Materials science: The ultrasmoothness of diamond-like carbon surfaces

The ultrasmoothness of diamond-like carbon coatings is explained by an atomistic/continuum multiscale model. At the atomic scale, carbon ion impacts induce downhill currents in the top layer of a growing film. At the continuum scale, these currents cause a rapid smoothing of initially rough substrates by erosion of hills into neighboring hollows. The predicted surface evolution is in excellent agreement with atomic force microscopy measurements. This mechanism is general, as shown by similar simulations for amorphous silicon. It explains the recently reported smoothing of multilayers and amorphous transition metal oxide films and underlines the general importance of impact-induced downhill currents for ion deposition, polishing, and nanopattering.

An electrokinetic sensor for studying immersed surfaces, using focused ultrasound

A novel method for obtaining information on the charge density of an immersed surface is presented. The technique uses focused ultrasound to excite oscillatory fluid motion in the plane of the solid-liquid interface, over a localised area. The displacement current (resulting from the motion of fluid-borne ions in the outer double-layer) is detected by electrodes in the liquid. The method is demonstrated as a means for monitoring protein adsorption, and for monitoring interactions between two different proteins. A second electrokinetic effect at the interface is identified, isolated from the first, and shown to provide additional information on the compressibility and charge density of the double-layer. © 2001 Elsevier Science B.V. All rights reserved.

THEORETICAL ROAD DAMAGE DUE TO DYNAMIC TYRE FORCES OF HEAVY VEHICLES. PART 1: DYNAMIC ANALYSIS OF VEHICLES AND ROAD SURFACES.

Theory is presented for simulating the dynamic wheel forces generated by heavy road vehicles and the resulting dynamic response of road surfaces to these loads. Sample calculations are provided and the vehicle simulation is validated with data from full-scale tests. The methods are used in the accompanying paper to simulate the road damage done by a tandem-axle vehicle.

The contact of rough surfaces carrying pressure sensitive boundary layers

When two rough surfaces are loaded together it is well known that the area of true contact is very much smaller then the geometric area and that, consequently, local contact pressures are very much greater than the nominal value. If the asperities on each surface can be thought of as possessing smooth summits and each of the solids is elastically isotropic then the pressure distribution will consist of a series of small, but severe, Hertzian patches. However, if one of both of the surfaces in question is protected by a boundary layer then both the number and dimensions of these patches, and the form of the pressure distribution within them, will be modified. Recent experimental evidence from studies using both Atomic Force Microscopy and micro-tribometry suggests that boundary films produced by the action of commercial anti-wear additives, such as ZDTP, exhibit mechanical properties, which are affected by local values of pressure. These changes bring about further modifications to local conditions. These effects have been explored in a numerical model of rough surface contact and the implications for the mechanisms of surface distress and wear are discussed. © 2000 Elsevier Science B.V. All rights reserved.