Increasing the load carrying capacity of hollow rotating disks by applying rotational autofrettage

Abstract

In this work, increasing the in-service rotational speed of hollow rotating disks by applying a recent autofrettage method, viz., rotational autofrettage is presented. The rotating disks are the integral part of a plethora of turbomachinery, such as gas turbine engines, flywheels, gears, etc. The disks rotate in-service at a very high speed that induces high tensile stresses near of the inner surface, that increase the susceptibility to inner cracking. Thus, safeguarding the disks against any mode of failure is a prime concern. An attempt is made to increase the rotational load carrying capacity of rotating disks via rotational autofrettage while preventing yielding, and simultaneously reducing the susceptibility of inner cracking of the disk. In practice, a large gamut of disk radii-ratios is used. Therefore, it is of interest to study the rotational load bearing capacity of rotating disks of various radii-ratios ranging from 2 to 100. It is found that for disks of radii-ratios of, r2/r1 ≥ 3.501, the introduction of the beneficial residual stress induced by rotational autofrettage results in an increase of 41.42% in the maximum allowable rotational speed. Alternatively, if the disk is autofrettaged, and the original maximum allowable rotational speed is kept, one can use a material with a lower yield stress, usually having a higher material toughness, and resulting in a larger critical crack length and a longer fatigue life. The effect of using a material with a lower yield stress and its impact on the disk's fatigue life is left for future work.