The behaviour of the lattice of polycrystalline iron in tension

Abstract

The stress-strain characteristics have been investigated for two distinct types of lattice plane in specimens of Swedish iron in tension. Earlier observations are confirmed that the metallic lattice under stress ceases to conform with Hooke's law when external plastic deformation occurs, but the deviation differs in the two cases. The elastic range for the (211) spacing appears to be greater than for the (310) spacing. On removal of stress in excess of the 'lattice yield', the two types of spacing show a residual strain of opposite sign to the strain under stress, but the magnitude is different. The residual strain is attributed to the onset of internal stresses as a result of plastic flow, and the difference in strain for the different types of plane to a difference in magnitude of the internal stress for grains of different crystallographic orientation. The internal stresses for both types of plane appear to consist of a longitudinal compression and a transverse compression. These components should be balanced by equivalent regions in tension, but none so far have been found. It may be necessary to conclude that such regions are in a state too disordered for coherent reflexion.