Nripen Saha

Application of ALE to airbag deployment simulation

For the past 15 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 makes the CV approach inappropriate for Out-of-Position-Safety (OOPS) analysis in which the airbag-occupant interaction occurs before the bag is fully inflated. This paper details the theory and application of a new airbag simulation tool, an Arbitrary-Lagrange-Eulerian (ALE)-based solution. This tool is aimed at using ALE as a Computational Fluid Dynamics (CFD) tool to simulate the gas flow inside a deploying airbag. This paper starts with the introduction to ALE. Then, the ALE-based CFD approach is described. To evaluate the feasibility and robustness of this new tool, the ALE code in LSDYNA-970 is applied to a series of tests. The tests used for evaluation include two inflator tank pressure tests, a series of nine pendulum tests and one OOPS test. Following the description of the tests will be the correlation results and the discussion of the results. The correlation shows that ALE can trace the gas flow inside a deploying airbag and therefore can be an efficient and accurate tool for OOPS simulation.

Extruded Aluminum Crash Can Topology for Maximizing Specific Energy Absorption

This paper describes how specific energy absorption (SEA) is a quantitative measure of the efficiency of a structural member in absorbing impact energy. For an extruded aluminum crash can, SEA generally depends upon the topology of its cross-section. An investigation is carried out to determine the optimal cross-sectional topologies for maximizing SEA while considering manufacturing constrains such as, permissible die radii, gauges, etc. A comprehensive Department of Energy (DOE) type matrix of cross-sectional topologies has been developed by considering a wide variety of practical shapes and configurations. Since it is critical to include all feasible topologies, much thought and care has been given in developing this matrix. Detailed finite element crash analyses are carried out to simulate axial crushing of the selected crash cans topologies and the resulting SEA is estimated for each case. Evidently, topologies with an outer and an inner ring joined together by a number of straight panels yields the highest SEA. Among single cell sections, hexagon and octagon are the most efficient topologies for crash energy management. Note that all conclusions drawn in this paper are based on CAE analysis results. The authors are currently pursuing physical testing to verify the CAE analysis results.

SIMULATION OF FRONTAL BARRIER OFFSET IMPACTS AND COMPARISON OF INTRUSIONS AND DECELERATIONS

This study examines various test conditions analytically. Detailed finite element models were developed. The models provided insight into energy management mechanism, load transfer and vehicle deformation patterns due to offset impacts on to perpendicular and angular barriers. Several potential offset conditions were simulated using the Finite Element Analysis (FEA) models. These were: (1) 50% offset perpendicular rigid barrier impact; (2) 40% offset perpendicular rigid barrier impact; (3) 40 and 50% offset perpendicular deformable barrier impact; and (4) 30 degree angular impact with and without an anti-skid device on the rigid barrier. Dash and toe board intrusions, and vehicle deceleration pulses, were compared to identify the key considerations. Deformation patterns in the engine compartment and in body side structures were also examined. Model predictions were validated against prototype test data. Details of the New Car Assessment Programme (NCAP) and offset impacts, comparison of model results for various impact conditions, and the correlations with test data are presented. For the covering abstract of the conference see IRRD 875833.

Effectiveness of Countermeasures in Upper Interior Head Impact

Trim covers made of impact resistant polymers on vehicle interior sheet metal can contribute to reduction of HIC(d) (Head Injury Criterion, dummy) during headform impact. Airgap between trim and interior sheet metal can also induce deceleration of striking headform before it forces trim to contact sheet metal surface. As evidenced from laboratory component testing, situations may arise where additional protective measures may need to be incorporated between trim and sheet metal in order to attain acceptable levels of HIC(d). Two such alternatives in the form of energy-absorbing foam, and trim with molded collapsible stiffeners are discussed in this paper. The effectiveness of these countermeasures is evaluated through nonlinear finite element analysis, and favorable comparison with laboratory results is reported. (A) For the covering abstract see IRRD 893297.

Shell Elements Performance in Crashworthiness Analysis

Crashworthiness analysis, a type of large deformation transient dynamics, has been an important and active area of researches and engineering applications. Several shell elements have been implemented in the finite element software for crashworthiness analysis. Among them, the 4-node quadrilateral Belytschko-Tsay element, using lower order integration technique is most commonly employed, due to its efficiency, robustness and overall accuracy. However, the lower order integration brings in some uncertainty. This paper is to conduct an engineering evaluation on performance of various shell elements, including Belytschko-Tsay, Belytschko-Leviathan (QPH), Bathe-Dvorkin, discrete Kirchhoff triangular elements, available in the commercial explicit finite element software. The study uses several linear and nonlinear benchmark examples and high-speed impact examples, to investigate the performance of these elements. Results of engineering interest and efficiency of computation are reported. Also, the behavior of finite element convergence, observed from the results by a sequence of refined meshes is investigated.© 2004 ASME

CRITICAL COMPARISONS OF US AND EUROPEAN DYNAMIC SIDE IMPACTS

While vehicle development and manufacturing process is becoming global, automotive safety regulations in various parts of the world have not been as uniform. A good example is the differing requirements for dynamic side impact protection of new vehicles. United States National Highway Traffic Safety Administration (NHTSA) and European Union (EU) have each produced their own distinct test procedures such as, different barrier faces, impact configurations, and anthropomorphic test devices (dummies). Although both test procedures have the same final objective - estimate occupant responses in side impacts, they differ greatly in execution and emphasis on occupant response requirements. This paper discusses the differences in both side impact test procedures and vehicle and dummy performance in each case. Both dynamic side impact test data and analytical models are employed for this purpose. A full vehicle dummy-structure finite element is developed to investigate the two test conditions. Comparison of a typical vehicle performance such as door and bodyside intrusion profiles, contact velocities with dummies, dummy kinematics in both test conditions are examined closely. It is determined that although each test induces different loading and responses, there may be some commonality in impacted vehicle performance. (A) For the covering abstract see IRRD 893297.

Target Setting for Vehicle Side Impact Using a Statistical Approach

Designing a vehicle for superior side impact performance is an important consideration in automotive product development. The challenges involved in this design are many as side impact is a relatively short duration event and interaction between the crash test dummy and vehicle side structure including side airbag (if present) is involved, and engagement of the moving deformable barrier with the stiffer underbody of a car may not always take place (unlike in the case of frontal NCAP test in which the front rails will necessarily play a major role in energy-absorption). The safety engineer nevertheless has to set targets for relevant side crash-related variables in the initial phase of design when very limited information on vehicle structure is available. As shown in the present study, linear regression-based relationships can be utilized for setting quantitative targets for structural response and packaging-related variables for side impact safety design of a new vehicle.Copyright