IHS ESDU Introduction to Damping 09005

Damping in structures is due to internal friction in the material (material damping), radiation of sound as the structure vibrates, friction between joints, local motion of the surrounding fluid caused by vibration andadditional effects from viscoelastic materials.Damping in structures can be specified by measures, such as, the loss angle, energy loss per cycle, loss factor, specific damping capacity, viscous damping ratio, quality factor and logarithmic decrement. Specific damping capacity and loss factor are particularly associated with material damping. Viscous damping ratio is frequently used for system damping where several types of damping may be present. The definitions of different damping measures are introduced in this Item, making use of SDOF mechanical systems with viscous and hysteretic dampers. MDOF systems are also considered and modal damping measures are specified. The measures used depend upon whether the vibration is free or forced. The logarithmic decrement is defined for free vibration, whilst the loss factor and quality factor are associated with forced vibration. The relationships between these damping measures are covered in the Item.