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Three-level multi-scale modeling of electrical contacts
sensitivity study and experimental validation
Vladislav A. Yastrebov, Georges Cailletaud, Henry Proudhon
MINES ParisTech, PSL Research University, Centre desMatériaux,
CNRS UMR 7633
Evry,
[email protected]@[email protected]
Frederick S. Mballa Mballa, Sophie Noël, Philippe Testé,
Frédéric Houzé
Laboratoire Génie électrique et électronique de Paris,UMR
CNRS-CentraleSupelec 8507, UPMC and Paris-Sud
Universities, Gif sur Yvette,
[email protected]
[email protected]@geeps.centralesupelec.fr
Abstract—An experimental and numerical study of
electricalcontact for low currents in sphere-plane set-up is
presented. Athree-level multi-scale model is proposed. We use the
finiteelement analysis for macroscopic mechanical and
electricsimulations. It takes into account the setup geometry,
elasto-plastic mechanical behavior of contacting components in
thefinite-strain-plasticity framework and electrostatic properties.
Asensitivity analysis with respect to the brass plastic behavior
andto the thickness of coating layers is also performed. The
finiteelement results are used for an asperity-based model,
whichincludes elasto-plastic deformation of asperities and their
mutualelastic interactions. This model enables us to simulate the
realmorphology of contact spots at the roughness scale using
theexperimentally measured surface topography. Finally,
theGreenwood multi-spot model is used to estimate the
electricalcontact resistance. This three-level model yields results
which arein good agreement with experimental measurements carried
outin this study.
Keywords: electrical contact, elasto-plastic
material,experimental measurements, multi-scale simulations.
I. INTRODUCTIONElectrical contacts can be critical components in
electronic
systems. Their electrical resistance and life duration depend
onmany factors such as life cycles, interaction with theenvironment
(oxidation and corrosion), surface morphology,surface chemistry and
bulk material electrical properties andmechanical behavior. In this
paper we study bothexperimentally and numerically the influence of
the materialsproperties and the geometry of the coating layers on
theelectrical contact resistance between a copper-beryllium
sphereindenting a brass flat substrate coated with nickel and
gold.
Electrical contacts performances and reliability
criticallydepend on the characteristics and evolution of the
so-called realarea of contact, composed of numerous zones whose
size anddistribution are determined by the macroscopic shape
ofbodies, the roughness of their surfaces, their mechanical
andelectric properties as well as by mechanical loads and
involvedelectric currents. Contact resistance mainly results from
theconstriction of current lines at these contacting spots. A
projecthas been set-up joining the efforts of two laboratories in
thefields of experimental and numerical studies to clarify the
interplay of multiscale and multiphysics mechanisms in
thiscomplex interfacial region.
Phenomenon of electrical contact combines mechanical andelectric
effects, as the electric current can pass mainly throughcontact
spots which result from mechanical deformation ofcontacting solids.
Thus, if the coupling between the mechanicaland electric effects
may be assumed unidirectional (which isoften the case for low
currents and moderate loads) then thiscoupled problem can be split
in two sub-problems: first, themechanical contact problem, second,
the electrostatic problemfor the geometry obtained from the
solution of the first. Withthis consideration in hand, one can
combine independentmodels for mechanical and electrical contacts.
For the latter,the simplest model consists in approximation of the
realconducting zone by a single circular conducting spot at
theinterface between semi-infinite planes [1]; for the case of
twofinite cylinders contacting at a circular spot, first terms in
theTaylor's expansion of the solution were obtained in [2].
Ageneralization of these simple models is the multi-spotGreenwood
model [3], which approximates the contactinterface by a cluster of
conducting circular spots at theinterface between two conducting
half-spaces. Some furthergeneralizations of this model are also
available in the literature,including models which take into
account aging of contactspots prone to the growth of oxide films
[4], modelsconsidering the current density distribution inside
contact spots[5], models adapted for saturated contacts, when the
electricalcontact area approaches the apparent contact area while
thenumber of contact spots remains small [6], models
includinginterface film resistance [7] and smoothed version
ofGreenwood model, which represents the discrete sums byintegrals
with specific kernels [8].
