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Technical Paper

A Validation Study for the Force Balance Method in Determination of Stiffness Coefficients

1999-03-01
1999-01-0079
The CRASH3 damage algorithm is widely accepted as being reasonably accurate in the field of accident reconstruction, however there has been very little objective validation studies completed. The basis of the algorithm is Newton’s Third Law of Motion which in essence states that forces between interacting bodies are equal in magnitude, opposite in direction and collinear. Therefore, the forces should be theoretically equal and opposite when applying the damage algorithm. By applying the force balance method in determination of crush stiffness coefficients, the CRASH3 algorithm is forced to comply with its own derivation and should produce the most accurate result possible for the provided input. The purpose of this paper is to examine the results of the application of the force balance method in determination of stiffness coefficients (and therefore is ΔV) in real car-car tests and Federal Motor Vehicle Safety Standards side-impact tests (FMVSS 214).
Technical Paper

Using Computer Reverse Projection Photogrammetry to Analyze an Animation

1999-03-01
1999-01-0093
Computer reverse projection photogrammetry (CRPP) is a technique of using computer software to obtain information from images. Use of this process can facilitate the analysis of a computer animation that depicts the reconstruction of an accident. This paper defines several digital image analysis techniques with a focus on CRPP and illustrates methods of employing their procedures. Specific aspects of animation validation and a description of the information needed to accurately complete an analysis also are described. In addition to discussing specific types of animation validation, the computer software and hardware required to perform analyses for a variety of platforms are mentioned.
Technical Paper

Crush Energy and Structural Characterization

1999-03-01
1999-01-0099
A key aspect of accident reconstruction is the calculation of how much kinetic energy is dissipated as crush. By far the most widely used methods are derivatives of Campbell’s work, in which a linear relationship between residual crush and closing speed is shown to imply an underlying linearity between force and crush. “Consant-stiffness model” is the term used for such a representation of structural behavior. Difficulties arise, however, when significant non-uniformities are present in the crush pattern (as in narrow-object and/or side impacts, for example). The term “residual crush” becomes more ambiguous. Do we mean maximum crush, area-weighted average crush, or some other measure of residual deformation? And is it sufficient to represent the non-uniform crush pattern by a single parameter? Such considerations led to a re-development of the fundamental structural models, with an eye to determining whether the classical constant-stiffness model is the most appropriate.
Technical Paper

Computer-Generated Trial Exhibits: A Post-Daubert Update

1999-03-01
1999-01-0101
Taking as its reference a pre-Daubert set of predictions [Bo:91] regarding the judicial reception to computer-generated (CG) animations and simulations, this paper surveys and analyzes the appellate rulings regarding CG imagery in the wake of the Daubert decision [Da:93]. It also reports on a survey carried out by the authors among 39 active accident reconstructionists regarding CG imagery that these investigators have encountered in their work. The results of this survey suggest that the use in court of CG animations is much less common than one might infer from either the popular press or the accident reconstruction press. The paper concludes that Daubert will in the short run, though probably not in the long, produce some strange results with respect to both acceptance and rejection of CG animations and simulations.
Technical Paper

Acceleration and Speeds of Young Pedestrians

1999-03-01
1999-01-0440
Accidents involving young pedestrians often have consequences which are both serious and expensive. One of the important factors involved in reconstructing these accidents is the speed of the pedestrian. There are limited data on the walking and running speeds of children but they are related to age and sex. Young children of any given age can vary substantially in height and weight, and this can influence their walking and running speeds. In some instances, the children move from a standing start only a short distance to the point of collision. In these cases, their acceleration is at least as important as their steady speeds. Little data on the acceleration of children are available. A study has been conducted of elementary school children to measure their acceleration characteristics, walking speeds and running speeds. Accelerations and speeds related to pedestrians’ age, sex, height and weight have been documented.
Technical Paper

