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The plastic deformation of polycrystalline metals is carried by the motion of dislocations on specific crystallographic glide planes. According to the thermodynamics theory of slip, in the regime of strain rates, roughly from 10 -5 /s to 10 5 /s, dislocation motion is thermally activated. Dislocations must overcome barriers in order to move, and this concept defines critical activation stresses on a slip system s that evolve as a function of strain rate and temperature. The fundamental flow rule in crystal visco-plasticity theory that involves in order to activate slip has a power-law form:. This form is desirable because it provides uniqueness of solution for the active slip systems that accommodate an imposed strain rate; however, it also introduces astrain rate dependence, which in order to represent the actual behavior of polycrystalline materials deforming in relevant conditions of temperature and strainrate usually needs to be describedby a high value of the exponent n. However, since until now the highest value of n was limited by numerical tractability, the use of the power-law flow rule frequently introduced an artificially high rate-sensitivity.All prior efforts tocorrect thisextraneous rate sensitivity have only lessened its effect and unfortunatelyalso at the expense of substantial increases in computation time. To this day, a solutionfor the power-law exponent reflecting true material behavior is still sought. This article provides a novel method enablingthe use of realistic material strain rate-sensitivity exponents to be used within the crystal vico-plasticity theory without increasing computation time involved in polycrystal simulations. Calculations are performed for polycrystalline pure Cu and excellent agreement with experimental measurement is demonstrated.

h i g h l i g h t sA multi-scale finite element model is built to simulate behavior of a-U to large plastic strains. Development of texture gradients during rolling in a-U is captured by the model. Role of deformation mechanisms in texture formation of a-U is discussed.Twinning is profuse during rolling but not active during through-thickness compression. Floor slip is responsible for the formation of two pronounced {001} texture peaks in rolling. a b s t r a c tWe study the mechanical response and texture evolution of alpha-uranium during simple compression and rolling at 573 K. In order to determine the underlying mechanisms governing plasticity and texture formation, we perform detailed characterizations using electron backscattered diffraction and constitutive modeling using a dislocation-density based hardening law within a visco-plastic self-consistent homogenization. We show that the model achieves good agreement with experimental measurements in terms of texture and stressestrain response. From detailed comparison of experimental and modeling results, we infer that in both through-thickness compression (TTC) and rolling at 573K, the active slip modes are floor slip (001)[100] and chimney slip 1=2f110g〈110〉 with slightly different ratios. However, f130g〈310〉 twinning is not active in TTC compression but profuse during rolling. Further analysis indicates that during rolling, floor slip (001)[100] results in the formation of two pronounced (001) texture peaks tilted 10e15 away from the normal toward the rolling direction.

This work presents estimations of average intragranular fluctuations of lattice rotation rates in polycrystalline materials, obtained by means of the viscoplastic self-consistent (VPSC) model. These fluctuations give a tensorial measure of the trend of misorientation developing inside each single crystal grain representing a polycrystalline aggregate. We first report details of the algorithm implemented in the VPSC code to estimate these fluctuations, which are then validated by comparison with corresponding full-field calculations. Next, we present predictions of average intragranular fluctuations of lattice rotation rates for cubic aggregates, which are rationalized by comparison with experimental evidence on annealing textures of fcc and bcc polycrystals deformed in tension and compression, respectively, as well as with measured intragranular misorientation distributions in a Cu polycrystal deformed in tension. The orientation-dependent and micromechanically-based estimations of intragranular misorientations that can be derived from the present implementation are necessary to formulate sound submodels for the prediction of quantitatively accurate deformation textures, grain fragmentation, and recrystallization textures using the VPSC approach.