Equivalently many models exist to solve the mechanicalcontact
between rough surfaces, whose solution determines themorphology of
the mechanical contact area, which may beconsidered as the upper
boundary for the electrical contact area[9]. Among these models
there are analytical asperity-basedmodels [10-13], which
approximate the effective roughness oftwo contacting surfaces by a
series of spherical or ellipsoidalnon-interacting asperities, with
specific distribution of theirgeometrical properties, which in turn
follow the randomprocess roughness model developed in [14,15]. A
multiscale
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generalization of asperity based models is suggested in
[16],which assumes however a kind of scale separation in thesurface
roughness. A different approach is developed in [17],which
considers a full contact for varying spectral content as astarting
point, and next extends the result for the case of partialcontacts
[18]. These models, associated approximations,limitations and
possible extensions are summarized in [19,20].Apart from these
analytical and semi-analytical models,various numerical methods may
be used to solve themechanical boundary value problem with contact
constrainsand explicitly integrated surface roughness for elastic
[21-23],visco-elastic [24] and elasto-plastic material models
[25,26].Different approaches and results of these full-scale
analyses aresummarized in [27].
In weakly coupled electro-mechanical contact problems,the
multiscale and multiphysics model is essentially acombination of
one of aforementioned mechanical andelectrical models. It is worth
mentioning that the mechanicalpart is sometimes simply neglected
and the spot distribution iseither simulated by a random model or
is obtained as a cross-section of a rough surface (geometrical
overlap model), see e.g.[8,28,29]. We refer to following references
[30-34], as to thestate of the art works, in which more complete
and accuratemodels are used for mechanical and electrical
contacts.Moreover, in [34] a link of aforementioned models with
arather different, incremental stiffness approach of Barber
isdiscussed [35]. In conclusion of the bibliographical review,
itshould be remarked that the electrical contact problem
isessentially similar to the one of thermal conductance throughthe
same configuration of contact spots, under condition thatthe
thermal expansion of solids and convective heat exchangeare
neglected. Hence, a rich bibliography on thermal contactconductance
[36,37] is partly relevant to our topic.
Our work combines within a unified framework severalnumerical
models for mechanical and electrical contacts. Amechanical finite
element model, which uses accurateconstitutive equations to capture
elasto-plastic materialbehavior, allows us to predict the
structural response forcomplex loading including cyclic loads in
contact. Animproved elasto-plastic asperity model with elastic
interactionsbetween asperities is then used to capture the
roughness effectusing the real topography of ours samples measured
withatomic force microscopy. This model provides us
withstatistically meaningful results and allows us to estimate
thedata dispersion . Finally, the original Greenwood model is
usedto analyze the electrical resistance of contact clusters.
Thismodel is validated on a series of fine experiments conducted
inthe project.
In Section II, the general methodology is described. SectionIII
presents the experimental setup and correspondingmeasurements. The
numerical approach (finite elementanalysis) as well as the
mechanical constitutive models whichare used in the simulations are
discussed in Section IV. Theroughness of the contacting surfaces is
analyzed in Section V;the multi-scale electro-mechanical model and
the associatedresults are presented in Section VI, followed by a
discussion.
II. METHODOLOGYThe general objective of the study is to predict
the
experimentally observed variation of the electrical
contactresistance for “real” sphere-plane contacts under cyclic
loadings using multiscale electro-mechanical simulations.
Toreach this objective, we integrate in the numerical model
(1)realistic constitutive material models (elasto-plastic
withisotropic and kinematic hardening), (2) an
accuraterepresentation of the roughness morphology of the
contactingbodies as measured by atomic force microscopy (AFM)
andinterferometric profilometry. The multiscale nature of
theelectric and mechanical contact manifests itself in a
separationof scales between the macroscopic geometry of the
contactingsolids and the microscopic roughness on a smaller scale
(Fig.1). In our study we use this scale separation in the
followingway. First, we conduct the mechanical simulation of
theindentation for various materials and coating
thicknessesassuming perfectly smooth surfaces (with no roughness).
Atevery load step, a complementary electrostatic simulation
isconducted to evaluate the electrical contact resistance.
Bothsimulations are carried out using a finite element softwarewith
implicit integration [38,39]. The effect of the roughnessand of the
microscopic deformation of asperities is then takeninto account in
a semi-analytical model of interactingasperities, which uses the
real roughness topography. Thismodel provides us with the exact
morphology of the contactspots, which is then used to estimate the
contact resistance viathe Greenwood model (Eq. (4) in [3]). The
sensitivity of themechanical model with respect to material
properties (initialyield stress) and to the thickness of coating
layers is thenanalyzed. The numerical results are compared with
theexperimental data.
