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.
This paper presents an analysis of the displacement measurement of the Hybrid III 50th percentile male dummy chest in quasistatic and dynamic loading environments. In this dummy, the sternal chest deformation is typically characterized using a sliding chest potentiometer, originally designed to measure inward deflection in the central axis of the dummy chest. Loading environments that include other modes of deformation, such as lateral translations or rotations, can create a displacement vector that is not aligned with this sensitive axis. To demonstrate this, the dummy chest was loaded quasistatically and dynamically in a series of tests. A string potentiometer array, with the capability to monitor additional deflection modes, was used to supplement the measurement of the chest slider.
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.
This work studies the effect of padding on the force levels in impulsively loaded dummy lower extremities. Tests include the effect of padding incorporated into the soles of shoes and an examination of the potential of shoe padding for mitigating impact loading on the lower extremities. Three different shoes and three paddings were studied using a pendulum impactor; two different padding levels were studied in an impact sled test with simulated translational structural intrusion. The tests indicate a greater than 20% variation in peak axial force imparted to the lower tibia between shoes, and a greater than 50% variation in peak axial force across the paddings tested. From sled tests with simulated structural intruaion, we see a decrease of approximately 15% in peak axial load and a decrease of over 20% in peak anterior/posterior moment.
Two sled systems capable of producing structural intrusion in the footwell region of an automobile have been developed. The first, System A, provides translational toepan intrusion using actuator pistons to drive the footwell structure of the test buck. These actuator pistons are coupled to the hydraulic decelerator of the test sled and are powered by hydraulic energy from the impact event. Resulting footwell intrusion is characterized using a toepan pulse analogous to the acceleration pulse used to characterize sled and vehicle decelerations. Sled tests with System A indicate that it is capable of accurately and repeatably simulating toepan/floorpan intrusion into the occupant footwell. Test results, including a comparison of lower extremity response between intrusion sled tests and no intrusion sled tests, indicate that this system is capable of repeatable, controlled structural intrusion during a sled test impact.
The University of Virginia is investigating the use of a magnetohydrodynamic (MHD) angular rate sensor to measure head angular acceleration in impact testing. Output from the sensor, which measures angular velocity, must be differentiated to produce angular acceleration. As a precursor to their use in actual testing, a torsional pendulum was developed to analyze an MHD sensor's effectiveness in operating under impact conditions. Differentiated and digitally filtered sensor data provided a good match with the vibratory response of the pendulum for various magnitudes of angular acceleration. Subsequent head drop tests verified that MHD sensors are suitable for measuring head angular acceleration in impact testing.
Recently, during the course of different experimental problem-solving activities on automotive vehicles, several examples have been found in which the identification of the cause of a particular vibration problem related to a specific component or subsystem involves detecting the presence of an impulsive effect on measured time signals. The difficulty in identifying such an effect arises due to the fact that the vibrational response signals measured during operation are dominated by relatively high amplitude harmonics which tend to mask the impulsive component. This article describes two case studies for this type of identification problem, a servo-assisted steering system and a front suspension shock absorber strut.
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.
The 3-D flow field inside an automotive torque converter was measured using laser velocimetry. For the tests, a torque converter completely machined from Plexiglas was operated at the 0.065 and 0.800 turbine/pump speed ratio, and detailed velocities were measured in 13 planes throughout the torque converter. Digital shaft encoder information was used to correlate measured velocities with the pump/turbine angular positions to generate blade-to-blade profiles, 3-D vector plots, and contour through flow plots. Results showed large flow separation regions, jet/wake flows, circulatory secondary flows, and significant flow unsteadiness in all three torque converter elements (pump, turbine, and stator). From the measured velocities, torque converter performance parameters such as mass flows, input/output torque, element incidence angles, slip factors, and vorticities were determined.
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.
This paper examines an originally designed airbag deployment system for use in static experimental testing. It consists of a pressure vessel and valve arrangement with pneumatic and electric controls. A piston functions like a valve when operated and is activated pneumatically to release the air in the tank. Once released, the air fills the attached airbag. The leading edge velocity can be controlled by the initial pressure in the tank, which can range up to 960 kPa. Three different test configurations were studied, which resulted in leading edge deployment speeds of approximately 20 m/s, 40 m/s, and 60 m/s. In experiments using this system, seven types of airbags were tested that differed in their material, coating, and presence of a tether. Data for each series of tests is provided. High speed video and film were used to record the deployments, and a pressure transducer measured the airbag's internal pressure.
