Creep Predictions For Turbomachinery Components

ABSTRACT

Several theories of creep and creep rupture are reviewed.

Specific attention is devoted to the brittle damage theory

proposed by Kachanov. Creep, damage and life predictions for

rectangular or circular cross section beams under bending

and tensile loads are presented. Comparison with data for a

Ni Superalloy showed life predictions could be 30X in excess

of experimental values. This beam model also revealed that

it is imperative that no bending moments be inadvertently

applied during tensile creep testing. The creep-damage

material model is· extended to multidimensional situations.

A refinement, whereby no damage accumulates in compression,

is incorporated. A User-Material subroutine for this

constitutive model has been formulated, and incorporated

into the ABAQUS FEM package. Several verification examples

are presented; one example is the creep-damage behaviour of

a notched bar in tension. The value of reference stress

techniques is discussed. Reference stress estimates for a

centrifugally loaded bar, as well as for a cantilever under

distributed loads, are presented. These could be useful in

turbine blade design.