抄録
The tensile properties of metals under dynamic loading have hitherto been studied by many investigators with it in view either to determine stress-strain curves or to measure the yield stress, the tensile strength, and the change in length of the specimen at failure, under the action of strain rates higher than encountered in the usual static test. Little or nothing has so far been made, however, to clarify the effect of strain rates on the internal structure and the mechanical properties of rapidly stretched materials. This investigation has been conducted to make a thorough examination of the problems given above.
An explosive-rapid tension tester used in the present experiment has provisions for measurement of instantaneous changes of load and elongation as a function of time or load-elongation diagram. The 0.12% and 0.37% carbon steel specimens have been used in this study. The test has been carried out by the following procedure.
(a) static and rapid tension test for annealed specimens
(b) static tension test for statically and rapidly stretched specimens
(c) rapid tension test for statically and rapidly stretched specimens
(d) hardness test and microscopic observation for statically and rapidly stretched specimens
The main results obtained are as follows:
(1) The strain rate gives a remarkable effect on the resistance in deformation of carbon steel in spite of its having been annealed and pre-stretched. The large increase in yield stress indicates that the friction stress increases greatly at high strain rates.
(2) It is recognized that the behavior of propagation of Lüder's band by rapid loading differs from that by static loading.
(3) It seems from the tension and the hardness test and the microscopic observation of the slip band that the change of internal structure caused by high strain rate gives some effect on the resistance in deformation.
