling and simulations of TB11, TB32 crash tests for selected road safety barriers on a horizontal concave arc with a small radius of 150 m, at a reliable and increased speed of a vehicle, were conducted. The authors developed the methodology of numerical modelling and simulation and published in the period 2015−2018. In this study, crash tests include two N2 class steel road barriers with the B-type guide rail, i.e. SP-05/1 (with 1.00 m post spacing) and SP-05/2 (with 2.00 m post spacing). Suzuki Swift and Dodge Neon vehicle models were taken from the National Crash Analysis Center (USA) library and modified, respectively. It was proved that road traffic safety on horizontal concave arcs with small radii is assured if the reliable velocity is not exceeded by drivers. Compacting the post spacing or the uses of a composite-foam protective overlay added to guide rails are not recommended.

Optimal design of pre-triggering airbag system for occupant protection performance during frontal crashes

With the rapid development of car crash sensing and identification technology, the application of pre-triggering airbag system is becoming an important option to improve vehicle safety. Thus, the present study aims to investigate the injury protection ability of pre-triggering airbag system and optimize its performance in frontal crashes regarding the key physical parameters. A driver restraint system model established and validated by National Crash Analysis Center was employed and validated for studying the injury protection ability of pre-triggering airbag system. Then, the influences of airbag triggering time, airbag volume scaling factor, inflator mass flow, and exhaust orifice size of pre-triggering airbag system on driver’s head and chest injuries were analyzed. Finally, the weighted injury criterion was selected as the evaluation index to optimize the pre-triggering airbag system. The results show the pre-triggering airbag should be designed with a larger airbag volume and inflator mass flow rate and smaller exhaust orifice. The optimized restraint system design presents a reduction of weighted injury criterion values in 100% and 40% overlapped frontal impacts reaching 25.63% and 42.23%, respectively.

Numerical analysis of collision between a tractor-trailer and bridge pier

Accidents involving collisions of heavy-duty trucks with highway bridge piers occurred occasionally, in which the bridge piers might be subjected to severe damage, and cause the collapse of the superstructure due to the loss of axial loading capacity. The existing researches are mostly concentrated on the light- or medium-duty trucks. This article mainly concerns about the collisions between the heavy-duty trucks (e.g. tractor-trailer) and bridge piers as well as the evaluation of the impact force. First, by modifying the finite element model of Ford F800 single-unit truck, which was developed by National Crash Analysis Center, the finite element model of a tractor-trailer is established. Then, the full-scale tractor-trailer crash test on concrete-filled steel pier jointly conducted by Texas Transportation Institute, Federal Highway Administration, and Texas Department of Transportation is numerically simulated. The impact process is well reproduced and the established model is validated by comparison of the impact force. It indicates that the tractor-trailer impact force time history consists of two or three peaks and the corresponding causes are revealed. Furthermore, the parametric influences on the impact force are discussed, including the diameter and cross section shape of the pier, cargo weight, impact velocity, relative impact position, and vehicle type. Finally, the finite element model of an actual reinforced concrete highway bridge pier is established, and the impact force and lateral displacement of the pier subjected to the impact of the tractor-trailer are numerically derived and discussed.

Performance of metallic defences submitted to vehicle impact

The main function of a road guardrail is to redirect an out of control vehicle avoiding a frontal collision or a dangerous veering off the road trajectory. Second, the energy absorption imposed by barrier deformation or any other energy dissipation method is beneficial to the car occupant safety. This study evaluates the performance of a W-Beam guardrail system, in accordance to Brazilian Standards, in respect to the kinetic energy absorption and to the vehicle return angle to the road. This evaluation of the guardrails is performed in a virtual environment using the finite element method. For the correct representation of the model, the material was characterised through experimental tests. Simplifications in the model are taken from the literature and a validated model of a vehicle is provided by the US National Crash Analysis Center.

