### Michele Ciavarella

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## Pubblicazioni

*Il seguente elenco è solo una parte della Produzione scientifica del docente.*

Per maggiori informazioni consultare il Catalogo Istituzionale dei prodotti della Ricerca (IRIS) .

Papangelo A and Ciavarella M.

**On the limits of quasi-static analysis for a simple Coulomb frictional oscillator in response to harmonic loads**.*JOURNAL OF SOUND AND VIBRATION*339:280–289, 2015. URL, DOI BibTeX@article{ 11589_3161, author = "Papangelo A and Ciavarella M", title = "On the limits of quasi-static analysis for a simple Coulomb frictional oscillator in response to harmonic loads", year = 2015, journal = "JOURNAL OF SOUND AND VIBRATION", volume = 339, abstract = "Due to the nonlinearity of the Coulomb friction law, even the simplest models of interfaces in contact show a very rich dynamic solution. It is often desirable, especially if the frequency of loading is only a fraction of the first natural frequency of the system, to replace a full dynamic analysis with a quasi-static one, which obviously is much simpler to obtain. In this work, we study a simple Coulomb frictional oscillator with harmonic tangential load, but with constant normal load. It is found that the quasi-static solution (which has only 2 stops) captures approximately the displacement peak as long as the forcing frequency is low enough for the dynamic solution to have 2 or, even better, more than 2 stops. Instead, the velocity peak is not correctly estimated, since the velocity becomes highly irregular due to the stick–slip stops, whose number increases without limit for zero frequency. In this sense, the classical quasi-static solution, obtaining by cancelling inertia terms in the equilibrium equations, does not coincide with the limit of the full dynamic solution at low frequencies. The difference is not eliminated by adding a small amount of viscous damping, as only with critical damping, the dynamic solution is very close to the quasi-static one. Additional discrepancies arise above a limit frequency whose value depends on the ratio of the tangential load to the limit one for sliding, and correspond to when the dynamic solution turns from 2 to 0 stop per cycle.", url = "http://www.sciencedirect.com/science/article/pii/S0022460X14009468", doi = "10.1016/j.jsv.2014.11.028.", pages = "280--289" }

Afferrante L, Ciavarella M and Demelio G.

**Adhesive contact of the Weierstrass profile**.*PROCEEDINGS. A*471, 2015. URL, DOI BibTeX@article{ 11589_55819, author = "Afferrante L and Ciavarella M and Demelio G", title = "Adhesive contact of the Weierstrass profile", year = 2015, journal = "PROCEEDINGS. A", volume = 471, keywords = "Adhesion; Energy release rate; Roughness; Weierstrass profile; Mathematics (all); Engineering (all); Physics and Astronomy (all)", url = "http://rspa.royalsocietypublishing.org/content/royprsa/471/2182/20150248.full.pdf", doi = "10.1098/rspa.2015.0248" }

Ciavarella M and Afferrante L.

**Adhesion of rigid rough contacts with bounded distribution of heights**.*TRIBOLOGY INTERNATIONAL*, 2015. DOI BibTeX@article{ 11589_55821, author = "Ciavarella M and Afferrante L", title = "Adhesion of rigid rough contacts with bounded distribution of heights", year = 2015, journal = "TRIBOLOGY INTERNATIONAL", doi = "10.1016/j.triboint.2015.10.033" }

Ciavarella M.

**On the rocking and walking flat punch: Effect of elastic dissimilarity**.*TRIBOLOGY INTERNATIONAL*83:130–138, 2015. URL, DOI BibTeX@article{ 11589_5844, author = "Ciavarella M", title = "On the rocking and walking flat punch: Effect of elastic dissimilarity", year = 2015, journal = "TRIBOLOGY INTERNATIONAL", volume = 83, abstract = "With an appropriate combination of constant and varying loads, a punch may “walk” or “ratchet”, if rigid body motion is allowed. Here, a full numerical analysis is conducted to study the effect of material dissimilarity on a simple configuration. It is found that walking starts from much lower loads than in the case of similar materials, and higher shift per cycle is predicted with the same load and rocking motion, even accounting for the change of the plane strain modulus. Both elastic shakedown or cyclic dissipation are found, and convergence in these cases is relatively slow, whereas it occurs after 2 cycles of oscillations, in the walking case.", url = "http://www.sciencedirect.com/science/article/pii/S0301679X14004149", doi = "10.1016/j.triboint.2014.11.012.", pages = "130--138" }

Barber JR and Ciavarella M.

