Creep predictions for turbomachinery components

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. Bibliography: pages 91-92