Energy losses during drop weight mechanical impacts with special reference to ignition of flammable atmospheres in nuclear decommissioning: theory and determination of experimental coefficients for impact analysis and prediction

The major purpose of this study is to provide a framework for determination of energy losses resulting from mechanical impacts of the kind that could occur during nuclear decommissioning of waste material. Measurements have been made of final translational and rotational velocities for impacts between projectiles of different length and a massive barrier. This enabled determination of experimental values of the impact coefficients and energy losses. It was found that the total energy losses could be accurately accounted for by the sum of those pertaining to the normal and tangential processes, thus indicating that these include any losses due to vibration. The results obtained clearly support an Amontons–Coulomb friction model and the previously held contention that there is a limiting value for the impulse ratio at low angles of barrier inclination. Although sliding surfaces are likely to be modified during impact, it is shown that any original contamination on the contacting surfaces results in a very large decrease in impulse ratio or friction coefficient. This represents an important finding in the context of mechanical ignition testing indicating that the state of the impact surfaces and their handling need to be taken into account. The difficulties in establishing appropriate values for the impact coefficients and dealing with the effect of mechanical vibrations on the energy losses are discussed and equations derived for determining the tangential and normal energy losses from known initial velocities.