A high speed tensile testing machine of a constant speed type, in which high speed tension is given to the test piece through a striking jaw from a projectile ejected by explosion pressure of explosive, is constructed. In the present state, the speed of the projectile reaches up to 210m/s, and the actual tensile speed of specimens up to 120m/s.
With this machine, high speed uniaxial tensile tests of materials, such as 2S-0 aluminium, 2024C-0 super duralumin, SPC-1 mild steel, 18-8 stainless steel, and ST-60 titanium, are carried out to obtain the relation between percent elongation and tensile speed in a range up to 120m/s. High speed elongation is larger than the static one for aluminium and its alloy, but smaller for mild steel and titanium. For 18-8 stainless steel the elongation seems to show little change with tensile speed. These experimental results seem to suggest that the high speed elongation is larger than or nearly equal to, the static elongation for metals of face centered cubic lattice, but smaller for metals of hexagonal close packed lattice, and that the behaviour of metals of body centered cubic lattice lies in between. The generality of this supposition should be studied further.
Drastic decreasing of percentage elongation at velocities beyond the critical impact velocities calculated by Karman's theory on plastic wave propagation is not clearly found in the range of the experiment. This seems to show the necessity of considering the factors such as the strain rate effect in stress-strain relation, etc. which are ignored in Karman's theory.
A theoretical analysis of plastic wave propagation in a specimen of finite length is carried out, and the difference in analytical results on specimens of finite and infinite lengths is clarified.
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