The lengths of cracks which were propagated under the repeated impact bending energy of 20kg-cm and 50kg-cm at -40°C, -18°C, and 0°C were measured. The results obtained are as follows:
(1) The lengths of cracks are exponential functions of repeated number, and their cyclic speeds are almost similar at respective temperature.
(2) In case of impact energy of 20kg-cm at 0°C and 30°C, the “hesitation period” appears at the initial stage of propagation by the effect of residual compressive stress, but disappears at lower temperature.
(3) The cracks under repeated impact at low temperature propagate with a similar tendency to those of fatigue at room temperature which have been observed by numerous investigators.
(4) In case of impact energy of 50kg-cm at -18°C and -40°C, the cleavage fracture occurs in a few repeated number. The growth of weak cracks are observed prior to the cleavage fracture.
(5) The plastic energy, which is consumed by the growth of the crack prior to the cleavage fracture, is proportional to the length itself.