Sources of error in relating nanoindentation results to material properties
type: CreativeWork
description: This dissertation consists of four submission-ready papers that address some of the key error sources that affect the accuracy of interpretation of nanoindentation test results to obtain material properties for elastoplastic materials. The first part of the work is a study of the effect of sample tilt on results of nanoindentation tests. Geometrical relations are used to develop a correction to account for the effect of tilt angle on the contact area. 3D FEA (Finite Element Analysis) shows that the assumptions made in deriving the geometric correction are valid, and the results for contact area, hardness and modulus match the predictions of the analytical model. It is shown that for both materials that sink-in and those that pile-up, the projected contact area for nanoindentation on tilted sample is higher than that estimated by the standard area function, which leads to overestimation of the hardness and elastic modulus. Experimental nanoindentation tests on tilted samples show lower sensitivity to sample tilt compared to FEA results because the compliance of the indenter holder causes the indenter tip to displace in the direction of the surface tilt, reducing the total penetration of the tip into the surface. For tips with very high compliance, this may even lead to significant underestimation of the hardness and modulus. The second part discusses the various factors that affect the accuracy of FEA of nanoindentation. With the understanding that contact area error arising from discretization of the continuum is a key contributor to noise in the hardness data, a self similar mesh is designed that results in a known amount of maximum error in contact area over a range of depths of penetration of the indenter. Based on the fact that contact area increases in discrete jumps, it is argued that the maximum force that a given area of contact can support, before the next element comes into contact, is the best measure of the true hardness of the material that can be obtai…
abstract: This dissertation consists of four submission-ready papers that address some of the key error sources that affect the accuracy of interpretation of nanoindentation test results to obtain material properties for elastoplastic materials. The first part of the work is a study of the effect of sample tilt on results of nanoindentation tests. Geometrical relations are used to develop a correction to account for the effect of tilt angle on the contact area. 3D FEA (Finite Element Analysis) shows that the assumptions made in deriving the geometric correction are valid, and the results for contact area, hardness and modulus match the predictions of the analytical model. It is shown that for both materials that sink-in and those that pile-up, the projected contact area for nanoindentation on tilted sample is higher than that estimated by the standard area function, which leads to overestimation of the hardness and elastic modulus. Experimental nanoindentation tests on tilted samples show lower sensitivity to sample tilt compared to FEA results because the compliance of the indenter holder causes the indenter tip to displace in the direction of the surface tilt, reducing the total penetration of the tip into the surface. For tips with very high compliance, this may even lead to significant underestimation of the hardness and modulus. The second part discusses the various factors that affect the accuracy of FEA of nanoindentation. With the understanding that contact area error arising from discretization of the continuum is a key contributor to noise in the hardness data, a self similar mesh is designed that results in a known amount of maximum error in contact area over a range of depths of penetration of the indenter. Based on the fact that contact area increases in discrete jumps, it is argued that the maximum force that a given area of contact can support, before the next element comes into contact, is the best measure of the true hardness of the material that can be obtai…
author: Kashani, Mahdi Saket
date published: 2010-05
date modified: 2026-07-24T06:06:46Z
provider: Wichita State University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Wichita State University