Examination of methods for the treatment of constraint effects within the FAD approach

This paper presents results of a study focusing on the effect of crack-tip constraint on the fracture behaviour of metallic materials. The principal goal is to validate two analytical methods for the consideration of constraint effects in engineering failure assessment - the R6/FITNET approach and the IST methodology. Those methods are briefly reviewed and applied to analyse available experimental data obtained in fracture tests on various cracked geometries and for two materials. Comparing to the conventional route which incorporates fracture toughness values derived in tests on highly constrained standard specimens, both methods provide an improved (less conservative) failure assessment. However, the assessment results from both methods are shown to be strongly dependent on the Weibull exponent which determination requires a certain level of expertise in the field of fracture mechanics. Since non-conservative results are possible when assuming high values, care should be taken to ensure a proper application of the respective assessment methodology.