Search Results

Computational simulations are conducted for several head impact scenarios using a three dimensional finite element model of the human brain in conjunction with accelerometer data taken from crash test data. Accelerometer data from a 3-2-2-2 nine accelerometer array, located in the test dummy headpart, is processed to extract both rotational and translational velocity components at the headpart center of gravity with respect to inertial coordinates. The resulting generalized six degree-of-freedom description of headpart kinematics includes effects of all head impacts with the interior structure, and is used to characterize the momentum field and inertial loads which would be experienced by soft brain tissue under impact conditions. These kinematic descriptions are then applied to a finite element model of the brain to replicate dynamic loading for actual crash test conditions, and responses pertinent to brain injury are analyzed.

Biomechanical data on the response of the face to localized and distributed loads are analyzed to provide performance goals for a biomechanically realistic face. Previously proposed facial injury assessment techniques and dummy modifications are reviewed with emphasis on their biomechanical realism. A modification to the Hybrid III dummy, called the GM Hybrid III Deformable Face, is described. The modification produces biomechanically realistic frontal impact response for both localized and distributed facial loads and provides for contact force determination using conventional Hybrid III instrumentation. The modification retains the anthropometric and inertial properties and the forehead impact response of the standard Hybrid III head.

Experimental tests using porcine brainstem samples were performed on a custom designed stress relaxation shear device. Tests were performed dynamically at strain rates >1 s−1, to three levels of peak strain (2.5%-7.5%). The directional dependence of the material properties was investigated by shearing both parallel and transverse to the predominant direction of the axonal fibers. Quasi-linear viscoelastic theory was used to describe the reduced relaxation response and the instantaneous elastic function. The time constants of the reduced relaxation function demonstrate no directional dependence; however, the relative magnitude of the exponential functions and the parameter representing the final limiting value are significantly different for each direction. The elastic function qualitatively demonstrates a dependence on direction. These results suggest that the brainstem is an anisotropic material.

The paper describes an evaluation of impact performance requirements for pedal cycle helmets. The paper examines the results of two related studies, evaluates other helmet test results and proposes performance criteria more effective for the amelioration of head injury. The two main studies are of pedal cycle helmet performance in real accidents (McIntosh and Dowdell IRCOBI 1992) and head impact tests conducted under conditions relevant to those occurring during pedal cycle accidents (McIntosh et al Stapp 1993). The results of other helmet evaluations are drawn upon. The paper examines a number of areas of helmet performance and focuses on head coverage and impact test criteria. The results of the studies demonstrate that pedal cycle helmets are failing to provide adequate coverage in the temporal region, and that standards tests are not sensitive to this problem.

A new three-dimensional human head finite element model, consisting of the scalp, skull, dura, falx, tentorium, pia, CSF, venous sinuses, ventricles, cerebrum (gray and white matter), cerebellum, brain stem and parasagittal bridging veins has been developed and partially validated against experimental data of Nahum et al (1977). A frontal impact and a sagittal plane rotational impact were simulated and impact responses from a homogeneous brain were compared with those of an inhomogeneous brain. Previous two-dimensional simulation results showed that differentiation between the gray and white matter and the inclusion of the ventricles are necessary in brain modeling to match regions of high shear stress to locations of diffuse axonal injury (DAI). The three-dimensional simulation results presented here also showed the necessity of including these anatomical features in brain modeling.

The paper reviews one hundred and three (103) cases of restrained children involved in motor vehicle crashes and admitted to the level I trauma center at Children's National Medical Center (CNMC). Thirty percent (30%) of these cases involved injuries with an Abbreviated InjuryScore (AIS) severity of 3 or greater. All cases are classified first by type of restraint system, i.e. infant seat, convertible seat, booster seat, lap belt, and lap and shoulder belt, and second, by type of injury sustained, i.e. head/face and neck, upper extremity, thorax, pelvic and abdominal, and lower extremity. The links between these classifications are examined to identify particular injury patterns associated with the use of individual restraint systems, e.g. the incidence of pelvic and abdominal injury associated with the use of both lap and lap and shoulder belts. For the severe injury cases the paper further examines the injury mechanisms for the most commonly observed patterns.