Drop testing of the Hybrid III dummy head was conducted to determine variations in Head Injury Criteria values with the point of head impact, and how the variations relate to actual head injuries. Head drop tests indicated that impacts to the temple and lower forehead posed the greatest injury risks. Moreover, the application of chamois or chalk over the head, a common practice among safety researchers to detect racial lacerations and head contacts, was found to significantly lower Head Injury Criteria values for all impact locations.
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.
Selectively reinforced, squeeze cast automotive pistons contain a boundary between the reinforced and unreinforced regions. This boundary is known as the macro-interface. Due to the difference in CTE between the composite and unreinforced matrix, the macro-interface can be the site of residual stress formation during cooling from the casting or heat treatment temperature. Subsequent thermal exposure, particularly thermal cycling, may produce cyclic stress at this interface causing it to experience fatigue. It has been found that matrix precipitates at the macro-interface and the aging behavior of the matrix also may play a role in defining the strength of the macro-interface during thermal cycling conditions.
The response and risk of injury for occupants in frontal crashes are more severe when structural deformation occurs in the vehicle interior. To reproduce this impact environment in the laboratory, a sled system capable of producing structural intrusion in the footwell region has been developed. The system couples the hydraulic decelerator of the sled to actuator pistons attached to the toepan and floorpan structure of the buck. Characterization of the footwell intrusion event is based on developing a toepan pulse analogous to the acceleration pulse used to characterize sled and vehicle decelerations. Preliminary sled tests with the system indicate that it is capable of simulating a complex sequence of toepan/floorpan translations and rotations.
Sixty-three simulated frontal impacts using cadaveric specimens were performed to examine and quantify the performance of various contemporary automotive restraint systems. Test specimens were instrumented with accelerometers and chest bands to characterize their mechanical responses during the impact. The resulting thoracic injury severity was determined using detailed autopsy and was classified using the Abbreviated Injury Scale. The ability of various mechanical parameters and combinations of parameters to assess the observed injury severities was examined and resulted in the observation that belt restraint systems generally had higher injury rates than air bag restraint systems for the same level of mechanical responses. To provide better injury evaluations from observed mechanical parameters without prior knowledge of what restraint system was being used, a dichotomous process was developed.
The University of Virginia is investigating the biomechanical response and the injury tolerance of the lower extremities. This paper presents the experimental and simulation work used to study the injury patterns and mechanisms of the ankle/foot complex. The simulation effort has developed a segmented lower limb and foot model for an occupant simulator program to study the interactions of the foot with intruding toepan and pedal components. The experimental procedures include static tests, pendulum impacts, and full-scale sled tests with the Advanced Anthropomorphic Test Device and human cadavers. In these tests, the response of the lower extremities is characterized with analogous dummy and cadaver instrumentation packages that include strain gauges, electrogoniometers, angular rate sensors, accelerometers, and load cells. An external apparatus is applied to the surrogate's lower extremities to simulate the effects of muscle tensing.
Recently there has been a greater awareness of the increased risk of certain injuries associated with air bag deployment, especially the risks to small occupants, often women. These injuries include serious eye and upper extremity injuries and even fatalities. This study investigates the interaction of a deploying air bag with cadaveric upper extremities in a typical driving posture; testing concentrates on female occupants. The goals of this investigation are to determine the risk of upper extremity injury caused by primary contact with a deploying air bag and to elucidate the mechanisms of these upper extremity injuries. Five air bags were used that are representative of a wide range of air bag ‘aggressivities’ in the current automobile fleet. This air bag ‘aggressivity’ was quantified using the response of a dummy forearm under air bag deployment.
This paper evaluates the biofidelity of the Hybrid III 5th percentile female dummy relative to seven small female cadavers tested as out-of-position drivers in static air bag deployment tests. In the out-of-position tests, the chest was positioned against the air bag module in an effort to recreate a worst-case loading environment for the thorax. Two pre-depowered production air bags and a prototype dual-stage air bag were evaluated. Thoracic accelerometers and chestbands were used to compare chest compression, velocity, acceleration, and Viscous Criteria. A statistical comparison of dummy and cadaver results indicate acceptable biofidelity of the Hybrid III dummy with significant differences observed only in the Viscous Criteria.