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MMMB Research Seminar

November 14 @ 11:30 am - 12:30 pm

Title

Strain path changes in steel and magnesium: experiments and  simulation using a dislocation-based model

Speaker

Carlos Tomé  (tome@lanl.gov)

MST Division, Los Alamos National Laboratory, NM, USA

Abstract

Polycrystal aggregates subjected to plastic deformation exhibit changes in the yield stress and extended transients in the flow stress when they are reloaded along a different strain path.  These effects, of which a well-known one is the Bauschinger effect, are related to the rearrangement of the dislocation structure induced during the previous loading.  Here we present a dislocation-based hardening model that accounts for dislocation recombination and back-stresses, implement it in the polycrystal plasticity code VPSC (Visco Plastic Self Consistent), and simulate strain path changes in low carbon steel and in Mg AZ31.  The path changes consist of tension followed by shear, and forward-reverse simple shear for the steel. In the case of Mg AZ31 the rolled plate is preloaded in tension along the rolling direction (RD) and reloaded in tension at different angles with respect to the RD.  The results are compared to experimental data and highlight the role that directional dislocation structures induced during preload play during the reload stage.

We also discuss the use of this model for the interpretation of cruciform test results. The test allows one to impose arbitrary plane stress conditions and path changes, but the results are difficult to interpret in terms of constitutive response. Here we show that, when combined with Finite Element simulations, the crystal plasticity model provides a valuable tool for interpreting cruciform test results.