title: Internally architectured materials with directionally asymmetric friction.
abstract: Internally Architectured Materials (IAMs) that exhibit different friction forces for sliding in the opposite directions are proposed. This is achieved by translating deformation normal to the sliding plane into a tangential force in a manner that is akin to a toothbrush with inclined bristles. Friction asymmetry is attained by employing a layered material or a structure with parallel 'ribs' inclined to the direction of sliding. A theory of directionally asymmetric friction is presented, along with prototype IAMs designed, fabricated and tested. The friction anisotropy (the ξ-coefficient) is characterised by the ratio of the friction forces for two opposite directions of sliding. It is further demonstrated that IAM can possess very high levels of friction anisotropy, with ξ of the order of 10. Further increase in ξ is attained by modifying the shape of the ribs to provide them with directionally dependent bending stiffness. Prototype IAMs produced by 3D printing exhibit truly giant friction asymmetry, with ξ in excess of 20. A novel mechanical rectifier, which can convert oscillatory movement into unidirectional movement by virtue of directionally asymmetric friction, is proposed. Possible applications include locomotion in a constrained environment and energy harvesting from oscillatory noise and vibrations.
authors.affiliation: 1] Centre for Advanced Hybrid Materials, Department of Materials Engineering, Monash University, Clayton, Victoria 3800, Australia [2] School of Fashion and Textiles, RMIT University, 25 Dawson Street, Brunswick, 3056, Australia.
authors.forename: Ehsan
authors.initials: E
authors.lastname: Bafekrpour
authors.affiliation: School of Civil and Resource Engineering, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia.
authors.forename: Arcady
authors.initials: A
authors.lastname: Dyskin
authors.affiliation: School of Mechanical and Chemical Engineering, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia.
authors.forename: Elena
authors.initials: E
authors.lastname: Pasternak
authors.affiliation: 1] Centre for Advanced Hybrid Materials, Department of Materials Engineering, Monash University, Clayton, Victoria 3800, Australia [2] Laboratory of Hybrid Nanostructured Materials, Moscow Institute of Steel and Alloys, Leninsky prosp. 4, Moscow 119049, Russia.
authors.forename: Andrey
authors.initials: A
authors.lastname: Molotnikov
authors.affiliation: 1] Centre for Advanced Hybrid Materials, Department of Materials Engineering, Monash University, Clayton, Victoria 3800, Australia [2] Laboratory of Hybrid Nanostructured Materials, Moscow Institute of Steel and Alloys, Leninsky prosp. 4, Moscow 119049, Russia.
authors.forename: Yuri
authors.initials: Y
authors.lastname: Estrin