The Yield, Flow and Creep Behaviour of Annealed En24 Steel under Combined Stress

Abstract

Constant stress-ratio tests under combinations of tension, torsion and internal pressure have been performed on annealed En24 steel. The initial yield locus conformed to the Maxwell Mises criterion under tension-internal pressure but lay between the Maxwell-Mises and Tresca criteria under tension-torsion. This implies a small degree of initial anisotropy. Post-yield behaviour showed the plastic strain and strain-rate vectors to be normal to the initial yield locus and to remain so with respect to both time and increasing stress. The work-hardening hypotheses of plasticity theory were unsatisfactory in correlating any of the combined-stress results but equivalence of the strains was established from a consideration of the strain components and the angle between the stress and plastic-strain vectors. This resulted in the graphs of equivalent stress versus equivalent plastic strain in different stress fields being superposable. Room-temperature creep of the logarithmic form ε a In t + c was exhibited by all strain components and correlation of the creep coefficients was established by a method similar to that introduced for plastic strains. This finally led to a complete correlation of the stress-strain-time behaviour of this material under complex stress.