A two-parameter approach to assess effects of constraint in cracks located at geometrical discontinuities

Abstract

This work provides an exploratory investigation into the applicability of a two-parameter fracture mechanics approach based on the J-Q methodology to characterize fracture behavior in cracks located at geometrical discontinuities of pressure vessels submitted to pressurization and depressurization cycles. Numerical models in plane-strain condition were employed to characterize crack driving forces and constraint changes in a flawed structure subjected to shakedown. The material exhibits elastic–plastic behavior and nonlinear kinematic hardening following the Chaboche model. The results indicate that the application of cycles of loading exceeding elastic limits, but still below the allowable stress for design of pressure vessels, increases the crack driving force and decreases the constraint level. It is possible to conclude that the methodology based on J-Q is highly effective to characterize the fracture conditions in geometrical discontinuities of pressure vessels. A lower probability of unstable fracture may be assumed for ductile and high-toughness materials after few cycles of pressurization and depressurization are applied. However, due to the increase in the driving force, the crack may be more susceptible to a subcritical tearing. Assuming that the material toughness is high enough to avoid any ductile tearing during pressurization and depressurization cycles, the observed phenomena close to the crack tip may be compared to instability of strains when shakedown is not guaranteed.