Philip H. Cheng

Delta-V, Barrier Equivalent Velocity and Acceleration Pulse of a Vehicle During an Impact

Delta-V and barrier equivalent velocity (BEV) are both terms used to describe some physical change in the vehicle state before an impact as compared to after an impact. Delta-V describes the change in the vehicle velocity vector from just before the impact until just after the impact, while BEV attempts to quantify the energy required to cause the damage associated with an impact. In order to understand what happens to a vehicle and its occupants during an impact, the acceleration pulse undergone by the vehicle during the impact must be examined. The acceleration pulse describes how the Delta-V occurs as a function of time, and is related with the deformation of the vehicle as well as the object contacted by the vehicle during an impact. While Delta-V and BEV are often used to describe the thresholds at which a passive restraint system will function, it is the acceleration pulse that the sensors of a restraint system measure, and that ultimately determines if, when and how passive vehicle restraints will be deployed in an impact. This paper examines this issue and presents vehicle acceleration pulses for several types of impacts. Findings show that the shape and duration of the acceleration pulse experienced by a vehicle in an impact can be affected by many variables, including the structure of the vehicle, the stiffness of the object impacted, and the location of the impact.

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.

Application of Force Balance Method in Accident Reconstruction

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 Newtons 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.

Pole and Vehicle Energy Absorption in Lateral Oblique Impacts with Rigid and Frangible Poles

Many vehicle-to-pole impacts occur when a vehicle leaves the roadway because of over-steering and loss of control in a lateral steering maneuver. Such a loss of control typically results in the vehicle having a significant component of lateral sliding motion as it crosses the road edge, so that impacts with objects off of the roadway often occur to the side of the vehicle. The response of the vehicle to this impact depends on the characteristics of the impacted object, the characteristics of the vehicle in the impacted zone, and the speed and orientation of the vehicle. In situations where the suspension or other stiff portions of a vehicle contacts a wooden pole, it is not uncommon for the pole to fracture. When this occurs, reconstruction of the accident is complicated by the need to evaluate both the energy absorbed by the vehicle as well as the energy absorbed by the pole. In addition, stiffness characteristics for the vehicle suspension and its mounts are not typically available since most side impact testing involves staged impacts between the vehicle wheels.

AN ANALYTICAL MODEL OF CHILDREN IN A PANIC BRAKING ENVIRONMENT WITH EXPERIMENTAL VALIDATION

This paper describes a linear acceleration sled device developed to study child responses to panic braking environments. A sled with a vehicle seat and soft simulated dash is accelerated by a drop weight in a similar fashion to actual vehicle decelerations when panic braking. A simple, two degree of freedom analytical model of the experimental device was developed to predict the dynamic performance of the sled and examine the sensitivity of various parameters in producing acceleration time histories of actual braking vehicles. This includes the study of drop weight size, drop weight distance, cable size, initial cable pretensioning and sled braking levels. A simple, two degree of freedom analytical model was also examined to simulate a child dummy sitting on the sled seat and verified by using actual sled acceleration-time pulses. The model was based on previously conducted vehicle braking tests with dummies and child dummy tests conducted on the linear acceleration sled device. Some of the parameters examined for dummy motion sensitivity were sled acceleration levels, sled acceleration duration, initial child position, seat surface friction, seat angle and child model joint stiffness.