Methods of measuring the adhesion of thin films to bulk substrates are critically reviewed, with particular emphasis on the value of scratch testing methods. Results obtained by this method for a range of metals and polymers show that in many cases there is a considerable electrostatic component of adhesion, which is both time and temperature dependent. An examination of electrical conduction in polyethylene shows space-charge-limited currents, due apparently to positive hole injection at the anode. It is suggested that a similar mechanisms is the cause of the adhesion results.

Assuming the anisotropic elastic constants of stearic acid as a function of layer height to be as determined by Akhmatov and Panova, the shear strengths of mono layers and multi layers are calculated. A computer programme describing the slip of a monolayer of an orthorhombic fatty acid crystal system about the methyl end groups is adapted to represent layer height by the use of a range of interaction potentials. Although the computed shear strengths are too high in magnitude compared with experimental results, as expected from strength calculations of an ideal crystal system, the correct trend of behaviour between multilayers and monolayers is shown.

The direction of flow of various metals (Pb, Al, Au, Ag, 62.1 At. % Au–Ag alloy, Cu, Ni, 25.7 At. % Ni–Cu, Mo, W, U, Ti, Mg, and Zn) past the faces of a ploughing Vickers diamond pyramid of dihedral angle 136° is shown in ploughing (a) parallel to the side of the initial square indentation, (b) parallel to the diagonal, (c) in and intermediate asymmetrical direction. In all these cases, with this obtuse indenter, the metal flow at the interface is close to the direction lying in a plane through the ploughing direction, normal to the surface of the specimen. Approximate theoretical expressions are derived for the friction coefficient µ for such conditions.The form of the flow past an indenter is also indicated by observations on the ploughing of macroscopic metal pyramids and cones in Plasticene built from superposed layers of different colours.Observations are also made on the widths of grooves ploughed by the diamond on various metals, compared with the width of the static indentation. These are considered in relation to the theoretical expressions and the factors which may affect the groove development.

The principles of reinforcement and the properties of fibre reinforced composites are briefly outlined and then discussed with particular regard to the role which the interface plays in controlling fibre strength and the utilization of fibre properties. The contradictory requirements for interfacial bond strength and the limitations of anisotropy are discussed, and the suggestion made that high performance composites may need to be designed with particular property requirements and component performance in mind.

The mode of fracture and the origins of fracture work have been investigated for several fibreglass laminate constructions. Crack propagation in woven fabric and cross-plied unidirectional ply laminates with fibres parallel and perpendicular to the load direction was resisted by splitting between the fibres in the load direction at the crack tip. Crack propagation occurred by successive split formation and failure of the region of fibres adjacent to the split. Although crack tip damage was often extensive, fracture was governed by the classical crack tip stress singularity in all cases. The fracture work determined from notched tension tests was quantitatively associated with the elastic strain energy decrease in the region of fibres adjacent to the split at the crack tip when the crack advanced. Variations of up to a factor of fifteen in longitudinal ply fracture work were realized by varying the ply configuration of Scotchply laminates. Predictable increases in fracture work with fibre volume fraction and woven fabric ply orientation were also achieved.

The effect of fibre surface treatments on the bond strength of 30 µm E-glass fibres, embedded in a polyester resin, have been studied by mechanical rupture of the interfacial bond using a shear debonding specimen. The surface treatments included water lubrication, silanes of different reactivity towards the resin, boundary lubricant, film forming polymer, silicone resin and blends of these components. The results of these studies suggest that the measured bond strengths are closely related to appropriate wetting of the fibre by the resin. An attempt has been made to interpret the bond strength in terms of the physical and chemical forces operating in the interface region.

