Hi Everyone,
I am just wondering if there is any specific formula for contact stress determination of a ball with particular radius under specific applied load in contact with hydrogel surface. Can we use hertzian contact for a soft material such as hydrogel?
If the particles are sufficiently rigid (elastic) and under the action of contact they do not have plastic deformations, then the sticking / tearing process becomes completely reversible. For such a case, Deryagin's theory leads to the formula
N = 3.14 r F
where N is the minimum value of the external force. which is necessary to attach to adhered convex particles so that they are detached from each other, F is the absolute value of the Gibbs interaction energy calculated per 1 cm2 of two plane-parallel surfaces, the r-parameter that depends on the geometry of the surfaces and for the spheres with radii r1 and r2 is
r = 2r1r2/r1+r2
В.В. Яминский ... Коагуляционные контакты в дисперсных системах. Москва. Химия. !982.
Surface tension or adhesion may play in such cases, depending on the properties of surfaces. Two references are given for your interest.
Mech. Mater. 2013, 56, 65-70
Int. J. Solid. Struct. 2016, 84, 133.
@ Gangfeng Wang Thanks for the reply, however I am not talking about nano indentation, and the ball size is in the range of few millimeters, so is there any specific formula to analytically determine the contact stress of flat surface of hydrogel when it is placed under a loaded rigid sphere ?
It is not necessary to be nano indentation. It depends on the ratio of surface tension to elastic modulus of hydrogel. Since the elastic modulus of hydrogel is low, i.e. 1Mpa,--Kpa. When the real contact radius reduces to microns, surface tension may get into playing. If the ball size is few millimeters, the real contact radius could be in microns. Otherwise, Hertzian contact model gives a perfect prediction.
@Gangfeng Wang Is there any analytical formula for determining the contact pressure, with taking surface tension into consideration?
@Mohammadreza Arjmandi
the pressure can not be presented anallytically with the account of surface tension.
@Yue Zheng, thanks for your answer. Please post the link to Professor Hu`s research articles if you know any.
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