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The evaluation of the performance of a particular inflator for the design of the entire airbag system is typically carried out by examining the pressure pattern in a standard tank test. This study assesses the adequacy of the tank test as a true measure of the likely performance of the actual inflator-airbag system. Theoretical arguments, numerical experiments, and physical experiments show that the time rate of pressure change may be an appropriate measure to evaluate performance of a specific type of inflator, particularly if variations in the inflator design maintain the same working gas components. However, when evaluating and comparing the dynamic behavior between different types of inflators, the time rate of pressure change provides useful but incomplete information.

A test series using eight unembalmed cadavers was conducted to investigate factors affecting the creation of cervical spine damage from impact to the crown of the head. The crown impact was accomplished by a free-fall drop of the test subject onto a load plate. The load plate striking surface was covered with padding to vary the contact force time characteristics. The orientations of the head, cervical spine, and torso were adjusted relative to a laboratory coordinate system to investigate the effects of head and spinal configuration on the damage patterns. Load and acceleration data are presented as a function of time and as a function of frequency in the form of mechanical impedance.

This paper describes the development of a rubber-like skin Finite Elements Model (FEM) for the Hybrid III headform and an experimental method to determine its material properties. The finite element modeling procedures, using material parameters derived from tests conducted on the headform skin (rubber) material, are described. Dynamic responses and computations of HIC using the developed headform model show that an Elastic-Plastic Hydrodynamic (EPH) material model of the rubber can be used for headform impact simulations. The results obtained from the headform simulation using an EPH rubber material model and drop tower tests of the headform on both a rigid and a deformable structure will be compared, in order to show the applicability of the EPH model.

Deployment of an airbag or charging of a tank by an inflator-canister system is a highly dynamic process. Quantification of energy storage, energy flux, work done, flow rates, thermodynamic properties, and energy conservation are essential to describe the deployment process. The concepts of available work and entropy production are presented as useful parameters when evaluating airbag aggressivity from tank test results for different types of inflators. This paper presents a computational methodology to simulate a pyro- and a hybrid-inflator-canister-airbag system to predict the force pattern that could occur on an out-of-position occupant when the airbag deploys. Comparisons with experimental data have been made in all cases where data were available. These include driver-, passenger-, and side-airbag designs.

One way to improve vehicle's fuel economy is to reduce its weight. Reducing weight, however has other consequences. One of these is reduced vehicle size. Almost invariably, lighter vehicles are smaller. Reducing vehicle weight has also been associated with a reduction in occupant protection; the lighter the vehicle, the greater the chance of injury when a crash occurs. For this study, a data-based model is used to evaluate the independent effects of size and weight. This model is constructed using the NASS database and information obtained from NCAP tests. The results indicate that although mass is the dominant factor, size also has an effect; some of the observed reduction in safety benefits associated with mass reduction is actually an effect of size reduction. The model is also used to evaluate the effects of varying stiffness.

The highly dynamic process in a pyrotechnic inflator and in a canister-airbag system was simulated by using two compressible gas thermal energy numerical models. First a 2-D model was used to simulate flow through the inflator porous media; then results from the first model were used as input to a second 2-D model to compute pressure, temperature and flow patterns in the airbag. Results show a complete picture of the dynamics of the airbag inflator - canister system during deployment.

A series of head impacts were conducted with 15 unembalmed cadavers. The purpose of the tests was to study the application of three-dimensional motion analysis using accelerometry, brain vascular system pressurization and high speed cineradiography to the understanding of head injury mechanics. The implementation of the techniques is described and their effectiveness is discussed. The three-dimensional accelerometry technique using nine accelerometers was found to be applicable in direct head impacts. Analysis of the head acceleration data indicates the existence of brain motions which are independent of the motion of the skull. These motions were confirmed by the high speed cineradiographic films. Brain vascular system pressurization and time after death were found to play a role in determining the extent of the brain motions and the resulting brain injuries.

