Search Results

Current techniques that can be used to evaluate and analyse lateral impact speeds of vehicle crashes with poles/trees are based on measuring the deformation crush and using lateral crash stiffness data to estimate the impact speed. However, in some cases the stiffness data is based on broad object side impacts rather than pole impacts. Some have argued that broad object side impact tests can be used for analysing narrow object impacts; however previous authors have identified the fallacy of this premise. Publicly available side pole crash test data is evaluated in terms of crush depth impact speed and impact energy for six general vehicle types. A range of simulated pole impact tests at various speeds and impact angles were conducted using LS-Dyna and PC-Crash. Publicly available Finite Element Vehicle models of a 1996 Ford Taurus, a 1994 Chevrolet C2500 and a 1997 Geo Metro (Suzuki Swift) were used, providing relationships among impact speeds, crush depths and impact angles.

This research compares vehicle dynamic simulations in PC-Crash 8.2 to data recorded during instrumented handling tests conducted by Mechanical Systems Analysis Incorporated (MSAI). The handling tests, which were used to examine rollover stability in a 1998 and a 1999 Ford Explorer, involve rapid steering inputs at speeds between 30 mph [48.3 kph] and 60 mph 96.6 [kph]. Vehicle weight, center of gravity (c.g) position, suspension stiffness parameters, tire parameters, steering angle, and vehicle speed data provided by MSAI were used as input for the PC-Crash model. Lateral acceleration, roll angle, roll rate, and yaw rate vehicle response from PC-Crash were compared to the MSAI sensor data. The authors modeled 26 handling tests. PC-Crash appeared to be a reasonable tool for modeling gross vehicle response. In addition, PC-Crash correctly predicted whether or not the test vehicle would experience rollover instability in a majority of the cases.

Due to the increasing number of minivans and sport utility vehicles, rollovers have become more significant. As a result, various accident reconstruction programs have been developed to address this issue. To reconstruct rollover crashes, various requirements have to be fulfilled. These consist of: providing a simple method that is able to model three dimensional environments that often play a major role in rollovers. including suspension, tire and collision models must be provided. This is particularily important in the rollover initiation phase. including proper vehicle geometry and contact stiffness must be available. These are important for simulation of body contacts that affect the vehicle motion. This study focuses on one program, PC-CRASH. This program was developed to allow simulations of vehicle 3-dimensional movements before, during and after the impact. The study also discusses the physical background of the models, their capabilities as well as their limitations.

When vehicle collisions are reconstructed using a discrete kinetic time forward simulation program, many trials have to be performed to reach a point where the simulation results are close to the actual ones. The pre-impact speeds and directions of travel of each vehicle are the main variables that affect the post-impact motion of the vehicles. However, other factors, such as the exact resultant position where the impact forces are exchanged, the vehicle positions with respect to each other at impact, and the coefficient of restitution are important variables that also affect the results. When a number of impact parameters are unknown, a reconstruction can take a great deal of time. An optimizer tool in PC-Crash is designed to minimize reconstruction time and error by automatically varying a selected number of impact parameters, comparing the resulting simulation for each combination of parameters with the actual incident.

The pedestrian model in PC-Crash is based on a multi-body system, where several bodies are interconnected by joints. Each of these bodies can have different properties to represent the different parts of the human body. The joint properties can be specified independently as well. The theoretical background of the pedestrian model has been introduced in SAE 1999-01-0445 and the model shows to give a good correlation of the gross movement of the pedestrian compared to crash test data. As there are many parameters, which can and have to be specified for the pedestrian model as input parameters, an in depth validation of the different parameters has to be done to validate this model. This paper describes in detail the validation process for the pedestrian model. A significant number of crash tests (approx. 30) was used as a basis to compare the results of the simulations and the real movement of the test subjects.

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.

When vehicle to vehicle collisions are analyzed using a discrete kinetic time forward simulation, several simulation runs have to be performed, to find a solution, where post impact trajectories and rest positions correspond with the real accident. This paper describes in detail a method to vary the pre-impact parameters automatically and to evaluate the simulation results. In a first step the different pre-impact parameters are discussed. Their influence on the impact and the post impact movement is shown. Furthermore the necessary specifications to define the post crash movement are presented. The necessity to define tire marks and rest positions of the vehicles involved is outlined. An effective evaluation criteria is derived, which is used to calculate a simulation error. This error is then used as a target function to control the optimization process. Two different optimization strategies are presented.

The program PC-CRASH was developed for the reconstruction of vehicle accidents and considers pre-impact, collision and post-impact phases. The present paper describes the physical and mathematical model which was added recently to PC-CRASH in order to enable the simulation of the dynamic behavior of articulated vehicles (with both single and double axle semi-trailers and with steered trailers). The trailer model, a discrete kinetic time forward simulation, builds on the vehicle and trajectory models described and validated earlier. The dynamic interaction of the towing vehicle and the trailer is outlined and the governing equations for the vehicle-trailer connection and the determination of the hitch force are presented. The momentum based collision model, relying on restitution rather than vehicle crush, is extended to simulate those vehicle collisions involving trailers. The ability of the model to predict speed-dependent off-tracking is demonstrated.

PC-CRASH is a windowso-based accident-reconstruction program which combines the simulation of pre-collision, collision, and post-collision dynamics for multiple vehicles in a graphical environment. This paper presents the trajectory and collision models on which PC-CRASH is based. PC-CRASH'S model for predicting the 3D kinematics of a vehicle's pre- and post-impact trajectory, which is based on a discrete- kinetic time forward simulation of vehicle dynamics rather than empirically-derived “spin-out coefficients”, is described. The tire-force model (which accommodates ABS), steer angle, wheel braking, weight shift, and suspension effects are introduced and the program's method of handling pre-impact yaw, braking, acceleration and pre-impact steering is outlined.