Session: 04-26-01: Nanoengineered, Nano Modified, Hierarchical, Multi-Scale Materials and Structures

Paper Number: 165493

Finite Element Analysis of Compressibility and Local Yield Strength in Atomic Force Microscopy Indentation of Heterogeneous Nanocomposite Systems 

Atomic Force Microscopy (AFM) is a widely used material characterization technique in fields such as polymer science, biology, medicine, chemistry, and semiconductors. This method involves raster-scanning the surface of a sample with a probe attached to a cantilever. By tracking the probe's deflection with a laser and photodiode, AFM creates high-resolution topologies of the specimen and can determine material properties at nano- and sub-nanometer resolutions through various measurement channels. Despite numerous innovations in AFM architecture, measurement modes, and experimental standards, achieving accurate results with AFM on heterogeneous materials, such as polymer nanocomposites and nanomembranes, remains a challenge.

Several parameters can create artifacts in the AFM signals and complicate the interpretation of AFM data. Researchers have identified various factors that contribute to these artifacts, such as interactions between the indentation stress field and nearby rigid substrates or particles. They have also developed techniques to isolate the effects of these factors from the data obtained through AFM. However, many of these parameters have not been thoroughly investigated in existing research. One critical phenomenon that requires further examination is the rigid body motion of embedded particles and the complexity of the contact response. Depending on the relative size and mass of the AFM probe and particle, either complete or partial rigid body motion can distort the AFM signal. Additionally, the size, location, and distribution of embedded particles within a membrane can lead to varying stiffness levels across the sample surface, making nondestructive indentation challenging in practice. The accidental local plasticization of the material may also influence the force-displacement data gathered from indentations taken at nearby sites.

In the authors' previous works, the effect of matrix damage on AFM data was quantified using finite element analysis (FEA) while assuming that contact-mode AFM indentation is quasi-static. In this paper, the authors simulate dynamic AFM indentation on a particle-matrix finite element model to investigate the effects of kinematic energy, partial debonding, particle motion, and matrix plasticization on the AFM signal. The AFM signal obtained from the dynamic simulation will be compared to the quasi-static condition and validated through experiments. Particles of various sizes, masses, locations, and embedment depths will be considered during the simulations. Additionally, the authors will explore the differences in indentation responses between healthy and post-indentation states. The Hertz, Derjaguin-Muller-Toporov (DMT), and Johnson-Kendall-Roberts (JKR) contact mechanics models will be applied to examine the interactions between the probe and the matrix, as well as to determine the elasticity and adhesion properties. The effects of material incompressibility and mobility around the particles will also be included in the plasticity model. The authors believe that the findings from this research will provide crucial insights into AFM-based characterization of membranes and heterogeneous nanocomposites.

Presenting Author: Max Westby Arizona State University

Presenting Author Biography: Max Westby is currently working toward his master's degree in mechanical engineering at Arizona State University. His primary focus areas are structural mechanics, polymer composites, and nanomaterials. After he obtains his master's degree, he plans to continue his research and graduate education in pursuit of his doctorate.

Authors:

Max Westby Arizona State University
Brian Raji Advanced Structural Engineering
Masoud Yekani Fard California Polytechnic State University