Development and Validation of Newborn Child Head Numerical Model Dummy for Impact Simulations

Computer simulation using Finite Element Model (FEM) are often used as a substitute for human experimental head injury studies, especially in predicting car accident injuries, enhance understanding of injury mechanism and develop prevention strategies. The use of FEM in crash test dummies is advantageous over physical dummies because of the lower cost and repeatability. Numerous adult FEM of the head have been developed, but there are relatively few paediatric FEM due to scarcity of material property data for children. Consequently, there are not enough models representing newborn child. Child head injury is a costly problem, both in terms of morbidity and direct medical costs. In fact, it is the leading cause of death and disability for children under the age 18-years-old. Despite its importance and effect on the population, the study of paediatric head injury is obstructed by the lack of available paediatric Post-Mortem Human Specimen (PMHS) data. As a substitute for PMHS testing, Anthropometric Test Devices (ATDs) and FEM have been developed to model the head. However, there is a scarcity of data for the design and validation of these models. This paper presents the development and validation of a newborn (NB) FEM for head dummy and simulated results compared with the child cadaver experimental data under drop test conditions. Itis intended for automotive crashworthiness assessment. The model was developed by using both deformable and rigid body materials. The newborn head anthropometric data were obtained from published journal articles. Using recent published material property data, the infant skull, skin and scalp FEM of the newborn ATD head was developed to study the response in head drop tests. The head assembly was validated by using three different head drop tests set-ups. The three impact locations are one frontal/forehead, and two lateral (right and left parietal) drop tests. All tests with drop height of 130 mm are the certification procedure. The benchmark model used in this study was a modified version of the 6-year-old numerical model developed by Livermore Software Technology Corporation and National Crash Analysis Center. A morphing method within LS-Prepost software was used.

Field Tests and Numerical Modeling of Vehicle Impacts on a Boulder Embedded in Compacted Fill

Landscape Vehicular Anti-Ram (LVAR) systems are a group of protective barriers, which are designed using natural materials (e.g., boulders) and have proven to both effectively protect sensitive structures against threats and be aesthetically pleasing. This paper presents two consecutive vehicular crash tests hitting the same single boulder embedded in AASHTO coarse aggregate fill. A LS-DYNA model was developed to simulate the field-scale tests, which were instrumented with high-speed cameras and pressure cells. A readily available truck model from the National Crash Analysis Center was modified and implemented in the LS-DYNA model. The boulder and surrounding soil were modeled using the Mohr-Coulomb failure criteria. The model parameters were calibrated using results from the first field-scale test with a truck traveling at 48.3 km/hr (30 mph) impacting the LVAR system. The calibrated model was then used to simulate the second field-scale test, which involved a truck traveling at 80.5 km/hr (50 mph) impacting the same LVAR system without resetting the boulder or soil. The calibrated model was able to provide the global response of the system, including the time-history of the translational displacement and rotation of the boulder, and was in good agreement with field-scale test results. This suggests that the overall global response was dominated by the dynamic behavior of the truck and boulder system upon impact. Hence, a simple material model for soil and boulder is sufficient for simulating the tests conducted.

차량 충돌에 의한 기둥의 콘크리트 기초 접합부 거동 평가

Dept of Civil and Architectural Engineering, Sungkyunkwan University, Suwon 440-746, KoreaABSTRACT Structures are often subject to vehicle collision which can be accidental or terrorist attack. Previous research shows that the damage in major columns may result in progressive collapse of a whole building. This study investigates the performanc e of a steel column standing on a reinforced concrete footing subjected to a vehicle collision. The size and the axial load of the steel column are determined based on the assumption that it is the first story corner column in a typical three-story building with s ix meter span length. The finite element model of a eight-ton single unit truck provided by the NCAC (National Crash Analysis Center) is used in the numerical analysis. The finite el ement analysis is performed using the LS - DYNA, and the results show that the beha vior of the column subjected to car impact depends largely on the column-foundation connection detail.Keywords : vehicle collision, progressive collapse, FEM explicit analysis

Development of a regulation for testing the effectiveness of a rigid side underride protection device (SUPD)

The development of a side underride protection device is a crucial aspect for improving the safety of small car to tractor–trailer collisions. Devices such as rear underride guards are already implemented and regulated in North America and many places around the world along with front underride devices, which are regulated in Europe. The large and unprotected gap between the rear axle and the kingpin of the trailer remains a hazard for small passenger vehicles passing underneath. To develop devices to prevent such accidents, a regulation for testing the underride guards must be implemented to determine their feasibility. This paper describes the background information and testing procedures of the existing regulations for front and rear underride guards to help develop the side regulation. A finite element tractor–trailer model is presented and a component model based on the trailer is created and validated in order to be used for simulations. Collisions with small passenger cars such as the National Crash Analysis Center's Toyota Yaris and Ford Taurus into rigid walls are conducted and methods are introduced to obtain a quasistatic model from the dynamic crash. Device dimensions are determined using tractor–trailer models in TruckSim in order to obtain the maximum allowable ground clearance of the devices. Feasible rigid guards are then created and tested with the proposed quasistatic regulation and compared to the results obtained from the dynamic tests.

