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Technical Paper

Constitutive Modeling of Polymers Subjected to High Strain Rates

A biaxial test procedure is used to assess the constitutive properties of polymers in tension. The constitutive constants are derived for high strain rate applications such as those associated with crashworthiness studies. The test procedure is used in conjunction with a time- and strain-dependent quasi-linear viscoelastic constitutive law consisting of a Mooney-Rivlin formulation combined with Maxwell elements. The procedure is demonstrated by describing the stress vs. strain relationship of a rubber specimen subjected to a step-relaxation input. The constitutive equation is transformed from a nonlinear convolution integral to a set of first order differential equations. These equations, with the appropriate boundary conditions, are solved numerically to obtain transient stresses in two principal directions. Material constants for use in the explicit LS-Dyna non-linear finite element code are provided.
Technical Paper

Advancements in Crash Sensing

The crash modes that occur each day on streets and highways have not changed dramatically over the past 50 years. The need to better understand those crash modes and their relation to rapidly emerging, tailorable restraint systems has intensified recently. The algorithms necessary for predicting a deployment event are based on an approach of coupling the occupant kinematics in a crash to the sensing technology that will activate the restraint system. This paper describes methods of computer modeling, occupant sensing and vehicle crash dynamics to define a crash sensing system that reacts to a complex set of input conditions to invoke an effective restraint response.
Technical Paper

A Madymo Model of the Foot and Leg for Local Impacts

It has been reported that lower extremity injuries represent a measurable portion of all moderate-to-severe automobile crash- related injuries. Thus, a simple tool to assist with the design of leg and foot injury countermeasures is desirable. The objective of this study is to develop a mathematical model which can predict load propagation and kinematics of the foot and leg in frontal automotive impacts. A multi-body model developed at the University of Virginia and validated for blunt impact to the whole foot has been used as basis for the current work. This model includes representations of the tibia, fibula, talus, hindfoot, midfoot and forefoot bones. Additionally, the model provides a means for tensioning the Achilles tendon. In the current study, the simulations conducted correspond to tests performed by the Transport Research Laboratory and the University of Nottingham on knee-amputated cadaver specimens.
Technical Paper

Effects of Humidity Fluctuations on Adsorption Columns Used for Air Purification in Closed Environments

Effects of a cabin-level humidity upset on an activated carbon column used for adsorption of trace compounds from air are examined through a series of experiments and computer simulations. Breakthrough curves measured for dichloromethane in the presence of water indicate that a rapid increase in relative humidity can displace large quantities of dichloromethane from the adsorbed phase resulting in effluent streams containing more than 20 times the feed concentration. Additionally, the breakthrough time for organic compounds is reduced significantly at high relative humidity. Numerical simulation results show favorable qualitative agreement with measured breakthrough curves, yet do not consistently predict accurate water or dichloromethane loadings at all experimental conditions.
Technical Paper

Open-Loop Chestbands for Dynamic Deformation Measurements

Originally designed for measuring closed-loop contours such as those around a human thorax, the External Peripheral Instrument for Deformation Measurement (EPIDM), or chestband, was developed to improve the measurement of dummy and cadaver thoracic response during impact. In the closed-loop configuration, the chestband wraps around on itself forming a closed contour. This study investigates the use of the chestband for dynamic deformation measurements in an open-loop configuration. In the open-loop configuration, the chestband does not generally form a closed contour. This work includes enhanced procedures and algorithms for the calculation of chestband deformation contours including the determination of static and dynamic chestband contours under several boundary conditions.
Technical Paper

A Simulation-Based Calibration and Sensitivity Analysis of a Finite Element Model of THOR Head-Neck Complex

The THOR-NT dummy has been developed and continuously improved by NHTSA to provide automotive manufacturers an advanced tool that can be used to assess the injury risk of vehicle occupants in crash tests. With the recent improvements of finite element (FE) technology and the increase of computational power, a validated FE model of THOR may provide an efficient tool for the design optimization of vehicles and their restraint systems. The main goal of this study was to improve biofidelity of a head-neck FE model of THOR-NT dummy. A three-dimensional FE model of the head and neck was developed in LS-Dyna based on the drawings of the THOR dummy. The material properties of deformable parts and the joints properties between rigid parts were assigned initially based on data found in the literature, and then calibrated using optimization techniques.
Technical Paper

New Method to Identify Dynamic Normal Stiffness and Damping of Shims for CAE Modeling

