The Influence of Size on the Brittle Strength of Steel

Abstract

Abstract In this paper the influence of size effect on the impact cold brittleness of carbon steel is discussed. Static bending of notched specimens shows the same size effect, so that an assumption of the special role played by high velocity must be rejected. The experiments on the determination of the critical temperature of brittleness for impact-tension tests also display the size effect and therefore exclude any possible influence of the stress gradient. Experiments on static tension and bending of cylindrical specimens of brittle phosphorous steel in liquid air reveal the statistical nature of the size effect and give a good qualitative verification of Weibull’s theory. Weibull’s homogeneity exponent m calculated from experiments with tension and bending is found to have nearly identical values (namely 23.5 and 25.4). The theoretical values of the brittle strength of small specimens calculated with this value of m differ from the experimental ones by about 3 per cent; the ratio of the strengths in the case of bending and tension is found experimentally to be 1.40 against 1.39, according to the theory. The “scatter” in particular values for large specimens, as predicted by theory, is smaller than for small ones.