Abstract
In order to determine the requisite value of toughness for friction welded joints on the basis of fracture mechanics, Charpy impact test and fracture toughness test were carried out at various temperatures on the friction welded butt joints composed of carbon steel JIS. S45C and the base metal.
The experimental results indicated that the Charpy absorbed energy of the friction welded joints was almost equal to that of the base metal in the temperature range below room temperature, while the absorbed energy of the joints was about a half of those for the base metal above room temperature. The fracture toughness of the friction welded joints increased with an increase in temperature, but the toughness was slightly lower than those of the base metal over the whole temperature range. Particularly, in the temperature range above 185K, the value of the net section stress σnet for fracture of the joint was higher than the 0.2% proof stress of the base metal.
When the transition temperature for the Charpy absorbed energy was compared with that for the fracture toughness, the former was much higher than the latter. This suggests that the fracture toughness for the joints is high enough, even when the Charpy absorbed energy is low. Furthermore, the usable critical stress for the friction joints with circumferential or penny-shaped cracks was estimated for various kinds of specimen size and temperature based on the experimental results of fracture toughness.
