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The contact mechanics of fractal surfaces

Nature Materials volume 2, pages 233–236 (2003)Cite this article

Abstract

The role of surface roughness in contact mechanics is relevant to processes ranging from adhesion to friction, wear and lubrication1,2. It also promises to have a deep impact on applied science, including coatings technology and design of microelectromechanical systems3. Despite the considerable results achieved by indentation experiments4, particularly in the measurement of bulk hardness on nanometre scales5,6,7, the contact behaviour of realistic surfaces, showing random multiscale roughness, remains largely unknown. Here we report experimental results concerning the mechanical response of self-affine thin films indented by a micrometric flat probe. The specimens, made of cluster-assembled carbon8,9,10,11 or of sexithienyl12,13, an organic molecular material, were chosen as prototype systems for the broad class of self-affine fractal interfaces, today including surfaces grown under non-equilibrium conditions14, fractures15, manufactured metal surfaces16,17,18,19 and solidified liquid fronts20. We observe that a regime exists in which roughness drives the contact mechanics: in this range surface stiffness varies by a few orders of magnitude on small but significant changes of fractal parameters. As a consequence, we demonstrate that soft solid interfaces can be appreciably strengthened by reducing both fractal dimension and surface roughness. This indicates a general route for tailoring the mechanical properties of solid bodies.

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Figure 1: AFM topographies acquired on self-affine thin films.
Figure 2: Shape and motion of the probe used for indentation experiments.
Figure 3: Experimental load–displacement curves for ns-C films (red and black symbols) and T6 films (blue symbols).
Figure 4: Comparison of experimental data with a theory assuming perfectly plastic contact.

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Acknowledgements

We thank E. Meyer and B.N.J. Persson for discussions and P. Milani for providing ns-C samples. We acknowledge support by INFM advanced project NANORUB and ASI grant CTRI/R/073/01.

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Authors and Affiliations

  1. INFM-Dipartimento di Fisica, Università di Genova, Via Dodecaneso 33, Genova, 16146, Italy

    Renato Buzio, Corrado Boragno, Francesco Buatier De Mongeot & Ugo Valbusa

  2. CNR-Istituto di Spettroscopia Molecolare, Via P. Gobetti 101, Bologna, 40129, Italy

    Fabio Biscarini

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  1. Renato Buzio
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  2. Corrado Boragno
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Correspondence to Renato Buzio.

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Buzio, R., Boragno, C., Biscarini, F. et al. The contact mechanics of fractal surfaces. Nature Mater 2, 233–236 (2003). https://doi.org/10.1038/nmat855

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