One of the most important means used for suppressing squeal noise in disc brakes is the application of shims on the pad backplates. In many cases this proves a very efficient tool depending on the type of shim applied in the specific cases. Building up knowledge on the effects of shims have been ongoing for several years, and measuring the important parameters characterizing the shims is crucial for understanding how to develop and implement the shims in an optimal way. Several methods are described in literature for measuring the constrained layer damping effect and one method is described for direct measurement of the shear stiffness and shear damping properties. However, up to now no method has been available that can measure and characterize the normal stiffness and damping properties of shims. This is one of the most important properties of shims as it controls the de-coupling effect in the direction of the normal forces.
Technical Paper

Brake Dynamometer Test Variability - Analysis of Root Causes

Modern project management including brake testing includes the exchange of reliable results from different sources and different locations. The ISO TC22/SWG2-Brake Lining Committee established a task force led by Ford Motor Co. to determine and analyze root causes for variability during dynamometer brake performance testing. The overall goal was to provide guidelines on how to reduce variability and how to improve correlation between dynamometer and vehicle test results. This collaborative accuracy study used the ISO 26867 Friction behavior assessment for automotive brake systems. Future efforts of the ISO task force will address NVH and vehicle-level tests. This paper corresponds to the first two phases of the project regarding performance brake dynamometer testing and presents results, findings and conclusions regarding repeatability (within-lab) and reproducibility (between-labs) from different laboratories and different brake dynamometers.
Technical Paper

Patterns of Acetabular Femoral Head Coverage

The size and shape of the acetabulum and of the femoral head influence the injury tolerance of the hip joint. The aim of this study is to quantify changes in acetabular cup geometry that occur with age, gender, height, and weight. Anonymized computed tomography (CT) scans of 1,150 individuals 16+ years of age, both with and without hip trauma, were used to describe the acetabular rim with 100 equally spaced points. Bilateral measurements were taken on uninjured patients, while only the uninjured side was valuated in those with hip trauma. Multinomial logistic regression found that after controlling for age, height, weight, and gender, each 1 degree decrease in acetabular anteversion angle (AAA) corresponded to an 8 percent increase in fracture likelihood (p≺0.001).
Technical Paper

Detached Eddy Simulation on a Swept Hybrid Model in the IRT

In recent years, there has been a growing desire to incorporate computational methods into aircraft icing certification practices. To improve understanding of ice shapes, a new experimental program in the NASA Icing Research Tunnel (IRT) will investigate swept hybrid models which are very large relative to the test section and are intended to operate at high lift coefficients. The present computations were conducted to help plan the experiments and to ascertain any effects of flow separation and unsteady forces. As they can be useful in robustly and accurately predicting large separation regions and capturing flow unsteadiness, a Detached Eddy Simulation (DES) approach has been adopted for simulating the flow over these large high-lift wing sections. The DES methodology was first validated using experimental data from an unswept NACA 0012 airfoil with leading-edge ice accretion, showing reasonable performance.
Technical Paper

Influence of Driver Input on the Touchdown Conditions and Risk of Rollover in Case of Steering Induced Soil-Trip Rollover Crashes

Some rollover testing methodologies require specification of vehicle kinematic parameters including travel speed, vertical velocity, roll rate, and pitch angle, etc. at the initiation of vehicle to ground contact, which have been referred to as touchdown conditions. The complexity of the vehicle, as well as environmental and driving input characteristics make prediction of realistic touchdown conditions for rollover crashes, and moreover, identification of parameter sensitivities of these characteristics, is difficult and expensive without simulation tools. The goal of this study was to study the sensitivity of driver input on touchdown parameters and the risk of rollover in cases of steering-induced soil-tripped rollovers, which are the most prevalent type of rollover crashes. Knowing the range and variation of touchdown parameters and their sensitivities would help in picking realistic parameters for simulating controlled rollover tests.
Technical Paper

Design and Development of Single Seat, Four Wheeled All-Terrain Vehicle for Baja Collegiate Design Series

There has been a rapid increase in popularity of multipurpose All-terrain vehicles (ATV) across the globe over the past few years. SAE BAJA event gives student-community an opportunity to delve deeper into the nitty-gritty of designing a single seat, four-wheeled off road vehicle. The design and development methodology presented in this paper is useful in conceptualization of an ATV for SAE BAJA event. The vehicle is divided into various subsystems including chassis, suspension, drive train, steering, and braking system. Further these subsystems are designed and comprehensively analyzed in software like SolidWorks, ANSYS, WINGEO and MS-Excel. The 3-D model of roll cage is designed in SolidWorks and analyzed in ANSYS 9.0 for front, rear and side impact along with front and side roll-over conditions. Special case of wheel bump is also analyzed. Weight, wall thickness and bending strength of tubing used for roll cage are comprehensively studied.
Technical Paper

Neck Validation of Multibody Human Model under Frontal and Lateral Impacts using an Optimization Technique

