EFFECT OF SPECIMEN GEOMETRY ON THE MULTIPLE-N BEHAVIOR OF AN AISI-1090 SPHEROIDIZED STEEL

The effect of specimen geometry on the multiple n behaviour of an AISI 1090 spheroidized steel is presented. Three different specimen geomet ries were used in the investigation: a Clausing plane stress/plane str ain specimen, a round uniaxial specimen and a non-standard square unia xial specimen. It was found that the double logarithmic stress-strain plot in all three cases is well described by a three linear segment fi t up to maximum load. The points at which the changes in linearity occ ur are called slope discontinuities (SDs), The slopes of these segment s 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 o f 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 i nitial stages of deformation the plane strain/plane stress field in th e Clausing specimen restricts the operation of concurrently active sli p systems, The uniaxial specimens allow for many slip systems to opera te simultaneously. Thus, n(1) is larger for the uniaxial specimens. Th e corners of the cross-section in the square uniaxial specimen constra in deformation and hence exhibits a larger value of n(1) as compared t o the round uniaxial specimen which undergoes uniform contraction. At strains corresponding to SD I, dislocation saturation is reached and t he slopes n(2) and n(3) attain similar values for all three specimen g eometries. Post-necking behaviour is not discussed.