NDT and fracture-mechanics - how can we improve the failure assessment by NDT? - Where we are - where we go?
A known fracture mechanics procedure for evaluating the failure risk of a component is given by the failure assessment diagram (FAD). This evaluation tool is recognised in international standards and technical rules. Algorithmic solutions exist for deterministic as well as for stochastic, ie probabilistic, evaluations. As well as the information delivered by NDT about the defect state in the component, the NDT expert learns that material properties also have an essential influence. The geometry of a flaw determines the stress intensity factor (SIF) together with the applied load. Since the SIF is calculated by means of analytic models or finite element analysis, the flaw geometry, because of the propagation of errors in the calculation, should be determined as exactly as possible by NDT. Knowing this demand, NDT experts try to develop defect reconstruction procedures like the tomography approaches used in medical diagnostics. The other parameters influencing the failure behaviour of a component are the material properties, ie the fracture toughness K1C, the yield strength Rp0.2 and the tensile strength Rm, which, as best estimates, should be known in the vicinity of the flaws. The load state, given as the superposition of applied and residual stresses, should also be known as a best estimate, for instance near the crack tip. This paper discusses the influence of these parameters on the failure risk by performing a sensitivity analysis using parameter variation.