6 - Distortional hardening cyclic plasticity: Experiments and modeling

Abstract

When the associative flow rule is used, the yield surface (YS) shape is related to the direction of plastic strain accumulation. In this case, accurate modeling of the YS shape and its changes is critical to predicting the strains seen during cyclic plastic loading. There are numerous experimental examples of the shape of the YS changing such that a sharp apex develops roughly in the direction of loading and flattening develops in the opposite direction as anisotropy develops in the material. The growth of this type of uneven distortion of the YS has been seen in a wide variety of metals under various load conditions and is often called directional distortional hardening (DDH). In this chapter, we review the literature on DDH and YS shape change and present a new segmented model for DDH. We calibrated this model and used it to simulate a directionally distorted yield surface and cyclic plastic loading. By directly comparing results with and without YS distortion, we are able to infer the role that DDH has in predicting the behavior of metals in cyclic plastic loading.