Crashworthiness Performance of Mass-Efficient Extruded Structures

Theoretical, numerical and experimental studies were conducted on the axial crushing behavior of traditional single-cell and innovative four-cell extrusions. Two commercial aluminum alloys, 6061 and 6063, both with two tempers (T4 and T6), were considered in the study. Testing coupons taken from the extrusions assessed the nonlinear material properties. A theoretical solution was available for the one-cell design, and was developed for the mean crushing force of the four-cell section. Numerical simulations were carried out using the explicit finite element code LS-DYNA. The aluminum alloy 6063T4 was found to absorb less energy than 6061T4, for both the one-cell and four-cell configurations. Both 6061 and 6063 in the T6 temper were found to have significant fracture in the experimental testing. Theoretical analysis and numerical simulations predicted a greater number of folds for the four-cell design, as compared to the one-cell design, and this was confirmed in the experiments. The theoretical improvement in energy absorption of 57% for the four-cell in comparison with the one-cell design was confirmed by experiment. The good agreement between the theoretical, numerical and experimental results allows confidence in the application of the theoretical and numerical tools for both single-cell and innovative four-cell extrusions. It was also demonstrated that these materials have very little dynamic strain rate effect.

Rails Deformation Pattern in Frontal Impact

During a vehicle crash stress waves can be generated at the impact point and propagate through the vehicle structure. The generation of these waves is dependent, in general, on the crash type and, in particular, on the impact contact characteristics. This has consequences with respect to different crash barrier interfaces for vehicle evaluation. The two barriers most commonly used to evaluate the response of a vehicle in a frontal impact are the rigid barrier and the offset deformable barrier. They constitute different crash modes, full frontal and offset. Consequently it would be expected that there are different deformation patterns between the two. However, an additional possible contributor to the difference is that an impact into a rigid barrier generates waves of significantly greater stress than impacts with the deformable one. If stress waves are a significant component of real world final deformation patterns then, the choice of barrier interface and its effective stiffness is critical. To evaluate this conjecture, models of two types of rails each undergoing two different types of impacts, are analyzed using an explicit dynamic finite element code. Results show that the energy perturbation along the rail depends on the barrier type and that the early phase of wave propagation has very little effect on the final deformation pattern. This implies that in the real world conditions, the stress wave propagation along the rail has very little effect on the final deformed shape of the rail.

Use of Stochastic Analysis for FMVSS210 Simulation Readiness for Correlation to Hardware Testing

The FMVSS210 regulation establishes requirements for seat belt assembly anchorages to be strong enough for effective occupant restraint. The belt separation from the vehicle structure in crash tests needs to be avoided. Federal government mandate requires use of Pelvic and Torso Body Blocks for testing belt anchor strengths for lap and shoulder belts respectively. The belt anchorages are expected to withstand loads of 13.34 kN if both lap and shoulder belts are used and 22.24 kN if only lap belts are used. The analytical simulation of the hardware test is done using explicit dynamic code LS-DYNA. Hardware testing is of quasi-static nature while the simulation uses the dynamic code. However the analysis could be made to approach the quasi-static test by adjusting some input parameters in the simulation. In addition some input parameters need adjustment for making the model robust and to make it correlate to the hardware test. This study involves the use of Optimal Symmetnc Latin Hypercube Design to explore the design space, and to develop a fast surface response model. This response model can be viewed as a surrogate model to the actual LS-DYNA simulation and is used in this work to rank the input parameters by the percent contdbution they make towards the variation of the desired output responses. After determining the fit of the response model, it is used to perform the stochastic simulation. The confidence interval for test correlation prediction can then be estimated. This technique can further be used to do design sensitivity studies and for optimizing the vehicle structure with respect to FMVSS210 regulation.

Locomotive Crashworthiness Testing at the Transportation Technology Center

This paper describes a series of full-scale impact tests to be conducted at the Federal Railroad Administration’s Transportation Technology Center (TTC), Pueblo, Colorado. The tests will be performed to investigate locomotive crashworthiness.

Dynamic Axial Crush of Automotive Rail-Sized Composite Tubes: Part 2 — Tubes With Braided Reinforcements (Carbon, Kevlar®, and Glass) and Non-Plug Crush Initiators