New Dimensions in Rollover Analysis

1999-03-01
1999-01-0448
Computer simulation and animation are used to build upon traditional methodologies for the evaluation of rollover accidents. The use of computer simulation allows for a more complete and detailed reconstruction than is possible with traditional methods. The use of computer animation allows a superior presentation of the reconstruction with detailed analytical results and real time visualization employing 3-D computer graphics. The accident scene and vehicle damage data are used together with results from rollover tests and computer simulation and computer graphics to reconstruct the vehicle path and vehicle dynamics in three dimensions. The significant previous papers, which provide the scientific basis for rollover accident reconstruction, are discussed with regard as to how this knowledge can be applied using HVE1 and 3-D Studio MAX2.
Technical Paper

A New Approach to Occupant Simulation Through the Coupling of PC-Crash and MADYMO

1999-03-01
1999-01-0444
During recent years the accident simulation program PC-Crash was developed. This software simulates vehicle movement before, during and after the impact, using 3D vehicle and scene models. When reconstructing car accidents, quite often questions arise regarding occupant movement and loading. Especially important is the influence of different types of restraint systems on the occupant. MADYMO® is a software tool which was developed by TNO in the Netherlands and which is well known in the automotive industry for the simulation of occupant movement. It allows the simulation of all kinds of modern restraint systems such as airbags and seatbelts with and without pretensioners. As the software is used in the automotive industry quite extensively, a huge validated database of dummy and human models is available. Since MADYMO® demands the setup of quite complicated input files, its use normally requires a high level of expertise.
Technical Paper

Factors Affecting the Accuracy of Non-Metric Analytical 3-D Photogrammetry, Using PhotoModeler

1999-03-01
1999-01-0451
The application of photogrammetry to the reconstruction of automotive accidents has been well documented and many techniques are available to the reconstructionist. However, the accuracy that can be expected from a photogrammetric project can vary by method and by application. Greater understanding of the factors affecting the accuracy of a photogrammetric reconstruction is desirable. Specific variables affecting the accuracy of 3-D, non-metric, analytical photogrammetry were studied using the commercially available software package, Eos Systems’ PhotoModeler. The 3-D co-ordinates of targets on a vehicle were first surveyed and then photographed with standard 35 mm camera equipment. The knowledge of camera properties, the method of image generation, photograph cropping, use of fiducial markings, and the number of control points were investigated to determine their relative effects on the accuracy of the solved coordinates.
Technical Paper

Use of Repeated Crash-Tests to Determine Local Longitudinal and Shear Stiffness of the Vehicle Front with Crush

1999-03-01
1999-01-0637
Crash-test-data on local longitudinal and shear stiffness of the vehicle front is needed to estimate impact severity from car deformation in offset or pole impacts, and to predict vehicle acceleration and compartment intrusion in car-to-car crashes. Repeated full frontal crash-tests were carried out with a load-cell barrier to determine the local longitudinal stiffness with increasing crush. Repeated off-set tests were run to determine shear stiffness. Two single high-speed tests (full frontal and offset) were carried out and compared to the repeated tests to determine the rate sensitivity of the front structure. Four repetitions at 33.4 km/h provided equivalent energy absorption to a single 66.7 km/h test, when rebound was considered. Power-train inertial effects were estimated from highspeed tests with and without power-train. Speed effects averaged 2% per [m/s] for crush up to power-train impact, and post-crash measurements were a reasonable estimate of front-structure stiffness.
Journal Article

Tire Mark Analysis of a Modern Passenger Vehicle with Respect to Tire Variation, Tire Pressure and Chassis Control Systems

2009-04-20
2009-01-0100
Tire mark analysis is an important factor in accident reconstruction. A precise determination of pre- and postcrash speeds as well as longitudinal and lateral accelerations from tire marks contributes significantly to a reliable accident reconstruction. Continuous advancements in tire and vehicle technology – in particular with respect to modern control systems such as anti-lock braking systems (ABS) – raises the question what role tire marks play in accident reconstruction today. Moreover, this accompanies the question to what extent potential interventions by vehicle control systems such as the electronic stability program (ESP®) resp. the electronic stability control (ESC) can be identified in a tire mark. The widespread use of these systems today makes them increasingly important in accident reconstruction.
Technical Paper

