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Item type:Publication, Access status: with files , On adhesive theories in multilayered interfaces, with particular regard to "surface force apparatus" geometryAdhesion is a key factor in many tribological processes, especially wear. We generalize a recent formulation for the indentation of a multilayered material using an efficient integral transform method, to the case of adhesion, using a simple energetic transformation in the JKR regime. Then, we specialize the study for the geometry of the Surface Force Apparatus, which consists of two thin layers on a substrate, where the intermediate layer is softer than the other two. We find the pull-off force under "force control" (i.e. for "soft" loading systems), as well as under "displacement control" (i.e. for "rigid" systems), as a function of the geometrical thicknesses and material properties ratios, and the method is fully implemented in a fast Mathematica code, available to the public (see Appendix).Publicationtype: Journal ArticleScopus© Citations 2 471 346 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Adhesion between a power-law indenter and a thin layer coated on a rigid substrateIn the present paper we investigate indentation of a power-law axisymmetric rigid probe in adhesive contact with a "thin layer" laying on a rigid foundation for both frictionless unbounded and bounded compressible cases. The investigation relies on the "thin layer" assumption proposed by Johnson, i.e. the layer thickness being much smaller than the radius of the contact area, and it makes use of the previous solutions proposed by Jaffar and Barber for the adhesiveless case. We give analytical predictions of the loading curves and provide indentation, load and contact radius at the pull-off. It is shown that the adhesive behavior is strongly affected by the indenter shape; nevertheless below a critical thickness of the layer (typically below 1 µm) the theoretical strength of the material is reached. This is in contrast with the Hertzian case, which has been shown to be insensitive to the layer thickness. Two cases are investigated, namely, the case of a free layer and the case of a compressible confined layer, the latter being more "efficient", as, due to Poisson effects, the same detachment force is reached with a smaller contact area. It is suggested that high sensitive micro-/nanoindentation tests may be performed using probes with different power law profiles for characterization of adhesive and elastic properties of micro-/nanolayers.Publicationtype: Journal ArticleScopus© Citations 15 340 272 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , The “sport” of rough contacts and the fractal paradox in wear lawsIn a recent paper in Science, namely, “The Contact Sport of Rough Surfaces”, Carpick summarizes recent efforts in a “contact challenge” to predict in detail an elastic contact between the mathematically defined fractal rough surfaces under (very little) adhesion. He also suggests the next steps that are needed to “fulfill da Vinci’s dream of understanding what causes friction”. However, this is disappointing as friction has been studied since the times of Leonardo and in 500 years, no predictive model has emerged, nor any significant improvement from rough contact models. Similarly, a very large effort we have spent on the “sport” of studying rough surfaces has not made us any closer to being able to predict the coefficient of proportionality between wear loss and friction dissipation which was already observed by Reye in 1860. Recent nice simulations by Aghababaei, Warner and Molinari have confirmed the criterion for the formation of debris of a single particle, proposed in 1958 by Rabinowicz, as well as Reye’s assumption for the proportionality with frictional loss, which is very close to Archard anyway. More recent investigations under variable loads suggest that Reye’s assumption is probably much more general than Archard’s law. The attempts to obtain exact coefficients with rough surfaces models are very far from predictive, essentially because for fractals most authors fail to recognize that resolution-dependence of the contact area makes the models very ill-defined. We also suggest that in the models of wear, rough contacts should be considered “plastic” and “adhesive” and introduce a new length scale in the problem.Publicationtype: Journal ArticleScopus© Citations 5 289 260 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Bone healing in mice : does it follow generic mechano-regulation rules?(University of Nis, 2015-12-01); ; Mechanical signals are known to influence bone healing progression. Previous studies have postulated inter-species differences in the mechanical regulation of the bone healing process. The aim of this study is to investigate whether mechanical “rules” explaining tissue formation patterns during bone healing in rat can be translated to a mouse model of bone regeneration. We have used an established mechano-biological computer model that uses finite element techniques to determine the mechanical conditions within the healing region and an agent-based approach to simulate cellular activity. The computer model is set up to simulate the course of bone healing in a femoral osteotomy model stabilized with an external fixator. Computer model predictions are compared to corresponding histological data. Generic mechano-regulation “rules” able to explain bone healing progression in the rat are not able to describe tissue formation over the course of healing in the mouse. According to the differentiation theory proposed by Prendergast, mechanical stimuli within the healing region immediately post-surgery are determined to be favorable for cartilage and fibrous tissue formation. In contrast, in vivo histological data showed initial intramembraneous bone formation at the periosteal side. These results suggest that in mice, bone does not require as much stability as is required in rat to reach timely healing. This finding emphasizes the need to further investigate the species-specific mechano-biological regulation of bone regeneration.Publicationtype: Journal Article16