A controlled experimental program was conducted to determine the response of humans and a human surrogate with experimental lap belt restraints in -Gz acceleration environments. In the program, lap belt anchorage position (belt angle) and belt tension/slack were varied. Human volunteers were subjected to a static -1.0 Gz acceleration for each restraint configuration. A 95th percentile male Hybrid Ill dummy was subjected to a nominal 4.25 m/s (9.5 mph), -5 Gz impact while restrained by each restraint configuration. For the -Gz acceleration, significant changes in occupant head excursion were observed with varied lap belt configurations. In general, less pre-crash belt slack and higher lap belt angles produced significant reductions in occupant vertical excursions. This research provides data for use in evaluating or developing occupant survivability systems for rollover crash environments.

Injuries to the lower extremities of belted car occupants in frontal collisions are frequent and can be impairing. Crash parameters and vehicle attributes increase or decrease the risk of injury. Real-world accident data collected within the UK under the Co-operative Crash Injury Study (CCIS) has been used to examine these effects. AIS 2+ injuries are most common below the knees of both drivers and passengers. Intrusion of the footwell increases the risk of leg injury to a greater extent than crash severity under the conditions experienced in the accident data. Intrusion is shown not to be a proxy variable for delta-V. The pedals increase the risk of leg injury by 54% when there is 20 cm of footwell intrusion. The study indicates the need for an improved understanding of the injury mechanisms involved and the mechanism through which intrusion increases leg injury.

The shearing and bending injury mechanisms of the knee joint are recognised as two important injury mechanisms associated with car-pedestrian crash accidents. A study on shearing and bending response of the knee joint to a lateral impact loading was conducted with a 3D multibody system model of the lower extremity. The model consists of foot, leg and thigh with concentrated upper body mass. The body elements are connected by joints, including an anatomical knee joint unit that consists of the femur condyles, tibia condyles and tibia1 intercondylar eminence as well as ligaments. The biomechanical properties of the model were derived from literature data. The model was used to simulate two series of previously performed experiments with lower extremity specimens at lateral impact speeds of 15 and 20 km/h.

Sophisticated computer simulation of human response during various violent force exposure situations requires not only the validated programs, but also high quality databases, especially the data sets that characterize human body structures. Although anthropometric surveys and stereophotometric studies have been performed to create geometric and inertial property databases for the human body, there have been limited efforts on establishing the joint kinematics and resistive torque data sets. This paper presents the development, implementation, and validation of the human articulating joint model parameters for crash dynamics simulations. Measured human joint data on the voluntary range of motion and passive resistive torques were used to mathematically model the shoulder, elbow, hip, knee, and ankle joints.

This paper presents the experimental dynamic tolerance and the force-deformation response corridor of the human cervical spine under compression loading. Twenty human cadaver head-neck complexes were tested using a crown impact to the head at speeds from 2.5 m/s to 8 m/s. The cervical spine was evaluated for pre-alignment by using the concept of the stiffest axis. Mid cervical column (C3 to C5) vertebral body wedge, burst, and vertical fractures were produced in compression. Posterior ligament tears in the lower column occurred under flexion. Anterior longitudinal ligament tears and spinous process fractures occurred under extension. Mean values were: force at failure, 3326 N; deformation at failure, 18 mm; stiffness, 555 N/mm. The deformation at failure parameter was associated with the least variance and should describe the most accurate tolerance measure for the population as a whole.

The absence of constitutive data on muscle has limited the development of models of cervical spinal dynamics and our understanding of the forces developed in the cervical spine during impact injury. Therefore, the purpose of this study is to characterize the structural and material properties of skeletal muscle. The structural responses of the tibialis anterior of the rabbit were characterized in the passive state using the quasi-linear theory of viscoelasticity (r = 0.931 ± 0.032). In passive muscle, the average modulus at 20% strain was 1.75 ± 1.18, 2.45 ± 0.80, and 2.79 ± 0.67 MPa at test rates of 4, 40, and 100 cm·s-1, respectively. In stimulated muscle, the mean initial stress was 0.44 ± 0.15 MPa and the average modulus was 0.97 ± 0.34 MPa. These data define a corridor of responses of skeletal muscle during injury, and are in a form suitable for incorporation into computational models of cervical spinal dynamics.

A new ten-speed Concept 2000 transmission has been developed to support heavy duty truck market needs for high product reliability, durability, and robustness to inadvertent abusive range shifting. These models maintain the strengths of the current Eaton® Fuller® Twin Countershaft design and provide a platform for high torque applications. Design enhancements include: modular shift controls, mainshaft washers, output sealing, gear and bearing strengths, mainshaft strength, and Power Take Off accessibility. The transmission uses a single shift rod and metric fasteners throughout. A Simultaneous Product and Process Development Team coordinated the launch from concept to customer. It required a major manufacturing plant investment and process approach upgrade.