Fig. 1. Separation of scales in the electric and mechanical
contact betweenrough solids: (a) the macroscopic scale is
characterized by nominally flat(smooth) surfaces, (b) at certain
magnification the discrete nature of thecontact is revealed. The
real contact area is considerably smaller than thenominal contact
area predicted at macroscopic scale with the Hertz contacttheory;
the real contact area can be approximated by a set of a-spots
(c).
III. SAMPLES AND EXPERIMENTAL SET-UPCyclic indentation tests
were performed on nominally flat
substrates by a copper beryllium ball of radius 1.75 mm.
Theflats were one millimeter thick brass alloy CuZn30 [CW505L,30
wt% Zn] planes coated with electrodeposited nickel andgold layers
both 1µm thick. Bare CuBe balls were used.Particular attention was
devoted to their surface. Several typesof experiments involving
different surface finishes of the ballswere performed. The balls
were either rinsed, thoroughlycleaned or mechanically polished
before the measurements.The experiments were conducted on a special
test benchdepicted in Fig. 2. The ball is mounted in a holder and
pressedagainst the plate with a stepping actuator (1/10 μm by
step),which is controlled by a displacement capacitive sensor
(apreliminary calibration procedure permits to convert the
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vertical displacement into the value of the normal force via
thestiffness of the guiding elastic rings). A water-cooling
circuitinsures the thermal stability of the set-up, specifically
thesensor’s measurements. The elements of the contact areconnected
to the electrical setup following the four-terminalmethod. The
electrical circuit includes a DC voltage/currentsource, an
electrometer and a digital voltmeter, all controlledover the
IEEE-488 bus. Once the required force is reached, aDC current I =
10mA is imposed to the contact; oppositepolarities are used to
eliminate thermoelectric voltages(current-reversal method) [40].
Measurements of the potentialdifference (U) enable us to calculate
the total electricresistance
(1)where Rc is the contact resistance and Rs is an
additionalresistance due to the bulk parts of ball-holder and brass
planebetween contact area and potential measurement terminals.
Inthe considered system Rs is estimated to be about 0.09 m.Under
assumption of elastic Hertzian contact and Holm'selectrical
contact, the first term can be estimated as follows:
(2)
where R is the ball radius, a is the contact radius, *
theeffective resistivity, E* the effective modulus, and * isusually
taken as a mean resistivity of CuBe and CuZn. Theeffective elastic
modulus is considered for the pair CuBe andCuZn
(3)
where v is the Poisson's ratio and E is the Young's modulus.
Fig. 2. (a) General layout of the contact resistance measurement
setup: 1 –rigid frame, 2 – capacitive force sensor, 3 – elastic
washers, 4 – insulatingblocks, 5 – ball holder, 6 – CuBe ball, 7 –
plane CuZn substrate coated withNi and Au, 8 – displacement
stepping motor. (b) Mounted CuBe ball, twowires (grey: current
feeding, red: voltage measurement) and the water coolingsystem
(tube); (c) sample holder for the plate (7) with connections.
Series of three loading-unloading cycles were performed
invarious conditions (ball finish and indentation
zone).Experimental data for a representative test as well as the
therange of experimental data obtained for different runs
(shadedarea) are depicted in Fig. 3 which shows the evolution of
themeasured resistance with respect to the applied load as well
asthe analytical estimation from Eq. (1,2). The first loading
isobserved to be distinct from the subsequent
loading-unloadingcurves because of the plasticity onset in the CuZn
substrate.
After the first hardening the system follows a stabilized
cycle:the loading and unloading curves follow the same
trajectories.The hysteresis is attributed to the kinematic
hardening inCuZn. The variability in the experimental results can
beexplained by differences in the surface states of the
balls(including roughness and contamination) and on the
localroughness of the plane at the location of the indentation.
Fig. 3. Experimental data and analytical estimation: left –
normal scale, right– logarithmic scale. Shaded area encloses all
the experimental data points forthe first three loading-unloading
cycles for different ball finishes and atdifferent locations on the
plate. The data points show three cycles of arepresentative
experiment; the dashed line shows a reference analyticalestimation
for elastic Hertzian contact Eq. (1,2) for Rs=0.09 m. Arrows
withthe color code indicate the load direction.
