It is well known that impact toughness can reflect the toughness of a material or welded joint, and the higher the impact value, the better the toughness. However, due to the small size of the impact specimen (thickness ≤ 10mm), it can only reflect local toughness. Therefore, for a welded structure with a thickness exceeding 50 mm, another method of toughness evaluation is generally employed. The CTOD experiment, based on the concept of fracture mechanics, is a way to test the toughness of full-thickness steel plates or welded joints.
CTOD is an abbreviation for Crack Tip Opening Displacement. Its value is usually expressed by δ. The larger the value, the better the fracture toughness, and the worse the toughness. For welded structures with a thickness of more than 50 mm, in order to reduce the construction cost, the classification society standard stipulates whether the PWHT can be exempted by the CTOD test. At present, the CTOD test has been widely used in marine engineering structures and ships using crack arresters. Figure 1 below shows the CTOD experimental system of ITW Asia Technology Center. More than 50 CTOD tests have been completed so far.
TWE-81K2 typical CTOD test results