EFFECT OF SPECIMEN GEOMETRY ON THE MULTIPLE n BEHAVIOUR OF AN AISI 1090 SPHEROIDIZED STEEL

摘要

The effect of specimen geometry on the multiple n behaviour of an AISI 1090 spheroidized steel is presented. Three different specimen geometries were used in the investigation: a Clausing plane stress/plane strain specimen, a round uniaxial specimen and a non-standard square uniaxial specimen. It was found that the double logarithmic stress-strain plot in all three cases is well described by a three linear segment fit up to maximum load. The points at which the changes in linearity occur are called slope discontinuities (SDs). The slopes of these segments give the values of the work hardening coefficients n_1, n_2 and n_3 for the first, second and third segments respectively. The values of n_2 and n_3 are similar for all three specimen geometries. However, n_1, is significantly different in each of the three cases. In the initial stages of deformation the plane strain/plane stress field in the Clausing specimen restricts the operation of concurrently active slip systems. The uniaxial specimens allow for many slip systems to operate simultaneously. Thus, n_1 is larger for the uniaxial specimens. The corners of the cross-section in the square uniaxial specimen constrain deformation and hence exhibits a larger value of n_1 as compared to the round uniaxial specimen which undergoes uniform contraction. At strains corresponding to SD I, dislocation saturation is reached and the slopes n_2 and n_3 attain similar values for all three specimen geometries. Post-necking behaviour is not discussed.