John F. Wiechel

HEAD IMPACT RECONSTRUCTION - HIC VALIDATION AND PEDESTRIAN INJURY RISK

Experimental reconstructions of pedestrian accidents involving head injury sustained primarily from hood impact were conducted to determine the relationship between HIC and injury severity. The purpose was to establish the capability of predicting pedestrian head injury severity in simple laboratory tests. The reconstruction test results were analyzed by a median ranking technique to provide a family of curves showing probability of injury of AIS 3, 4, and 5 severities as a function of HIC. Results of the two analyses were compared to determine the degree of agreement between the HIC/injury-risk relationship derived from controlled experiments with cadavers and that derived from uncontrolled accidents involving live people. Specific accident cases are cited to illustrate the use of this relationship by the accident reconstructionist in estimating probable vehicle speed from injury outcome.

Vehicle and Occupant Response in Heavy Truck to Car Low-Speed Rear Impacts

Despite efforts by industry to reduce the problem of injury in rear impacts, there continues to be a large number of such claims. This is true even in low speed impacts which result in little or no damage to the vehicles involved. Recent studies of such incidents have been described in the literature. These studies have concentrated primarily on simple bumper to bumper impacts where the front bumper of the striking vehicle contacts the rear bumper of the struck vehicle. Perhaps a more common type of rear impact is one in which the bumper of the striking vehicle rides over or under the rear bumper of the struck vehicle. The heavy truck to car rear impact is an example of an overriding impact. This paper describes several staged impacts of this type in which vehicle and occupant responses were measured using fully instrumented Hybrid III dummies or human volunteers. These impacts often result in significantly greater damage than bumper to bumper impacts at identical speeds, while imparting lower accelerations and forces to the occupants of the struck vehicle. (A) For the covering abstract see IRRD 893297.

An Overview of the Evolution of Computer Assisted Motor Vehicle Accident Reconstruction

This paper presents an overview of the evolution of computer simulations in vehicle collision and occupant kinematic reconstructions. The basic principles behind these simulations, the origin of these programs and the evolution of these programs from a basic analytical mathematical model to a sophisticated computer program are discussed. In addition, a brief computer development history is discussed to demonstrate how the evolution of computer assisted vehicle accident reconstruction becomes feasible for a reconstructionist. Possible future research in computer reconstruction is also discussed.

MADYMO modeling of the IHRA head-form impactor

The International Harmonization Research Activities Pedestrian Safety Working Group (IHRA PSWG) has proposed design requirements for two head-forms for vehicle hood (bonnet) impact testing. This paper discusses the development of MADYMO models representing the IHRA adult and child head-forms, validation of the models against laboratory drop tests, and assessment of the effect of IHRA geometric and mass constraints on the model response by conducting a parameter sensitivity analysis. The models consist of a multibody rigid sphere covered with a finite element modeled vinyl skin. The most important part in developing the MADYMO head-form models was to experimentally determine the material properties of the energy-absorbing portion of the head-form (vinyl skin) and incorporate these properties into MADYMO using a suitable material model. Three material models (linear isotropic, viscoelastic, hyperelastic) were examined. It was determined that the vinyl material behaved as a hyperelastic material when comparing MADYMO simulation results with laboratory certification test results. The MADYMO model of the IHRA adult head-form was validated with laboratory head-form drop tests from four different heights. Parameter sensitivity analysis was conducted by varying the head-form parameters within their respective IHRA tolerances. Because of physical limitations of locating accelerometers near the head-form center of gravity, this analysis was much more easily accomplished using a MADYMO model. It was found that the peak acceleration was well within the IHRA-specified range for both the adult and child head-forms when the mass and geometric parameters were varied within the IHRA tolerances.

Enhancement Of The Hybrid III Dummy Thorax

Etude de cadavres pour mesurer le parametre (deflection, acceleration) qui peut etre utilise pour differencier des traumatismes severes thoraciques

Simplified MADYMO Model of the IHRA Head-form Impactor

Interest in pedestrian head injury has prompted a need to measure the potential of head injury resulting from vehicular impacts. A variety of head impactors have been developed to fulfill this measurement need. A protocol has been developed by the International Harmonization Research Activity (IHRA) to use head impactor measurements to predict head injury. However, the effect of certain characteristics of the various head impactors on the measurement procedure is not well understood. This includes the location of the accelerometers within the head-form and testing the head-form under the variety of conditions necessary to establish its global performance. To address this problem, a simple model of the IHRA head-form has been developed. This model was created using MADYMO and consists of a solid sphere with a second sphere representing the vinyl covering. Stiffness and damping characteristics of the vinyl covering were determined analytically from drop test data of an IHRA head-form. The model was validated by comparing its response to a drop test of 0.5 meters onto a steel plate. The results show that the model is an effective, simple solution to evaluating an IHRA impactor. The results also indicate that a more complete description of the vinyl covering (i.e., finite elements) would be appropriate for certain impact configurations.

