Priya Prasad

Injury Risk Curves for Children and Adults in Frontal and Rear Collisions

This paper describes the development of injury risk curves for measurements made with the CRABI and Hybrid III family of biofidelic child and adult dummies that are used to evaluate restraint systems in frontal and rear-end collision simulations. Injury tolerance data are normalized for size and strength considerations. These data are analyzed to give normalized injury risk curves for neck tension, neck extension moment, combined neck tension and extension moment, sternal compression, the rate of sternal compression, and the rate of abdominal compression for children and adults. Using these injury risk curves dummy response limits can be defined for prescribed injury risk levels. The injury risk levels associated with the various injury assessment reference values currently used with the CRABI and Hybrid III family of dummies are noted.

Dynamic Axial Tolerance of the Human Foot-Ankle Complex

Dynamic axial impact tests to isolated lower legs were conducted at the Medical College of Wisconsin laboratory in the USA. The aim is to develop a more definitive and quantitative relationship between biomechanical parameters such as specimen age, axial force, and injury. Twenty-six intact adult lower legs excised from unembalmed human cadavers were tested under dynamic loading using a mini-sled pendulum device. Results from these tests were combined with the data from the studies by Wayne State University and Calspan Corporation, both in the USA. The total sample size available was 52. Statistical analysis of these data was performed using Weibull techniques. Age and dynamic axial force were the most significant discriminant variables that defined the injury risk function. Consequently, the probability of foot-ankle injury was described in terms of specimen age and force. The findings are a first step towards the quantification of the dynamic tolerance of the human foot-ankle complex under the axial impact modality.For the covering abstract of the conference see IRRD 891635.

A general failure criterion for spot welds under combined loading conditions

Abstract The circumferential failure mode of spot welds is investigated under combined loading conditions. Failure mechanisms of spot welds under different loading conditions are first examined by the experimental observations and a plane stress finite element analysis. An approximate limit load analysis for spot welds is then conducted to understand the failure loads of spot welds under combinations of resultant forces and resultant moments with consideration of the global equilibrium conditions only. The approximate limit load solution for circumferential failure is expressed in terms of sheet thickness, nugget diameter and combinations of loads. Failure contours are generated for spot welds under opening and shear loading conditions. The results indicate that failure contours become smaller when the ratio of the sheet thickness to the nugget diameter increases. Based on the approximate limit load solution, a general quadratic failure criterion for spot welds under combined three resultant forces and three resultant moments is proposed with correction factors determined by fitting to the experimental results of spot welds under combined loading conditions. The failure criterion can be used to characterize the failure loads of spot welds with consideration of the effects of sheet thickness, nugget diameter and combinations of loads. Experimental spot weld failure loads under combined opening and shear loading conditions and those under combined shear and twisting loading conditions are shown to be characterized well by the proposed failure criterion. Finally, a simplified general failure criterion for spot welds under three resultant forces and three resultant moments is proposed by neglecting the coupling terms of the resultant forces and moments for convenient use of the failure criterion for engineering applications.

A Biomechanical Analysis of Head, Neck, and Torso Injuries to Child Surrogates Due to Sudden Torso Acceleration

The authors report on the injuries to the head, neck and thorax of fifteen child surrogates, subjected to varying levels of sudden acceleration. Measured response data in the child surrogate tests and in matched tests with a three-year-old child test dummy are compared to the observed child surrogates injury levels to develop preliminary tolerance data for the child surrogate. The data are compared with already published data in the literature.

Relationships between passenger car seat back strength and occupant injury severity in rear end collisions: field and laboratory studies

To determine what effect seat back stiffness and other seat characteristics have on occupant responses, several seats were evaluated in dynamic Hyge rear impact sled simulations. The results of the sled tests indicate that stiffer seats do not have any consistent advantages over yielding seats for the complete range of speeds tested. Even a seat with a head restraint located closer to the center of gravity of the occupants head did not perform better than the baseline seat. Throughout the testing, the most sensitive response to seat design and crash severity was the lower neck extension moment.

BIOFIDELITY OF ANTHROPOMORPHIC TEST DEVICES FOR REAR IMPACT

This study examines the biofidelity, repeatability, and reproducibility of various anthropomorphic test devices (ATDs) in rear impacts. The Hybrid III, the Hybrid III with the Rear Impact Dummy (RID) neck, and the 50th% Thoracic Assessment Device (TAD-50) were tested in a rigid bench condition in rear impacts with velocity changes (delta Vs) of 16 and 24 kph. The results of the tests were then compared to J. Mertz and L.M. Patricks data. The Hybrid III and the Hybrid III with the RID neck were also tested on standard production seats in rear impacts for a delta V of 8 kph. Comparison testing of the Hybrid III and TNO Rear Impact Dummy (TRID) necks were conducted on production seats with different Neck Injury Factor (NIF) scores at delta Vs of 8 and 16 kph. The Hybrid III and the Hybrid III with the pedestrian pelvis were also tested with standard production seats to determine if hip joint stiffness affected the kinematics of the ATD in rear impacts. The standard Hybrid III is a molded pelvis while the pedestrian pelvis is a cut pelvis. It can be concluded that the standard Hybrid III dummy is suitable for rear impact testing. (A) For the covering abstract of the conference see IRRD E201172.

