title: Surface strain measurements of fingertip skin under shearing.
abstract: The temporal evolution of surface strain, resulting from a combination of normal and tangential loading forces on the fingerpad, was calculated from high-resolution images. A customized robotic device loaded the fingertip with varying normal force, tangential direction and tangential speed. We observed strain waves that propagated from the periphery to the centre of the contact area. Consequently, different regions of the contact area were subject to varying degrees of compression, stretch and shear. The spatial distribution of both the strains and the strain energy densities depended on the stimulus direction. Additionally, the strains varied with the normal force level and were substantial, e.g. peak strains of 50% with a normal force of 5 N, i.e. at force levels well within the range of common dexterous manipulation tasks. While these observations were consistent with some theoretical predictions from contact mechanics, we also observed substantial deviations as expected given the complex geometry and mechanics of fingertips. Specifically, from in-depth analyses, we conclude that some of these deviations depend on local fingerprint patterns. Our data provide useful information for models of tactile afferent responses and background for the design of novel haptic interfaces.
authors.affiliation: Institute of Neuroscience (IoNS), Université catholique de Louvain, Brussels and Louvain-la-Neuve, Belgium Institute of Information and Communication Technologies, Electronics and Applied Mathematics (ICTEAM), Université catholique de Louvain, Brussels and Louvain-la-Neuve, Belgium Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL, USA.
authors.forename: Benoit
authors.identifier: http://orcid.org/0000-0003-3974-7921
authors.initials: B
authors.lastname: Delhaye
authors.affiliation: Institute of Neuroscience (IoNS), Université catholique de Louvain, Brussels and Louvain-la-Neuve, Belgium Institute of Information and Communication Technologies, Electronics and Applied Mathematics (ICTEAM), Université catholique de Louvain, Brussels and Louvain-la-Neuve, Belgium.
authors.forename: Allan
authors.identifier: http://orcid.org/0000-0002-1094-4596
authors.initials: A
authors.lastname: Barrea
authors.affiliation: Physiology Section, Department of Integrative Medical Biology, Umeå University, Umeå, Sweden.
authors.forename: Benoni B
authors.identifier: http://orcid.org/0000-0001-9010-5612
authors.initials: BB
authors.lastname: Edin
authors.affiliation: Institute of Neuroscience (IoNS), Université catholique de Louvain, Brussels and Louvain-la-Neuve, Belgium Institute of Information and Communication Technologies, Electronics and Applied Mathematics (ICTEAM), Université catholique de Louvain, Brussels and Louvain-la-Neuve, Belgium.
authors.forename: Philippe
authors.identifier: http://orcid.org/0000-0003-2032-3635
authors.initials: P
authors.lastname: Lefèvre
authors.affiliation: Institute of Neuroscience (IoNS), Université catholique de Louvain, Brussels and Louvain-la-Neuve, Belgium Cliniques Universitaires Saint-Luc, Physical and Rehabilitation Medicine Department, Université catholique de Louvain, Brussels and Louvain-la-Neuve, Belgium jean-louis.thonnard@uclouvain.be.
authors.forename: Jean-Louis
authors.identifier: http://orcid.org/0000-0003-2081-9139
authors.initials: JL
authors.lastname: Thonnard
mesh_terms: D005385:Fingers; D006801:Humans; D033081:Shear Strength; D012867:Skin; D013314:Stress, Mechanical
keywords: friction; skin mechanics; tactile perception; touch