The development of fracture mechanics has defined one.; Crack tip opening displacement; (Crack Tip Opening Displacement, CTOD), which can accurately evaluate the toughness of welded joints. In 1991, the British Welding Research Institute put forward the standard BS7448 Part 1, which gives the test methods of critical CTOD, J integral and KIC of metal materials. In 1997, the second part of the bid, BS7448 Part II, Method for Determining KIC, Critical CTOD and J-integral of Weld Metal Materials, was put forward. In view of the characteristics such as non-uniformity of performance and residual stress in each area of welded joints, BS7448 Part 1 was supplemented, which is generally recognized by the international engineering community, Test standard for determining the CTOD fracture toughness value of welded joints.

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