A REVIEW OF MATHEMATICAL OCCUPANT SIMULATION MODELS

This chapter reviews the basic features of some mathematical occupant simulation models. Models reviewed include 2D/3D complicated gross-motion simulators, such as MADYMO 2D/3D and CAL3D, an integrated crash victim simulator (CVS) model with various finite element analysis (FEA) airbag models and their couplings with CVS programs for automotive safety applications. Historical development, analytic formulation/solution, experimental validation, application, and the experience with these models is discussed. Development trends in FEA approaches by integrating structure/occupant simulation models for safety/crashworthiness analysis are also discussed, and state-of-the-art simulation models for predicting injuries of human brain, neck, and lower extremities are presented.

Foot and Ankle Severity Scale (FASS)

Increasing use of air bags and seat belts has led to the saving of many lives. However, the orthopaedic surgeon is now left to manage increasing numbers of serious foot and ankle trauma. It is important to injury prevention programs to have an injury severity scale for these injuries. The Abbreviated Injury Scale is used widely; however, it is intended primarily to gauge possibility of death after accidents. It is not sensitive enough to give meaningful data about the foot and ankle trauma epidemic. The Trauma Committee of the American Orthopaedic Foot and Ankle Society has developed a rank order list of 91 foot and ankle injuries that commonly occur in vehicular crashes. The injuries are ranked according to severity (FASS-S). Estimated long-term impairment is also given for each injury (FASS-I). This scale is designed as a guideline to help rank importance and impairment of vehicular crash injuries. It is expected that the scale will be modified as future validity testing and other research dictates.

Head Injury Potential Assessment in Frontal Impacts by Mathematical Modeling

The potential of head injury in frontal barrier impact tests was investigated by a mathematical model. This model consisted of: a finite element human head model, a four segments rigid dynamic neck model, a rigid body occupant model, and a lumped-mass vehicle structure model. The finite element human head model represents anatomically an average adult head. The rigid body occupant model simulates an average adult male. The structure model simulates the interior space and the dynamic characteristics of a vehicle. The neck model integrates the finite element human head to the occupant body to give a more realistic kinematic head motion in a barrier crash test. Model responses were compared with experimental cadaveric data and vehicle crash data for the purpose of model validation to ensure model accuracy. Model results show a good agreement with those of the tests. The model was used to assess head injury severity, when the occupant was restrained by an airbag only (31 mph barrier test) and by an airbag and a 3-point belt (35 mph barrier test). Head acceleration, stress and strain in the brain were investigated as injury parameter indicators. The model advances the study of brain motions and accompanying stresses during large linear and angular displacements encountered in vehicle frontal collisions. (A) For the covering abstract of the conference see IRRD 879189.

Visocelastic shear responses of the cadaver and Hybrid III lumbar spine

Due to the scarsity of cadaver lumbar shear stiffness data, tests on functional lumbar spinal units and a complete lumbar section (T12-L5) were done in both the anterior and posterior directions. Similar tests were performed on the Hybrid III lumbar spine for comparison. Sixteen lumbar motion segments were tested quasi-statically for their viscoelastic properties in a multi-directional (5-axis) spine machine. A hydraulic testing machine was used to carry out dynamic tests including cyclic tests and relaxation tests. In the quasi-static tests the shear response was linear and the anterior stiffness (155 about 90 N/mm) was found to be higher than posterior stiffness (104 about 38 N/mm). In the relaxation tests the load decreased to approximately 60% of its peak value after 30 seconds. Moderate non-linearity was observed in cyclic loading with shear stiffness up to 750 N/mm, depending on the loading rate. Soft tissue only failures occurred in the unconstrained tests at 1290 N (0.5 mm/sec) and 1770 N (50 mm/sec) for anterior loading. Anterior constrained testing failures involved hard tissue at 2800 N and were not rate dependent. The Hybrid III spine elicited higher initial stiffness than cadaver specimens, but was comparable at shear loads greater than 500 N. It also had considerably greater hysteresis than cadaver specimens. For the covering abstract of the conference see IRRD 879189.