Coefficient Of Friction Evolution Research Articles

Experimental studies on the effect of application methods on the lubricant performance during serial production in automotive industry

Lubricant breakdown and galling phenomena are widely observed at the tooling surface during the stamping of aluminium components for the automotive industry, which compromise the formed surface quality and reduce tool-life. The lubricant performance has been found to be significantly influenced by its method of application. In the present research, a dedicated lubricant was evaluated by utilizing an advanced lab-scale friction testing system, TriboMate, and the effects of lubricant application method and lubricant quantity on the coefficient of friction evolution were investigated. It has been found that lubricant performance was significantly improved when the lubricant was applied on the hot workpiece blank, compared to the cold tooling surface, and when the lubricant quantity was increased. The gradual increase of friction evolution despite lubricant application on the workpiece blank was found to be due to the formation of an aluminium transfer layer at the tooling surface.

On the Tribocorrosion Behavior of Fe-Mn-Al-C Alloys in Ringer’s Solution

The long-term performance of steels is affected by the simultaneous actions of wear and corrosion, known as tribocorrosion. The tribocorrosion behavior of fully austenitic steels: Fe-Mn-xAl-C (x = 0, 3.5 and 8.3 wt.%) in Ringer’s solution was investigated by using a pin on disk tribometer adapted with a three-electrode corrosion cell. Open circuit potential and coefficient of friction evolution as well as polarization curves were measured. Corrosion rates were calculated by the Tafel extrapolation method, and wear rates were calculated by using a linear profilometer. Pure and total wear rates were higher for the 3Al alloy due to the greater precipitation and embedded calcium minerals, hydroxides, and oxides on the surface, to the detachment of the deformed layer and its adhesion to the counterbody. Additionally, the 8Al alloy exhibited the lowest tendency to corrosion and corrosion rate and the greatest synergistic effect, indicating that this alloy is more sensitive to this effect than the other alloys. For the three materials, the change in the wear rate due to corrosion had a greater contribution to the synergy than the change in corrosion rate due to wear and the damage in the materials was derived mainly from pure mechanical wear.

Coefficient of friction evolution with temperature under fretting wear for FeCrAl fuel cladding candidate

A leading cause of fuel failures in U.S. pressurized water reactor power plants is grid-to-rod fretting. One of the major variables affecting fretting wear is the coefficient of friction (COF). Reliability of the fuel cladding is influenced by the COF and thus it is important to know how the material's COF will be affected by temperature transients. Kanthal advanced powder metallurgy technology or APMT, a FeCrAl steel alloy, is being investigated as a commercial alternative to conventional fuel cladding in a nuclear reactor due to its potentially favorable performance under accident conditions. This leaves APMT steel fretting performance to be examined. Tests were performed to examine the evolution of the COF with temperature under fretting. The contact was simulated with both a cylindrical and a rectangular specimen over a line contact area. Confocal scanning laser microscopy was used to obtain a 3D map of the surface, which was used to calculate the wear rate coefficient of the samples. The wear rate coefficient was compared to wear volume to show the effects of the COF and temperature on wear. Energy Dispersive Spectroscopy was performed to qualitatively describe the microchemical changes the material underwent in the fretted region. Nanoindentation was used to compare microstructural properties inside and outside the fretting scar after fretting at different temperatures. COF measurements showed that APMT steel's COF and wear decreases with temperature up to 350 °C.

Tribological Behavior and Microstructure of Carbon Fiber–Reinforced Polymer against Ti6Al4V Alloy in Fretting Contact

ABSTRACTThis article investigates the tribological behavior of carbon fiber–reinforced polymer (CFRP) against Ti6Al4V alloy for fretting contacts. Tests were conducted for CFRP against Ti6Al4V in a ball-on-flat configuration. The fretting coefficient of friction (COF) was measured and worn surfaces were characterized. Three-dimensional topographies and surface roughness of fretting scars with different fretting amplitudes were examined. The relationships between COF and various fretting amplitudes, normal force, frequency, fibers orientation, and temperature are presented. The results shows that these factors influence the fretting friction coefficient as follows: fretting amplitude applied load fiber orientation frequency, and temperature and fretting mode have a combined action on the evolution of COF. The surface properties of fretting scars under various fretting amplitudes were demonstrated. In addition, fibrous polishing and shear fracture and fatigue cracking of the matrix are the main fretting wear mechanisms under low fretting amplitude.

Finite element analysis of fretting wear under variable coefficient of friction and different contact regimes

Fretting wear is a material damage in contact surfaces due to micro relative displacement between two bodies. It causes some unexpected results, such as loosening of fasteners or sticking in components supposed to move relative to each other. Since this micro motion of fretting wear is difficult to measure in experiments, finite element method (FEM) is widely used for investigating the evolution of contact variables and wear scars during fretting wear process. In most FEM simulations of fretting wear, coefficient of friction (CoF) is assumed to be constant in order to simplify the models. As measured in experiments, however, the evolution of CoF has a relation with the wear number of cycles, especially during the running-in stage. In this research, the effects of variable CoF are considered in both gross sliding and partial slip conditions of fretting wear. The wear scar and wear volume predicted by FEM models for constant and variable CoF cases are calculated. Results indicate that, in gross sliding condition, whether or not using a variable CoF has little effect on wear volume at the end of the steady state stage of fretting wear cycles. However, when considering partial slip or running-in stage of gross sliding conditions, FE models with variable CoF achieve predictions that are closer to experimental results.