Assessment of Crack Arrest Behaviour in Modern Structural Steels

Fracture mechanics based Fitness-For-Service (FFS) assessment of engineering structures is normally based upon the failure criterion, which is the initiation of crack extension by brittle fracture or ductile tearing at specified temperatures. The philosophy behind crack arrest is that if a crack initiates in a region of high stress or local embrittlement, it will be arrested in the surrounding material to prevent failure of the entire structure. The basic, simple idea for ensuring crack arrest is that the materials must have sufficient crack arrest toughness to ensure that fast propagating cracks, initiated in regions of low toughness and/or high stress, are arrested after they emerge from the critical zone. Obviously, during the design stage of ships, pipelines and some specific pressure vessels, analysis of crack arrest is of vital importance. The effect of temperature is another factor that needs to be taken into account in the course of the assessment of crack arrest or during design against crack arrest. The main aim of this project is to derive empirical models, which can be used to define crack arrest toughness from small test specimens (i.e. Charpy tests). It is also proposed to investigate and quantify the differences between the crack initiation and arrest toughness of two types of steels and explain the differences based on material microstructure. Finite Element modelling techniques will also be incorporated to understand crack arrest behaviour by analysing crack tip conditions in relation to a particular microstructure under specified loading condition.