This paper presents an overview of the role of adhesion in various tribological phenomena.We discuss(1)adhesion and adhesive hysteresis in rough contacts,(2)adhesive contribution to dry friction,(3)properties of adhes...This paper presents an overview of the role of adhesion in various tribological phenomena.We discuss(1)adhesion and adhesive hysteresis in rough contacts,(2)adhesive contribution to dry friction,(3)properties of adhesive contacts under tangential loading,(4)“negative adhesion”and superlubricity,and(5)adhesive wear.Based on theoretical considerations,simulations with the boundary element method and experiments,we argue that the key process underlying all these phenomena is jump-like changes of the contact boundary.These jumps are an essential property of adhesive contacts and are solely responsible for energy dissipation in both adhesive hysteresis and adhesive friction.On the mesoscale,the aforementioned instabilities give rise to boundary line friction,which forms a convenient tool for understanding the properties of adhesive contacts both under normal and tangential loading,including changes of contact area and the phenomenon of the“sticking zone”.On the macroscale,the concept of boundary line friction can be approximated by simple adhesive contact with two different works of adhesion—a smaller one for closing the adhesive crack(attachment)and a larger one for opening it(detachment).The well-known equivalence between the adhesive contact boundary and the Griffith crack also leads to the application of the same ideas to wear.In this context,we discuss the modified Rabinowicz criterion for wear particle formation and argue that the adhesive nature of wear all but rule out Archard’s law.Finally,we note that adhesive forces are not necessarily attractive and discuss how“negative”,i.e.,repulsive,adhesion can account for the phenomenon of superlubricity.展开更多
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 th...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).展开更多
基金support from Deutsche Forschungsgemeinschaft(DFG)(Grant Nos.PO 810/55-3,PO 810/63-2,PO 810/69-1,and PO 810/71-1).
文摘This paper presents an overview of the role of adhesion in various tribological phenomena.We discuss(1)adhesion and adhesive hysteresis in rough contacts,(2)adhesive contribution to dry friction,(3)properties of adhesive contacts under tangential loading,(4)“negative adhesion”and superlubricity,and(5)adhesive wear.Based on theoretical considerations,simulations with the boundary element method and experiments,we argue that the key process underlying all these phenomena is jump-like changes of the contact boundary.These jumps are an essential property of adhesive contacts and are solely responsible for energy dissipation in both adhesive hysteresis and adhesive friction.On the mesoscale,the aforementioned instabilities give rise to boundary line friction,which forms a convenient tool for understanding the properties of adhesive contacts both under normal and tangential loading,including changes of contact area and the phenomenon of the“sticking zone”.On the macroscale,the concept of boundary line friction can be approximated by simple adhesive contact with two different works of adhesion—a smaller one for closing the adhesive crack(attachment)and a larger one for opening it(detachment).The well-known equivalence between the adhesive contact boundary and the Griffith crack also leads to the application of the same ideas to wear.In this context,we discuss the modified Rabinowicz criterion for wear particle formation and argue that the adhesive nature of wear all but rule out Archard’s law.Finally,we note that adhesive forces are not necessarily attractive and discuss how“negative”,i.e.,repulsive,adhesion can account for the phenomenon of superlubricity.
基金This work has been conducted under partial financial support from German Research Foundation(DFG)(Grant No.PO 810/55-1)the Tomsk State University Academic D.I.Mendeleev Fund Programthe German ministry for research and education(BMBF)(Grant No.13NKE011A).
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).