IV. NUMERICAL SIMULATIONS AND MATERIAL MODELSThe macroscopic
calculation is made on an axisymmetric
model, as shown in Fig. 4. A convergence study has beenperformed
in order to choose the optimum element size in thecontact zone.
Linear elements are used in the finite elementmesh to ensure an
optimal contact treatment. The nickel andgold layers are
discretized by two element layers in thickness.Elements in the
vicinity of the contact have a size of 500 nm.The number of
elements in contact reaches more than 80 at thepeak load. A
prescribed displacement is imposed on theequatorial plane of the
half sphere (A in Fig.4), which remainsflat due to a multi-point
constraint condition, while the bottomof the mesh representing the
substrate (B in Fig.4) is fixed invertical direction. The
mechanical simulation allows us toobtain the evolution of the
radius of the contact surface withrespect to the applied force. At
each load step, the two initiallyseparate meshes are fused in the
contact zone for thecomputation of the electrical problem. Doing
so, there is nodiscontinuity in electric potential at the boundary
between thesphere and the plane. The electrical model at
macroscopicscale thus assumes a perfect contact between the two
bodies(no resistive interfacial film).
Non linear constitutive equations were used for the
threematerials of the substrate (CuZn, Au and Ni), while an
elastic
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behavior is considered for the ball CuBe material model. Ineach
case, the material data are taken from literature(respectively
[41,42] and [43] for brass, gold and nickel). Thematerial models
incorporate either only non-linear kinematichardening (Au, Ni) or a
combination of isotropic and severalkinematic hardening (CuZn), in
order to correctly representcyclic responses of the materials. The
expressions aresummarized below, Eq.(4-9). The yield function, f,
in Eq.(4)uses the von Mises invariant, denoted by J, of the
effectivestress (the stress minus the kinematic variable), as
specified inEq.(5). The size of the elastic domain is defined by
the sum ofthe initial yield stress, y, and the isotropic hardening
variable,R. Two material parameters, namely the possible amount
ofhardening Q and the parameter characterizing the saturationrate,
b, are present in Eq.(6) to define isotropic hardening.
Theexpression of kinematic hardening has a driving termproportional
to the plastic strain rate, and a fading memoryterm proportional to
its actual value. The product D(p)characterizes the non linearity
of the stress evolution inside acycle. Its initial value is D and
the final D, that allowsrepresenting a sharper hysteresis loop
after a few cycles. Thevariable p brought into play in both Eq.(6)
and Eq.(7) is thecumulated plastic deformation, defined by its
rate, as shown inEq.(9).
(4)
(5)
(6)
(7)
(8)
(9)
where s is the deviatoric part of the stress tensor σ, the
dotrepresents the time derivative and the colon represents
tensorcontraction.
A simple sensitivity analysis was carried out with respectto the
yield stress of the brass: 53 MPa < σy < 550 MPa and tothe
thickness of both coating layers in the range 0.5
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orthogonal directions and by the height distribution; both
aredepicted in Figs. 7-8, respectively.
Fig. 5. Results of finite element analysis: contact radius
(left) and electricresistance (right) evolution in cycling loading.
The shaded area spans allexperimental results and the dashed line
is the reference analyticalestimation for elastic Hertzian contact
Eq. (1,2) computed for Rs=0.09m.
Fig. 6. Example of roughness measurements (AFM) on the coated
brasssubstrate.
The roughness is observed to be anisotropic (mainlybecause of
the rolling) with a particular scaling in terms of thePSD; the
height distribution is not Gaussian, with a ratherpronounced tail,
which arises due to numerous high asperities(see Fig. 8).
Rigorously, such a surface cannot be analyzed bystandard methods of
the random process model [14,15,44]. Itshould be noted that the
surface anisotropy does not imply astrong anisotropy of asperities,
equivalently the isotropy of thesurface does not imply the isotropy
of asperities. As wasshown in [45], according to the random process
model, themean ratio of asperity principal curvatures is
approximatelythree and the probability to find a circular asperity
is zero.
