Abstract
Tensile tests of rimmed steels with specimens having brittle pre-cracks of various length at their one side were performed at temperature ranges of 10°C and -50°C.
The size of test specimens were 70mm width and 500mm length, and the length of pre-crack varied between 0.5mm and 25mm.
The preparation of specimens were done in the following way. First, large size specimens of about 100mm width with a machined notch at their one side were prepared. Then, inserting a spltting wedge at the machined notch, a small hammering to the wedge was given to produce a brittle crack at sufficient low temperature by immersing the specimen in liquid oxygen. Any desired length of brittle crack was obtained by controlling the intensity of hammering and by trimming off the marginal side of specimen having pre-crack.
The test results show that the breaking stress under constant temperature were inversery proportional to the square root of the initial crack length approximately, and the length of short fibrous crack formed at the tip of the brittle pre-crack decreased as the test temperature lowered.
A new theory on the mechanism of brittle fracture propagation is proposed, using the yielding stress curve, the brittle fracture stress curve, and the fibrous fracture stress curve of the material, and satisfactory coincidence is found between the proposed theory and experimental results.
