A Numerical Model for Rotational Autofrettage of Disks Based on von Mises Yield Criterion and its Application in Strengthening Flanged Disks Used for Joining High-Pressure Pipelines

In this work, a numerical analysis of the recently proposed rotational autofrettage method for strengthening hollow circular disks is carried out. The analysis of this new process is in nascent stage. Some analyses are available in the literature to study rotational autofrettage based on Tresca yield criterion. However, in general, the von Mises yield criterion closely replicates the yielding behavior of metals. Thus, in this work, the rotational autofrettage of disks is analyzed incorporating von Mises yield criterion. The governing differential equations are obtained for the elastic and plastic deformations in the disk under centrifugal loading based on the assumption of axisymmetric condition and plane stress incorporated in von Mises yield criterion. A numerical scheme is then followed to solve the set of governing differential equations along with the boundary conditions to obtain the stress distribution in an elastic-perfectly plastic disk during loading stage of rotational autofrettage. The residual stress distribution in the disk after unloading of the centrifugal loading are also obtained. The rotationally autofrettaged disk of typical radial dimension is numerically experimented for its different in-service load carrying capacities. Significant improvements are achieved in in-service pressure, radial temperature and centrifugal load carrying capacities in the autofrettaged disk as compared to their non-autofrettaged counterpart. Different numerical results are compared with corresponding solution due to Tresca yield criterion. Further, the present solution of rotational autofrettage is proposed to apply in strengthening industrial standard flanged disks of various dimensions used in connecting high pressure pipelines. It is found that the maximum pressure carrying capacity of flanged disk can be increased up to 77% for wall thickness ratios more than 3.5 by employing rotational autofrettage.