A Finite Element Study of Elastic-Plastic Analysis and Autofrettage Optimization for Thick-Walled Pressure Vessels with Cracks

Abstract

This study conducts a detailed finite element analysis of thick-walled pressure vessels under internal pressure, focusing on how yield criteria selection, autofrettage optimization, and external axial cracks affect structural integrity. Using a numerical model developed in ABAQUS with aluminum alloy 6061-T6, results were closely aligned (within 2%) with classical Lamé solutions. The analysis focused on yield theories, especially those due to Von Mises and Tresca, and indicated a large variation of 15.4% in elastic limit prediction with direct implications for design compliance and resource utilization. In autofrettage analysis, kinematic hardening was employed with a high degree of Bauschinger effect accuracy, resulting in a difference of 12.4% compared with isotropic hardening.

Based on mesh convergence analysis, it was found that dividing the wall into 15 segments is most efficient with a 1.7% difference at the interface between the inner and outer walls. Notably, external axial cracks notably reduced capacity; a 10 mm crack led to a 26.1% drop in yield-based limit pressure. The fracture mechanics analysis shows a requirement for a minimum safe working pressure of 34 MPa, reflecting a 70.7% reduction needed to prevent catastrophic crack propagation. The autofrettage operation at 120 MPa improved the elasticity limit by 27% and created a positive compressive residual stress of 85 MPa in the inner bore. The significance of a different approach to the design of a cracked vs. an uncracked vessel is highlighted with heavy emphasis.