Planar Double-Slip Model for Polycrystal Plasticity and Micro Tension Tests of Pure Nickel and Copper

Many natural minerals and manmade materials are aggregates of crystals or polycrystalline solids with a nonrandom distribution of grain orientations. Macroscopic behavior in such textured polycrystals depends on directions and is thus anisotropic. In this paper we develop experimental and theoretical procedures for investigating grain orientation evolution and its effect on the tensile stress-strain curve. The micro-tensile experiments were executed in a self-developed micro-forcing-heating device together with a micro-recorder-image analyzer system. In the experiments the 0.1 mm thin foil specimens of pure nickel and copper were gradually loaded toward final failure and the evolution of grain boundaries and slip bands inside grains was observed and recorded digitally via microscope and CCD camera throughout the whole time history. The texture image data were then used in a theoretical micro-macro transformation procedure to simulate the orientation evolutions and the stress-strain curves. The procedure was based on a double-slip model of polycrystal plasticity and on averaging of polycrystalline behavior over all grain orientations weighted by an orientation distribution function. The comparisons made between the simulated and experimental data of orientation evolutions and between the simulated curves and the macro-curves concurrently obtained in the experiments confirm the proposed procedures capable of simulating the considered micro-macro relations.