The surface roughness was analyzed numerically. First thedata
were filtered in Fourier space by a low pass cut-off filterat
|k|=512. Next the data were processed to identify allasperities and
their relevant properties: in-plane coordinatex,y, peak height z
and principal curvatures κ1,κ2. These datawere then used in the
following section to obtain the realisticcontact morphology (real
contact area) for different loads and
various indentation zones. Note that the roughness of the ballis
not included here.
Fig. 7. Power spectral density of the surface roughness in the
direction X(left) and Y (right): gray triangles represent all the
measured surfaces, redcircles correspond to the average data.
Fig. 8. Distribution of surface heights: gray triangles
represent all themeasured surfaces, red circles correspond to the
average data. In the inset anexample of a high asperity; whose
population changes significantly thedistribution tail.
VI. THREE-LEVEL MULTISCALE MODELA realistic estimation of the
electrical contact resistance
needs to take in consideration the roughness of the
contactingsurfaces. The approach in this work is based on
theconsecutive use of three computational tools:
(1) a finite element analysis to solve the indentationproblem
for smooth coated substrate within finite strainplasticity
framework;
(2) a semi analytical iterative tool based on
elasto-plasticdeformation of elastically interacting
asperities;
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(3) Greenwood's model [3] to estimate the electrical
contactresistance through a localized cluster of a-spots:
(10)
where ai is the radius of the i-th contact spot and sij is
thedistance between centers of spots i and j.
In model (1) (described in detail in Section IV) for eachvalue
of the load F we obtain the contact radius a0 and thepressure
distribution in the contact zone p(r), r
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hysteresis, comes from a kinematic hardening in the
brasssubstrate. To capture the non-linear material behavior,
ourmechanical finite element analysis uses adequate materialmodels,
which include kinematic and isotropic hardening forisotropic
J2-plasticity [48]. In agreement with experiments, itenables us to
distinguish between the first loading and thesubsequent cycles,
however, the stabilized hysteresis, found inexperiments, was not
reproduced in simulations for variousmaterial parameters. The
electrical contact resistanceevaluated at macroscopic scale under
assumption of perfectlyconducting interface does not display a
stabilized cycle for therange of tested material and geometrical
parameters (see Fig.5). Such a strong hysteresis should be
associated withkinematic hardening of the brass at macroscopic
scale and ofCuBe and Au at the scale of asperities. Frictional
dissipationand adhesion may also contribute to this hysteresis. For
thesubsequent studies, the frictional contribution has to
beconsidered and all material models have to be more
properlyadjusted especially in terms of the kinematic
hardening.However, in the framework of the currently used
asperitybased model, the cyclic elasto-plastic deformation at
asperityscale cannot be properly taken into account, which is also
thecase for most elasto-plastic models.
Fig. 10. a-spots in the multiscale model for different contact
spot radius (a)a=10 μm, (b) a=16 μm, (c) a=22 μm.
The roughness of the studied surface (rolled brass coatedwith
nickel and gold), while being frequently encountered inreal world
applications, is not typical for theoretical models, inwhich
roughness is often assumed to be fractal, Gaussian andisotropic.
The surface in this work obeys none of theseassumptions and
requires an accurate characterization andinterpretation. For
example, the contact spots, aligned in therolling direction, form
contact (conducting) bands separatedby non-contact regions (see
Fig. 10).
Comparison between the three-level computational modelproposed
in the paper and experiments shows that the modelcaptures
quantitatively the evolution of the electrical contactresistance
during the first loading. However, it cannot predictthe large
variability of experimentally obtained results (this isprobably
because of too different finishes of the ball used inexperiments).
On the contrary, the model predicts thenarrowing of the resistance
values dispersion with increasingload, while in the experiments the
variability remains large forhigh loads (compare dots with shaded
area in Fig. 9). Thereare several reasons for this discrepancy:
1. apart from the contact roughness, the contactresistance is
also associated with possible presence of oxide
films or other contamination on contacting surfaces:
theelectrical contact area is not equivalent to the
mechanicalcontact area and can be significantly smaller in presence
ofpoorly conducting spots [9];2. the roughness and the surface
state of the CuBe ballwas neglected (probably it is the most
criticalapproximation);3. the passage from the finite element
macroscopicresult to the asperity based model requires a lot
ofassumptions, which in realistic case are only partly
satisfied(see Section IV);4. the asperity based model cannot take
into account themerge of contact zones associated with different
asperities[49] and the curvature variation of asperities;5. Hertz
contact theory even being extended to elasto-plastic material
behavior cannot take into account thelayered composition of the
substrate and the finite strainhardening as well as it cannot
capture a cyclic loading withkinematic hardenings.
