Study on Brittle Fracture Initiation from Weld Defect (Second Report) : Fracture from Notch of Poor Penetration Type

The brittle fracture from a weld defect of through-thickness type (crack length 2a=10-30 mm) for mild steel, which had relatively low toughness, was investigated and compared with the behavior of base metal with machined notch. Results are summarized as follows:1) In bending COD tests, δc(-10)=0.3 mm and δc(-40)=0.2 mm were obtained for a weld defect notch on the manual arc welding. While for the same notch on non-gas arc welding, δc(-10)=0.3 mm and S δc(-40)=0.09 mm were obtained. For the latter, COD characteristic depended well on the temperature.2) In tensile tests on notched specimen of welded joint and base metal at -10°C and -40°C, low stress fracture did not occur and overall strain el exceeded yielding strain ey. But the value of e1 for welded joint was larger than that for base metal. In welded joints, the yielding of parent metal adjacent to weld occured preceding to yielding in the net ligament of weld metal which had higher yielding stress than parent metal. Consequently, for these overmatched joints the Burdekin's design curve gave a conservative estimate in the yielding range.