**JKR solution for an anisotropic half space**.*JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS*64:367–376, 2014. URL, DOI BibTeX@article{ 11589_6798, author = "Barber JR and Ciavarella M", title = "JKR solution for an anisotropic half space", year = 2014, journal = "JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS", volume = 64, abstract = "In this paper, the classical JKR theory of the adhesive contact of isotropic elastic spheres is extended to consider the effect of anisotropic elasticity. The contact area will then generally be non-circular, but in many cases it can reasonably be approximated by an ellipse whose dimensions are determined by imposing the energy release rate criterion at the ends of the major and minor axes. Analytical expressions are obtained for the relations between the contact force, the normal displacement and the ellipse semi-axes. It is found that the eccentricity of the contact area decreases during tensile loading and for cases when the point load solution can be accurately described by only one Fourier term, it is almost circular at pull-off, permitting an exact closed form solution for this case. As in the isotropic JKR solution, the pull-off force is independent of the mean elastic modulus, but we find that anisotropy increases the pull-off force and this effect can be quite significant.", keywords = "Indentation, ; Anisotropic elasticity, ; Adhesion,", url = "http://www.sciencedirect.com/science/article/pii/S0022509613002500", doi = "http://dx.doi.org/10.1016/j.jmps.2013.12.002", pages = "367--376" }

Stingl B, Ciavarella M and Hoffmann N.

**Frictional dissipation in elastically dissimilar oscillating Hertzian contacts**.*INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES*72:55–62, 2013. URL, DOI BibTeX@article{ 11589_3160, author = "Stingl B and Ciavarella M and Hoffmann N", title = "Frictional dissipation in elastically dissimilar oscillating Hertzian contacts", year = 2013, journal = "INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES", volume = 72, abstract = "We consider the problem of a cyclic Hertzian indentation between elastically dissimilar materials. In the case of loading, the problem was solved by Spence in a series of seminal papers, where he proved a relationship between the solution for a rigid square-shaped punch, to that for a power-law indenter. For example, the stick area is a constant ratio of the contact area, independently on the shape of the punch. “Unfortunately”, on unloading, many of the simple properties of the self-similar loading case are lost, there is a complicated development of an external region of slip which cycles in the two directions (forward and back-slip), and an inner region which continues to slip in the forward direction of the first loading cycle. However, this inner region gradually disappears, and further cyclic loading generates a convergence to a steady state solution which involves residual “locked-in” tangential slip displacements in a permanent stick zone, provided the contact is not fully unloaded. Dissipation in the steady state therefore occurs only in the external region of slip, and we provide some results for the energy dissipation per cycle, as a function of the governing parameters: coefficient of friction, Dundurs’ dissimilarity constant, normal load amplitude. We also show the likely independence of energy dissipation on initial conditions, limited to the possible scenario of overloading. It is seen that dependence of energy dissipation per cycle on load amplitude is closer to quadratic than to cubic, and this may explain some experimental findings which so far were not expected from oscillatory loading of elastically similar half-spaces.", keywords = "Contact mechanics, ; Hertzian contact, ; Cyclic loading,", url = "http://www.sciencedirect.com/science/article/pii/S0020740313000970", doi = "http://dx.doi.org/10.1016/j.ijmecsci.2013.03.012.", pages = "55--62" }

Ciavarella M.

