抄録
Fracture path deviation (FPD) is often observed in the standard Charpy V-notch (STD-Cv) test on laser welded joint due to the steep gradient of hardness distribution. The side notched Charpy V-notch (SN-Cv) test is often used to avoid FPD. Fundamental study on the comparison between STD- and SN-Cv tests on laser welded joint for high strength ultra-fine grained steel and on base metal for conventional steels indicates that the results obtained from SN-Cv test gives higher transition temperature and lower absorbed energy compared with those of STD-Cv test.
A big difference between these two tests is observed on the fracture surface. The fracture surface is divided into three types; that is, flat ductile fracture observed at the notch tip and the specimen end (Df), slant fracture at both sides (Ds) and brittle fracture (B). SN-Cv specimen has smaller area of Df and no Ds. The areas of each fracture surface were measured and the unit fracture energies for these fracture surfaces are determined by using regression analysis method. Unique relationships of EB/EDf=0.1 and EDN/EDf=2.3 are obtained irrespective of steels tested. The difference of fracture surface areas between SN-Cv and STD-Cv are formulated and finally, STD-Cv absorbed energy is well estimated from SN-Cv test results.
