In this report we dicussed, from the points of dynamics, the mechanisms of
(a) Shrikage stress of the deposit metal itself.
(b) Thermal stress of the mother metal caused by heating and cooling.
(c) Transformation stress.
The wave-figures of the deposit metal can be considered as a kind of isotherms of the deposit metal at the time of cooling. In the last report, we discussed the relation between a family of isotherms and constraing rate, and concluded that the maximum principal stcesses act in the tangential direction of isotherms. As the cracking is considered as a kind of bittle rupture which in practically not accompanied with deformation, the maximum principal stress theory will be applied to such a rupture. Indeed the cracks occur in the normal direction of the wave figures of the deposit metal. (Fig.1)
Finally we an3lYsed the limiting curve for the cracking from the constraing rate and showed that this curve could be expressed by the formula i√v=const. or i²v=const. (Fig.4).