The Stress-Strain Relationships Of Thin Films Characterized By Nanoindentation

Recently, more and more attentions have been paid to thin films, and research of the mechanical properties of thin films gets to be a hot subject. As a method to evaluate the mechanical properties of thin films, nanoindentation technique is in the popularity for its high displacement resolution, ultra low load and the capability of continuous measurement. In this master thesis, the stress-strain relationships of thin films were measured by nanoindentation combined with dimensional analysis and finite element method.Two main parts are contained in this master thesis. In the first part, a theory frame was established to extract the stress-strain relationships of thin films by nanoindentation. In the second part, the stress-strain relationship of electrodeposited nickel coating was measured.At the beginning of this thesis, related research background and research status were introduced, then nanoindentation technology and the background of this master thesis were interpreted detailedly. A theory frame to measure the mechanical properties of four kinds of film/substrate systems, namely, brittle film on tough substrate, brittle film on brittle substrate, tough film on brittle substrate and tough film on tough substrate, was established. We can get the mechanical properties of thin films with following steps: first, dimensional analysis was applied to derive the relationship between indentation and mechanical properties of material, such as Young's modulus, yield strength, strain hardening exponent etc. Then, the indentation process was simulated by finite element method. At last, the mechanical parameters were extracted from the true load-displacement curves. Another important work in this master thesis is the detailed introduction of extracting stress-strain relationship of electrodeposited nickel coating from nanoindentation. ABAQUS was used to simulate the process that the Berkovich indenter indented into the electrodeposited nickel coating about 1000nm, then according to the real Load-Depth curves got in the nanoindentation experiments and the dimensionless functions, the yield strength and strain hardening exponent were figured out. The work measuring the mechanical properties of tough film on brittle substrate finished by Ma Dejun was cited in this thesis. The feasibility of this theory frame was proved by both of the examples.