SIMULATION OF VEHICULAR FRONTAL CRASH-TEST

This paper “SIMULATION OF FRONTAL CRASH-TEST” The simulation of vehicle crashes by using computer softwares has become an indispensible tool for shortening automobile development time and lowering costs. It also has huge impact on the crashworthiness of an automobile. This work reports on the simulated crash test of an automobile. The objective of this work is to simulate a frontal impact crash of an automobile and validate the results. The aim is also to alter some of the materials of the components with a view to reduce the forces experienced during the crash. Computer models were used to test the crash characteristics of the vehicle in the crash. The model used here was that of a Chevrolet C1500 pick-up truck. The software used for the simulation is LS-DYNA. It is widely used by the automotive industry to analyze vehicle designs. It accurately predicts a car's behavior in a collision. The results obtained by the simulation were then validated by comparing it with the test results of the same test performed by the NCAC (National Crash Analysis Center).

Comparison of Crash Test and Simulation Results for Impact of Silverado Pickup into New Jersey Barrier under Manual for assessing Safety Hardware

The National Crash Analysis Center (NCAC) at the George Washington University simulated the crash of a 2,270-kg Chevrolet Silverado pickup truck into a standard 32-in. New Jersey shape concrete barrier under the requirements of Test 3–11 of the Manual for Assessing Safety Hardware (MASH). The new, detailed finite element (FE) model for the Chevrolet Silverado was used as the surrogate for the MASH 2270P test vehicle. An FE model of the New Jersey barrier was drawn from the array of NCAC hardware models. The primary objective of this analysis was to simulate the crash test conducted to evaluate how this commonly used, NCHRP 350–approved device would perform under the more rigorous MASH crashworthiness criteria. A secondary objective was to use newly developed verification and validation (V&V) procedures to compare the results of the detailed simulation with the results of crash tests undertaken as part of another project. The crash simulation was successfully executed with the detailed Silverado FE model and NCAC models of the New Jersey concrete barrier. Traditional comparisons of the simulation results and the data derived from the crash test suggested that the modeling provided viable results. Further comparisons employing the V&V procedures provided a structured assessment across multiple factors reflected in the phenomena importance ranking table. Statistical measures of the accuracy of the test in comparison with simulation results provided a more robust validation than previous approaches. These comparisons further confirmed that the model was able to replicate impacts with a 2270P vehicle, as required by MASH.

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

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.

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.

From the Feds: Research, programs, and products

From the Feds: Research, programs, and products

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

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 today's fuel efficiency (80 miles per gallon or BTU equivalent) and cost no more to own and operate than today's comparable vehicles. At the same time, this new generation of vehicles should maintain the size, utility and performance standards of today's 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.

Development of a Detailed Vehicle Finite Element Model Part II: Material Characterization and Component Testing

A detailed multi-purpose finite element model of a 1996 Plymouth Neon was developed at the FHWA/NHTSA National Crash Analysis Center. The model was developed to address vehicle safety issues, including front, side and rear performances. In part I of this paper, the methodology used in the development of the Neon model was presented. Issues concerning material characterization and the necessity of component wise testing were discussed. This paper will focus on material and component testing and validation. Conclusions will be made on the effect of material characterization to the overall model behaviour. Results of the component tests will be presented. Simulations, using LS-DYNA, of the body-in-white model will be performed. Visual validation of the body-in-white frontal impact will be conducted to evaluate the accuracy and validity of the model.

Validation of an Analytical Model of a Right-Angle Collision between a Vehicle and a Fixed, Rigid Object

This paper presents a validation of a simplified analytical model of vehicle collisions recently proposed by the authors. This model predicts the kinematics of a right-angle side impact collision, between two vehicles. In this paper, the analytical model is modified to correspond to the case of a right angle collision between a vehicle and a fixed rigid object, such as a pole. The advantage of this model lies in its inherent simplicity, making it a convenient tool for preliminary accident reconstruction studies or vehicle collision research. Two approaches are employed to validate the analytical model. First, a finite element model of a Ford Festiva was retrieved from the public domain model catalog of the National Crash Analysis Center and was used to simulate two frontal impacts, one against a rigid fixed pole and the other against a fixed rigid wall. The explicit finite element code LS-DYNA3D is used for these simulations. The results are then compared with those originated by the proposed mathematical model. Next, the results of the vehicle crash test FOIL 95S008, “Ford Taurus Broadside Collision with a Narrow Fixed Object”, are compared with those originated by the analytical model. These results are then compared with those originated by the proposed mathematical model