Application of CTOD experiment in offshore and shipbuilding industry

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.

CTOD test equipment

The commonly used test specifications at home and abroad are ISO standards 12135 and 15653, which are the acceptance values for the test results, and the DNV standard values are often used as the acceptance values. Through the customer process evaluation and the classification society witness, the CTOD test results of many products of Tiantai brand are good, and have been used in many projects. Figure 2 shows the typical CTOD test results of the TWE-81K2 product.

TWE-81K2 typical CTOD test results

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