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

Paper Number: 149717

149717 - Multiscale Modeling of Acoustoplasticity 

Acoustoplasticity is defined as plasticity aided by high intensity acoustic waves. Understanding the fundamental mechanism of acoustoplasticity is important since it is becoming increasingly utilized in metal forming, welding, and machining. Previously, researchers have explored the concepts of stress superposition, thermal softening, and frictional effect between the Sonotrode and workpieces to model acoustic softening. The most common method to model acoustoplasticity is the thermo-mechanical finite element models to model the deformation induced by ultrasonic vibration. The thermal softening effect on material properties was used as the foundation for these models. However, other studies suggested that the temperature rise on the specimen during in situ ultrasonic application is almost negligible and cannot account for the acoustoplasticity effect. More recently, dislocation mechanisms have been proposed, but have not been explored as much from a multiscale perspective. The aim of this work is to develop a multiscale model that accounts for dislocation-based plasticity. Developing a model will allow us to further simulate the ultrasonic aided manufacturing process with better accuracy and improve the prediction of resulting properties.  

It has been observed that ultrasonic vibration can cause dislocation de-pinning and further cause the dislocation to become mobile, which softens the material. This de-pinning behavior may be influenced by the frequency and amplitude of ultrasonic vibrations. We performed molecular dynamic simulations to model the dislocation depinning at GHz-MHz frequencies to understand the fundamental de-pinning process. The acoustic stress amplitude and frequency and pre-stress were changed in the MD model to understand the acoustoplasticity phenomenon in the high frequency domain.  

In the continuum scale, a finite element model was developed based on the modified Johnson-Cook model. Multilinear hardening plasticity is incorporated to feed the modified JC model and solved through ANSYS. Symmetric boundary conditions were included to optimize the computation time. Compressive quasi static loading with high frequency vibration was applied on the modeled specimen. The acoustoplasticity effect on continuum scale was demonstrated from the stress strain behavior of this model. To compare the stress reduction, the FEM model with no ultrasonic vibration application was tested using conventional JC model. 

To bridge the dislocation-based plasticity behavior to the continuum level models, a modified JC model is proposed. The yield stress, hardening coefficient, and hardening exponent term of the conventional JC model were modified based on the MD results, specifically the amplitude and frequency effect on dislocation depinning. This multiscale model can be used to demonstrate the frequency and amplitude dependence on the acoustoplasticity process. Additionally, a comparison of the proposed analytical model and finite element model with ultrasonically assisted compression from existing literature will be presented. 

Presenting Author: Upama Biswas Tonny Michigan State University

Presenting Author Biography: I am a Ph.D. student in the Electrical and Computer Engineering department at Michigan State University. I completed my B.Sc in Mechanical Engineering from Bangladesh University of Engineering and Technology
from Bangladesh. My current research interests are Ultrasonics, Acoustoplasticity, and Material Characterization.

Authors:

Upama Biswas Tonny Michigan State University
Chang Yang North Carolina State University
Liming Xiong North Carolina State University
Sunil K. Chakrapani Michigan State University