Numerical investigations of the elasto-plastic behavior of hybrid nanolaminates under nanoindentation loadings

Details

Supervisors

Pardoen, Thomas

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil mécanicien, à finalité spécialisée

Abstract

Abstract The advancements in the high-tech industries have gained a higher momentum recently, with inventing new technologies and making improvements in the current state of the arts. The advent of these new promising technologies as a response to the growing demands of the new AI-enabled industrial era, has increased the need for developments of new functional materials. Nanolaminates are a group of synthetic materials made by stacking layers of materials in the order of nanometer, made up of metals or ceramics, to form a layered composite, which aims at delivering different functionalities especially in the extreme conditions like high temperature, among which the thin film coatings used in applications like microelectronics and nuclear cladding have been proved to be irreplaceable. On the other hand, nanoindentation is a nondestructive depth-sensing characterization method, which allows the determination of some important mechanical properties, including Young's modulus, hardness, fracture toughness, etc., by applying several steps of loading-unloading on the surface of the materials, and estimating the contact area. Oliver-Pharr method has been utilized extensively to analyze the data of the indentation and extract the mechanical parameters. This technique has been subject of comprehensive research and evolved extensively. Applying this technique to nanolaminates allows for investigating the overall elasto-plastic behavior and specially mechanical properties of these materials. Given the restrictions on the applications of the experimental methods, resorting to the numerical simulations has been established as a useful approach to help gain better understanding of this phenomenon. A 2D axisymmetric numerical model was made, using the general purpose FE code Abaqus, by developing a Python script, aiming at conducting comprehensive parametric studies on the elasto-plastic behavior of different nanolaminates under nanoindentation loadings. The data were treated by a Python code developed based on the Oliver-Pharr method, considering different formulations for estimations of the contact area of the indentation zone. A phenomenological hardening law was considered which is a function of the equivalent plastic strain and strain rate, having hardening and rate sensitivity exponents. This law was implemented either by developing a {\small \texttt{UHARD}} in Abaqus or in tabular way. The normalized Young's modulus and hardness were extracted in different conditions. Different conclusions are made, such as the importance of a realistic approximation of contact area, which is key in obtaining reasonable results. The curve-fitting based formulations are proved to be the best approach in estimation of the contact area, and also the effects of the hardening and strain rates on the results. It is also found that with higher hardening and higher strain rates or rate sensitivity, higher hardness values are expected.