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Wettability and friction of polytetrafluoroethylene film: effect of prebonding treatments
VOL. 1 (IwW9
161
WEAR
Literature
and Current
Events
The purpose of the following sections is to build up gradually an information centre on the various aspects of wear. Contributions in English are invited. All items of these 6 sections will be finally included in a separate “Volume-Index of Literature and Current Events” : I. Systematic Abstracts on current literature will be prepared by Battelle Memorial Institute and will begin to appear in issue no. 3 or 4 of Volume r. Systematic abstracts covering the years 1952-56 will also be published in Volume I. z. A selected number of Authors’ Abstracts (in English), giving more detailed information than the “Systematic Abstracts”, will be accepted for publication. 3. Bibliographies on work in specialized fields or on work in languages other than those of this Journal, will also be published. 4. Recent Events should assist readers in following progress reported in lectures and in finding the names and addresses of specialists and technical groups or societies interested in the various aspects of friction, lubrication and wear. 5. Forthcoming Events will give notice of conferences, meetings, or discussion panels of interest to readers of WE A R. 6. Notes on Contributors should facilitate personal contacts between workers interested in wear problems.
Authors’
Abstracts
FRICTION Adhesion
and Friction
F. P. BOWDEN (Cambridge) - Endeavour, 16 (1957) 5-18; (16 fig., 13 ref.). Although the fundamental laws of friction are simple and have long been known, it is only comparatively recently that is has been possible to gain some understanding of the local changes that occur when one solid slides on another under various conditions. Knowledge so gained is not only important for an understanding of the physics of solids, but of great practical significance in such diverse fields as the construction and lubrication of bearings, the polishing of diamonds, the de-icing of aircraft, and the formulation of adhesives. Wettability Treatments
and
Friction
of Polytetrafluoroethylene
Film:
Effect of Prebonding
A. J. G. ALLAN (Polychemicals Department, E.I. du Pont de Nemours & Company, Inc., Wilmington, Delaware) -J. Polymer Sci., 24 (1957) (May) 461, (3 fig., rz ref.). The wettability of polytetrafluoroethylene film surfaces hasbeen studied by observing the equilibrium advancing contact angle formed by a drop of liquid on the surface. The surface treatment required to give good adhesion to various substrates produces a marked increase in the polarity of the surface as measured by the contact angles with a series of solutions of ethyl alcohol in water. Measurement of the coefficient of kinetic friction shows that the untreated side of treated material has the same coefficient as completely untreated film, but the treated side has a considerably higher friction. This higher friction of the treated surfaces is ascribed to the shearing of junctions in the bulk rather than shearing at the interface.
LITERATURE
162
AND
CURRENT
EVENTS
VOL.* 1
(I957/54
FRACTURE
Note: The following group of papers from the Akers Research Laboratories of I.C.I. should be read in conjunction with the monograph: Stress Waoes in Solids by H. Kotsrc~; Oxford Univ. Press, London, 1953. (Ed.) Brittle
Fractures
near Equilibrium
F. C. ROESLER (Imperial Chemical Industries Limited, Akers Research Laboratories, Welwyn, Herts.) - Proc. Phys. Sot., B 69 (1~56) 981-992; (5 fig.. 4 ref.). Conical indentation fractures in silicate glass are stable, so that the speed at which they spread can be controlled. The validity of the Griffith fracture condition (energy balance) has been tested for such fractures and confirmed, with qualifications. Measurements on cone fractures are a method for determining accurately the specific fracture energy of brittle materials under physical and chemical conditions that can be chosen at will. Indentation
Hardness
of Glass as an Energy
Scaling
Law
F. C. ROESLER (Imperial Chemical Industries Limited, .4kers Research Laboratories, Welwyn, Herts.) - Proc. Phys. Sac., B 59 (1~56) 55-60; (16 ref.). A number of independently found empirical laws for the occurrence of Hertzian ring cracks are all equivalent and can be put in the form of an energy scaling law. It is suggested that this is the true explanation of the observed size effects, which would then lie in the dynamical similarity relations of geometrically similar stress fields and fracture Surfaces. Fracture
of Glass by Spherical
Indenters
J, P. A. TI~LETT (Imperial Chemical Industries Limited, Akers Research Laboratories, Welwyn, Herts.) - Proc. Phys. Sot., B 69 (1956) 47-53; (5 fig.). The production of ring cracks in silicate glass, by the impact of steel balls and by the application of a static load to spherical indenters, has been studied for a large range of indenter curvature. It has been found that in impact tests a greater height of fall is required to produce ring cracks than predicted by a critical stress criterion of fracture. In static experiments, two different relations between the force required to produce fracture and indenter size have been found. Below a radius of curvature of approximately 3.5 cm the force is proportional to the radius and above this value to the square of the radius. Impact tests have also been carried out on a specimen of an organic glass-like material, with results similar to those of the impact experiments on silicate glass. The Tensile
