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

Experimental data on shear macrobands and fracture of flat specimens of Fe3%Si alloy having only a few grains in a cross-section are analyzed. Four t ypes of band structures that determine the stress-strain curves involving d ifferent loading behavior and ductility of the alloy are singled out. The l owest plasticity and strength are exhibited when a singular shear macroband is formed on the front face of a specimen at an angle of 45 degrees to the axis of tension (epsilon (p) = 3-4%). Formation of a dipole out of two int ersecting macrobands on the lateral surface of a specimen increases plastic ity (epsilon (p) = 6-7%). Accommodation bands between the macrobands of the dipole increase the plasticity even more (epsilon (p) = 9-11%). It is the highest (epsilon (p) = 19-21%) when the flat grains filling up all of the s pecimen's cross-section are contained between smaller-sized grains. Ductile fracture of such a specimen is governed by coupling of the conjugate macro bands that interact via a mechanism of auto-oscillations.