Session: 16-01-01: Government Agency Student Poster Competition

Paper Number: 150173

150173 - Atomistic and Multiscale Simulations of the Thz Wave-Dislocation Interactions 

Plastically deformed metallic materials typically contain a high density of dislocations that are pinned by various obstacles. This pinning significantly affects the mechanical properties of the material, as the movement of dislocations is a primary mechanism of plastic deformation. When such materials are subjected to ultrasonic waves, the vibrational energy can cause these pinned dislocation segments to oscillate and potentially detach from their obstacles, leading to a phenomenon known as acoustic softening. Understanding and quantifying how ultrasonic waves interact with pinned dislocations is crucial for developing predictive models and optimizing material performance for various applications.

In this study, we aimed to probe the fundamental mechanisms of ultrasonic wave interaction with pinned dislocations and to quantify their contribution to acoustic softening. We utilized molecular dynamics (MD) and concurrent atomistic-continuum (CAC) simulations to achieve a detailed understanding of these interactions at different scales.

Firstly, we demonstrated the capability of CAC simulations in modeling the pinning and bowing of micron-long dislocation lines from nano-sized obstacles. Using both nanoscale molecular dynamics (MD) and microscale CAC simulations, we measured the critical stress required for the dislocation to bow out from the obstacles. Our results showed a clear dependence of critical stress on the spacing between obstacles. This relationship is essential for understanding how dislocation motion is impeded by obstacles and how it can be overcome by external stresses. These simulation results were then used to calibrate constitutive models at the continuum level. One such model is the BKS model, which describes the obstacle-induced strengthening effect. By integrating our simulation data into this model, we provided a more accurate representation of the material's mechanical response under various conditions.

Secondly, we predicted the ultrasonic response of the material containing pinned dislocations through CAC simulations. By simulating the propagation of ultrasonic waves through the material, we were able to measure the nonlinearity parameter (β), which characterizes the material's response to ultrasonic excitation. Our simulations revealed that β also depends on the obstacle spacing (L), providing a quantitative measure of how the microstructural features of the material influence its macroscopic acoustic properties.

A key advantage of our approach is the deployment of coarse-grained (CG) domains away from the obstacles, which allows us to simulate larger systems more efficiently while maintaining accuracy near the dislocation-obstacle interactions. This approach brings our simulations closer to experimental conditions, enabling more realistic predictions of material behavior. By spanning obstacle spacings from nanometers to micrometers, our simulations cover a wide range of microstructural configurations, making our findings broadly applicable.

The relationship between β and L derived from our simulations provides a critical input for continuum models that describe acoustoplasticity in materials. Acoustoplasticity refers to the alteration of material properties due to the combined effects of acoustic and plastic deformation processes. In practical applications, ultrasonic wavelengths are typically on the order of millimeters, frequencies are in the kilohertz range, and obstacle spacings are on the micrometer scale. Our β-L relation enables more accurate modeling of these effects, contributing to the design and optimization of materials for applications where ultrasonic waves are used, such as in non-destructive testing, material processing, and even medical treatments.

In conclusion, our study provides a comprehensive framework for understanding the interactions between ultrasonic waves and pinned dislocations in plastically deformed metals. By combining atomistic and multiscale simulations, we have elucidated the mechanisms of dislocation vibration and detachment under ultrasonic excitation and quantified their contribution to acoustic softening. Our findings offer valuable guidelines for the design of materials with tailored acoustic and mechanical properties, paving the way for advancements in various technological fields. The integration of our simulation results into continuum models enhances the predictive capability of these models, facilitating the development of materials with improved performance and reliability.

Presenting Author: Chang Yang North Carolina State University

Presenting Author Biography: Chang Yang earned my BS and MS degrees in University of Washington and University of Pennsylvania, respectively. He is now a 2nd-year PhD student in Dr. Xiong’s group at North Carolina State University. In the past years, he has taken all the core courses in finite element and solid mechanics. He delivered his first conference presentation at TMS 2024.

Authors:

Thanh Phan North Carolina State University
Liming Xiong North Carolina State University
Chang Yang North Carolina State University
Sunil Chakrapani Michigan State University
Upama Tonny Michigan State University