The purpose of this paper is three fold: to serve as a tutorial for engineers new to the field of drivetrain; to function as a reference manual for those who wish to retrieve some information on a topic they have not visited for some time; and to show the direction that four-wheel-drive technology should be taking. A brief history of four-wheel-drive is followed by some examples showing the broad range of four-wheel-drive vehicles in use today. All components of typical systems are discussed in some detail. The mechanics, function, purpose, and logic of different types of systems are described, as are their advantages and disadvantages. Handling characteristics and traction capabilities of some different systems are analyzed. A majority of the vehicles produced today have systems that simply lock all drive axles together when in four-wheel-drive mode. This limits their use to off-road or extremely slippery conditions.

In this paper,the flywheel is considered to be linear elastic composition in accordance with its operating characteristic, mechanical and mathematical model are presented,the finite element method is employed to carry out the numerical analysis of steady and unsteady stresses within the high speed flywheel in the regenerative braking system of a city bus,and these provide the basis foŕ its structural modification and further rational design.

The powertrain suspension package which includes the engine, transmission, and both drive and steerable axles, in conjunction with the steering system, has a very definite role in determination of vehicle ride characteristics. The position of the engine and transmission in relationship to the drive axle and the effect on the handling capability of the vehicle had to be evaluated, along with the full axle suspension system, because of the drastic change in componentry and configuration in the low-floor transit buses. Correlation between wheel geometry and ride characteristics has been proven mathematically, with test results and also by representative statistics provided by various vehicle operators.

One of the main factors of the drum brake performance and quality is the accuracy of “S” profiles of the cam shafts. To reduce cost, most axle and brake manufacturers use cam shafts with forged “S” cams, in some cases decreasing the accuracy of “S” profile, brake performance, and quality as compared to a machined “S” profile option. Today's highly competitive market, especially the bus market, requires the highest possible brake performance at reduced cost. This paper shows how to meet both requirements for cam shaft manufacturing, high “S” profile accuracy and low machining cost, at the same time.

An Emergency Tire Inflation System (ETIS) designed for use on commercial trucks was evaluated and tested. The ETIS is provided in kit form and designed to be installed by a truck operator to provide emergency air to inflate a low or punctured tire on tractor drive axles. The ETIS will continue to supply air to the tire until the system pressure falls below a safe air pressure level. The system is designed to allow the rig to be driven 500 miles to a tire repair station or to a safe location where tire repair service is available. The installation kit (Figure 1), which can fit under a truck seat, includes all the necessary equipment to install the system on the most common drive axles. The ETIS supplies air to the under-inflated tire through a previously qualified1 Rotary Union design. The Rotary Union is attached to the axle flange of the drive axle by a threaded adapter and two adjustable links that allow the Rotary Union to be placed at the center of rotation of the axle.

The driving performance of 17 heavy-truck drivers was monitored under alert and fatigued conditions on a closed-circuit track to determine whether driver fatigue could be indirectly measured in the vehicle control inputs or outputs. Data were recorded for various potential physiological indicators of fatigue (EEG, heart rate and a subjective evaluation of drowsiness), for vehicle speed, steering, and accelerator pedal movements, and for vehicle position on the track. The objective was to determine whether a simple set of vehicle-based control measures correlated with the fatigue indicators. Correlations between other vehicle-based measures reported in the literature and the fatigue indicators were also calculated. The results indicate that there are measures which correlate sufficiently well with driver fatigue that they could potentially be used for an unobtrusive vehicle-based fatigue-detection algorithm.

An Automatic Tire Inflation System (ATIS), specifically designed for use on commercial long haul trailers underwent complete testing and evaluation in 1993/1994.1 Testing and evaluation included a field test of a prototype system and a controlled laboratory evaluation of the Rotary Union which is the only component subject to wear. The testing of the prototype system indicated that design improvements were necessary before the system could be installed in fleet operations. The design improvements were completed and field installation of production ATIS began. The design improvements were intended to improve overall system durability, decrease installation time, to have less effect on the axle structure than the original design, implement the use of SAE or DOT Approved pressure components and increase overall dependability of the system. ATIS systems have now been developed and tested for most domestic trailer axle configurations.