Session: 12-23-01: Symposium on Multiphysics Simulations and Experiments for Solids

Paper Number: 149107

149107 - A Physics-Based Crystal Plasticity Model With Applications in Simulation of Micropillar Compression and Strengthening Effect of Multilayered Copper-Graphene Nanocomposites 

A new crystal plasticity model based on the dislocation mechanism is developed to study the mechanical behavior of face-centered cubic (FCC) single crystals under heterogeneous inelastic deformation through a crystal plasticity finite element method (CPFEM). The main feature of this work is generalized constitutive relations that incorporate the thermally activated and drag mechanisms to cover different kinetics of viscoplastic flow in metals at a variety of ranges of stresses and strain rates. The constitutive laws are founded upon integrating continuum description of crystal plasticity framework with dislocation densities which is relevant to the geometrically necessary dislocation (GND) densities and the statistically stored dislocation (SSD) densities. The model describes the plastic flow and the yielding of FCC single-crystal employing evolution laws of dislocation densities with mechanism-based material parameters passed from experiments or small-scale computational models. The GNDs evolve on account of the curl of the plastic deformation gradient where its associated closure failure of the Burgers circuit exists. A minimization scheme termed -norm is utilized to secure lower bounds of the GND densities on slip systems. The evolution equations of SSDs describe the complex interactions between two distinct dislocation populations, mobile, and immobile SSDs, relying on generation, annihilation, interactions, trapping, and recovery. The experiments of a micropillar compression for the copper single crystal are compared to the computational results obtained using the formulation. The physics-based model clarifies the complex microstructural evolution of dislocation densities in metals and alloys, allowing for more accurate prediction.

This study also investigates the plastic deformation configurations of copper-graphene composites and copper polycrystals, as well as the evaluation of the mechanical properties of copper-graphene nanolayered composites. The simulation results showed that the deformation of the copper polycrystal was uniform, whereas the nanolayered composite system demonstrated a complex deformation pattern. The simulation results, as determined from the true stress-true strain curves, confirmed the existence of a Hall-Petch-like hardening effect, which is dependent on the governing length scale. The respective slopes of the log-log plots were in close agreement with the Hall-Petch exponent, suggesting a high level of dislocation accumulation at the interface, conforming with experiments on copper-graphene nanolayered composites. The simulation results demonstrate the impact of layer thickness and the presence of graphene on the relationship between true stress and true strain in nanopillars. The results show that graphene is more effective at preventing dislocation propagation than grain boundaries and the Hall-Petch-like effect is confirmed by the increased number of graphene layers. The CuGr200 composite exhibits a combination of starvation and strain hardening, while CuGr125 and CuGr070 exhibit a mixture of SAS operation and SN mechanisms, producing forest hardening and leading to a Hall-Petch-like strengthening effect. The probability distribution of dislocations in the CuGr200 composite is more widely distributed compared to Cu100 polycrystals, while the probability distributions of dislocations in CuGr125 and CuGr070 surpass the balance between generation and depletion of dislocations.

Presenting Author: George Z. Voyiadjis Louisiana State University

Presenting Author Biography: George Z. Voyiadjis is the Boyd Professor at the Louisiana State University, in the Department of Civil and Environmental Engineering. This is the highest professorial rank awarded by the Louisiana State University System. He is also the holder of the Freeport-MacMoRan Endowed Chair in Engineering. He joined the faculty of Louisiana State University in 1980. He is currently the Chair of the Department of Civil and Environmental Engineering. He holds this position since February of 2001. He also served from 1992 to 1994 as the Acting Associate Dean of the Graduate School. He currently also serves since 2012 as the Director of the Louisiana State University Center for GeoInformatics (LSU C4G).
http://c4g.lsu.edu//
Voyiadjis is a Foreign Member of the Academia Europaea (Physics & Engineering Sciences), the European Academy of Sciences, and the European Academy of Sciences and Arts (Technical and Environmental Sciences). He is also a Foreign Member of both the Polish Academy of Sciences, Division IV (Technical Sciences) and the National Academy of Engineering of Korea. He is the recipient of the 2008 Nathan M. Newmark Medal of the American Society of Civil Engineers and the 2012 Khan International Medal for outstanding life-long Contribution to the field of Plasticity. He was also the recipient of the of the ICDM2 Lifetime Achievement Medal for his significant contribution to Continuum Damage Mechanics, presented to him during the Second International Conference on Damage Mechanics (ICDM2), Troyes, France July 8-11, 2015. This is sponsored by the International Journal of Damage Mechanics and is held every three years. In 2022 he was the recipient of the American Society of Mechanical Engineers, ASME, Nadai Medal, of the Materials Division. He received the 2023 Blaise Pascal Medal for Engineering from the European Academy of Sciences. He recently received the American Society of Civil Engineers’ Engineering Mechanics Institute the 2024 Theodore von Karman Medal.

Authors:

George Z. Voyiadjis Louisiana State University
Juyoung Jeong Los Alamos National Laboratory