**A simple approximate expression for finite life fatigue behaviour in the presence of 'crack-like' or 'blunt' notches**.*FATIGUE & FRACTURE OF ENGINEERING MATERIALS & STRUCTURES*35:247–256, 2012. DOI BibTeX@article{ 11589_4044, author = "Ciavarella M", title = "A simple approximate expression for finite life fatigue behaviour in the presence of 'crack-like' or 'blunt' notches", year = 2012, journal = "FATIGUE & FRACTURE OF ENGINEERING MATERIALS & STRUCTURES", volume = 35, abstract = "In this note, we explore the possibility of simple extensions of the heuristic El Haddad formula for finite life, as an approximate expression valid for crack-like notches, and of the Lukas and Klesnil equation for blunt notches. The key starting point is to assume, in analogy to the Basquin power-law SN curve for the fatigue life of the uncracked (plain) specimen, a power law for the finite lifeintrinsic El Haddad crack size. The approach has similarities with what recently proposed by Susmel and Taylor as a Critical Distance Method for Medium-Cycle Fatigue regime. Reasonable agreement is found with the fatigue data of Susmel and Taylor for notches, and in particular the error seems smaller in finite life than for infinite life, where these equations are already used. In these respects, the present proposal can be considered as a simple empirical unified approach for rapid assessment of the notch effect under finite life.", doi = "10.1111/j.1460-2695.2011.01612.x", pages = "247--256" }

Greenwood JA, Putignano C and Ciavarella M.

**A Greenwood & Williamson theory for line contact**.*WEAR*270:332–334, 2011. DOI BibTeX@article{ 11589_4045, author = "Greenwood JA and Putignano C and Ciavarella M", title = "A Greenwood & Williamson theory for line contact", year = 2011, journal = "WEAR", volume = 270, abstract = "Analyses of rough surface contact sometimes study the two-dimensional problem to avoid some of the difficulties of three-dimensional contacts, or to reduce the size of the calculations in numerical work. But two-dimensional elastic contacts introduce their own difficulties. The mean real contact pressures will be much lower than in three dimensions, and will depend strongly on the thickness of the 'slab' used to represent the elastic half-space. (C) 2010 Elsevier B.V. All rights reserved.", doi = "10.1016/j.wear.2010.11.002", pages = "332--334" }

Afferrante L, Ciavarella M, Dell'Orco M and Demelio G.

**Rolling cylinder on an elastic half-plane with harmonic oscillations in normal force and rotational speed. Part II: Energy dissipation receptances and example calculations of corrugation in the short-pitch range**.*INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES*53:1000–1007, 2011. DOI BibTeX@article{ 11589_6368, author = "Afferrante L and Ciavarella M and Dell'Orco M and Demelio G", title = "Rolling cylinder on an elastic half-plane with harmonic oscillations in normal force and rotational speed. Part II: Energy dissipation receptances and example calculations of corrugation in the short-pitch range", year = 2011, journal = "INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES", volume = 53, doi = "10.1016/j.ijmecsci.2011.08.005", pages = "1000--1007" }

Afferrante L, Ciavarella M and Sackfield A.

**Rolling cylinder on an elastic half-plane with harmonic oscillations in normal force and rotational speed. Part I: Solution of the partial slip contact problem**.*INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES*, pages 989–999, 2011. DOI BibTeX@article{ 11589_51951, author = "Afferrante L and Ciavarella M and Sackfield A", title = "Rolling cylinder on an elastic half-plane with harmonic oscillations in normal force and rotational speed. Part I: Solution of the partial slip contact problem", year = 2011, journal = "INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES", doi = "10.1016/j.ijmecsci.2011.08.004", pages = "989--999" }

Putignano C, Ciavarella M and Barber JR.

