ON THE OPTIMALITY OF DISKS OF UNIFORM CREEP STRENGTH AGAINST BRITTLE RUPTURE

Abstract

Axisymmetric rotating disks of uniform brittle rupture under creep conditions are considered. The similarity of deviators, according to the flow theory, and the time hardening hypothesis combined with the Kachanov-Sdobyrev brittle rupture rule are used as the governing equations for the unsteady creep problem. The concept of a fully damaged design method is applied, when the appropriate iteration of the thickness (the decision variable) is introduced such that the local condition of the Kachanov type ( ↓x_i t_r) = 0 (the objective) to be satisfied for each x_i under the constant volume condition (the constraint). In general, the disk of uniform creep strength, with geometry changes neglected, is found either as optimal or non-optimal with respect to the lifetime. In case of non-stationary loading (due to prestressing), and the geometric constraints allowed for, an additional small improvement of the lifetime is obtained when shape corrections are imposed upon the disk of uniform creep rupture strength

KEY WORDS:

• Rotating disks
• creep
• brittle rupture