The Finite Element predictions of the physical response of foams during impact by a rigid body (such as, the Hybrid III head form) is determined by material law equations generally approximated based on the theory of elastoplasticity. However, the structural aspect of foam, its discontinuous nature, makes it difficult to apply the laws of continuum mechanics and construct constitutive equations for foam-like material. One part of the problem relates to the state of stress. In materials such as steel, the state of hydrostatic stress does not affect the stress strain behavior under uniaxial compression or tension in plastic regime. In other words, when steel is subject to hydrostatic pressures the stress strain characteristic can be predicted from a uniaxial test. However, if the stresses acting on a section of foam are triaxial, the response of a head-form may be different than predicted from uniaxial test data.

A statistical theory is used to quantify the amount of information transmitted from a transducer (i.e., accelerometer) to the air bag controller during a vehicle crash. The amount of information relevant to the assessment of the crash severity is evaluated. This quantification procedure helps determine the effectiveness of different testing conditions for the calibration of sensor algorithms. The amount of information in an acceleration signal is interpreted as a measure of the ability to separate signals based on parameters that are used to assess the severity of an impact. Applications to a linear spring-mass model and to actual crash signals from a development vehicle are presented. In particular, the comparison of rigid barrier (RB) and offset deformable barrier (ODB) testing modes is analyzed. Also, the performance of front-mounted and passenger compartment accelerometers are compared.

The impact response of foam is investigated using Finite Element Analysis (FEA). A procedure will be described for determining the material constants used in the FEA material models. The procedure uses compressive uniaxial, force versus displacement, and triaxial, pressure versus volume-change, data. After the material model is constructed using the uniaxial and triaxial data, FEA is used to predict the results of a free-moving-mass striking rigidly backed foam. The limitations of the current material models are also addressed.

The relationship of the airbag fire-distribution as a function of impact velocity to the airbag fire-time is studied through the use of an optimization procedure. The study is conducted by abstracting the sensor algorithm and its associated constraints into a simple mathematical formulation. An airbag fire objective function is constructed that integrates the fire-rate and fire-time requirements. The function requires the input of a single acceleration time history; it produces an output depending on the airbag fire condition. Numerical search of the optimal fire threshold curve is achieved through parameterizing this curve and applying a modified simplex search optimization algorithm that determines the optimal threshold function parameters without computing the complete objective function in the parameter space. Numerical results are given to show the effectiveness and potential difficulties with the automatic search scheme.

A test series using 12 unembalmed cadavers was conducted to investigate factors affecting the creation of cervical spine damage due to impact to the top of the head. The test subjects were instrumented to measure head, T8 thoracic spine, and sternum acceleration responses. Photographic targets on the head and torso allowed analysis of impact motions from high-speed movies. The stationary test subject was struck by a guided, moving impactor mass of 56 Kg at 4.6-5.6 m/s. The impactor striking surface consisted of a biaxial load cell with padding to vary the contact force-time characteristics of the head/impactor. The orientation of the head, cervical spine, and torso was adjusted relative to the impactor axis to investigate the effect of spinal configurations on the damage patterns. Load and acceleration data are presented as functions of time and as functions of frequency in the form of mechanical impedance.

This study Investigates the response of human cadavers1, and live anesthetized and post-mortem primates and canines2, to blunt lateral thoraco-abdominal impact. There were 12 primates: 5 post-mortem and 7 live anesthetized; 10 canines; 1 post-mortem and 9 live anesthetized; and 3 human cadavers. A 10 kg free-flying mass was used to administer the impact in the right to left direction. To produce the varying degrees of injury, factors including velocity, padding of the impactor surface, location of impact site, and impactor excursion were adjusted. The injuries were evaluated by gross autopsy, and in the case of live subjects, current clinical methods such as sequential peritoneal lavage and biochemical assays were also employed. Mechanical measurements included force time history, intraortic pressure, and high-speed cineradiography to define gross organ motion.