Creep damage and remnant life prediction of rotating hollow shaft based on the design strain and theta projection concept

ABSTRACT

In this paper, creep damage and remnant life of a rotating hollow shaft made of niobium-modified 9Cr-1Mo steel is investigated based on the design strain and Robinson's rule. The shaft is subjected to an internal pressure and a temperature gradient. Creep behavior of the material is described by the Θ projection concept the parameters of which are taken from the existed literature. The initial thermoelastic solution is achieved from the equilibrium, strain-displacement and stress-strain relations by setting the total accumulated creep strains equal to zero. Later with considering creep strains and differentiating the constitutive differential equation with respect to time, a differential equation for displacement rate containing radial and circumferential creep strain rates is obtained. Using Prandtl–Reuss relations and the theta projection model, creep strain rates are evaluated. Displacement rates are then calculated and stress rates are determined. The stress histories are finally calculated iteratively. Having the effective stress histories and the temperature distribution, the time required to reach certain amount of creep strain such as 0.1%, 0.5% and 0.9% are calculated based on which the damages and remnant lives are evaluated. It has been found that the inner region of the shaft is the most damaged zone with minimum remnant life while the outer part of the shaft carried minimum damages for all three cases.

KEYWORDS:

• Creep damage
• rotating hollow shaft
• remnant life
• design strain
• theta projection

Acknowledgment

The authors are grateful to University of Eyvanekey for supporting this research work.