Development and validation of full-field indentation microscopy (FIM) for anisotropic materials

Indentation offers several advantages over other mechanical testing methods, such as being non-destructive, capable of probing individual layers or thin films, and enabling localized measurements in heterogeneous materials. However, current indentation methods have limitations when characterizing soft polymers and tissues. The unimodal force-displacement data collected by gold-standard techniques like atomic force microscopy offer little information about material nonlinearity and no information about material anisotropy. This work presents the development and validation of Full-Field Indentation Microscopy (FIM), a new material characterization framework that overcomes the limitations of traditional indentation methods. Experimentally, FIM uses the weight of a glass microsphere to deform a soft material and a confocal microscope to take 3D images before and after indentation; the images are then used to estimate displacement fields. The inverse modeling framework for FIM, developed here, is based on the virtual fields method (VFM), a full-field inverse method, which can leverage the heterogeneous deformation inherent to indentation to extract nonlinear and anisotropic material parameters from a single indentation test. Specifically, this initial work aims to develop and validate the inverse analysis for FIM for anisotropic linear elastic materials. The objectives are (1) to identify efficient virtual fields to accurately estimate linear elastic-anisotropic material properties via FIM, (2) examine the feasibility of identifying nonlinear isotropic and nonlinear anisotropic material properties and (3) to investigate the domain size (i.e., field-of-view) required for experiments.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Kulkarni, Yuvam

Contributors dc:contributor

• Luetkemeyer, Callan M

• Inverse methods
• soft-material mechanical characterization
• full-field methods
• finite element analysis
• indentation
• virtual fields method

Statement dc:rights

• Copyright 2025 Yuvam Kulkarni

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/129282

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F129282