On the Thermodynamic Theory of the Strength of Solids:
2. Ultimate Strength

A. I. Rusanov

Mendeleev Center, St. Petersburg State University, Universitetskaya nab. 7, St. Petersburg, 199034 Russia

Received June 13, 2007

Abstract—The current theory of the strength of solids is supplemented by an account of thermodynamic linear
tension and its variations in the course of crack growth. For the case of dispersion interactions, two mechanisms
of crack growth are compared, i.e., the conformal mechanism (when the angle at the crack tip is conserved) and
the depth mechanism (when the width of crack mouth is conserved); it is shown that the second mechanism is
more energy favorable. For both mechanisms, as well as for the case of constant linear tension, relations for the
ultimate strength are derived, irrespective of the type of interactions, which clarify known Griffith and Sack cri-
teria for linear and disc-like cracks, respectively. It is established that the role of linear tension in similar criteria
increases with the narrowing of the crack and becomes significant in nanocracks. It is shown that an increase
of linear tension upon the introduction of sorbate into the crack does not interfere with the effect of adsorption-
induced reduction of strength (the Rehbinder effect).

DOI: 10.1134/S1061933X08010146

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