James Chih Cheng

Modeling and Design for Vehicle Pitch and Drop of Body-on-Frame Vehicles

Vehicle pitch and drop play an important role for occupant neck and head injury at frontal impact. The excessive vehicle header drop, due to vehicle pitch and drop during crash, induces aggressive interaction between occupant head and sun visor/header that causes serious head and neck injuries. For most of body-on-frame vehicles, vehicle pitch and drop have commonly been observed at frontal impact tests. It is because the vehicle body is pulled downward by frame rails, which bend down during crash. Hence, the challenges of frame design are not only to absorb crash energy but also to manage frame deformation for minimizing vehicle pitch and drop. In this paper, the finite element method is used to analyze frame deformation at full frontal impact. To ensure the quality of CAE model, a full vehicle FEA model is correlated to barrier tests. In addition, a study of CAE modeling affecting vehicle header drop is performed. The effective factors for vehicle header drop, identified as mesh size, material strain rate, body mount modeling, and weight distribution, are discussed. Furthermore, the root cause of vehicle pitch and drop and the design countermeasures for resolving this issue are discussed.

Advanced development of explicit FEA in automotive applications

Abstract Today, nonlinear analysis is no longer new to finite element society, but the explicit finite element method could still be fresh. Since DYNA3D was developed, the explicit finite element method for nonlinear transient dynamics has found its successful applications in automobile safety simulations. Ford Motor Company is one of the pioneer industry companies that uses a great deal of CAE in product design and manufacturing. This helps Ford engineers make faster and better design, eliminates a large number of prototype vehicle tests and significantly reduces the costs. Presented in this report are selected examples of our applications in safety simulations and other CAE activities, all done by Ford in-house crash simulation code FCRASH.

Development and Validation of an ALE-Based Airbag Simulation Methodology

For the past fifteen years, automotive safety engineers have mainly relied on the Control Volume (CV) approach to simulate airbag deployment. The CV approach assumes that the gas is uniformly distributed in an inflated bag and therefore the airbag fabric is subject to uniform pressure. This assumption is true only when the airbag is fully deployed, and therefore makes CV approach inappropriate for Out-of-Position (OOP) safety analysis in which an occupant is in close proximity to the air bag module when it deploys, and therefore airbag-occupant interaction occurs before the bag is fully inflated. This paper describes the theory and validation of a new airbag simulation tool, an ALE-based (Arbitrary-Lagrange-Eulerian) approach. This tool, developed by Livermore Software Technology Corporation (LSTC), is aimed at using ALE as a CFD (Computational Fluid Dynamics) tool to model the gas flow inside a deploying airbag and the interaction between the airbag and the inflator gas. The validation of this methodology is performed through comparing the simulation results with test results of various test setup and airbag design.Copyright

Testing and Modeling of Mounts for Improved Safety Design and Crashworthiness Analysis

This paper describes (1) the findings from the implementation of a component test methodology for body, engine and transmission mounts [1-3], and (2) the associated CAE model development and mount design robustness enhancement. A series of component tests on light truck body, engine and transmission mounts have been conducted to not only obtain their characteristics as inputs for crashworthiness analysis, but also drive mount design direction for frontal impacts. In this paper, the lessons learned from implementation of the mount testing and modeling methodology [1-3] are reported in three areas: firstly, improvement of test setup and data collection over an existing approach to achieve test robustness, time efficiency and cost effectiveness; secondly, the confirmation of the thread effect on body mount performance for improved body mount design; and thirdly, the confirmation of a dual spring modeling methodology for better simulating engine and transmission mounts based on test finding and existing practice. Component test results and the new mount modeling methodology are incorporated into full vehicle CAE models for crashworthiness analysis of frontal crashes. Simulated results with implementation of the mount modeling methodology, when compared with full vehicle test data, indicate that the quality and the prediction accuracy of the full vehicle CAE models have been improved. Both the test and CAE methodology are implemented into vehicle program for support in crash safety analysis.

Testing of Cooling Module Component for Frontal Impact and Sensor Modeling Development

This paper discusses the development of a component test methodology for testing a cooling module including radiator, condenser and trans. cooler and the CAE model development. A series of light truck/SUV cooling module component tests were conducted to obtain their characteristics as inputs for frontal impact and sensor modeling development. First, the cooling module component CAE sub-model was developed using soft springs along with fine-mesh sheet metal shell elements. Then, simulated sub-model results were correlated fairly well with the test data and finally the component CAE sub-model was incorporated into a full vehicle CAE model that was used for frontal impact (NCAP) and sensor development. The results indicated that the proposed test method for cooling module components provided consistent data and the results from cooling module sub-model can be incorporated into the full vehicle CAE model for improving the quality and accuracy of CAE models.

Integration of Hydroforming Analysis of Front-End Structures Into Full Vehicle Crash Analysis

Changes in gauge and material properties are the trademarks of hydroforming process used for any parts. These changes may be large enough to affect the vehicle responses under impact loading in a significant way. An investigation was carried out to determine how full vehicle crash responses are affected by these changes and the findings are reported in this paper. Key to this study has been a methodology to map the gauge and property changes, obtained from a forming simulation, to FEA models created for crash analyses. The mapping process thus allows one to consider the property and gauge changes as an initial condition during crash simulation. A number of full vehicle crash simulations were conducted and the results are compared with the corresponding test data. The entire procedure has been verified using the CAE models developed for simulating hydroforming and frontal impact behavior of a vehicle program. The implementation of the developed methodology to other vehicle programs is straightforward.Copyright

Role of the Body Mount on the Passenger Compartment Response of a Frame/Body Structured Vehicle in Frontal Crash

This paper presents a comprehensive strategy to investigate the role of the body mounts on the passenger compartment response in a frontal crash. The study included quasi-static vehicle crash testing, development of a component-level dynamic body mount test methodology, lumped-mass computer modeling, and technical analysis. The paper also addresses the means of investigating the effects of the body mounts on the passenger compartment response during a frontal barrier impact.