To avoid the oversimplification of the elasto-plastic
Hertzcontact used for asperities, one may use a properly
tunedheuristic model based on a series of finite element
simulationsof a single asperity on a layered substrate [26]. To
overcomethe ensemble of the aforementioned difficulties of
themultiscale model a full scale finite element [26] or
boundaryelement model for elasto-plastic material [50] (or
theircombination) with an accurate representation of the
surfaceroughness should be used. This mechanical model should
becomplemented with a subsequent full scale finite
elementsimulation of the current flux through the contact
interfacesimilar to what was done in [31]. However, to solve
properlyboth the mechanical and electric problems at the
roughnessscale, a significantly finer meshes would be needed,
seediscussions in [22,51]. This task appears realistic in
thepresent state of hardware and finite element software.
Note that such a weak electro-mechanical coupling ispossible
only for low electric currents as the Joule heating inthe interface
is negligibly small and thus does not affectmaterial properties of
contacting elements. However, whenconsidering high electric
currents a strongly coupled thermo-electro-mechanical model with
roughness should beintroduced similar to [31].
Finally, regardless all inherent drawbacks, the
three-levelmultiscale and multiphysics model for electrical
contactsyields reasonable results in good agreement with
experiments.The model uses the real roughness topography and has
noadjustable parameters, only material mechanical and
electricalproperties.
ACKNOWLEDGMENTThis work has benefited from the financial support
of the
LabeX LaSIPS (ANR-10-LABX-0040-LaSIPS) managed bythe French
National Research Agency under the"Investissements d'avenir"
program (n°ANR-11-IDEX-0003-02).
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REFERENCES[1] R. Holm, “Electrical Contacts, Theory and
Applications,” Springer-
Verlag, Berlin, 1967.[2] R. Timsit, “The potential distribution
in a constricted cylinder,” Journal
of Physics D: Applied Physics, vol. 10, no. 15, pp. 2011-2017,
1977.[3] J.A. Greenwood, “Constriction resistance and the real area
of contact,”
British Journal of Applied Physics, vol. 17(12) pp. 1621-1632,
1966.[4] R.D Malucci, “Multispot model of contacts based on surface
features,"
In Electrical Contacts. Proceedings of 36th IEEE Holm Conference
on,pp. 625-634, 1990.
[5] I. Minowa, and M. Nakamura, “Simulation for the current
densitydistribution in a contact spot,” Electronics and
Communications in Japan(Part II: Electronics), vol. 77(2) pp.
88-95, 1994.
[6] L. Boyer, S. Noël, and F. Houzé, “Constriction resistance of
a multispotcontact: an improved analytical expression,” In
Electrical Contacts.Proceedings of the 36th IEEE Holm Conference
on, and the 15thInternational Conference on Electrical Contacts,
pp. 646-650. IEEE,1990.
[7] L. Boyer, “Contact Resistance Calculations: Generalizations
ofGreenwood's Formula Including Interface Films,” IEEE Transactions
onComponents and Packaging Technologies, vol. 24(1), pp. 50-58,
2001.
[8] Y.H. Jang, J.R. Barber, “Effect of contact statistics on
electrical contactresistance,” Journal of Applied Physics, vol.
94(11), pp. 7215-7221,2003.
[9] R. S. Timsit, “Electrical contact resistance: Fundamental
principles,” inElectrical Contacts: Principles and Applications, P.
G. Slade, Ed. CRCPress, pp. 3-111, 2013.
[10] J.A. Greenwood, J.B.P. Williamson, “Contact of nominally
flatsurfaces,” Proceedings of the Royal Society of London. Series
A:Mathematical, Physical and Engineering Sciences, vol. 295, pp.
300-319, 1966.
[11] A.W. Bush, R.D. Gibson, T.R. Thomas, “The elastic contact
of a roughsurface,” Wear, vol. 35(1), pp. 87-111, 1975.
[12] T.R. Thomas, “Rough Surfaces,” 2nd edition, Imperial
College Press,1999.
