J Estimation Method for a Semi-Elliptical Surface Flaw in a Cylinder

Abstract

With the emergence of readily available simple J solutions for various types of structures through J estimation techniques, J -integral-based elastic-plastic fracture mechanics has become a common tool for analyzing ductile materials. This paper presents elastic-plastic solutions for semi-elliptical surface flaws of four different crack depths. Solutions are developed from a series of finite element analyses using the ABAQUS computer program with a deformation plasticity material constitutive law. Although the solutions are directly applicable to a single set of Ramberg-Osgood material parameters, they may be extended to include various amounts of strain hardening by a ratioing technique utilizing calibration functions from the EPRI handbook for continuous flaws. This paper addresses cylindrical structures loaded by internal pressure, and excludes any consideration of thermal loadings. Elasticplastic J solutions, determined for pressures up to 5000 psi (12700 Pa), or twice the design pressure, depart from plastic-zone-corrected linear elastic predictions at approximately 3000 psi (7620 Pa) pressure. The h1 plastic calibration functions derived in this paper are limited to the point of greatest crack depth in 6:1 aspect ratio semi-elliptical inside surface flaws in cylindrical pressure vessels.