Strengths
of Viscous
Liquids
under
Dynamic
Loading
T. H. BULL (Imperial Chemical Industries Ltd., Akers Research Laboratories, Welwyn, Herts.) -Byit. J. AQpl. Phys., 7 (1~56)416-18; (4fig.,3ref.).Seealso PhiZ.Mag.,Ser.8.r(1~56) 153-165. LJnder similar conditions of transient loading the cavitation thresholds of syrup and olive oil are For fluids with a viscosity (q) in the 130 x 10~ dyne/cm2 and 29 x 10s dyne/ems, respectively. range 0.01 to 400 P the cavitation threshold pressure PC is given by the empirical relation P, = k,f*. This result can be interpreted on the basis of the growth of cavitation nuclei in viscous liquids subjected to transient stresses. MEcHANIS&l OF WEAR PROCISSSES The Wear
of Metals
under
Unlubricated
Conditions
J. F. ARCHARD AND W. HIRST (Research Laboratory, Associated Electrical Industries Limited, Aldermaston, Berks.) - Proc. Roy. Sot., A 236 (1956) 387-410; (II fig., 21 ref.). The wear of a wide range of material combinations has been studiedin unlubricated conditions. Loads of 50 g to IO kg and speeds of 2 to 660 cmjsec have been used. A representative selection of the results is given. As a broad classification two contrasting mechanisms of wear have been observed. In nearly all experiments, and for all types of wear mechanism, once equilibrium surface conditions are established the wear rate is independent of the apparent area of contact. The wear rate is accurately proportional to the load for only a limited number of combinations but there are many other examples for which the relation between wear rate and load shows only a small deviation from direct proportionality. It is suggested that with the same surface conditions the wear rate is proportional to the load; in practice this simple relation is modified because the surface conditions depend on the load. These rules of wear may be derived, on a priori grounds, from the experimental results, or from more detailed theoretical calculations.
161
WEAR
Literature
and Current
Events
The purpose of the following sections is to build up gradually an information centre on the various aspects of wear. Contributions in English are invited. All items of these 6 sections will be finally included in a separate “Volume-Index of Literature and Current Events” : I. Systematic Abstracts on current literature will be prepared by Battelle Memorial Institute and will begin to appear in issue no. 3 or 4 of Volume r. Systematic abstracts covering the years 1952-56 will also be published in Volume I. z. A selected number of Authors’ Abstracts (in English), giving more detailed information than the “Systematic Abstracts”, will be accepted for publication. 3. Bibliographies on work in specialized fields or on work in languages other than those of this Journal, will also be published. 4. Recent Events should assist readers in following progress reported in lectures and in finding the names and addresses of specialists and technical groups or societies interested in the various aspects of friction, lubrication and wear. 5. Forthcoming Events will give notice of conferences, meetings, or discussion panels of interest to readers of WE A R. 6. Notes on Contributors should facilitate personal contacts between workers interested in wear problems.
Authors’
Abstracts
FRICTION Adhesion
and Friction
F. P. BOWDEN (Cambridge) - Endeavour, 16 (1957) 5-18; (16 fig., 13 ref.). Although the fundamental laws of friction are simple and have long been known, it is only comparatively recently that is has been possible to gain some understanding of the local changes that occur when one solid slides on another under various conditions. Knowledge so gained is not only important for an understanding of the physics of solids, but of great practical significance in such diverse fields as the construction and lubrication of bearings, the polishing of diamonds, the de-icing of aircraft, and the formulation of adhesives. Wettability Treatments
and
Friction
of Polytetrafluoroethylene
Film:
Effect of Prebonding
A. J. G. ALLAN (Polychemicals Department, E.I. du Pont de Nemours & Company, Inc., Wilmington, Delaware) -J. Polymer Sci., 24 (1957) (May) 461, (3 fig., rz ref.). The wettability of polytetrafluoroethylene film surfaces hasbeen studied by observing the equilibrium advancing contact angle formed by a drop of liquid on the surface. The surface treatment required to give good adhesion to various substrates produces a marked increase in the polarity of the surface as measured by the contact angles with a series of solutions of ethyl alcohol in water. Measurement of the coefficient of kinetic friction shows that the untreated side of treated material has the same coefficient as completely untreated film, but the treated side has a considerably higher friction. This higher friction of the treated surfaces is ascribed to the shearing of junctions in the bulk rather than shearing at the interface.
