Centrifugal Clutch-Augmented Rotational Autofrettage

Autofrettage pre-strengthens pressure vessels by inducing controlled plastic deformation through internal loading, creating compressive residual stresses at the inner wall upon unloading. Among the various autofrettage techniques, the present study focuses on rotational autofrettage, which achieves the required plastic deformation by high-speed rotation of the cylinder about its axis. The cylinder is then decelerated and brought to rest, permitting elastic unloading. A significant practical challenge in this concept is maintaining precise alignment and secure holding of the cylinder during high-speed rotation. This study proposes and presents a numerical investigation of a novel Centrifugal Clutch-Augmented Rotational Autofrettage (CARA) system with spring-loaded shoes arranged in a circular array. The shoes are initially oversized relative to the cylinder's inner diameter and pre-loaded against the cylinder, ensuring an interference fit and precise alignment before rotation. During operation, the shoes augment the autofrettage load through contact pressure while accommodating radial expansion. The results indicate that the CARA process increases compressive residual hoop stress at the inner wall by up to 15% compared to conventional rotational autofrettage at equivalent speeds, while reducing the required rotational speed for a given plastic penetration. The peak contact pressure obtained in the range 12–15 MPa also ensures firm alignment and compensates for rotation-induced expansion. The study is conducted using finite element method (FEM) based on ABAQUS® package. Analytical models for the contact pressure distribution, force transfer and elastic-plastic formulation of a cylinder subjected to a combined pressure load and rotation are also developed and used for validation.