Evolution of aggregate surface texture due to tyre-polishing

Three kinds of aggregates were polished by genuine pneumatic rubber tyres.The initial states of surface texture and dynamic friction coefficient were measured and their developments in polishing process were monitored.The characterizations of height distribution and power spectral density of aggregate surface texture were estimated.The changes of micro-texture were also investigated based on a fractal filtering method with sound theoretical backgrounds of rubber friction on rough surfaces.Global height reduction and differential removal of mineral component are observed in polishing process.It is concluded that the tyre-polishing action plays the critical roles in the micro-scale texture,and the evolution of friction of aggregate is governed by the micro-texture changes due to the differential removal of mineral component.

Effect of surface roughness on the surface lubrication performance of galvanized steel sheets with a self-lubricated coating

Four kinds of galvanized steel sheets having different surface roughness values were used to prepare the steel sheets with a self-lubricated coating. The effects of surface roughness on the surface lubrication performance of the steel sheets were examined using a friction coefficient tester. Results revealed large dynamic friction coefficients for the galvanized steel sheets, which increased remarkably with surface roughness. Once the self-lubricated coating was applied, significant drops in the dynamic friction coefficients were measured. After the first stage of the friction test,the coefficients were almost unchanged, which reflected a weak dependence on the surface roughness of the self-lubricated steel sheets. However, the dynamic friction coefficients gradually increased as the test progressed, where these increase clearly correlated with the surface roughness of the self-lubricated steel sheets.

Development and validation of an integrated mechatronic apparatus for measurement of friction coefficients of agricultural products

An integrated mechatronic apparatus was developed based on tilting plate method in order to precisely measure static friction coefficient(SFC)and dynamic friction coefficient(DFC)of agricultural products.The apparatus consisted of two main parts(mechanical and electrical parts).The main element of mechanical part was rotary container.Meanwhile,the electrical part included control,display,goniometer,level controller,rotational power supply,and infrared unit.The apparatus was initially simulated in simulation environment and practically calibrated to achieve high precision measurements.To appraise performance of the apparatus,the SFC and DFC of three grains were measured on five contact surfaces.Experiments were also conducted by means of a typical apparatus operating based on puling force method.Some statistical descriptor parameters such as mean absolute percentage error(MAPE),average of absolute values of measurement errors(AAVME),maximum of absolute values of measurement errors(MAVME),and correlation coefficient were used to compare accuracy of the apparatus with the typical one.The acceptable AAVME(<10%),MAVME(<10%),MAPE(<5%),and correlation coefficient(>0.9)indicated high accuracy,stability,and efficiency of the apparatus for automatic measurements of the SFC and DFC.From practical point of view,the mechatronic apparatus would be a beneficial tool for experimental,educational,demonstrational,and research works.

Laser Surface Textured PTFE Inhibitation for Stick-Slip Phenomenon Under Boundary Lubrication

When the machine tool is in the start-and stop-stages,the stick-slip phenomenon will be observed and highprecision positioning,machining accuracy and fretting feed will not be guaranteed. The most critical reason is that there is the difference between the dynamic and the static friction coefficients. Textures with different area ratios are fabricated on the surfaces of the upper PTFE-based composite and the friction tests are carried out on a reciprocating tribotester under the boundary lubrication and flat-on-flat contact conditions. The results show that there exists an optimal textured area ratio of 19.6% that can minimize the difference between the dynamic and the static friction coefficients.