溶接継手の破壊性能評価のための靭性評価手法に関する考察

Shallow Notch CTOD試験の意義

抄録

The use of CTOD bend specimen with a deep notch whose length is equal to the plate thickness is not always appropriate to obtain the toughness data applicable to fracture performance evaluation of weld joints. In this paper, HAZ-notched bend test and tension test have been conducted using specimens with different notch depth, which were extracted from a multipass weld joint of 30 mm thick high strength steel (TMCP type) with 460 MPa class yield point. The critical CTOD value at unstable fracture initiation obtained by the deep notch bend test was apparently smaller than that for the tension specimen. Fracture mode was also affected by the specimen type : Perfect cleavage fracture was dominant in the deep notch bend specimen, whereas unstable fracture preceded by a large amount of stable crack growth was observed in the tension specimen. Difference between CTOD results for the deep notch bend specimen and the tension specimen can be attributed to the crack tip constraint effect. The deep notch bend specimen exhibits significantly elevated crack tip stress and higher stress triaxiality compared to the tension specimen. By contrast, a shallow notch bend specimen showed a similar fracture behavior and critical CTOD value as the tension specimen. For the assessment of fracture resistance of welds by the CTOD bend test, the notch depth should be designed to simulate the plastic constraint expected in weldments.