ABSTRACT
The contact between solids in metal-forming operations often involves temperature-dependent viscoplasticity of the workpiece. In order to estimate the real contact area in such contexts, both the topography and the deformation behaviour should be taken into account. In this work, a deterministic approach is used to represent asperities in appropriately shaped quadratic surfaces. Such geometries are implemented in indentation finite element simulations, in which the indented material has thermo-viscoplastic properties. By creating a database of simulation data, investigations in terms of contact load and area for the specifically shaped asperities allow for an analysis on the influence of the material properties on the load-area relation of the contact. The temperature and viscoplasticity greatly define how much load is supported by a substrate due to an indenting asperity, but the description of the deformation behaviour at small values of strain and strain rate is also relevant. The pile-up and sink-in regions are very dependent on the thermo-viscoplastic conditions and material model, which consequently affect the real contact area calculation. The interplay between carried load and contact area of a full surface analysis indicates the role that different sized asperities play in the contact under different thermomechanical conditions.
ABSTRACT
A post-processing method, which maps the punctiform atoms in molecular dynamics (MD) simulations of boundary lubrication onto smoothed particles, is used to estimate the asperity contact area defined by the minimum cross-section of the formed solid bridges. It is then shown that this asperity contact area excellently agrees with the projected area resulting from a Voronoi tessellation of the corresponding contact zone, and that it can be applied to compute the constitutive system parameters of a three-term friction law, which is found to hold for any boundary-lubricated nanotribological system. Finally, an attempt is made to relate the load-independent friction offset observed in boundary-lubricated nanotribological systems without solid-solid contact to the structural order as measured by the entropy, which is estimated within the single macromolecule approach based on covariance (super)matrices of the carbon backbone atoms in the lubricant.
ABSTRACT
Industrially ground surfaces often have a characteristic surface topography known as chatter marks. The surface finishing is mainly monitored by optical measurement techniques. In this work, the monitoring of an industrial belt grinding process with a light scattering sensor is presented. Although this technique is primarily applied for parametric surface roughness analysis, here it is shown that it enables also the measurement of the surface topography, i.e., the chatter marks occurring during the belt grinding process. In particular, it is proven that the light scattering method is appropriate to measure online the topography of chatter marks. Furthermore, the frequency analysis of the data reveals that the wavelength of chatter marks strongly depends on process parameters, such as the grinding speed.