Features of destruction of a ferrite-martensitic composite

The behavior of a crack in steel with the structure of a ferriticmartensitic composite is studied. The modes of heat treatment for obtaining a composite structure with alternating layers of ferrite and martensite are given. The kinetics of crack development during cyclic tests was studied. The obtained data show that the rate of development of the crack in the material with the structure of the composite is substantially lower than for the usual sorbite structure. It is shown that the frontal growth of the crack in the composite is carried out with “stops”, on which the matrix deforms and its stratification occurs in the direction normal to the front of the crack motion.

The transition from subsonic to supersonic cracks

We present the full analytical solution for steady-state in-plane crack motion in a brittle triangular lattice. This allows quick numerical evaluation of solutions for very large systems, facilitating comparisons with continuum fracture theory. Cracks that propagate faster than the Rayleigh wave speed have been thought to be forbidden in the continuum theory, but clearly exist in lattice systems. Using our analytical methods, we examine in detail the motion of atoms around a crack tip as crack speed changes from subsonic to supersonic. Subsonic cracks feature displacement fields consistent with a stress intensity factor. For supersonic cracks, the stress intensity factor disappears. Subsonic cracks are characterized by small-amplitude, high-frequency oscillations in the vertical displacement of an atom along the crack line, while supersonic cracks have large-amplitude, low-frequency oscillations. Thus, while supersonic cracks are no less physical than subsonic cracks, the connection between microscopic and macroscopic behaviour must be made in a different way. This is one reason supersonic cracks in tension had been thought not to exist.