Peter Berke

Coupled friction and roughness surface effects in shallow spherical nanoindentation

When nanoindentation is used for thin film characterization, usually shallow indents are made to avoid the spurious effect of the substrate. However, surface effects stemming from surface roughness and friction can become important in shallow indentation depths, potentially resulting in the variation of nanoindentation results. A numerical study is conducted aiming for a more complete understanding of the coupled influence of friction and sample surface roughness in nanoindentation of pure nickel, using a slip rate dependent friction law. Two experimentally used post-treatment methods are applied to obtain the elastic properties from the raw numerical data. Results confirm the strong interaction between these two contributions of surface effects, and their cumulative effect leads to significant variations in both the indenter load vs. displacement curves and the evaluated elastic modulus. The resulting dispersion is somewhat higher than the one computed for a slip rate independent Coulomb friction. The velocity-weakening nature of the used friction law, is observed to induce a stick-slip behavior which has a manifestation similar to pop-ins in the load-displacement curves.

Variation of the Electrostatic Adhesion Force on a Rough Surface due to the Deformation of Roughness Asperities During Micromanipulation of a Spherical Rigid Body

The micromanipulation of objects of size between 10 μm and 1 mm is often disturbed by the adhesion between the contacting surfaces. The electrostatic force in the contact alone can significantly perturb the micromanipulation by its important adhesion effect. The electrostatic adhesion force is influenced by many factors, i.e., the materials of the contacting bodies and the topography of the contact surface. Micromanipulation by contact involves applying a squeezing force to hold the object firmly which causes the contact surface to deform, flattening the surface asperities. The prime purpose of this work is to study the influence of the plastic deformation of the surface asperities on the electrostatic adhesion force considering the contact between two conductors. A single-level model of the surface roughness was considered in this study, approximating the shape of a surface asperity by a sine function. A simulation tool based on the finite element method was used to compute the elastic–plastic deformation of the model surface asperities during micromanipulation. Another numerical model was used to compute the electrostatic adhesion force acting on the surface asperities in the initial and in the deformed configurations. A magnification factor of up to 20 was obtained for the electrostatic force in the contact evaluated numerically, related to the flattening of the surface asperities, which can potentially lead to perturbations when releasing the object. The observed effect is merely a lower bound of the real one, considering the simplifying assumptions of the numerical models.

Simulation of the nanoindentation procedure on pure nickel on the smallest length scale: A simple atomistic level model

An atomic scale model has been developed to study the response of the pure nickel material during nanoindentation with shallow indentation depths (necessarily used for thin film applications) as an alternative to the frequently used continuum methods.

Numerical simulation of the nanoindentation experiment: sensitivity analysis of the experimental parameters

The use of certain metallic materials in micro-mechanical systems applications is promising for chirurgical applications because of their bio-compatibility and interesting mechanical and wear properties compared to the widely used silicon. The reliability of miniaturized components, the building blocks of such systems depends largely upon the reliability of the techniques applied to characterize the materials, in relation with numerical simulations.