1994 年 12 巻 2 号 p. 179-185
The influence of the heat input on the crack ratio (length of crack versus welded length) has been investigated using both the conventional and reverse Houldcroft type hot cracking tests for A5052 aluminum alloy sheet. In the conventional type test, where the temperature distribution around the molten pool is the main factor, the crack ratio decreased linearly when the heat input increased. In the reverse type test, where restraint is the main factor instead of the temperature distribution, the crack ratio increased when the heat input increased. This is the same tendency which is experienced actually in welding. Hence, the reverse type test is recommended as a better test. The study also showed that the crack would propagate more easily in the case of equiaxed dendrites than in the case of columnar crystals.
The rotation angle at the tip of the crack was observed using.a video camera from the back side of the specimen. The rotation angle had a maximum value of about 0.08 rad near the start of the welding, and decreased gradually as the crack propagated. The crack stopped when the rotation angle reached from about 0.01 to 0.03 rad. It was made clear that the rotation angle greatly influences the propagation and arrest of the crack.
