Evaluation of Fracture Safety According to Plastic Deformation with High Strength Steel Weld Joints

Fracture toughness of plastic strain (pre-strain) effect was determined as a function of the temperature in structural steels of the 600 to 780 MPa class. Cyclic loading during earthquakes produces plastic strain in the component, which is enhanced at the region of strain concentration. When the great earthquake occur, the steel structure 10-15% strain deformation was recorded at the beam-to-column connection. The steel structure fracture was more likely to occur. Therefore evaluate of plastic stain effect in steel structure to avoid unstable fracture especially in the weld joint (heat-affected zone; HAZ). The critical fracture toughness value (crack tip opening displacement, CTOD) in a large structure with plastic strain, which was applied to the HAZ region, was estimated from a small-scale plastic stained three-point bend specimen. The critical fracture toughness value is a very useful parameter to evaluate the safety of huge structural to avoid unstable fracture. In this study, it was proposed to critical fracture toughness value (CTOD) to avoid unstable fracture with each plastic strain effect. Key words: Plastic strain, Fracture toughness, Brittle fracture, CTOD (crack tip opening displacement)