**Frictional energy dissipation in contact of nominally flat rough surfaces under harmonically varying loads**.*JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS*59:2442–2454, 2011. DOI BibTeX@article{ 11589_1901, author = "Putignano C and Ciavarella M and Barber JR", title = "Frictional energy dissipation in contact of nominally flat rough surfaces under harmonically varying loads", year = 2011, journal = "JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS", volume = 59, abstract = "If the nominal contact tractions at an interface are everywhere below the Coulomb friction limit throughout a cycle of oscillatory loading, the introduction of surface roughness will generally cause local microslip between the contacting asperities and hence some frictional dissipation. This dissipation is important both as a source of structural damping and as an indicator of potential fretting damage. Here we use a strategy based on the Ciavarella-Jager superposition and a recent solution of the general problem of the contact of two half spaces under oscillatory loading to derive expressions for the dissipation per cycle which depend only on the normal incremental stiffness of the contact, the external forces and the local coefficient of friction. The results show that the dissipation depends significantly on the relative phase between the oscillations in normal and tangential load a factor which has been largely ignored in previous investigations. In particular, for given load amplitudes, the dissipation is significantly larger when the loads are out of phase. We also establish that for small amplitudes the dissipation varies with the cube of the load amplitude and is linearly proportional to the second derivative of the elastic compliance function for all contact geometries, including those involving surface roughness. It follows that experimental observations of less than cubic dependence on load amplitude cannot be explained by reference to roughness alone, or by any other geometric effect in the contact of half spaces. (C) 2011 Elsevier Ltd. All rights reserved.", doi = "10.1016/j.jmps.2011.09.005", pages = "2442--2454" }

Paggi M and Ciavarella M.

**The coefficient of proportionality K between real contact area and load, with new asperity models**.*WEAR*268:1020–1029, 2010. DOI BibTeX@article{ 11589_4046, author = "Paggi M and Ciavarella M", title = "The coefficient of proportionality K between real contact area and load, with new asperity models", year = 2010, journal = "WEAR", volume = 268, abstract = "Most recent numerical works on fractal surfaces have simply compared the low load limit of the coefficient of proportionality kappa of the relationship between real contact area and load In particular, that provided by Persson's theory, and that obtained from the Bush. Gibson and Thomas (BGT-A) asperity contact theory, which is a generalized form of the Greenwood and Williamson (GW) one. The two theories differ only by a numerical constant kappa = root 8/pi approximate to 1 6 vs kappa = root 2 pi approximate to 2 5, but neither of the two provide an accurate prediction, Persson's value being generally too low, and BGT-A's limit being only valid for extremely large separations A detailed numerical comparison using a range of generated fractal surfaces permits to compare the existing models, finding for example that bandwidth is more Important than Gaussianity of the surfaces. Then, we propose two new theoretical equations generalizing GW and BGT to take into account interaction effects in an approximate way (GW-I and BGT-I, respectively), which significantly improve the accuracy of original asperity models. Further, as a practical alternative to the tribologist, we suggest a new very simple discrete form of the GW model (called GW-RI) whose accuracy is similar to BGT-I, but with much lower computational cost, comparable to analytical solutions since the latter require the evaluation of the variance of the profile slopes, sigma(2)(m), with a surface defined at a given set of points The GW-RI model additionally avoids an ambiguity over how to define numerically the variance of the profile slopes, sigma(2)(m)", keywords = "Contact mechanics; Fractals; Greenwood-Williamson theory; Real contact area; Roughness", doi = "10.1016/j.wear.2009.12.038", pages = "1020--1029" }

Afferrante L and Ciavarella M.

**Short pitch corrugation of railway tracks with wooden or concrete sleepers: An enigma solved?**.*TRIBOLOGY INTERNATIONAL*43:610–622, 2010. DOI BibTeX@article{ 11589_1902, author = "Afferrante L and Ciavarella M", title = "Short pitch corrugation of railway tracks with wooden or concrete sleepers: An enigma solved?", year = 2010, journal = "TRIBOLOGY INTERNATIONAL", volume = 43, abstract = {British Railways (BR) in the 1970s observed an increased level of short pitch corrugation after the electrification of the West Coast main line, which involved (among other things) the change from wooden to concrete sleepers. Here, using a simple model for the two systems, we find a different sensitivity to lateral creepage, a doubled growth at the "pinned-pinned" resonance regime shifted from about 600 to about 1000 Hz, but a reduced growth in the 300-600 Hz range, where most data for both systems seem to lye. Hence, despite it would be tempting to associate the increased corrugation simply to the increased (doubled) peak of normal load, there is discrepancy in the corresponding wavelength predicted by the model. Hence, there is still an "enigma" about the reasons for the enhanced corrugations. (C) 2009 Elsevier Ltd. All rights reserved.}, doi = "10.1016/j.triboint.2009.09.010", pages = "610--622" }

Ciavarella M and Monno F.

