The strain hardening of micro-sized face-centered-cubic single crystal metals: A crystal plasticity study

Huili Guo,Xu Zhang,Chenlin Li,Fulin Shang

doi:10.1063/1.5051361

Huili Guo, Xu Zhang + Show 2 more

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https://doi.org/10.1063/1.5051361

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Journal: AIP Advances	Publication Date: Dec 1, 2018
Citations: 2	License type: cc-by

Affiliation: Zhengzhou University, Xi'an Jiaotong University

Abstract

Recent experimental and theoretical studies indicate the “external geometry” and “internal structure” are the controlling factors to characterize the size-dependent plastic flow for micro-sized single crystal metals. i.e., increasing yield strength with decreasing sample size. This paper aims to investigate the strain hardening behavior for micro-sized face-centered-cubic (FCC) metals by employing crystal plasticity approach. The size-dependent dislocation density evolution law incorporates the dimensional parameters of internal structure and external geometry in order to consider the dislocation surface annihilation and dislocation source controlled plastic mechanisms. The current shear yield strength for micro-sized FCC metals is formulated by introducing the dislocation source length in classical anisotropic hardening model of Franciosi type. Combined with the above two aspects, crystal plasticity finite element method is developed to examine the strain hardening behavior of single crystal micro-sized metals during uniaxial compression. The validity of the new theoretical formulation and modeling approach is checked by comparing the simulation results with the experimental results available in literatures. The simulation results indicate that the micro-sized FCC metals have significant size effect. Further studies are performed to evaluate the influences of the initial dislocation density and the number of dislocation sources on strain hardening behavior of micro-sized FCC metals.

Highlights

Theoretical analysis and experimental studies of size-scale effect in micro/nano-structures are of great importance in the fabrication and exploitation of micro-electromechanical (MEMS) and nano-electromechanical (NEMS) devices.[1,2,3,4,5] It has been found that the changes in the dimensions of an internal feature or structure or in the physical dimensions of a sample can lead to the change in material properties
The related CPFE analysis is performed by implementing ABAQUS user-material subroutine user material interface (UMAT) within crystal plasticity formulation.[49]
The higher flow stress is found in the smaller sample with smaller λlongest. These results indicate that both external geometry and internal structure are the controlling factors to characterize the size-dependent strain hardening of the micron samples

Summary

Introduction

Theoretical analysis and experimental studies of size-scale effect in micro/nano-structures are of great importance in the fabrication and exploitation of micro-electromechanical (MEMS) and nano-electromechanical (NEMS) devices.[1,2,3,4,5] It has been found that the changes in the dimensions of an internal feature or structure or in the physical dimensions of a sample can lead to the change in material properties. A comprehensive understanding of the physical mechanism of plasticity for FCC metals has been discussed elaborately.[6] It is well known that the dislocation source plays a very important role in the plastic flow of micron single crystal.[7] Since the high ratio of surface-to-volume, the double-pinned Frank-Read source will be truncated to the single arms dislocation source (SAS).[7] The stress required to operate the truncated SAS depends on the distance from the pin to the free surface. The limited slip distance for smaller sample results

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