Proposed reduction of thickness factors based on fracture mechanics considerations

Abstract

It is considered that the avoidance of brittle failure of marine structural components may be achieved by employing an appropriate reduction of thickness factor from the base material at the lowest service temperature anticipated. Together with good design of structural joints, especially at intersection points, disastrous failures may be eliminated, or be no more likely than when mild steel is employed (i.e. scantlings derived from such). Comparison of the proposed factors, which are based upon a fracture mechanics derived approach, with those previously proposed – on fatigue bases and those by DnV and Lloyd’s Register shows good agreement at 0° C service temperature, and at a probability level of failure of 50%. The higher the required probability of survival of the structures the more closer are the values of both the fatigue and the fracture mechanics proposed factors. Nevertheless, it would be preferable to apply the fracture mechanics based factors in some situations or circumstances where avoidance of brittle failure is to have higher priorities over any other failure criteria.