Meshless microscale simulation of wear mechanisms in scratch testing

- Mesh-free smooth particle hydrodynamics method to simulate scratch tests.
- Strong influence of hardening parameters on topography, scratch hardness and friction.
- Neglecting the real contact area dramatically influences measured scratch hardness.
- Minimum in σy/E ratio suggests wear mechanism regime transitions.
- Simulated load curves exhibit periodic instabilities also observed experimentally.

Scratch testing is an inexpensive technique used for determining the mechanical/wear properties of materials and coatings. In contrast to instrumented indentation, where quantitative relations have been established, only few studies are devoted to quantitatively understanding the material response during scratch testing. Most modelling approaches rely on the finite element method, which is particularly suitable for calculating stresses during plastic deformation, but cannot straightforwardly reproduce gross deformations or material detachment. The present work relies on smooth particle hydrodynamics (SPH) for overcoming this issue. SPH approximates a continuous field using a set of kernel functions centred about so-called particles. These carry the physical properties of the system, e.g. mass, internal energy, or velocity, thus discretising the set of underlying partial equations. By using a discrete method, material detachment is intrinsically taken into account. A parameter study was undertaken on the basis of the elastic-viscoplastic material model of Johnson-Cook. The aim of this work is to investigate the role of material/wear properties and load on the scratch behaviour via a parameter study. The influences of strain hardening, yield strength and Young's modulus on the scratch behaviour are pointed out. The results of the scratch simulations are in good agreement with experimental data for single phase alloys. Relaxation phenomena known from scratch experiments are reproduced for the first time using a numerical method.