[13] L. Afferrante, G. Carbone, G. Demelio, “Interacting and
coalescingHertzian asperities: a new multiasperity contact model,”
Wear, vol. 278-279, pp. 28-33, 2012.
[14] M.S. Longuet-Higgins, “Statistical properties of an
isotropic randomsurface,” Philosophical Transactions of the Royal
Society A:Mathematical, Physical & Engineering Sciences, vol.
250, pp. 157-174,1957.
[15] P.R. Nayak, “Random process model of rough surfaces,”
Journal ofLubrication Technology (ASME), vol. 93, pp. 398-407,
1971.
[16] W.E. Wilson, S.V. Angadi, and R.L. Jackson, “Surface
separation andcontact resistance considering sinusoidal
elastic-plastic multi-scalerough surface contact,” Wear, vol.
268(1), pp. 190-201, 2010.
[17] B.N.J Persson, “Theory of rubber friction and contact
mechanics.Journal of Chemical Physics, vol. 115, 3840-3861,
2001.
[18] C. Yang, B.N.J. Persson, “Contact mechanics: contact area
andinterfacial separation from small contact to full contact,”
Journal ofPhysics: Condensed Matter, vol. 20(21), pp. 215214,
2008.
[19] M. Paggi, M. Ciavarella, “The coefficient of
proportionality k betweenreal contact area and load, with new
asperity models,” Wear, vol. 268,pp. 1020-1029, 2010.
[20] G. Carbone, F. Bottiglione, “Asperity contact theories: do
they predictlinearity between contact area and load?” Journal of
the Mechanics andPhysics of Solids, vol. 56, pp. 2555-2572,
2008.
[21] C. Campañá, M.H. Müser, “Practical Green's function
approach to thesimulation of elastic semi-infinite solids, Physical
Review B, vol. 74, pp.075420, 2006.
[22] L. Pastewka, N. Prodanov, B. Lorenz, M.H. Müser, M.O.
Robbins,B.N.J. Persson, “Finite-size scaling in the interfacial
stiffness of roughelastic contacts, Physical Review E, vol. 87, pp.
062809, 2013.
[23] C. Putignano, L. Afferrante, G. Carbone, G. Demelio, “A new
efficientnumerical method for contact mechanics of rough
surfaces,”
International Journal of Solids and Structures, vol. 49(2), pp.
338-343,2012.
[24] C. Putignano, G. Carbone, “A review of boundary
elementsmethodologies for elastic and viscoelastic rough contact
mechanics,”Physical Mesomechanics, vol. 17(4), pp. 321-333,
2014.
[25] L. Pei, S. Hyun, J.F. Molinari, M. Robbins, “Finite element
modeling ofelasto-plastic contact between rough surfaces,” Journal
of the Mechanicsand Physics of Solids, vol. 53, pp. 2385-2409,
2005.
[26] V.A. Yastrebov, J. Durand, H. Proudhon, and G. Cailletaud,
“Roughsurface contact analysis by means of the finite element
method and of anew reduced model,” Comptes Rendus Mécanique, vol.
339(7), pp. 473-490, 2011.
[27] V.A. Yastrebov, G. Anciaux, J.F. Molinari, “From
infinitesimal to fullcontact between rough surfaces: evolution of
the contact area,”International Journal of Solids and Structures,
vol. 52, pp. 83-102, 2015.
[28] R.D. Malucci, “Multi-spot model showing the effects of
nano-spotsizes,” In Electrical Contacts. Proceedings of the 51st
IEEE HolmConference on, pp. 291-297. IEEE, 2005.
[29] A. Majumdar, C. Tien, “Fractal network model for
contactconductance,” Journal of Heat Transfer, vol. 113(3), pp.
516-525, 1991.
[30] B. Arrazat, P.Y. Duvivier, V. Mandrillon, and K. Inal,
“Discrete analysisof gold surface asperities deformation under
spherical nano-indentationtowards electrical contact resistance
calculation,” In Electrical Contacts,Proceedings of the 57th Holm
Conference on, pp. 1-8. IEEE, 2011.
[31] P. Shanthraj, O. Rezvanian, and M.A. Zikry,
“Electrothermomechanicalfinite-element modeling of metal
microcontacts in MEMS,” Journal ofMicroelectromechanical Systems,
vol. 20(2), pp. 371-382, 2011.
