#### Vol. 1, No. 2, 2006

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Observations of anisotropy evolution and identification of plastic spin parameters by uniaxial tensile tests

### Yangwook Choi, Mark E. Walter, June K. Lee and Chung-Souk Han

Vol. 1 (2006), No. 2, 301–323
##### Abstract

Micromechanical effects such as the development of crystallographic texture and of dislocation structures lead to evolution of material anisotropy during plastic deformation. The anisotropy of sheet metals is commonly quantified by its $R$-values. The $R$-value is defined as the ratio of the transverse strain to the thickness strain at a certain longitudinal strain, and it changes if the anisotropy changes. Conventional hardening models do not account for the evolution of anisotropy along an arbitrary orientation. Therefore, although $R$-values are measured from experiments, predictions of hardening behavior based on $R$-values using conventional hardening models do not reproduce the experiments for arbitrary orientation. The $R$-value evolution for large strains can be observed in simple uniaxial tension tests by measuring the transverse and longitudinal strains continuously up to large strains. A digital image correlation (DIC) method is introduced as superior to strain gages for measuring large strains. To model the experimental response, a rotational-isotropic-kinematic (RIK) hardening model is investigated. Because of this model’s ability to represent the rotational evolution of the anisotropy, it can predict the hardening behavior for non-RD and non-TD directions. Methods to identify the plastic spin and kinematic hardening parameters are also discussed.

##### Keywords
Anisotropy evolution, $R$-value evolution, DIC measurements, rotational hardening