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| 1 | The research works of Coulomb and Amontons and generalized laws of friction显示文摘The paper is devoted to the contributions of Coulomb and Amontons to the physics of friction from the viewpoint of current discussions and attempts to formulate generalized laws of friction. | Elena POPOVA Valentin L.POPOV | 2015 | Friction2015，3，2： | 4 |
| 2 | Adhesive wear and particle emission: Numerical approach based on asperity-free formulation of Rabinowicz criterion显示文摘In 1953 Archard formulated his general law of wear stating that the amount of worn material is proportional to the normal force and the sliding distance, and is inversely proportional to the hardness of the material. Five years later in 1958, Rabinowicz suggested a criterion determining the minimum size of wear particles. Both concepts became very popular due to their simplicity and robustness, but did not give thorough explanation of the mechanisms involved. It wasn't until almost 60 years later in 2016 that Aghababaei, Warner and Molinari(AWM) used quasi-molecular simulations to confirm the Rabinowicz criterion. One of the central quantities remained the 'asperity size'. Because real surfaces have roughness on many length scales, this size is often ill-defined. The present paper is devoted to two main points: First, we generalize the Rabinowicz-AWM criterion by introducing an 'asperity-free' wear criterion, applicable even to fractal roughness. Second, we combine our generalized Rabinowicz criterion with the numerical contact mechanics of rough surfaces and formulate on this basis a deterministic wear model. We identify two types of wear: one leading to the formation of a modified topography which does not wear further and one showing continuously proceeding wear. In the latter case we observe regimes of least wear, mild wear and severe wear which have a clear microscopic interpretation. The worn volume in the region of mild wear occurs typically to be a power law of the normal force with an exponent not necessarily equal to one. The method provides the worn surface topography after an initial settling phase as well as the size distribution of wear particles. We analyse different laws of interface interaction and the corresponding wear laws. A comprehensive parameter study remains a task for future research. | Valentin L.POPOV Roman POHRT | 2018 | Friction2018，6，3： | 3 |
| 3 | 60 years of Rabinowicz' criterion for adhesive wear显示文摘60 years ago, in 1958, Ernest Rabinowicz published a 5 page paper titled 'The effect of size on the looseness of wear fragments' where he suggested a criterion determining the minimum size of wear particles. The criterion of Rabinowicz is based on the consideration of the interplay of elastic energy stored in 'asperities' and the work of separation needed for detaching a wear particle. He was probably the first researcher who explicitly emphasized the role of adhesion in friction and wear. In a recent paper in Nature Communications, Aghababaei, Warner and Molinari confirmed the criterion of Rabinowicz by means of quasi-molecular dynamics and illustrated the exact mechanism of the transition from plastic smoothing to formation of wear debris. This latter paper promoted the criterion of Rabinowicz to a new paradigm for current studies of adhesive wear. The size arguments of Rabinowicz can be applied in the same form also to many other problems, such as brittle-ductile transition during indentation, cutting of materials or ultimate strength of nano-composites. | Elena POPOVA Valentin L.POPOV Dae-Eun KIM | 2018 | Friction2018，6，3： | 1 |
| 4 | Adhesion and friction in hard and soft contacts: theory and experiment显示文摘This paper is devoted to an analytical,numerical,and experimental analysis of adhesive contacts subjected to tangential motion.In particular,it addresses the phenomenon of instable,jerky movement of the boundary of the adhesive contact zone and its dependence on the surface roughness.We argue that the'adhesion instabilities'with instable movements of the contact boundary cause energy dissipation similarly to the elastic instabilities mechanism.This leads to different effective works of adhesion when the contact area expands and contracts.This effect is interpreted in terms of“friction”to the movement of the contact boundary.We consider two main contributions to friction:(a)boundary line contribution and(b)area contribution.In normal and rolling contacts,the only contribution is due to the boundary friction,while in sliding both contributions may be present.The boundary contribution prevails in very small,smooth,and hard contacts(as e.g.,diamond-like-carbon(DLC)coatings),while the area contribution is prevailing in large soft contacts.Simulations suggest that the friction due to adhesion instabilities is governed by'Johnson parameter'.Experiments