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Development of equations for strain rate sensitivity of UFG aluminum as a function of strain rate

Mohebbi, M. S ; Sharif University of Technology

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  1. Type of Document: Article
  2. DOI: 10.1016/j.ijplas.2017.01.003
  3. Abstract:
  4. Strain rate sensitivity (m-value) of ultrafine grain (UFG) AA 1050 and AA 5052 sheets processed by accumulative roll-bonding is investigated versus strain rate by stress relaxation (SR) test at ambient temperature. The results show a weak viscous nature of deformation for AA 5052 specimens as compared to AA 1050 ones. So that much less stress relaxation and negligible strain rate sensitivity are obtained for this material due to dislocation and grain boundary mobility limitation caused by Mg solute atoms. In order to formulate strain rate sensitivity of UFG aluminum as a function of strain rate, three phenomenological and two empirical models are developed and assessed by the experimental results. It is shown that since thermally activated dislocation glide is not the single governing phenomenon, the model developed based on this mechanism of deformation fails to predict the variation of m-value by strain rate. Contribution of grain boundary sliding (GBS) can result in a model fitted on the experimental results at lower strain rates, yet not suitable for higher strain rates. However, the third phenomenological model in which dislocation annihilation was taken into account besides the mentioned phenomena can well predict the trend of m-value at full range of the strain rate. Since this is a parametric model formulated by independent variable of time and with no analytical solution, two empirical equations are presented as more simple and straightforward models. It is shown that these models give useful formulas for estimation and extrapolation of the m-value at relatively high strain rates of common deformation processes where a monotonic variation by the strain rate is expected. © 2017 Elsevier Ltd
  5. Keywords:
  6. Modeling ; Ultrafine grain aluminum ; Aluminum ; Deformation ; Grain boundaries ; Grain boundary sliding ; Models ; Roll bonding ; Single crystals ; Stress relaxation ; AA 5052 ; Accumulative roll bonding ; Dislocation annihilation ; Grain-boundary mobility ; Grain-boundary slidings ; Phenomenological modeling ; Strain rate sensitivity ; Ultra fine grain ; Strain rate
  7. Source: International Journal of Plasticity ; Volume 90 , 2017 , Pages 167-176 ; 07496419 (ISSN)
  8. URL: https://www.sciencedirect.com/science/article/pii/S0749641917300281