Fracture Tests to Study the Behaviour of Simulated Sub-Surface Flaws in a Reactor Pressure Vessel Steel - a Continuation of the NESC-IV project

摘要

The NESC-IV project (2000 - 2005) addressed the transferability of fracture toughness data from laboratory specimens to applications that assess the integrity of reactor pressure vessels. This project included a series of uniaxial bend tests on large beams with a simulated shallow, sub-surface flaw. The results of these experiments pointed towards a significant constraint-loss effect in the ductile-to-brittle transition temperature range of the used steel, but in view of the inherent scatter in fracture toughness of low alloy steels in the given regime, further testing was recommended.Therefore the scope of present project was to perform a set of six additional tests with nominally identical test piece geometry, material and loading arrangements, so as to obtain a statistically more relevant data set. The Institute for Energy contracted the Nuclear Research Institute in Rez to perform these experiments. Following the successful execution of the tests, a preliminary fracture mechanics analysis was made to compare estimates of the stress intensity values at failure with the material's Master Curve. The results confirmed the constraint-loss effect, which had been observed in the previous NESC-IV test series. Moreover it was found that some aspects needed further attention, such as detailed finite element modelling of the experimental arrangements and accurate characterization of the test material's fracture toughness. The latter should also consider material inhomogeneity issues.