**A comparison of multiaxial fatigue criteria as applied to rolling contact fatigue**.*TRIBOLOGY INTERNATIONAL*43:2139–2144, 2010. DOI BibTeX@article{ 11589_9971, author = "Ciavarella M and Monno F", title = "A comparison of multiaxial fatigue criteria as applied to rolling contact fatigue", year = 2010, journal = "TRIBOLOGY INTERNATIONAL", volume = 43, abstract = {Under rolling contact fatigue (RCF) existing multiaxial fatigue criteria are not well validated and predict significantly different results. Results for simple typical Hertzian RCF pure rolling are shown as previously remarked by the authors, the Dang Van criterion applied to RCF gives over-optimistic fatigue limits, due to the large influence of the hydrostatic component of the stress, particularly under some conditions. It is here shown that the "simpler" Crossland criterion gives a more realistic fatigue limit of Hertzian peak pressure, and the more "elaborate" Papadopoulos criterion gives an even more conservative value, of about 3-3.5 times higher than the fatigue limit under pure shear. It is suggested that the multiaxial criteria per se do not give a reliable estimate of the fatigue limit, and perhaps an integration within Weibull-like theories should be attempted in the future, as well as a more "unified" approach and mix of criteria taken from gears design, rolling contact in railways, and in rolling bearings. (C) 2010 Elsevier Ltd. All rights reserved.}, doi = "10.1016/j.triboint.2010.06.003", pages = "2139--2144" }

Afferrante L and Ciavarella M.

**Corrugation models and the "roaring rails" enigma: a simple analytical contact mechanics model based on a perturbation of Carter's solution**.*JOURNAL OF MECHANICS OF MATERIALS AND STRUCTURES*4:191–209, 2009. DOI BibTeX@article{ 11589_9013, author = "Afferrante L and Ciavarella M", title = {Corrugation models and the "roaring rails" enigma: a simple analytical contact mechanics model based on a perturbation of Carter's solution}, year = 2009, journal = "JOURNAL OF MECHANICS OF MATERIALS AND STRUCTURES", volume = 4, abstract = {Corrugation in railways, and especially short pitch corrugation (30-80 mm), is still considered something of an enigma, despite extensive research. Models based on repeated impacts or differential wear, such as Grassie and Johnson's (1985) and Bhaskar et al.'s (1997), seem not to be conclusive, or not to suggest the correct wavelength. Further models have been suggested, either linear (Frederick, Valdivia, Hempelmann, Vassilly and Vincent) or nonlinear (Mueller), but most suggest a constant frequency mechanism invariably connected to vertical resonances of the system either in the low frequency range (50-100 Hz, the resonance of the vehicle's unsprung mass on the track stiffness referred to here as the "P2 resonance", close to the Hertz contact resonance), or at about 1000 Hz (pinned-pinned resonance, in which the rail vibrates almost as if it were a beam pinned at sleepers), or even higher frequencies still (1700-1800 Hz). The experimental data available, by contrast, do not fit these frequency ranges. The discrepancy is tentatively explained with "contact filtering" and varied traffic ideas, but do not convince completely. In this paper, we stress the importance of wheel inertia in coupling the oscillations of normal load, with the variations of tangential load and longitudinal creepage. A simple zeroth order perturbation of the classical rolling contact solutions is suggested, which obtains good qualitative agreement with experimental evidence. The model also leads to the recognition that vertical resonances are not crucial in explaining corrugation, as believed in previous models, since we use an extremely simple model of an Euler beam with no elastic support, having no resonances. Important factors for the growth of corrugation are the friction coefficient and the tractive ratio. High longitudinal creepage is needed to promote rapid development, and this can arise from curving, hunting motion or misaligned axles, and is probably exacerbated by high contact conformity, since this increases the fluctuating component of longitudinal creepage due to the movement of the contact point. With discrete supports, we expect a modulation of corrugation wavelength and amplitude, but this requires a separate investigation, not just the inclusion of pinned-pinned resonance.}, doi = "10.2140/jomms.2009.4.191", pages = "191--209" }

Afferrante L and Ciavarella M.