This paper documents the braided reinforcement portion of a successful fundamental study of the dynamic axial crush of automotive rail-sized composite tubes. Braided reinforcements were comprised principally of carbon fiber but also of Kevlar® and E-glass and combinations of the three. Fourteen different braids were used, six of which were tri-axial and the remainder bi-axial. Tubes were manufactured using Resin Transfer Molding (RTM) with processing and molding techniques that are suitable for the low cost high volume needs of the automotive industry. Braids were obtained as continuous rolls of tubular sock-like material and pulled over metal mandrels one ply at a time. Carbon fiber tow sizes ranged from 6k to 48k. Dow Derakane 470 vinylester resin was used for all tubes. Tube geometry, a 88.9×88.9 mm square cross section with 2.54 mm thick walls, approximated that of the first 500 mm of the lower rail of a typical mid-size vehicle. Note in particular that tube wall thickness was fixed at a single value in this study. A 45° bevel on the outside edge of the lead end of each tube served as the crush initiator. In total 71 dynamic axial crush tests were conducted. In terms of important findings, consistent with the woven fabric portion of this program [1], desirable dynamic axial crush response was demonstrated for RTM’d automotive rail-sized carbon fiber reinforced tubes. For almost all parameter configurations, the tubes exhibited stable and progressive crush with a reasonably flat plateau force level and an acceptable crush initiation force, i.e. one that can be withstood by the backup structure. Additionally, crush debris from such tubes was found to neither contain objectionable sharp brittle splinters nor pose a health risk. Displacement average values of dynamic axial crush force ranged from 11.88 to 26.51 kN and values of SEA (specific energy absorption) ranged between 10.42 and 22.44 kJ/kg. In terms of parameter effects, the fiber type and reinforcement architecture were found to be capable of more than doubling/halving the dynamic axial crush force and SEA.

Automated Finite Element Modeling of Tube Frame Structure Parametric Design

This research was intended to address the last step in the development of a tube-frame (termed B2B) parametric crashworthiness model - automated finite element modeling of the parametric design. We have added the generation of finite element models to the previously built Unigraphics Version 16 (UG V16) parametric model, so that finite element models could be quickly built. UG/WAVE was used to design the vehicle parametrically and UG/SCENARIO, a pre- and post-processor integrated in UG, was used to automatically construct the finite element mesh. We established the quality of the finite element meshes, generated for two new designs, which were created by changing overall dimensions of the vehicle. This was done using objective criteria for the finite element mesh. The component data was added to the automatically generated mesh, and the results from the crashworthiness analysis of this model compared favorably with the ‘hand-built’ model using traditional model building techniques. The results from this work will be useful in the development of the parametric design process. The use of automatically generated finite element meshes will also be useful for the automated evaluation of these parametric designs.

The Latest Trends in Reducing Noise and Vibrations in Large Commercial Vehicles

This session-long tutorial will encompass some of the latest research in the area of reducing noise and vibrations in large commercial vehicles, such as railway locomotives, heavy trucks, and transit busses. The tutorial will be conducted by Professor Mehdi Ahmadian, Director, Advanced Vehicle Dynamics Laboratory at Virginia Tech. The session participants will have an opportunity to participate in an open forum about their experience with the methods that are discussed by the presenter.

Integrated Piezoelectric Linear Motor for Vehicle Applications

The focus of this research was to create a linear motor that could easily be packaged and still perform the same task of the current DC motor linear device. An incremental linear motor design was decided upon, for its flexibility in which the motor can be designed. To replace the current motor it was necessary to develop a high force, high speed incremental linear motor. To accomplish this task, piezoelectric actuators were utilized to drive the motor due their fast response times and high force capabilities. The desired overall objectives of the research is to create an incremental linear motor with the capability of moving loads up to one hundred pounds and produce a velocity well over one inch per second. To aid the design process a lumped parameter model was created to simulate the motor’s performance for any design parameter. Discrepancies occurred between the model and the actual motor performance for loads above 9.1 kilograms (20 pounds). The resulting model, however, was able to produce a good approximation of the motor’s performance for the unloaded and lightly loaded cases. The incremental linear motor produced a velocity of 4.9 mm/sec (0.2 in/sec) at a drive frequency of 50 Hz. The velocity of the motor was limited by the drive frequency that the amplifiers could produce. The motor was found to produce a stall load of 17 kilograms (38 pounds). The stall load of the design was severely limited by clearance losses.

Dynamic Behavior of Monolithic and Composite Materials by Split Hopkinson Pressure Bar Testing

A Split Hopkinson Pressure Bar (SHPB), an experimental apparatus for testing of solid materials at high strain rates, was in-house designed and realized by the Mechanical Engineering Dept. of WSU: it can test different types of materials and provide their dynamic mechanical properties (e.g. Young’s modulus, hardening or plasticization coefficients, yield strength). This SHPB works at strain rate levels between 1000 and 3000 s-1 and impact speeds between 6 and 9 m/s. The specimen is simply a 6 mm dia. 3 mm long cylinder. The apparatus and its software were benchmarked by means of tests on Aluminum and Titanium, whose mechanical properties are well known, and later successfully applied to non-metallic materials like Nylon, Epoxy, Carbon fiber and glass fiber reinforced composites.

Stochastic Simulation for Crash and Other Performance Improvements: How to Balance Value and Cost

Stochastic simulation is the technique of including the uncertainties into a numeric model. The value of stochastic simulation has been emphasized in literature through different applications in product development process. These applications include simulation of several product performance attributes including crashworthiness, safety, durability and comfort. The comparative cost of running stochastic simulation is usually an order higher than traditional deterministic analysis. However, if properly applied, the value obtained through this technology far exceeds than that through deterministic methods. The higher cost implies that the value has to be clearly defined, measured and balanced against the additional investment. The objective of this paper is to outline a framework for setting up guidelines for stochastic simulation as applied to product development process. Discussions are made on how the model complexity and model accuracy strongly influence the value obtained from stochastic simulation.