金屬材料の不連續變形

抄録

The load-elongation diagram of a soft steel tested at the temperature of blue shortness indicates continuous serrations after yield point up to the breaking stage. Although this phenomenon has been widely investigated, no satisfactory cxplanation has yet been given. Moreover, such a serrated deformation is not peculiar for a low carbon steel, as it is observable in some ferrous and non-ferrous alloys tested under a suitable condition. In order to contribute some light for this problem, the present author has studied it with carbon steels of various compositions and structures, some special steels, single cr_??_ stals of iron, duralumin, brass, copper, nickel, aluminium and zinc at temperatures ranging from the liquid nitrogen to the red heat. From these experiments two cases are classified for the serrated elongation. The one case is that when the materials having, to a certain extent, impurities or structural flaws are tested at a proper temperature and under a slow rate, if possible. The other is observable when the metals of high purity are tested at a rate as quickly as possible. These results are explained as follows:- In the fomer case the crystal grains are temporarily brought to an unstable state, by concentrated stress due to notch effect and in the latter case they are brought successively to an unstable state by overstress due to rapid loading and followed by yielding.