Analysis of Stand-Up Forklift Operator Injuries in Off-the-Dock and Tip-Over Incidents With a Latched Door on the Operator Access Opening

A series of tip-over and off-the-dock impact tests were performed with stand-up forklifts to investigate the potential for injury to the operator of a forklift in these types of accidents, when the...

Vehicle and Occupant Response in Low-Speed Go-Kart Crash Tests

Go-karts are a common amusement park feature enjoyed by people of all ages. While intended for racing, contact between go-karts does occur. To investigate and quantify the accelerations and forces which result from contact, 44 low-speed impacts were conducted between a stationary (target) and a moving (bullet) go-kart. The occupant of the bullet go-kart was one of two human volunteers. The occupant of the target go-kart was a Hybrid III 50th percentile male anthropomorphic test device (ATD). Impact configurations consisted of rear-end impacts, frontal impacts, side impacts, and oblique impacts. Results demonstrated high repeatability for the vehicle performance and occupant response. Go-kart accelerations and velocity changes increased with increased impact speed. Impact duration and restitution generally decreased with increased impact speed. All ATD acceleration, force, and moment values increased with increased impact speed. Common injury metrics such as the Head Injury Criterion (HIC), Nij, and Nkm were calculated and were found to be fairly low. These results indicate that the potential for serious injury is low during low-speed go-kart impacts.Copyright

Results From Calculating the Acceleration at an ELR Using Measured Responses From Four Steering-Induced Rollover Crashes

Four steer-induced rollover crashes were analyzed by calculating the local three-dimensional accelerations at hypothetical seat positions’ Emergency Locking [seat belt] Retractor (ELR). The method for calculating the local acceleration was described in a recent Society of Automotive Engineers (SAE) paper and assumed three-dimensional rigid body motion, recorded acceleration and recorded roll rates at the center of gravity. For a threshold of 0.7 g, results demonstrated that intervals in the vehicle’s response that may cause the ELR’s inertial sensor to move into a neutral zone were limited to localized high-magnitude negative vertical acceleration events during the rollover segment with a maximum calculated duration of 31.7 ms. Changing the threshold to 0.35 g reduced the interval count by 70 percent and maximum duration by approximately 50 percent. Results of the analysis were consistent with prior published research that noted limited and brief periods of instances in rollover crashes when the inertial sensor may be in a neutral zone. Calculating an interval that a vehicle’s response may allow a retractor to move into a neutral zone did not mean that a specific retractor will move into a neutral zone. To asses if a specific retractor will move into a neutral zone its performance should be analyzed. As identified in prior research, occupant kinematics analysis was necessary in determining whether an inertial sensor in a neutral zone during a rollover event will result in belt spool out. It is beyond the scope of the paper to include a complete analysis of occupants’ kinematics.Copyright

Human Fall Evaluation Using Motion Capture and Human Modeling

Reconstructing the mechanics and determining the cause of a person falling from a height in the absence of witness observations or a statement from the victim can be quite challenging. Often there is little information available beyond the final resting position of the victim and the injuries they sustained. The mechanics of a fall must follow the physics of falling bodies and this physics provides an additional source of information about how the fall occurred. Computational, physics-based simulations can be utilized to model the free-fall portion of the fall kinematics and to analyze biomechanical injury mechanisms. However, an accurate determination of the overall fall kinematics, including the initial conditions and any specific contributions of the person(s) involved, must include the correct position and posture of the individual prior to the fall. Frequently this phase of the analysis includes voluntary movement on the part of the fall victim, which cannot be modeled with simulations using anthropomorphic test devices (ATDs). One approach that has been utilized in the past to overcome this limitation is to run the simulations utilizing a number of different initial conditions for the fall victim. While fall simulations allow the initial conditions of the fall to be varied, they are unable to include the active movement of the subject, and the resulting interaction with other objects in the environment immediately prior to or during the fall. Furthermore, accurate contact interactions between the fall victim and multiple objects in their environment can be difficult to model within the simulation, as they are dependent on the knowledge of material properties of these objects and the environment such as elasticity and damping. Motion capture technology, however, allows active subject movement and behaviors to be captured in a quantitative, three-dimensional manner. This information can then be utilized within the fall simulation to more accurately model the initial fall conditions.This paper presents a methodology for reconstructing fall mechanics using a combination of motion capture, human body simulation, and injury biomechanics. This methodology uses as an example a fall situation where interaction between the fall victim and specific objects in the environment, as well as voluntary movements by the fall victim immediately prior to the accident, provided information that could not be otherwise obtained. Motion capture was first used to record the possible motions of a person in the early stages of the fall. The initial position of the fall victim within the physics based simulation of the body in free fall was determined utilizing the individual body segment and joint angles from the motion capture analysis. The methodology is applied to a real world case example and compared with the actual outcome.Copyright