Tire Models for Vehicle Dynamic Simulation and Accident Reconstruction

2009-04-20
2009-01-0102
Various vehicle dynamic simulation software programs have been developed for use in reconstructing accidents. Typically these are used to analyze and reconstruct preimpact and postimpact vehicle motion. These simulation programs range from proprietary programs to commercially available packages. While the basic theory behind these simulations is Newton's laws of motion, some component modeling techniques differ from one program to another. This is particularly true of the modeling of tire force mechanics. Since tire forces control the vehicle motion predicted by a simulation, the tire mechanics model is a critical feature in simulation use, performance and accuracy. This is particularly true for accident reconstruction applications where vehicle motions can occur over wide ranging kinematic wheel conditions. Therefore a thorough understanding of the nature of tire forces is a necessary aspect of the proper formulation and use of a vehicle dynamics program.
Journal Article

Evaluating Self-Unlocking Doors in Rollover Accidents using a Shock Testing Machine

2009-04-20
2009-01-0073
Automotive manufacturers often rely upon features such as automatic locking to enhance the security and crashworthiness of doors in rollover accidents. This can be verified in warnings conveyed to vehicle owners through some owner's manuals. At the present time, there are no requirements on the dynamic performance of door locking systems within the Federal Motor Vehicle Safety Standards (FMVSS), although some static inertia requirements exist for latch systems. Field accident investigation and laboratory testing has revealed that some locked doors can self-unlock in rollover accidents when a vehicle sustains a roof impact. Using standard laboratory shock testing machinery, the acceleration boundaries required to trigger self-unlocking have been mapped for some sample doors. Impact pulses of surprisingly low levels of acceleration, when combined with sufficient duration have been found to trigger this response.
Technical Paper

Study on Characteristics of Event Data Recorders in Japan

2009-04-20
2009-01-0883
To understand the performance of Event Data Recorder (EDR) for the improvement of accident reconstruction using reliable and accurate information, two types of crash test data are analyzed. The first type is the J-NCAP crash tests for understanding the EDR characteristics under fundamental crash conditions and the second type involves three crash tests reconstructing typical real-world accidents for grasping the EDR performance under more complex crash conditions than J-NCAP crash tests. Data obtained from EDRs are compared with data obtained from instrumented sensors and high-speed video cameras. The velocities determined from pre-crash data and the maximum change in velocity, delta-V, obtained from post-crash data are analyzed. EDR pre-crash data shows good accuracy. In J-NCAP testing, all differences between the EDR recording value and the laboratory test velocity were less than 4%. EDR post-crash data has more difference from instrumented sensor data.
Journal Article

Comparison of Heavy Truck Engine Control Unit Hard Stop Data with Higher-Resolution On-Vehicle Data

2009-04-20
2009-01-0879
Engine control units (ECUs) on heavy trucks have been capable of storing “last stop” or “hard stop” data for some years. These data provide useful information to accident reconstruction personnel. In past studies, these data have been analyzed and compared to higher-resolution on-vehicle data for several heavy trucks and several makes of passenger cars. Previous published studies have been quite helpful in understanding the limitations and/or anomalies associated with these data. This study was designed and executed to add to the technical understanding of heavy truck event data recorders (EDR), specifically data associated with a modern Cummins power plant ECU. Emergency “full-treadle” stops were performed at many combinations of load-speed-surface coefficient conditions. In addition, brake-in-curve tests were performed on wet Jennite for various conditions of disablement of the braking system.
Technical Paper

A Study on Head Injury Risk in Car-to-Pedestrian Collisions Using FE-Model

2009-06-09
2009-01-2263
Head injury is quite frequently occurred in car-to-pedestrian collisions, which often places an enormous burden to victims and society. To address head protection and understand the head injury mechanisms, in-depth accident investigation and accident reconstructions were conducted. A total of 6 passenger-cars to adult-pedestrian accidents were sampled from the in-depth accident investigation in Changsha China. Accidents were firstly reconstructed by using Multi-bodies (MBS) pedestrian and car models. The head impact conditions such as head impact velocity; position and orientation were calculated from MBS reconstructions, which were then employed to set the initial conditions in the simulation of a head model striking a windshield using Finite Element (FE) head and windshield models. The intracranial pressure and stress distribution of the FE head model were calculated and correlated with the injury outcomes.
Technical Paper