**Short-pitch rail corrugation: a possible resonance-free regime as a step forward to explain the “enigma”?**.*WEAR*266:934–944, 2009. DOI BibTeX@article{ 11589_2475, author = "Afferrante L and Ciavarella M", title = "Short-pitch rail corrugation: a possible resonance-free regime as a step forward to explain the “enigma”?", year = 2009, journal = "WEAR", volume = 266, abstract = {Rail corrugation has been noticed at least for 100 years, but (particularly short pitch one in the range 20-80 mm) has been considered an enigma because measured corrugation wavelength did not relate well with wear-instability models. The apparently large number of governing parameters has resulted in many independent efforts to generate models, which do not entirely correspond to the collected experimental evidence, and therefore there is still some uncertainty over the possible critical factors dominating the phenomenon. We show in the paper that there is a simple possible mechanism of corrugation in longitudinal direction, apparently not noticed before in the literature by other authors, which does not necessarily correspond to a resonance in the system, not even the pinned-pinned resonance associated with the effect of discrete supports, but may depend on geometrical and loading conditions (normal load, creepage ratio, shape of the contact area, etc.), in general overall agreement with experiments. Additionally, some approximate calculations including discrete supports, using a typical concrete sleepers vertical receptance of BR use, show no evidence of corrugation mechanism at the pinned-pinned resonance, at least in the longitudinal direction. A full comparison between lateral and longitudinal mechanisms would depend on the particular value of the lateral creepage vs. longitudinal creepage, system-specific. The present "resonance-free" mechanism is a possible alternative for the data which fall outside the pinned-pinned resonance range. (C) 2008 Elsevier B.V. All rights reserved.}, doi = "10.1016/j.wear.2008.12.003", pages = "934--944" }

Hoffmann NP, Ciavarella M, Stolz U and Weiss C.

**The effect of long-wavelength stiffness variation on wear pattern generation**.*JOURNAL OF SOUND AND VIBRATION*322:785–797, 2009. DOI BibTeX@article{ 11589_9972, author = "Hoffmann NP and Ciavarella M and Stolz U and Weiss C", title = "The effect of long-wavelength stiffness variation on wear pattern generation", year = 2009, journal = "JOURNAL OF SOUND AND VIBRATION", volume = 322, abstract = "In many systems with moving contacts spatially periodic wear patterns related to structural resonances emerge. Often, however, the structural properties of file sliding system vary periodically with position. Based on a generic minimal model the present work investigates the effect of a spatially periodic structural stiffness on wear pattern generation. Linear stability of the resulting wear dynamics is analysed using spatial Floquet analysis. It turns out that the emergence of wear patterns by instability can in general not be evaluated through stability analysis based oil spatially local parameters alone. A spatially periodic stiffness can stabilize file system, depending on the wavelength and the amplitude of file spatially periodic parameter variation. The relevance of the effect is discussed and open points are addressed. (C) 2008 Elsevier Ltd. All rights reserved.", doi = "10.1016/j.jsv.2008.11.027", pages = "785--797" }

Barber JR, Ciavarella M, Afferrante L and Sackfield A.

**Effect of small harmonic oscillations during the steady rolling of a cylinder on a plane**.*INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES*50:1344–1353, 2008. DOI BibTeX@article{ 11589_2016, author = "Barber JR and Ciavarella M and Afferrante L and Sackfield A", title = "Effect of small harmonic oscillations during the steady rolling of a cylinder on a plane", year = 2008, journal = "INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES", volume = 50, abstract = "If a wheel rolling over a rail transmits a tangential traction, frictional microslip occurs in part of the contact area, resulting in energy dissipation and localized wear. If the applied forces oscillate in time, the resulting wear will be non-uniform, resulting in 'corrugations' that can grow with progressive passes, depending on the dynamics of the overall system. In this paper, a linear perturbation method is used to obtain closed-form expressions for the receptance of a two-dimensional rolling contact subjected to small oscillations in normal force and rotational speed superposed on a mean value in the limit of large coefficient of friction. Corresponding expressions are also obtained for the amplitude and phase of the energy dissipation in the contact, which is expected to correlate with the local wear rate. The results are compared with a simpler Winkler model of the contact and with other models that have been used for the analysis of rail corrugation. Surprisingly good agreement is obtained with numerical results due to Gross-Thebing for the receptances due to oscillations in rotational speed. (C) 2008 Elsevier Ltd. All rights reserved.", doi = "10.1016/j.ijmecsci.2008.07.011", pages = "1344--1353" }

Ciavarella M, Dibello S and Demelio G.

