The brittle fracture initiation characteristics from surface notch in weld fusion line of the welded joints, both manual arc welded and submerged arc welded made of 80kg/mmz high strength steel with a plate thickness of 50mm, were investigated using the wide plate tension test specimen with an angular distortion and a surface notch. And the results were analyzed by application of the conventional fracture mechanics. The main results are summarized as follows:
(1) In case the joint has a notch (defect) in weld fusion line, its brittle fracture strength is lowered as. its angular distortion and notch length increase. It also diminishes with a temperature drop.
(2) The test results can be adjusted quantitatively by stress intensity factor of Eq. (5). However in. the tests with a specimen with angular distortion the results show a large variation depending on the end. restraint condition of the specimen, so this difference should be introduced in the calculation concerned, using km of Eq. (6). Generally, the end restraint condition proves to give an intermediate value between the two different theoretical values, one for the fixed condition and the other for the supported condition. km is obtained from the bending moment of the weld zone estimated from the deformation behavior of the specimen which is measured by strain gages.
(3) The fracture toughness of the weld fusion line is high if the specimen is left as welded, but drops extremely low when the specimen is annealed for stress relief. In the specimens as welded, the manual arc welded joints show higher fracture toughness than the submerged arc welded joints.
(4) Characteristics of fracture initiated from the weld toe can be calculated by assuming that the crack is continuous and has an equivalent crack depth of about lmm.
(5) The effectiveness of preloading in increasing fracture stress was verified.
(6) We calculated relation between fracture stress and crack depth of infinite plate for welded structure in the stress field where bending stress is twice as much as tensile stress.
