ASSESSMENT OF THE DUCTILE-TO-BRITTLE TRANSITION REGION WITH 1X-WOL SPECIMENS

Several of the nuclear reactor surveillance programs that were started in the early 1970s incorporated some 1X-WOL type fracture mechanics s pecimens. The 1X-WOL is an early specimen design intended specifically to obtain valid K-Ic values on highly embrittled materials. This spec imen is now known to be unsuitable when the material being tested has sufficient fracture toughness to develop elastic-plastic performance. The objective of this project was to evaluate modifications that can b e easily made by machining within the hot cell to make the specimens v iable for evaluation in the ductile-to-brittle transition region using elastic-plastic data development and analyses. Three modifications we re tried: (1) remove 7.4 mm from the back face to make the compact spe cimen H/W ratio of 0.6; (2) a side groove of 25% to decrease the initi al remaining ligament strength; and (3) combining side grooving and ba ck face removal, both in lesser amounts, to weaken the remaining ligam ent strength. An A 533 grade B steel that had already been well docume nted in toughness properties was selected for this work. The first mod ification did not work because the remaining ligament was made too sma ll to sufficiently control loss of constraint. The second and third mo difications were successful from the standpoint of reproducing the res ults of the previous material characterization. A recommendation is ma de for the adoption of the second modification since it is more easily performed as a machining operation in the hot cell.