4.7 Article

A crystal plasticity finite element model embedding strain-rate sensitivities inherent to deformation mechanisms: Application to alloy AZ31

Journal

INTERNATIONAL JOURNAL OF PLASTICITY
Volume 143, Issue -, Pages -

Publisher

PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.ijplas.2021.103031

Keywords

A; Microstructures; B; elastic-viscoplastic material; B; rate-dependent material; B; Crystal plasticity; C; Finite elements; T-CPFE UMAT

Funding

  1. U.S. National Science Foundation [CMMI1650641]
  2. Seaborg Institute under the Los Alamos National Laboratory LDRD program

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This paper introduces a numerical method to embed any value of the power-law exponent in a crystal plasticity finite element model, reflecting the true material strain-rate sensitivity, and successfully applies it to predict the complex strain-rate sensitive response of AZ31 Mg alloy. Calculations show that the model captures the phenomena related to the effect of changing applied strain-rate on mechanical response.
The fundamental power-law relationship representing the flow rule in crystal visco-plasticity ensures uniqueness in the selection of slip systems accommodating imposed plastic strain-rates. The power-law relationship also introduces an artificially high strain-rate sensitivity in crystal plasticity simulations, unless a high value of the power-law exponent is used. However, the use of high values for the exponent is limited by numerical tractability. This paper presents a numerical method implemented in a crystal plasticity finite element (CPFE) model for embedding any value of the power-law exponent reflecting the true material strain-rate sensitivity. Importantly, the method does not increase computation time involved in the simulations. The enhanced CPFE model is used to interpret and predict a complex strain-rate sensitive response and microstructural evolution of AZ31 Mg alloy. Measured values of strain-rate sensitivity for slip and twinning modes are used in the simulations. Calculations show that the model successfully captures the phenomena pertaining to the effect of changing applied strain-rate on the mechanical response including flow stress and evolution of texture and twinning for a broad range of strain-rates ranging from 10-3 s- 1 to 103 s-1 and loading orientations in tension and compression. It is shown that such predictions are a consequence of not only relative amounts of slip and twinning activities driven by a set of accurately characterized hardening law parameters but also values of the strain-rate sensitivities inherent to individual deformation mechanisms. Besides, the model validates the measured strain-rate dependency of deformation mechanisms while accurately reproducing the mechanical data. Hence, the model can be used to verify and further refine or infer measured strain-rate sensitivity per deformation mechanism by reproducing experimental data.

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