Service failures Of gas-turbine blades can be attributed in many cases to high cycle fatigue caused by large resonant stresses.
To avoid such failures, designers of aircraft engines frequently incorporate friction devices into turbine designs in order to increase damping and reduce vibratory stresses, called friction dampers.
A damper is a simple metallic piece . In an operating turbine, centrifugal force (equal to normal load) acting on the damper lifts it gradually, at a certain speed, to fully engage the platform or cover plate at a predesigned location.
The concept, which has been developed over the past four decades or so, is now commonly employed industry-wide and is based on the principle that relative motion can take place as the blade vibrates.
This relative motion can dissipate vibratory energy and prevent blade amplitudes from escalating to undesirable levels. The important damping devices are blade-to-ground dampers and blade-to-blade dampers.
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