Abstract
Recently high energy rate forging has been developed. In a high speed stamp forging, the indentation velocity reaches the range of several decades or 100m/s. High speed indentation involves numerous interesting problems from the view points of plasticity, metal physics and metallurgy. The high speed indentation of mild steel has been investigated using cylindro-conical punches of several cone angles.
In this paper is reported the comparison of strain figure in dynamic indentation with that in static indentation. And in this report the characteristics of strain figures are also studied. By comparing the strain figure with the recrystallized stress zone, it can be concluded that the domain which is uniformly etched in the strain figure agrees with the recrystallized field of the stress zone. In static indentation the uniformly etched domain is wide, and the domain which is etched in the form of individual curved lines is narrow and there are but a small number of lines. On the other hand, in dynamic indentation the uniformly etched domain is narrow, but the domain which is etched in individual curved lines is wide, and there are a large number of lines. In both cases of indentation, static and dynamic, the uniformly etched domain in the strain figure agrees with the work hardening region.
From the above mentioned points, the following conclusions appear to be valid.
(1) The strain figure is useful in the research of plastic deformation. Especially so when the strain figure is used with hardness test etc.
(2) In static indentation the workhardening region is wide. On the contrary in dynamic indentation the workhardening region is narrow, but the irregularly deformed region which is etched in individual curved lines in the strain figure is wide.