Optimization Techniques Applied to the Problem of Ground Vehicles Accidents Reconstruction

2005-11-22
2005-01-4063
One of the most interesting and challenging applications in engineering is the solution of inverse problems. In this kind of problem we have as an example the scientific approach of the ground vehicle accident reconstruction. Another directly related theme is collisions analysis, either in the context of an accident reconstruction, or in the context of the vehicle crashworthiness, associated to its structural integrity and their occupants’ passive safety. In this paper the application of optimization techniques for the treatment of ground vehicles collision inverse problem using models of rigid or flexible bodies is discussed. We present an example of the classic approach, the conjugated directions method, and one of the modern, the genetic algorithms.
Technical Paper

A Parametric Study of Frictional Resistance to Vehicular Rotation Resulting from a Motor Vehicle Impact

2005-04-11
2005-01-1203
The equations of rotational motion used to calculate pre-impact vehicle speeds using the rotational displacement of the vehicles following a collision are well known. The technique uses the rotational momentum exchange during impact and the principle of conservation of rotational energy to calculate the post impact vehicle angular velocity from the energy dissipated during the vehicle's rotation to a stop (product of torque and rotational displacement). Integral to the calculation of the stopping torque on the vehicle is the determination of the effective rotational coefficient of friction (fr) between the tires and the roadway. The interactions of the road with the tires to produce the rotational coefficient of friction (fr) are more complex and less understood than those of linear coefficient of friction (deceleration factor). A derivation of the post impact equations of motion and the kinematics of vehicles in rotation are examined.
Technical Paper

The Application and Reliability of Commercial Vehicle Event Data Recorders for Accident Investigation and Analysis

2005-04-11
2005-01-1177
Heavy duty truck and engine manufacturers have been installing various forms of electronic Event Data Recorders (EDRs) on their products over the past decade, the most common being the Electronic Control Module (ECM). The primary purpose of the ECM is to control electrical and mechanical systems on the engine. As well, it monitors other vehicle systems. The ECM stores data in a manner that allows reports to be generated that aid fleet managers to monitor the performance of their equipment and that assist mechanics to diagnose problems. Some of the data in these reports can be of value in accident investigation and analysis even though these reports may not have been originally intended for this purpose. This paper discusses the specifics of data collection from the various ECMs and the reliability of such data when used for the purposes of accident analysis based on testing.
Technical Paper

Application of Force Balance Method in Accident Reconstruction

2005-04-11
2005-01-1188
In the field of accident reconstruction, there has been a significant amount of effort devoted to the calculation and derivation of vehicle crush energy and vehicle stiffness. Crush energy is usually calculated with a crush profile and crush stiffness. But, oftentimes, crush profiles and/or crush stiffnesses are not available and accident constructionists face the situation of insufficient information. In some such cases, the force balance method can be used to reduce the uncertainty. The method follows from Newton's Third Law, i.e., the impact force exerted on one vehicle is balanced by the force exerted on the other vehicle. With the help of this method, crush profile or crush stiffness can be derived. As a result, the crush energy can then be calculated with improved accuracy. This ultimately increases the accuracy of the overall accident reconstruction. In this paper, examples will be given to illustrate the use of such a methodology.
Technical Paper

Off-Throttle Turning Performance of Personal Watercraft for Accident Reconstruction

2005-04-11
2005-01-1198
The average off-throttle steering trajectories were determined for four commercially available personal watercraft at a test speed of 30 mph (48 km/h). The off-throttle steering performance of a personal watercraft (PWC) with a simple add-on, off-throttle steering system and a 16 ft runabout with a 140 hp outboard motor were also tested. The watercraft were tested according to the SAE J2608 Recommended Practice - Off-Throttle Steering Capabilities of Personal Watercraft. The trajectories of these watercraft were quantified in an off-throttle steering maneuver. These trajectories can be used as a guideline to reconstruct PWC accidents. The off-throttle turning capabilities of the test watercraft can be classified into two categories; those with effective off-throttle turning capability and those without effective off-throttle turning capability.
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