Impact Loading: Impact loading differs from quasi-static loading in that a load is applied over a very short time instead of being introduced gradually at some constant rate. This causes significant changes in the observed material properties from those associated with normal static tests. In the case of impact loading the effects measured are of a dynamic nature, with vibration and possibly fracture being observed.
There are two methods of impact testing in common use: Charpy or Izod Method:
The Notched Bar test, where
specimens are subjected to axial, bending or torsion loads using
specialized testing machines. The technique involves swinging a
weight of W from a certain specified height h to strike the notched
specimen, breaking it as it passes through, and arriving at a
height h', lower than the initial position of the pendulum.
The energy expended in rupturing the specimen can be described
using the equation U = W(h-h'). An animated model of the impact
testing process with notched bar specimens is shown below.
The other testing method uses specimens with no notches for the purpose of obtaining either stress - strain diagrams of material specimens under loads or load - distortion diagrams of structural members or composite structures as they are completely fractured in testing.