Preparation and evaluation of stress-elastic and plastic strain diagrams of sintered steels

The differences in Young's moduli (E) and Poisson's ratios (ν), calculated by the stress-strain diagrams from tensile testing (TT) and the sound velocities from an acoustic pulse method (APM), of sintered steels were compared. The values of ETT and νTT were smaller than those of EAPM and νAPM, respectively, because not only the elastic strain, but also the plastic strain are included in the stress-strain diagram of the sintered steels. Furthermore, by using the longitudinal and transverse elastic strains calculated from the values of EAPM and νAPM, the longitudinal and transverse plastic strains were separated from the stress-longitudinal and transverse strain diagrams. Consequently, the elastic limit or 0.2% yield strength was simply defined from the stress-longitudinal plastic strain diagram, in the case of the sintered steels which does not show a linearity of stress-strain diagram at the lower stresses. The differences in the elastic and plastic strains versus stress of each sample were explained on the basis of the pore characteristics, such as size, shape, and interconnection, and microstructures.