A CRITICAL-STUDY OF THE APPLICABILITY OF RIGID-BODY COLLISION-THEORY

This article deals with the collision of steel bars with external surf aces. The central issue of the article is the investigation of the fun damental concepts that are used to solve collision problems by using r igid-body theory. We particularly focus on low-velocity impacts of rel atively rigid steel bars to test the applicability of these concepts. An experimental analysis was conducted to study the rebound velocities of freely dropped bars on a large external surface. A high-speed vide o system was used to capture the kinematic data. The number of contact s and the contact time were determined by using an electrical circuit and an oscilloscope. Tests were performed by using six bar lengths and varying the pre-impact inclinations and the velocities of the bars. T he experimental results were used to verify the applicability of Coulo mb's law of friction and the invariance of the coefficient of restitut ion in the class of impacts considered in this study. Then, given the unusual variation the coefficient of restitution as a result of changi ng pre-impact inclinations, a theoretical model was developed to expla in this variation. A discrete model of the bar was used to obtain the equations of motion during impact, Computed and experimental results w ere compared to establish the accuracy of numerical model. The interna l vibrations of the bar and multi impacts between the bar and the surf ace were found to be two main factors that cause the variation of the coefficient of restitution. Furthermore, a slenderness factor was prop osed to identify, the subset of collision problems where the coefficie nt of restitution was invariant to the inclination angle.