Twin boundaries as crack nucleation sites

Coherent twin boundaries (TBs) in f.c.c. metals are considered to have low energy. Nevertheless, even TBs are preferred sites for crack nucleation in materials loaded at very small alternating plastic strain amplitudes (high cycle fatigue). In the present paper, the mechanism of short crack propagation starting from TBs was studied for medium amplitudes and described taking into account both elastic and plastic anisotropy effects. A strong dependence of the TB crack density on the meso-texture of the material was found. The twin part of the meso-texture was described by the <1 1 1> rotation vectors of the TBs observed using the EBSD technique in the SEM. The rotation vectors of the damaged TBs were arranged in a damaging cone around the specimen axis. The risk of TB cracks in texturized rolling plates can be reduced by a favourable alignment of the specimen in the rolling plate avoiding the damaging cone of rotation vectors.