Fracture analysis of surface cracks in cylindrical pressure vessels applying the two parameter fracture criterion (TPFC)

The Two Parameter Fracture Criterion provides a capability for the determination of failure stresses in vessels with semi-elliptical surface cracks provided the fracture parameters m and K f have been established on at least two selected vessels, which will be called the baseline vessels. It has been found beneficial to select the baseline vessels such that the values of the function aF 2 Q for these vessels encompass or are at least similar to those of the vessels to be assessed. The selection of the baseline vessels is of minor importance if m is determined in accordance with equation (39) of this paper or if m values greater than 1 are equated to 1 and those smaller than 0 are equated to 0. Where the fracture parameters are determined not on a small number of baseline vessels but rather on small fracture mechanics specimens made of the same material, it is possible to establish the stresses for the onset of crack extension in the vessels with satisfactory accuracy, while the prediction of failure stresses is conservative but highly inaccurate. This is attributed to the distinctly different crack resistance behaviour of the small fracture mechanics specimens as compared to that of the vessels tested.