Containment of high-energy fragments in aeroengines

Modern aeroengines are designed to contain the fragments that may arise from the possible failure of rotating components such as blades. The kinetic energy of a missile is absorbed through elastic deformation, which transfers energy to supporting flanges where it is dissipated through friction, plastic deformation of the target and of the missile and plugging. The role and relative importance of each process is examined by means of simple experiments in which a circular plate is exposed to the impact of a short rod. The stiffness of the target is shown to increase the value of the impact force and hence the deceleration of the missile. This may result in a change of failure mode, from large plastic deformation of the target to plugging with the possibility of adiabatic shearing. As a result, there is a reduction in the efficiency of the shield, measured in terms of the perforation energy per unit thickness. Possible ways of overcoming this problem, consisting of using multi-layered or bimetallic constructions are explored. Rules for scaling experimental results to full size containment shields are proposed.