Stanimir Karapetkov

In most cases, the dynamic investigation of vehicle collisions with stationary obstacles concerns solutions to complex tasks related to the identification of occupant position in the vehicle. The motion of the bodies in the car is determined by the intensity of the inertial coordinate system, also known as moving reference frame, invariably fixed to the vehicle’s center of mass. The focus of the study is on how forces of inertia change their magnitude and direction in the car’s motion. This requires specific analysis carried out by dividing the vehicle trajectory into separate stages according to certain indicators, such as free motion, impact process, and post-impact residual motion. Particular attention has been paid to the impact itself, in which the forces of inertia are the most intense, and their magnitude and direction change abruptly. A solution to a Cauchy problem has been found, in which initial kinematic parameters of the crash process are considered, satisfying the kinematic values at rest position.

Although vehicles as a whole are symmetric, car crashes rarely follow the symmetric line (crashes are axisymmetric). In this paper, we examine car crashes by an updated Momentum 360 method, and car symmetry helps us easily find out what happens within the accident. We propose an improvement of the Momentum 360 method by taking into account the frictional forces between the wheels and the road surface during the time of impact. According to the momentum change theorem for the duration of the impact for each car and the kinetic moment change theorem for the relative motion of the given vehicle around its center of mass, the impact problem is introduced and solved. The solution considers the impulses of the principal vectors of the wheel friction forces, the gravity force, and the aerodynamic force for each car at the time of impact, as well as the principal moments of the friction forces between the tires and the road surface as a function of time. A mechano-mathematical multi-mass 3D model and a computer simulation of the movement (“Expertcar” software) are used to study the movement of each vehicle after the impact. Through successive approximations, the velocity vectors of the mass centers of the vehicle immediately before the impact are determined, and the location of the impact is identified. The presented decision model significantly improves the accuracy of road accident investigations.