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A numerical study on the nanoindentation response of a particle embedded in a matrix

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posted on 23.02.2017, 00:02 authored by Low, Teck Fei
An indentation test is an experimental method whereby an indenter is pressed into a specimen in order to create a contact impression. Based on experimental input and the mechanical response of a specimen, an indentation test can be used to measure material properties of a specimen. A nanoindentation test is an instrumented indentation test where the indentation depth is at the submicron scale, utilising the interpretation of recorded load-displacement data. Nanoindentation tests have proven to be popular commercially due to their non-destructive nature, with the Oliver-Pharr method being one of the most prominent analysis methods applied. In this research, nanoindentation tests on a semi-spherical particle embedded in a semi-infinite matrix were simulated using the finite element method. Dimensional analysis was utilised to conduct a numerical study of the nanoindentation response obtained from finite element simulations. The Oliver-Pharr method to estimate contact area from a nanoindentation test is unsuitable for the cases with pile-up deformation. In an indentation of a hard particle embedded in a soft matrix, the mismatch of material properties will cause the particle to indent itself into the matrix, which creates a secondary indentation effect. This makes it difficult to investigate the pile-up and sink-in behaviour for hard particle reinforced composites because the definition of pile-up for monolithic materials is no longer valid. In this research, a feasible method to quantify pile-up and sink-in for particle-matrix systems is proposed. Using a reference height, it was found that particle pile-up and sink-in can be quantified when the maximum indentation depth is less than 15% of the particle’s radius. The influence of particle and matrix material property on pile-up and sink-in was explored. Within the maximum indentation depth, which is less than 15% of the particle’s radius, it was found that only the mechanical properties of the particle represented by particle’s elastic modulus, particle’s yield strength, and particle’s work-hardening exponent, have a significant influence on the degree of pile-up and sink-in from a nanoindentation test. In a nanoindentation test of a particle embedded in a matrix, the matrix material properties may influence the measured indentation hardness of the particle. A numerical study was carried out to identify the influence of particle and matrix material properties on the measured hardness. Results reveal that a mismatch in material properties is more sensitive on the measured hardness of a hard particle embedded in a soft matrix than a soft particle embedded in a hard matrix. Finally, a parametric study was carried out to identify a particle-dominated depth, within which the particle’s hardness obtained from a nanoindentation test can be measured with confidence. Simulation results from the finite element analysis of a variety of material properties determined that when the maximum indentation depth is less than 13.5% of the particle’s radius, the measured hardness is in good agreement with the particle’s true hardness, with a maximum error of 5%. This finding can be applied in practice as a guideline to measure the hardness of a particle embedded in a matrix from a nanoindentation test and provide the theoretical basis to develop a particle-embedded method to measure the hardness of individual particles.

History

Campus location

Australia

Principal supervisor

Wenyi Yan

Year of Award

2014

Department, School or Centre

Mechanical and Aerospace Engineering

Course

Master of Engineering Science (Research)

Degree Type

MASTERS

Faculty

Faculty of Engineering