Thìs work evidences the different dynamical behavìour of cut and cracked bars by showing their response from both the numerica] and experìmental points of view. Different energy dissipation mechanisms evident from experimental results show that the bar behaviour cannot be modelled as viscous or the structural damping. A crack dissipates more energy than a cut because of the friction of the two contact surfaces. When damping is being considered, it is therefore not always acceptable to study diagnostic problems in the laboratory, as ìs frequently done by generating cuts rather than cracks because i t is simpler.