Scratching Simulation Research Articles

Smoothed particle hydrodynamics simulation and experimental analysis of SiC ceramic grinding mechanism

Crack induced surface/subsurface damage in SiC ceramic grinding limits the industrial application. A single-grain scratching simulation based on the smoothed particle hydrodynamics (SPH) has been used to analyze the SiC grinding mechanism, including the material removal process, scratching speed effect on crack propagation, ground surface roughness, and scratching force. The simulation results showed that the material removal process went through the pure ductile mode, brittle assisted ductile mode, and brittle mode with the increase of the depth of cut. The critical depth of cut for ductile-brittle transition was about 0.35 µm based on the change of ground surface crack condition, surface roughness, and maximum scratching force. Increasing the scratching speed promoted the transformation of deep and narrow longitudinal crack in the subsurface into the shallow and wide transverse crack on the surface, which improved the surface quality. The SPH simulation results were indirectly validated by the cylindrical grinding experiments in terms of the critical single grain depth of cut for ductile-brittle transition, and the trend of ground surface roughness and grinding forces.

Atomistic insights on the nanoscale single grain scratching mechanism of silicon carbide ceramic based on molecular dynamics simulation

The precision and crack-free surface of brittle silicon carbide (SiC) ceramic was achieved in the nanoscale ductile grinding. However, the nanoscale scratching mechanism and the root causes of SiC ductile response, especially in the atomistic aspects, have not been fully understood yet. In this study, the SiC atomistic scale scratching mechanism was investigated by single diamond grain scratching simulation based on molecular dynamics. The results indicated that the ductile scratching process of SiC could be achieved in the nanoscale depth of cut through the phase transition to an amorphous structure with few hexagonal diamond structure. Furthermore, the silicon atoms in SiC could penetrate into diamond grain which may cause wear of diamond grain. It was further found out that the chip material in the front of grain flowed along the grain side surface to form the groove protrusion as the scratching speed increases. The higher scratching speed promoted more atoms to transfer into the amorphous structure and reduced the hexagonal diamond and dislocation atoms number, which resulted in higher temperature, smaller scratching force, smaller normal stress, and thinner subsurface damage thickness, due to larger speed impaction causing more bonds broken which makes the SiC more ductile.

Analysis of grit interference mechanisms for the double scratching of monocrystalline silicon carbide by coupling the FEM and SPH

Three-dimensional twice scratching and double scratching of monocrystalline silicon carbide with two cone-shaped grains were simulated by coupling the finite element (FEM) and smoothed particle hydrodynamics (SPH) to resolve the mesh distortion problem caused by using the FEM. Twice-scratching experiments were performed under three different conditions to validate the coupled finite element (FE) and SPH model in the scratching simulation with two diamond grits. The experimental results were compared to the simulation results. For twice scratching, the simulation results conform with the experimental results, indicating the validity of the coupled FE and SPH model. Thus, the coupled FE and SPH model was used to simulate the double-scratching process under different conditions. The results of the double-scratching simulation showed that the interference damages in the scratching process occurred under three circumstances: the interference of lateral cracks, the interference of lateral cracks and plastic damage, and the interference of plastic damage. The influence of distance on the interference damage of the two diamond grits in the Y-direction was analysed. The changes in the maximum depth and width in the interference region and the scratching force with the distance of the two grains in the Y-direction are illustrated.

Research on the Stress and Material Flow with Single Particle—Simulations and Experiments

The scratching process of particle is a complex material removal process involving cutting, plowing, and rubbing. In this study, scratch experiments under different loads are performed on a multifunctional tester for material surface. Natural diamond and Fe-Cr-Ni stainless steel are chosen as indenter and workpiece material, respectively. The cutting depth and side flow height of scratch are measured using a white light interferometer. The finite element model is developed, and the numerical simulation of scratching is conducted using AdvantEdgeTM. The simulated forces and side flow height under different cutting depths correspond well with experimental results, validating the accuracy of the scratching simulation. The mises stress distribution of the particle is presented, with the maximum stress occurring inside the particle rather than on the surface. The pressure distribution of the particle is also given, and results show that the maximum pressure occurs on the contact surface of particle and workpiece. The material flow contour is presented, and material flow direction and velocity magnitude are analyzed.

Meshless microscale simulation of wear mechanisms in scratch testing

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.

Modeling and simulation of the probe tip based nanochannel scratching

This paper presents the theoretical modeling and numerical simulation of the probe tip based nanochannel scratching. According to the scratching depth, the probe tip is modeled as a spherical capped conical tip or a spherical capped regular three side pyramid tip to calculate the normal force needed for the nanochannel scratching. In order to further investigate the impact of scratching speed, scratching depth and scratching direction on the scratching process, the scratching simulation is implemented in LS-DYNA software, and a mesh-less method called smooth particle hydrodynamics (SPH) is used for the sample construction. Based on the theoretical and simulated analyses, the increase of the scratching speed, the scratching depth and the face angle will result in an increase in the normal force. At the same scratching depth, the normal forces of the spherical capped regular three side pyramid tip model are different in different scratching directions, which are in agreement with the theoretical calculations in the d3 and d4 directions. Moreover, the errors between the theoretical and simulated normal forces increase as the face angle increases.

Experimental and simulative strain field investigation of nano- and microscratches on nanolaminated (Cr, Al)N coating

Micro- and nanoscratches were made on a nanolaminated CrN/AlN coating under different loads and velocities. The remaining vertical strain fields under the scratches were determined by measuring the bilayer periods in cross-fracture images using scanning electron microscopy. These results were compared with the remaining vertical strain fields obtained from scratch simulations utilizing the strain-rate-dependent material properties examined in preliminary work. The effect of the friction coefficient and residual stress on the strain and stress fields was investigated using simulations. The experimental and simulated strain fields show good quantitative agreement for the nanoscratches. Furthermore, the appearance of fractures and microcracks under the scratches could be correlated with strong shear stresses in simulations during indenter overrun. This method and the results obtained enable the stress–strain fields of coatings under dynamic mechanical loads to be determined quantitatively. Additionally, the possibility of determining failure criterions using scratch tests enables the simulative prediction of a coating's resistivity under real loading conditions.

Atomic scale stick-slip caused by dislocation nucleation and propagation during scratching of a Cu substrate with a nanoindenter: a molecular dynamics simulation

Scratching of a Cu surface using a nanoindenter was studied by molecular dynamics simulation using embedded atom potentials. The simulation was carried out using a rigid Ni tip (radius = 2.5 nm) scratching on a Cu{0 0 1} surface. The Cu substrate contained 200,000 atoms and various scratching conditions were simulated by the rigid body translation of the tip at different indentation depths (0–0.36 nm), speeds (4.2–49.8 m/s), and temperatures (4–300 K). Atomic scale stick-slip was observed during the scratching simulation and it was associated with dislocation nucleation and propagation. The stick-slip accompanies the slow increase of friction force during the elastic deformation and is followed by an abrupt decrease of the friction force due to plastic yielding. The stick-slip was repeated with an approximately same period and it was pronounced at certain ranges of sliding conditions in terms of scratching depth, speed, and temperature. The simulation also exhibited that the V-shaped dislocations consisting of Shockley partial dislocations were constructed and they propagated near the free surface along the slip system of an fcc crystal. Detailed analysis of friction oscillation suggested that the nucleation of the dislocation during scratching plays more important roles in determining the abrupt drop during stick-slip than subsequent propagation of partial dislocations.