Structural integrity assessment procedures conventionally categorise flaws either as infinitely sharp cracks or local thinning areas (LTAs). Defects failing an LTA geometry check are assumed to be sharp cracks, and a fracture mechanics based approach is followed for the assessment. The LTA rule may be appropriate for general corrosion or mechanical gouges where there is a change in wall thickness and plastic collapse is considered to be the failure mechanism. However, for non-sharp defects, the failure mechanism is not clearly defined, in principle.
Simplifying blunt defects to LTAs can be non-conservative on one hand, and to sharp cracks can be excessively so on the other hand. As a result, there is a need to develop procedures that account for non-sharp defects more realistically.
This PhD is based on basic constraint procedures in standards (R6, BS7910) and aims to expand the capabilities to allow less conservative assessment of non-sharp defects.
|