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CATEGORIES:Engineering - Mechanics and Materials Seminar Seri
 es
SUMMARY:Calculation of adhesion between elastic spheres fr
 om molecular forces - Dr Jim Greenwood\, CUED
DTSTART;TZID=Europe/London:20120203T140000
DTEND;TZID=Europe/London:20120203T150000
UID:TALK35726AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/35726
DESCRIPTION:The Johnson\, Kendall\,& Roberts (JKR) theory of a
 dhesion in effect uses fracture mechanics to show 
 that the adhesive force between two elastic sphere
 s will be. But earlier Bradley\, by integration of
  the forces between every pair of “molecules” of t
 he two spheres\, calculated the force to be: and s
 ince the JKR value is independent of the elastic m
 odulus\, it too applies to rigid spheres\, and we 
 have a conflict.  Tabor offered a resolution of th
 e conflict\, later confirmed when Derjaguin and hi
 s collaborators introduced a method of analysing t
 he problem by assuming that the forces due to the 
 molecular interactions could be replaced by a surf
 ace force law acting across the gap between the tw
 o bodies\, and that the surface force law could be
  treated as applying a surface traction to the bod
 ies. The deformation is then calculated by the usu
 al methods of elastic contact mechanics.\nThe unex
 pected results of this analysis will be described\
 ; and are generally accepted when the spheres are 
 large and the region of interaction small..... in 
 effect for a “Hertzian” geometry. But recent advan
 ces in MEMS and in studying biological adhesion\, 
 as well as in powder technology\, have drawn atten
 tion to small spheres with large areas of ‘contact
 ’: and here the basic equivalence between the mole
 cular forces and a surface force law is suspect. V
 arious ‘improvements’ will be described: particula
 rly the author’s preferred option with its absurd 
 conclusion that the radius of the ‘contact’ area c
 an exceed the radius of the sphere!
LOCATION:Oatley Seminar Room\, Department of Engineering
CONTACT:Ms Helen Gardner
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