Influence of the 6061 Aluminium Alloy Thermo-Viscoplastic Behaviour on the Load-Area Relation of a Contact

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.

A Closer Look at the Contact Conditions of a Block-on-Flat Wear Experiment

“…The bumped surface contains a parabolic protuberance of 1 mm wide and a couple of micrometers in height located in the middle of the otherwise flat profile. The rough surface is a cross section from an artificially generated random isotropic 3D topography, similar to the one used in [16]; it is inserted between x = −1.85 mm and x = 1.85 mm and has an average roughness of 1.53 µm in this interval. The three surfaces are identical at the edges (i.e., for |x| > 1.85 mm).…”

“…This, of course, implies modelling the contact first, for which different approaches are available. The finite element method (FEM) is an attractive option-while it is true that FEM may be computationally much more expensive than other methods, such as the boundary element method [15], the FEM provides great versatility to include multiple physical phenomena [16]. In any case, the contact solution can subsequently serve as input to wear models [17]; the most used one, and practically a standard in the tribology community, is often referred to as Archard's wear equation (or Archard's law), which can be expressed by rewriting Equation (1) in a dynamic format as…”