Biomedical Engineering Reference
In-Depth Information
a
b
c
Surface 1
Adsorbed
liquid
Instability
Flow
Surface 2
e
f
d
Solid contact
g
r
Fig. 3
Outline of the adhesive contact between two surfaces. (
a
) Approaching. (
b
) The force of
molecular attraction draws the liquid into the region where the surfaces are closer. (
c
) When liquid
films fuse and the meniscus is formed, more liquid is attracted to the region. (
d
) The approach ends
when the roughness of the surfaces touch themselves. (
e
) Withdrawing. (
f
) Detached surfaces.
(
g
) Detail of the contact showing the geometric variables
(continued)
The second radius is neglected in (
1
), because it is much higher than the
first (r
2
r
1
). The adhesion pressure becomes
2
d
p
YL
.d /
Q
D
:
(2)
h5. At a distance d
1
when the roughness of the surfaces touch each other
a reaction force arises, for the contact between solids (see Fig.
3
d). At
this distance the adhesion pressure is maximal, i.e. max .p
YL
.d //
D
p
YL
.d
1
/. For preventing the interpenetration of the solid surfaces, the
