Effect of Biaxiality on Engineering Critical Assessments

Abstract

Common practice for the integrity assessment of structures, follows the use of Fitness for Service procedures, such as BS 7910/R6. There are many common structures (e.g. pipes) that are under biaxial loading. Even though the load biaxiality has been proven experimentally to have an effect on both the fracture toughness and the limit load of a component, the influence of biaxial stresses is not always directly addressed in the procedures. In order to address the effect of biaxiality on engineering critical assessments, BS 7910 and R6 fitness for service procedures are applied to four biaxially loaded wide plate tests previously conducted on A533B steel. The plates had been loaded in biaxial tension, with different biaxiality ratios, while the temperatures of the plates tested correspond to lower transition fracture toughness. The assessments include failure assessment lines created using Option 1, which requires the knowledge of the yield stress and tensile strength, Option 3 which is a material, structure and load dependent option, as well as a constraint modified Option 3 failure assessment line. To obtain Option 3 failure assessment lines, finite element analyses are conducted for the specimens. The tests are first assessed with the proximity to plastic collapse (Lr) and fracture (Kr) being calculated with the use of the main fracture clauses of BS 7910/R6, which do not take into account the effects of biaxiality. The conventional assessment is then followed by a more detailed assessment using the values calculated from Finite Element Analyses (FEA).