Shear bands and fracture of imperfect Fe+3%Si polycrystals

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Experimental data on shear macrobands and fracture of flat specimens of Fe+3%Si alloy having only a few grains in a cross-section are analyzed. Four types of band structures that determine the stress-strain curves involving different loading behavior and ductility of the alloy are singled out. The lowest plasticity and strength are exhibited when a singular shear macroband is formed on the front face of a specimen at an angle of 45° to the axis of tension (εp = 3–4%). Formation of a dipole out of two intersecting macrobands on the lateral surface of a specimen increases plasticity (εp = 6–7%). Accommodation bands between the macrobands of the dipole increase the plasticity even more (εp = 9–11%). It is the highest (εp = 19–21%) when the flat grains filling up all of the specimen's cross-section are contained between smaller-sized grains. Ductile fracture of such a specimen is governed by coupling of the conjugate macrobands that interact via a mechanism of auto-oscillations.

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