Effect of Contact Pressure on High Temperature Fretting Fatigue.

Abstract

The fretting fatigue tests under various levels of contact pressure were carried out at both room and elevated temperatures using 12Cr-MoW -V steam turbine steel in order to investigate the effect of contact pressure on fretting fatigue properties such as fatigue life and fatigue strength. Two step tests, where fretting action is removed at certain cycles, were also carried out at elevated temperature to investigate the effects of contact pressure on fretting fatigue behavior and propagation rate of fretting fatigue crack. Although the fretting fatigue strength decreased with increasing contact pressure, it attained a constant value when the contact pressure was higher than 100 MPa. The fretting fatigue crack initiated at the early stage of life and its growth rate was accelerated by fretting action. This acceleration of fatigue crack was significant in the case of the higher contact pressure of 300MPa. The effect of fretting on fatigue life seemed to appear within 30% or 40% of fretting fatigue life regardless the contact pressure level and test temperature. This result was explained by comparing two fatigue crack growth curves with and without fretting.

Life assessment for creep and fatigue of steam turbine components

“…The crack growth behavior observed in the 0.3% strain range test of the component specimen was similar to cracks observed in fretting fatigue tests of a smooth specimen with an attached pad [10][11][12][13]. In these fretting fatigue tests, fatigue cracks initiated at an early stage and showed arresting behaviors in the later stage of life [10].…”