Analysis of fracture tests on large bend beams containing an embedded flaw

As part of a collaborative project to investigate the transferability of Master Curve technology to shallow flaws in reactor pressure vessel applications, a series of fracture tests were performed on large scale bend beams, which were fabricated from a reactor pressure vessel steel and contained simulated sub-surface defects. A 2-dimensional finite element model was used to simulate the behaviour of the test pieces and to study the variation in crack tip constraint at both the near surface and deep crack tips with increasing load. Wallin's two-parameter model, which uses the Master Curve representation of the fracture toughness transition curve together with the elastic crack tip Tstress parameter to estimate the shift in the T0 reference temperature due to constraint loss, has been applied to arrive at estimates of fracture initiation probability. These are found to be consistent with the experimental results.