Abstract:

This Item is concerned with material damping, a type of damping which is intrinsic in a structure in vibration. The emphasis is on materials which have engineering applications. Small amounts of damping at low stress levels can arise in all materials from thermoelasticity, which is amplitude-independent and frequency-dependent. With high applied stress, the damping is nonlinear. Nonlinear damping in metals and alloys is amplitude-dependent and frequency-independent. The main mechanisms responsible for nonlinear damping are associated with amplitude-dependent dislocations, magnetostriction, the heterogeneous structure of materials and phase transformations, all of which can give rise to relatively high damping with SDC values above 10%. In the case of composites, where fibres are embedded in a matrix, the damping is associated with damping within the matrix, as well as that which originates from relative slipping between the matrix and the fibre reinforcement. Metallic materials with high damping and good engineering properties are referred to as Hidamets and have specific damping capacities in excess of 10%. The damping of different materials has been compared in the Item. Composites have SDC values from 0.5 to 15%. The damping of steels has a wide range of SDC values from 0.05 to 5%, with the higher values occurring because of magnetomechanical damping. Hidamets include cast irons with a coarse flake structure and alloys of manganese with copper.