DESCRIPTION OF NONPROPORTIONAL CYCLIC RATCHETTING BEHAVIOR

It is now widely recognized that the nonlinear kinematic hardening rul e of Armstrong-Frederick (AF) type (1966), although proven very accura te for description of most first order effects associated with cyclic plasticity, is deficient in its representation of second order cyclic strain accumulation (ratchetting) under asymmetric loading with mean s tress ([Clement & Gionnet, 1985]; [Bower, 1989]; [Bower & Johnson, 198 9]; [Chaboche, 1989, 1991]; [Chaboche & Nouailhas, 1989]; [McDowell & Lamar, 1989]; [Lacey, 1991]; [Gionnet, 1992]). This inadequacy is mani fested by unrealistic unloading-reloading behavior associated with sub cycle events under even uniaxial conditions [Chaboche, 1989]. In parti cular, the reloading compliance predicted by the AF rule significantly exceeds that observed experimentally. Likewise ratchetting rates are, in general, overpredicted by this rule. In this paper, the nonlinear dynamic recovery modification of the AF rule recently proposed by Ohno & Wang [1991a, 1991b] is considered. Several important criteria are d iscussed for models capable of representing stress state and amplitude dependence of ratchetting behavior. Experimental results obtained on a carbon rail steel subjected to various uniaxial and nonproportional loading conditions are presented and correlated with an extension of t he Ohno & Wang model which accounts for a broader range of stress stat e and amplitude effects.