[32] M. Myers, M. Leidner, H. Schmidt, H. Schlaak, “Extension
andExperimental Verification of a New 'First Contact' Method to
ModelPerformance of Multilayer Contact Interfaces,” In Electrical
Contacts.Proceedings of the 54th IEEE Holm Conference on, 1-8.
IEEE, 2008.
[33] R.L. Jackson, R.D. Malucci, S. Angadi, J.R. Polchow, “A
SimplifiedModel of Multiscale Electrical Contact Resistance and
Comparison toExisting Closed Form Models,” In Electrical Contacts.
Proceedings ofthe 54th IEEE Holm Conference on, 2009.
[34] S. Lee, H. Cho, Y.H. Jang, “Multiscale electrical contact
resistance inclustered contact distribution,” Journal of Physics D:
Applied Physics,vol. 42, pp. 165302-165309, 2009.
[35] J.R. Barber, “Bounds on the electrical resistance between
contactingelastic rough bodies,” Proceedings of the Royal Society
of London.Series A: Mathematical, Physical and Engineering
Sciences, vol.459(2029), pp. 53-66, 2003.
[36] M.M. Yovanovich, “Four decades of research on thermal
contact, gap,and joint resistance in microelectronics,” IEEE
Transactions onComponents and Packaging Technologies, vol. 28(2),
pp. 182-206,2005.
[37] C.V. Madhusudana, “Thermal contact conductance,” Springer,
2ndedition, 2014.
[38] J. Besson, and R. Foerch, “Large scale object-oriented
finite elementcode design,” Computer Methods in Applied Mechanics
andEngineering, vol. 142(1), pp. 165-187 , 1997.
[39] http://www.zset-software.com/[40] S. Guessab, L. Boyer, F.
Houzé, S. Noël, and O. Schneegans, “Influence
of temperature and pressure on the static contact resistance of
vacuumheat-treated polyacrylonitrile films,” Synthetic metals, vol.
118(1), pp.121-132, 2001.
[41] J.V. Carstensen, “Structural Evolution and Mechanisms of
Fatigue inPolycrystalline Brass,” PhD thesis, Riso National
Laboratory, Roskilde,Denmark, 1998.
[42] J.H. Kim, A. Nizami, Y. Hwangbo, B. Jang, H.J. Lee, C.S Woo
et al.“Tensile testing of ultra-thin films on water surface,”
Naturecommunications vol. 4, 2013.
[43] R. Schwaiger, B. Moser, M. Dao, N. Chollacoop, and S.
Suresh, “Somecritical experiments on the strain-rate sensitivity of
nanocrystallinenickel,” Acta materialia, vol 51(17) pp. 5159-5172,
2003.
[44] P.R. Nayak, “Random process model of rough surfaces in
plasticcontact,” Wear, vol. 26, pp. 305-333, 1973.
-
[45] J.A. Greenwood, “A simplified elliptic model of rough
surface contact,”Wear, vol.261, pp. 191-200, 2006.
[46] Z. Song, K. Komvopoulos, “Elastic-plastic spherical
indentation:deformation regimes, evolution of plasticity, and
hardening effect,”Mechanics of Materials, vol. 61, pp. 91-100,
2013.
[47] F.S. Mballa Mballa, V.A. Yastrebov, G. Cailletaud, S. Noël,
F. Houzé,and Ph. Testé, “Electric Contact: Experiments and
Multiscale Electro-Mechanical Simulations,” unpublished.
[48] J. Besson, G. Cailletaud, J.L. Chaboche, and S. Forest,
“Non-linearmechanics of materials,” Springer, 2009.
[49] J.A. Greenwood, “A note on Nayak's third paper,” Wear, vol.
262(1), pp.225-227, 2007
[50] C. Jacq, D. Nelias, G. Lormand, and D. Girodin,
“Development of athree-dimensional semi-analytical elastic-plastic
contact code,” Journalof Tribology, vol. 124(4), pp. 653-667,
2002.
[51] V.A. Yastrebov, G. Anciaux, J.F. Molinari, “Contact
betweenrepresentative rough surfaces,” Physical Review E, vol.
86(3),pp.035601, 2012.
I. IntroductionII. MethodologyIII. Samples and Experimental
Set-UpIV. Numerical simulations and material modelsV. Surface
roughnessVI. Three-Level Multiscale modelVII. Conclusion