Adhesion Friction Coefficient Research Articles

Preparation and properties of Al-alloy coconut shell char particulate composites

A technique to produce cast Al-11.8 pct Si alloy composites containing up to 40 vol pct (15 pct by weight) dispersions of 125 µm size coconut shell char particles is described. The technique consists of stirring shell char particles into the vortex created by mechanical stirring of melts and subsequent casting of composite melts in suitable molds. The composite melts were also pressure die cast at a pressure of 100 MPa into cylindrical castings. The incorporation of large volume fraction of shell char particles is aided by (a) preheating of the particles to about 500 ‡C to 600 ‡C for two hours before introduction into the melts, and (b) alloying of Al-11.8 pct Si melts with 3 to 6 pct Mg. Electron Probe Micro Analysis (EPMA) analysis indicated an Mg enriched region around dispersed char particles in the composite indicating that prealloying with Mg probably improves wetting between char particles and the melt. Dispersions of 15 pct wt of char particles lead to decreases in hardness (from 85 BHN to 55 BHN), compression strength (from 542.30 MPa to 218.68 MPa), U. T. S., (from 164.16 MPa to 63.75 MPa), and electrical conductivity (from 27.8 pct I ACS to 11 pct I ACS). However, since these decreases are accompanied by a decrease in density, specific strength values of Al-11.8 pct-shell char composites are adequate for a variety of applications. Adhesive wear rates and friction coefficient values at low sliding speeds (0.56 m per second, and at loads of 10 N and 60 N) decrease with increase in wt pct of char particles under dry conditions.

On the Mechanism of Contact between Solid Surfaces : 4th Report, Surface Roughness Effects on Dry Friction

A study was made of surface roughness effects on dry friction between two metals, assuming that the asperities are cones of slopes which depend on the surface roughness. Theoretical expressions were derived for ploughing, adhesion and total friction coefficients of cones, spheres and aquare pyramids ploughing along the soft metal surface. A comparison of calculated values based on this theory with experimental data shows good agreement. Moreover, theoretical discussion was made of surface roughness effects on dry friction on the basis of the analysis of mechanism of abrasive friction. The theoretical estimation of the coefficient of friction between two metal surfaces can be carried out using the relations between the surface roughness and the slope of the asperities, and the coefficient of friction due to the adhesion at the interface. The experiments also showed that the maximum displacement between two metal surfaces in contact before gross sliding occurs, increases with an increase of the surface roughness.