Modelling nondestructive impacts macroscopically

Rigid body motion resulting in impact can be modelled on either a microscopic or a macroscopic level. Three methods of modelling impact macroscopically, where the post-impact motion of the impacting bodies is of primary concern, are discussed: the rigid body impulse-momentum model, the spring-damper model, and the elastic model. The impulse-momentum model is limited by an assumption of point contact and by the difficulty of accurately predicting the coefficient of restitution. Since it stems from rigid body dynamics, the model does not consider elastic deformation and is unable to predict tangential rebound during a collision. The spring-damper model is a conceptual model rather than a physical model and does not provide for an accurate method of determining its parameters. The elastic model is based on a finite area of contact and allows simultaneously some slipping areas and some sticking areas. It is limited to treating only spherical-like objects in fully elastic impacts. When compared with two-dimensional experimental impact data, the three models were shown to be unable to predict accurately the motion of bodies after impact. A modified elastic impact model, with the coefficient of friction varying with tangential velocity and normal force, was shown to match the experimental data more closely.