Predicting the flow stress and dominant yielding mechanisms: analytical models based on discrete dislocation plasticity

TL;DR

This paper develops analytical models based on discrete dislocation dynamics to predict the dominant yielding mechanisms in small crystalline copper specimens, accounting for size and strain rate effects, and validates them with simulations and experiments.

Contribution

It introduces physics-based analytical models that accurately predict the transition between dislocation multiplication and surface nucleation mechanisms in small crystals.

Findings

Transition from dislocation multiplication to surface nucleation observed

Models show good agreement with simulation and experimental data

Models help estimate material strength under various conditions

Abstract

Dislocations are the carriers of plasticity in crystalline materials. Their collective interaction behavior is dependent on the strain rate and sample size. In small specimens, details of the nucleation process are of particular importance. In the present work, discrete dislocation dynamics (DDD) simulations are performed to investigate the dominant yielding mechanisms in single crystalline copper pillars with diameters ranging from 100 to 800 nm. Based on our simulations with different strain rates and sample size, we observe a transition of the relevant nucleation mechanism from "dislocation multiplication" to "surface nucleation". Two physics-based analytical models are established to quantitatively predict this transition, showing a good agreement for different strain rates with our DDD simulation data and with available experimental data. Therefore, the proposed analytical models help to understand the interplay between different physical parameters and nucleation mechanisms and are well suitable to estimate the material strength for different material properties and under given loading conditions.