**Conductance of rough random profiles**.*INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES*45:879–893, 2008. DOI BibTeX@article{ 11589_10068, author = "Ciavarella M and Dibello S and Demelio G", title = "Conductance of rough random profiles", year = 2008, journal = "INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES", volume = 45, abstract = "Recently, the real contact area and the compliance and electrical resistance for a rough surface defined with a Weierstrass series have been studied under the assumption that superposed self-affine sine waves had well separated wavelengths, extending the celebrated procedures pioneered by Archard [Archard, J.F., 1957. Elastic deformation and the laws of friction. Proc. R. Soc. Lond. A 243, 190-205]. Here, more realistic fractal rough surface profiles are considered, by using the Weierstrass series with random phases, and with much lower separation of the various scales, using a full or a hybrid numerical/analytical technique. A non-linear layer algorithm is developed which is a very efficient approximate tool to study this problem, avoiding the need for averaging over various realizations of profiles with random phases. The multiscale problem is solved by a cascade of 2-scales problems, each of which is solved with a few elements for an imposed contact area, deriving load as a function of indentation and the conductance by differentiation using Barber's analogy theorem. Dimensionless results for the conductance as a function of applied pressures show that the conductance seems to be close to a power law at low loads, and is nearly linear at intermediate loads (following the normalized single sinusoidal case except at the origin). At high loads, the conductance becomes strongly dependent on fractal dimension because of weak dependence on the contribution of small wavelength scales (higher order terms in the series). Since roughness tends to be squeezed out, the conductance tends to increase more than linearly (more so, the smaller is the fractal dimension). However, another limit could be found in terms of the finite size of the specimen, which may suggest reaching a finite limit. The resulting curves could then be sigmoidal, as confirmed by qualitative comparisons with experiments in the literature. (c) 2007 Elsevier Ltd. All rights reserved.", doi = "10.1016/j.ijsolstr.2007.09.009", pages = "879--893" }

Afferrante L and Ciavarella M.

**Thermo-Elastic Dynamic Instability (TEDI) - a review of recent results**.*JOURNAL OF ENGINEERING MATHEMATICS*61:285–300, 2008. DOI BibTeX@article{ 11589_10067, author = "Afferrante L and Ciavarella M", title = "Thermo-Elastic Dynamic Instability (TEDI) - a review of recent results", year = 2008, journal = "JOURNAL OF ENGINEERING MATHEMATICS", volume = 61, abstract = "Frictional instabilities arise in a number of engineering and scientific contexts, when the presence of friction renders unstable the uniform motion between parts under nominally uniform conditions. Various classes of friction instabilities exist, those involving friction weakening with speed, and those at constant coefficient of friction. In the latter class, in turn, there are Dynamic Instabilities (DI) and Thermo-Elastic Instabilities (TEI). Recently, by including inertia terms in the formulations of the simple models already studied, the merging of TEI and DI has shown that, although the coupling of dynamic and thermal terms is generally weak (given the significant difference in the typical time scales of the two processes), thermal effects are capable of making otherwise neutrally stable dynamic modes unstable, rendering the new form of instability TEDI (ThermoElastoDynamic Instability) potentially interesting in a number of applications. Some results involving 1D and 2D models of TEDI are reviewed.", doi = "10.1007/s10665-007-9184-0", pages = "285--300" }

## Attività Didattiche

Meccanica dei materiali (Taranto) [Laurea in Ingegneria Meccanica] (Primo semestre - Terzo Anno)

Progettazione meccanica I (Taranto) [Laurea in Ingegneria Meccanica] (Primo semestre - Terzo Anno)

Optimization methods [Laurea Magistrale in Ingegneria Meccanica] (Secondo semestre - Primo Anno)