Fracture Mechanics Based Assessment of a Pressure Vessel Using R6 Procedure

Pressure vessels are susceptible to flaws which may be introduced during fabrication. Hence, existing approach based on plasticity is insufficient for failure prediction for all the materials. Methodology based on fracture mechanics is required for the design. Fracture analysis of a pressure vessel structure made up of AA2219-T87 Al alloy material was carried out using R6 procedure. R6 procedure is being widely used because of its applicability in elasto-plastic regime and accuracy of Failure Assessment Diagram (FAD). Service surface cracks were chosen; for each crack size and specimen/pressure vessel thickness, FAD was obtained. A typical pressure vessel having the configuration of cylindrical shell capped with tori-spherical end domes was considered for the study. Burst pressure was found based on plasticity approach as well as fracture methodology (R6 method). Stresses at critical locations were used for estimation of assessment points. Fracture based burst pressure was found which, as expected, proved to be less than that found by plasticity approach. The result insists the additional requirement of fracture mechanics design principles for analyzing critical structures. The difference between the two approaches in the analysis carried out was quantified.