Tom Thomas

Wear of cylinder bore microtopography

Atomic force microscopy (AFM) reveals additional 3D topography information on tribology surfaces previously measured and evaluated by conventional 2D stylus technologies. This paper deals with the implications of the more detailed topographical information scanned from cast iron automotive cylinder liners. Worn and unworn surfaces measured both by AFM and stylus techniques were compared visually and quantitatively using an effective relocation technique. Quantitative comparison was made of 3D and 2D surface parameters, such as root mean square roughness, and slope, significant for the tribological behaviour of the surfaces. The extra surface features found by the AFM measurements (e.g. steeper slopes and more peaks and valleys) significantly change the numerical values of the roughness parameters, and this scale-dependent difference, when compared with conventional stylus-measured parameters, points to the possibilities of deepening the understanding of cylinder liner lubrication in the light of more finely detailed measurements.

On in-vivo skin topography metrology and replication techniques

Human skin metrology is an area of growing interest for many disciplines both in research and for commercial purposes. Changes in the skin topography are an early stage diagnosis tool not only for diseases but also give indication of the response to medical and cosmetic treatment. This paper focuses on the evaluation of in vivo and in vitro methodologies for accurate measurements of skin and outlines the quantitative characterisation of the skin topography. The study shows the applicability of in-vivo skin topography characterisation and also the advantages and limitations compared to conventional replication techniques. Finally, aspects of stripe projection methodology and 3D characterisation are discussed as a background to the proposed methodology in this paper.

Surfaces generated by abrasive finishing processes as self-affine fractals

Self-affine fractals offer a tool for characterising surface roughness. Fractal parameters are scale-invariant and can be derived from the Structure Function (SF): if computation of the SF is not practicable then parameters can be derived from roughness parameters available on many commercial software packages. The three-dimensional SF gives information about anisotropy. SFs can offer a demonstration of the effect of wear on surface topography in tribological investigations. Finally the SF can be used with material properties to obtain a low-pass cutoff for the calculation of surface data for use in rough contact mechanics.

The Stedman diagram revisited

The Stedman diagram has been used for some years to display aspects of the performance of instruments measuring surface roughness. Such diagrams are herein employed to compare the features of a range of proprietary measuring instruments, including contact and non-contact devices. An extension of the basic diagram is proposed, which would allow it to include a further aspect: the speed of data collection. Figures of merit based on the revised diagram are computed, which enable instruments to be ranked on these particular aspects of their performance. Contact instruments emerge as comparable to non-contact, as their slower rate of data acquisition can be offset by the greater area they can access in amplitude–wavelength space.

Implementation of Whitehouse's method for calculating properties of self-affine fractal profiles

Many software packages for roughness analysis offer the possibility of calculating the fractal dimension D of surface profiles by techniques, which assume them to be self-similar and therefore uniquely defined by D. However, fractal profiles are not self-similar but self-affine, so that two profiles of quite different roughnesses may share the same fractal dimension. To distinguish between them requires the calculation of an additional scaling factor, the so-called topothesy Λ. Traditionally, D and Λ are derived laboriously from the slope and intercept of the profiles structure function. A quicker and more convenient derivation from standard roughness parameters has been suggested by Whitehouse. Based on this derivation, it is here shown that D and Λ depend on two dimensionless numbers: the ratio of the mean peak spacing to the rms roughness and the ratio of the mean local peak spacing to the sampling interval. Using this approach, values of D and Λ are calculated from the measurements on surface profiles produced by polishing, plateau honing, and various single-point machining processes. Different processes are shown to occupy different regions in D–Λ space, and polished surfaces show a relationship between D and Λ, which is independent of the surface material.

10th International Conference on Metrology a Properties of Engineering Surfaces : Guest editorial

10th International Conference on Metrology & Properties of Engineering Surfaces : Guest editorial