Multibody human models are widely used to investigate responses of human during an automotive crash. This study aimed to validate a commercially available multibody human body model against response corridors from volunteer tests conducted by Naval BioDynamics Laboratory (NBDL). The neck model consisted of seven vertebral bodies, and two adjacent bodies were connected by three orthogonal linear springs and dampers and three orthogonal rotational springs and dampers. The stiffness and damping characteristics were scaled up or down to improve the biofidelity of the neck model against NBDL volunteer test data because those characteristics were encrypted due to confidentiality. First, sensitivity analysis was performed to find influential scaling factors among the entire set using a design of experiment.
Technical Paper

Finite Element Analysis of Hard and Soft Tissue Contributions to Thoracic Response: Sensitivity Analysis of Fluctuations in Boundary Conditions

Thoracic trauma is the principle causative factor in 30% of road traffic deaths. Researchers have developed force-deflection corridors of the thorax for various loading conditions in order to elucidate injury mechanisms and to validate the mechanical response of ATDs and numerical human models. A corridor, rather than a single response characteristic, results from the variability inherent in biological experimentation. This response variability is caused by both intrinsic and extrinsic factors. The intrinsic factors are associated with individual differences among human subjects, e.g., the differences in material properties and in body geometry. The extrinsic sources of variability include fluctuations in the loading and supporting conditions in experimental tests.
Technical Paper

Intelligent Selection of Materials for Brake Linings

Friction materials used in the brake linings of automobiles, trucks, buses and other vehicles are required to satisfy a number of performance demands: they must provide a dependable, consistent level of friction, excellent resistance to wear, adequate heat dissipation, structural integrity, low cost and, if possible, light weight. No single material can meet all of these often conflicting performance criteria, and as a consequence, multiphase composites have been developed, consisting typically of a dozen or more different materials. The choice of materials is crucial in determining the performance attained, yet to date, braking material compositions have been developed largely on the basis of empirical observations.
Technical Paper

Diesel Fuel Injection Control for Optimum Driveability

Performance and refinement are key factors which influence the market acceptance of passenger cars, and consequently in the area of diesel fuel injection control there is increasing pressure for improved driveability. “Driveline shunt” is one important and problematic aspect of driveability, which is also known as “judder”, “chuggle” or “cab-nod”. It has been defined as an objectionable vehicle oscillation which takes place following a rapid throttle input or increase in engine load. This phenomenon is caused by driveline vibrations which can occur as a consequence of variations in engine torque demand. Mathematical modelling and experimentation techniques have been used to establish the behaviour of a fuel injection system, engine and vehicle driveline. Vehicle tests have been conducted in order to relate objective metrics and subjective opinion.
Technical Paper

A Finite Element Model of the Lower Limb for Simulating Pedestrian Impacts

A finite element (FE) model of the lower limb was developed to improve the understanding of injury mechanisms of thigh, knee, and leg during car-to-pedestrian impacts and to aid in the design of injury countermeasures for vehicle front-ends. The geometry of the model was reconstructed from CT scans of the Visible Human Project Database and commercial anatomical databases. The geometry and mass were scaled to those of a 50th percentile male and the entire lower limb was positioned in a standing position according to the published anthropometric references. A "structural approach" was utilized to generate the FE mesh using mostly hexahedral and quadrilateral elements to enhance the computational efficiency of the model. The material properties were selected based on a synthesis on current knowledge of the constitutive models for each tissue.
Technical Paper

Viscous Fan Drive Model for Robust Cooling Air Flow Simulation

One Dimensional models for front end air flows through the cooling system package are very useful for evaluating the effects of component and front end geometry changes. To solve such models for the air flow requires a robust iterative process that involves a number of non-linear sub-models. The cooling fan (s) constitute a major part of the difficulty, especially when they employ a viscous or “thermal” fan drive. This drive varies the torque coupling between the input and output shafts based on the radiator outlet air temperature. The coupling is achieved by viscous shear between two grooved disks and is regulated by a bimetal strip valve that varies the amount of fluid between the disks. This paper presents a mathematical model by which the input/output speed ratio may be determined as a function of the air temperature and input speed. Coefficients in the model are estimated from standard supplier performance information.
Technical Paper

Robust Compressor Model for AC System Simulation

Simple component models are advantageous when simulating vehicle AC systems so that overall model complexity and computation time can be minimized. These models must be robust enough to avoid instability in the iteration method used for determining the AC system operating or “balance” point. Simplicity and stability are especially important when the AC system model is coupled with a vehicle interior model for studies of transient performance because these are more computationally intensive. This paper presents a semi-empirical modeling method for compressors based on dimensionless parameters. Application to some sample compressor data is illustrated. The model equations are simple to employ and will not introduce significant stability problems when used as part of a system simulation.