In materials science, asperity, defined as "unevenness of surface, roughness, ruggedness" (from the Latin asper—"rough"[1]), has implications (for example) in physics and seismology. Smooth surfaces, even those polished to a mirror finish, are not truly smooth on a microscopic scale. They are rough, with sharp, rough or rugged projections, termed "asperities". Surface asperities exist across multiple scales, often in a self affine or fractal geometry.[2] The fractal dimension of these structures has been correlated with the contact mechanics exhibited at an interface in terms of friction and contact stiffness.
The top image shows asperities under no load. The bottom image depicts the same surface after applying a load.
When two macroscopically smooth surfaces come into contact, initially they only touch at a few of these asperity points. These cover only a very small portion of the surface area. Friction and wear originate at these points, and thus understanding their behavior becomes important when studying materials in contact. When the surfaces are subjected to a compressive load, the asperities deform through elastic and plastic modes, increasing the contact area between the two surfaces until the contact area is sufficient to support the load.
The relationship between frictional interactions and asperity geometry is complex and poorly understood. It has been reported that an increased roughness may under certain circumstances result in weaker frictional interactions while smoother surfaces may in fact exhibit high levels of friction owing to high levels of true contact.[3]
The Archard equation provides a simplified model of asperity deformation when materials in contact are subject to a force. Due to the ubiquitous presence of deformable asperities in self affine hierarchical structures,[4] the true contact area at an interface exhibits a linear relationship with the applied normal load.[2]
^ abHanaor, D. A. H.; Gan, Y.; Einav, I. (2015). "Contact mechanics of fractal surfaces by spline assisted discretisation". International Journal of Solids and Structures. 59: 121–131. arXiv:2106.01466. doi:10.1016/j.ijsolstr.2015.01.021.
^Zappone, B.; Rosenberg, K.J.; Israelachvili, J. (2007). "Role of nanometer roughness on the adhesion and friction of a rough polymer surface and a molecularly smooth mica surface". Tribology Letters. 26 (3): 191–201. doi:10.1007/s11249-006-9172-y. ISSN 1023-8883. S2CID 137230450.
^ Carbone, G.; Bottiglione, F. (2008). "Asperity contact theories: Do they predict linearity between contact area and load?". Journal of the Mechanics and Physics of Solids. 56 (8): 2555. Bibcode:2008JMPSo..56.2555C. doi:10.1016/j.jmps.2008.03.011.
External links
The dictionary definition of asperity at Wiktionary
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asperity, materials, science, this, description, needs, additional, citations, verification, please, help, improve, this, article, adding, citations, reliable, sources, unsourced, material, challenged, removed, find, sources, asperity, materials, science, news. This description needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Asperity materials science news newspapers books scholar JSTOR April 2015 Learn how and when to remove this template message In materials science asperity defined as unevenness of surface roughness ruggedness from the Latin asper rough 1 has implications for example in physics and seismology Smooth surfaces even those polished to a mirror finish are not truly smooth on a microscopic scale They are rough with sharp rough or rugged projections termed asperities Surface asperities exist across multiple scales often in a self affine or fractal geometry 2 The fractal dimension of these structures has been correlated with the contact mechanics exhibited at an interface in terms of friction and contact stiffness The top image shows asperities under no load The bottom image depicts the same surface after applying a load When two macroscopically smooth surfaces come into contact initially they only touch at a few of these asperity points These cover only a very small portion of the surface area Friction and wear originate at these points and thus understanding their behavior becomes important when studying materials in contact When the surfaces are subjected to a compressive load the asperities deform through elastic and plastic modes increasing the contact area between the two surfaces until the contact area is sufficient to support the load The relationship between frictional interactions and asperity geometry is complex and poorly understood It has been reported that an increased roughness may under certain circumstances result in weaker frictional interactions while smoother surfaces may in fact exhibit high levels of friction owing to high levels of true contact 3 The Archard equation provides a simplified model of asperity deformation when materials in contact are subject to a force Due to the ubiquitous presence of deformable asperities in self affine hierarchical structures 4 the true contact area at an interface exhibits a linear relationship with the applied normal load 2 See also EditSurface roughness Burnishing metal References Edit Asperity Oxford English Dictionary Online ed Oxford University Press Subscription or participating institution membership required a b Hanaor D A H Gan Y Einav I 2015 Contact mechanics of fractal surfaces by spline assisted discretisation International Journal of Solids and Structures 59 121 131 arXiv 2106 01466 doi 10 1016 j ijsolstr 2015 01 021 Zappone B Rosenberg K J Israelachvili J 2007 Role of nanometer roughness on the adhesion and friction of a rough polymer surface and a molecularly smooth mica surface Tribology Letters 26 3 191 201 doi 10 1007 s11249 006 9172 y ISSN 1023 8883 S2CID 137230450 Carbone G Bottiglione F 2008 Asperity contact theories Do they predict linearity between contact area and load Journal of the Mechanics and Physics of Solids 56 8 2555 Bibcode 2008JMPSo 56 2555C doi 10 1016 j jmps 2008 03 011 External links Edit The dictionary definition of asperity at Wiktionary This article about materials science is a stub You can help Wikipedia by expanding it vte Retrieved from https en wikipedia org w index php title Asperity materials science amp oldid 1122160860, wikipedia, wiki, book, books, library,