LITERATURE
162
AND
CURRENT
EVENTS
VOL.* 1
(I957/54
FRACTURE
Note: The following group of papers from the Akers Research Laboratories of I.C.I. should be read in conjunction with the monograph: Stress Waoes in Solids by H. Kotsrc~; Oxford Univ. Press, London, 1953. (Ed.) Brittle
Fractures
near Equilibrium
F. C. ROESLER (Imperial Chemical Industries Limited, Akers Research Laboratories, Welwyn, Herts.) - Proc. Phys. Sot., B 69 (1~56) 981-992; (5 fig.. 4 ref.). Conical indentation fractures in silicate glass are stable, so that the speed at which they spread can be controlled. The validity of the Griffith fracture condition (energy balance) has been tested for such fractures and confirmed, with qualifications. Measurements on cone fractures are a method for determining accurately the specific fracture energy of brittle materials under physical and chemical conditions that can be chosen at will. Indentation
Hardness
of Glass as an Energy
Scaling
Law
F. C. ROESLER (Imperial Chemical Industries Limited, .4kers Research Laboratories, Welwyn, Herts.) - Proc. Phys. Sac., B 59 (1~56) 55-60; (16 ref.). A number of independently found empirical laws for the occurrence of Hertzian ring cracks are all equivalent and can be put in the form of an energy scaling law. It is suggested that this is the true explanation of the observed size effects, which would then lie in the dynamical similarity relations of geometrically similar stress fields and fracture Surfaces. Fracture
of Glass by Spherical
Indenters
J, P. A. TI~LETT (Imperial Chemical Industries Limited, Akers Research Laboratories, Welwyn, Herts.) - Proc. Phys. Sot., B 69 (1956) 47-53; (5 fig.). The production of ring cracks in silicate glass, by the impact of steel balls and by the application of a static load to spherical indenters, has been studied for a large range of indenter curvature. It has been found that in impact tests a greater height of fall is required to produce ring cracks than predicted by a critical stress criterion of fracture. In static experiments, two different relations between the force required to produce fracture and indenter size have been found. Below a radius of curvature of approximately 3.5 cm the force is proportional to the radius and above this value to the square of the radius. Impact tests have also been carried out on a specimen of an organic glass-like material, with results similar to those of the impact experiments on silicate glass. The Tensile
Strengths
of Viscous
Liquids
under
Dynamic
Loading
T. H. BULL (Imperial Chemical Industries Ltd., Akers Research Laboratories, Welwyn, Herts.) -Byit. J. AQpl. Phys., 7 (1~56)416-18; (4fig.,3ref.).Seealso PhiZ.Mag.,Ser.8.r(1~56) 153-165. LJnder similar conditions of transient loading the cavitation thresholds of syrup and olive oil are For fluids with a viscosity (q) in the 130 x 10~ dyne/cm2 and 29 x 10s dyne/ems, respectively. range 0.01 to 400 P the cavitation threshold pressure PC is given by the empirical relation P, = k,f*. This result can be interpreted on the basis of the growth of cavitation nuclei in viscous liquids subjected to transient stresses. MEcHANIS&l OF WEAR PROCISSSES The Wear
of Metals
under
Unlubricated
Conditions
J. F. ARCHARD AND W. HIRST (Research Laboratory, Associated Electrical Industries Limited, Aldermaston, Berks.) - Proc. Roy. Sot., A 236 (1956) 387-410; (II fig., 21 ref.). The wear of a wide range of material combinations has been studiedin unlubricated conditions. Loads of 50 g to IO kg and speeds of 2 to 660 cmjsec have been used. A representative selection of the results is given. As a broad classification two contrasting mechanisms of wear have been observed. In nearly all experiments, and for all types of wear mechanism, once equilibrium surface conditions are established the wear rate is independent of the apparent area of contact. The wear rate is accurately proportional to the load for only a limited number of combinations but there are many other examples for which the relation between wear rate and load shows only a small deviation from direct proportionality. It is suggested that with the same surface conditions the wear rate is proportional to the load; in practice this simple relation is modified because the surface conditions depend on the load. These rules of wear may be derived, on a priori grounds, from the experimental results, or from more detailed theoretical calculations.