31 research outputs found
Contact of a spherical probe with a stretched rubber substrate
We report on a theoretical and experimental investigation of the normal
contact of stretched neo-Hookean substrates with rigid spherical probes.
Starting from a published formulation of surface Green's function for
incremental displacements on a pre-stretched, neo-Hookean, substrate (L.H. Lee
\textit{J. Mech. Phys. Sol.} \textbf{56} (2008) 2957-2971), a model is derived
for both adhesive and non-adhesive contacts. The shape of the elliptical
contact area together with the contact load and the contact stiffness are
predicted as a function of the in-plane stretch ratios and
of the substrate. The validity of this model is assessed by contact
experiments carried out using an uniaxally stretched silicone rubber. for
stretch ratio below about 1.25, a good agreement is observed between theory and
experiments. Above this threshold, some deviations from the theoretical
prediction are induced as a result of the departure of the mechanical response
of the silicone rubber from the neo-Hokeean description embedded in the model
Elastic contact to nearly incompressible coatings -- Stiffness enhancement and elastic pile-up
We have recently proposed an efficient computation method for the
frictionless linear elastic axisymmetric contact of coated bodies [A. Perriot
and E. Barthel, J. Mat. Res. 19 (2004) 600]. Here we give a brief description
of the approach. We also discuss implications of the results for the
instrumented indentation data analysis of coated materials. Emphasis is laid on
incompressible or nearly incompressible materials (Poisson ratio ): we
show that the contact stiffness rises much more steeply with contact radius
than for more compressible materials and significant elastic pile-up is
evidenced. In addition the dependence of the penetration upon contact radius
increasingly deviates from the homogeneous reference case when the Poisson
ratio increases. As a result, this algorithm may be helpful in instrumented
indentation data analysis on soft and nearly incompressible layers
Adhesive contact of model randomly rough rubber surfaces
We study experimentally and theoretically the equilibrium adhesive contact
between a smooth glass lens and a rough rubber surface textured with spherical
microasperities with controlled height and spatial distributions. Measurements
of the real contact area versus load are performed under compression by
imaging the light transmitted at the microcontacts. is found to be
non-linear and to strongly depend on the standard deviation of the asperity
height distribution. Experimental results are discussed in the light of a
discrete version of Fuller and Tabor's (FT) original model (\textit{Proceedings
of the Royal Society A} \textbf{345} (1975) 327), which allows to take into
account the elastic coupling arising from both microasperities interactions and
curvature of the glass lens. Our experimental data on microcontact size
distributions are well captured by our discrete extended model. We show that
the elastic coupling arising from the lens curvature has a significant
contribution to the relationship. Our discrete model also clearly shows
that the adhesion-induced effect on remains significant even for
vanishingly small pull-off forces. Last, at the local asperity length scale,
our measurements show that the pressure dependence of the microcontacts density
can be simply described by the original FT model
Role of uncrosslinked chains in droplets dynamics on silicone elastomers
We report an unexpected behavior in wetting dynamics on soft silicone
substrates: the dynamics of aqueous droplets deposited on vertical plates of
such elastomers exhibits two successive speed regimes. This macroscopic
observation is found to be closely related to microscopic phenomena occurring
at the scale of the polymer network: we show that uncrosslinked chains found in
most widely used commercial silicone elastomers are responsible for this
surprising behavior. A direct visualization of the uncrosslinked oligomers
collected by water droplets is performed, evidencing that a capillarity-induced
phase separation occurs: uncrosslinked oligomers are extracted from the
silicone elastomer network by the water-glycerol mixture droplet. The sharp
speed change is shown to coincide with an abrupt transition in surface tension
of the droplets, when a critical surface concentration in uncrosslinked
oligomer chains is reached. We infer that a droplet shifts to a second regime
with a faster speed when it is completely covered with a homogeneous oil film
Weak non-linearities of amorphous polymer under creep
The creep behavior of an amorphous poly(etherimide) (PEI) polymer is
investigated in the vicinity of its glass transition in a weakly non linear
regime where the acceleration of the creep response is driven by local
configurational rearrangements. From the time shifts of the creep compliance
curves under increasing applied stresses in the range 1-15~\si{\mega\pascal},
we determine a macroscopic acceleration factor. At the start of creep, the
stress is homogeneous and the macroscopic acceleration can be assimilated to
that of the local rearrangements which is shown to vary as with , where is the local stress and is a
decreasing function of compliance. This experimental result is in agreement
with the recent theory of Long \textit{et al.} (\textit{Phys. Rev. Mat.} (2018)
\textbf{2}, 105601 ) which predicts . From a mean field approximation, we
interpret the variation of with compliance as the result of the development
of stress heterogneities during creep
Comportement viscoelastique et tenue en fatigue statique de composites verre/epoxy. Influence du vieillissement hydrothermique
SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 79736 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
Frottement et adhĂ©sion dâĂ©lastomĂšres dans des contacts en torsion
Les interactions entre adhésion et
frottement sont un sujet encore largement ouvert en Tribologie. Ces phénomÚnes
interviennent de façon cruciale lors de la mise en frottement â ou striction â de
contacts mettant en jeu des élastomÚres. Nous avons récemment développé une approche
expĂ©rimentale permettant dâapprĂ©hender ces phĂ©nomĂšnes Ă partir dâune mesure du champ de
cisaillement local Ă lâinterface. Par imagerie de contacts formĂ©s entre un Ă©lastomĂšre et
une lentille en verre, nous avons pu obtenir une mesure spatialement trÚs résolue du
champ de dĂ©placement induit par des sollicitations mĂ©caniques. Lâinversion de ce champ
de déplacement par des théories de mécanique du contact élastique fournit alors le champ
de cisaillement correspondant Ă lâinterface. Cette mĂ©thodologie a Ă©tĂ© appliquĂ©e Ă une
configuration originale de contact en torsion permettant lâĂ©tude de la rupture
dâadhĂ©sion dans des conditions de mode III pur plus simples Ă analyser que les modes
mixtes inhérents au glissement linéaire. Les observations révÚlent que la rupture de
lâadhĂ©sion met en jeu la propagation dâune zone de micro-glissement de la pĂ©riphĂ©rie
vers le centre du contact. Lâanalyse des champs de cisaillement au niveau de la zone de
fracture séparant les domaines adhésif et frottant permet de discuter des effets de
lâadhĂ©sion. Les rĂ©sultats expĂ©rimentaux seront discutĂ©s en sâappuyant sur un modĂšle de
zone cohésive intégrant les effets du frottement