suggest that for soft bodies like rubber,the stresses in the contact area can be characterized by a constant critical value.Experiments were carried out using a setup allowing for observing the contact area with a camera placed under a soft transparent rubber layer.Soft contacts show a great variety of instabilities when sliding with low velocity–depending on the indentation depth and the shape of the contacting bodies.These instabilities can be classified as'microscopic'caused by the roughness or chemical inhomogeneity of the surfaces and'macroscopic'which appear also in smooth contacts.The latter may be related to interface waves which are observed in large contacts or at small indentation depths.Numerical simulations were performed using the Boundary Element Method(BEM). | Valentin L.POPOV Qiang LI Iakov A.LYASHENKO Roman POHRT | 2021 | Friction2021，9，6： | 0 |
| 5 | Method of reduction of dimensionality in contact and friction mechanics:A linkage between micro and macro scales显示文摘Computer simulations have been an integral part of the technical development process for a long time now.Industrial tribology is one of the last fields in which computer simulations have,until now,played no significant role.This is primarily due to the fact that investigating tribological phenomena requires considering all spatial scales from the macroscopic shape of the contact system down to the micro-scales.In the present paper,we give an overview of the previous work on the so-called method of reduction of dimensionality(MRD),which in our opinion,gives a key for the linking of the micro-and macro-scales in tribological simulations.MRD in contact mechanics is based on the mapping of some classes of three-dimensional contact problems onto one-dimensional contacts with elastic foundations.The equivalence of three-dimensional systems to those of one-dimension is valid for relations of the indentation depth and the contact force and in some cases for the contact area.For arbitrary bodies of revolution,MRD is exact and provides a sort of“pocket edition”of contact mechanics,giving the possibility of deriving any result of classical contact mechanics with or without adhesion in a very simple way.A tangential contact problem with and without creep can also be mapped exactly to a one-dimensional system.It can be shown that the reduction method is applicable to contacts of linear visco-elastic bodies as well as to thermal effects in contacts.The method was further validated for randomly rough self-affine surfaces through comparison with direct 3D simulations.MRD means a huge reduction of computational time for the simulation of contact and friction between rough surfaces accounting for complicated rheology and adhesion.In MRD,not only is the dimension of the space reduced from three to one,but the resulting degrees of freedom are independent(like normal modes in the theory of oscillations).Because of this independence,the method is predestinated for parallel calculation on graphic cards,which brings further acceleration.The method opens completely new possibilities in combining microscopic contact mechanics with the simulation of macroscopic system dynamics without determining the“law of friction”as an intermediate step. | Valentin L.POPOV | 2013 | Friction2013，1，1： | 0 |
| 6 | Approximate contact solutions for non-axisymmetric homogeneous and power-law graded elastic bodies:A practical tool for design engineers and tribologists显示文摘In two recent papers,approximate solutions for compact non-axisymmetric contact problems of homogeneous and power-law graded elastic bodies have been suggested,which provide explicit analytical relations for the force–approach relation,the size and the shape of the contact area,as well as for the pressure distribution therein.These solutions were derived for profiles,which only slightly deviate from the axisymmetric shape.In the present paper,they undergo an extensive testing and validation by comparison of solutions with a great variety of profile shapes with numerical solutions obtained by the fast Fourier transform(FFT)-assisted boundary element method(BEM).Examples are given with quite significant deviations from axial symmetry and show surprisingly good agreement with numerical solutions. | Valentin L.POPOV Qiang LI Emanuel WILLERT | 2024 | Friction2024，12，2： | 0 |
| 7 | Guest editorial: Special Issue on Science of Wear显示文摘Among the basic tribological phenomena of contact,adhesion, friction, lubrication and wear, wear remains the least scientifically understood. At the same time,wear remains one of the most important tribological phenomena in practice, affecting all aspects of our lives and current technologies. The impact of wear | Yonggang MENG Valentin L.POPOV Jean-Fran?ois MOLINARI | 2018 | Friction2018，6，3： | 0 |
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