The tensile mechanical properties of carbon fibre reinforced nylon 6.6 and polypropylene have been studied. Two distinct ranges of fibre length and a range of fibre volume fraction from 0 to 0.2 have been examined in each matrix. Longer fibres are more effective in improving strength and stiffness than are equivalent fractions of short fibres. The fibre matrix bond strengths are higher than the yield strength of unfilled matrix for both systems and it is suggested that this is due to a modification in matrix structure occurring at the fibre/matrix interface. A critical fibre length exists such that fibres of critical length or longer strain by the same amount as the matrix at their centres. The value of critical length is related to the strain in the matrix and the fibre matrix bond strength. Fibres which are subcritical in length carry a constant stress, and fibres which become subcritical by fracture continue to carry stress at the level appropriate to their new length as strain increases. Some specimens of each material failed at strains which exceed the mean fibre failure strain. In these cases considerable multiple fracture of the fibres occurred. In specimens failing below the mean fibre fracture strain less fibre breakdown occurred. It is suggested that failure in these composites may be initiated in the matrix and not by fibre fracture.

Observation of the first stages in the electrodeposition of oxide and of metals on to metallic substrates is considered. The paper is concerned with applications of electron and ion microscopy and with the possibility of correlating microscopic observations with electrochemical experiments. Mechanical effects of the electrochemical treatment are mentioned briefly.

Grazing-incidence electron diffraction at 50–60 kV shows the surface structure of smooth electropolished Cu (110) faces and of the epitaxial Ni deposits on them from the bath: Ni(SO3· NH2)2· 4H2O 350 g/l., NiCl2· 6H2O 5g/l., H3BO3 35 g/l.The Ni deposits were all f.c.c. The effects of c.d. (up to 600 mA/cm2), thickness (100–60 000 Å), temperature (50 and 20°C), and vigorous stirring, are shown in detail. The effects of codeposition of Ni(OH)2 at high c.d. are also shown.Special points of interest are: (1) at 50°C although {111} twinning of the “parallel” epitaxial Ni was strong near the interface (100–200 Å Ni deposits) at up to ∼150 mA/cm2, it was weaker at 200 and absent at 300–600 mA/cm2(at least up to thousands of Å thickness), and this is similar to our results for Ni on (100) and (111) Cu; (2) at up to ∼150 mA/cm2 at 50°C with unstirred bath the strongly twinned Ni at up to 1000 Å thickness showed no “directed disorientation” though accompanied by an extremely small trace of widely disoriented (random?) Ni, possibly associated with the epitaxial misfit and contacting crystal nuclei; (3) at 10 000 Å or more, at up to ∼150 mA/cm2 at 50°C with unstirred bath, additional weak arcs showed a small amount of {100} Ni, and at 30 000–60 000 Å these arcs became strong and showed a {100} Ni orientation but limited to azimuths associated with those of the {111} twins of the “parallel” Ni, arising from the twins by a “directed disorientation”(a range of rotation round the horizontal [10] Ni direction, presumably due to contacts between the twins, as they grow, with misfit stresses and strains at their interface), followed by cube face development leading to preferred growth of crystals in {100} orientation.

Thin films of polystyrene drastically degrade, on a molecular scale, when subjected to mechanical forces. An examination, by gel permeation chromatography, of the molecular weight distributions of the degraded polymers shows that the polymer molecules do not undergo the random scissions or bisections that have been postulated in the many prior theoretical treatments of polymer degradation, but rather degrade via non-random multiple scissions. The mode of degradation is such that while medium molecular weight polystyrene molecules degrade directly to a limiting low molecular weight species, high molecular weight polystyrene degrades both indirectly through an intermediate species and directly to the limiting species. An analysis of the degradation data from a wide molecular weight distribution polystyrene sample yields a rate equation which is a decreasing function of molecular weight. A model is proposed which predicts the form of the degradation rate equation on the basis of molecular size: the mode of degradation is explained by the concept of polymer chain entanglement. Possible degradation pathways are differentiated using a computer simulation.

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Torsional shear napkin-ring test-pieces have been used in adhesion studies with two titanium alloys, modified epoxy and epoxy-phenolic adhesives. The temperature profiles have been obtained and the failure surfaces studied. The metallography of the surfaces is recorded and the effect of a variety of preparative surface treatments. Most treatments lead to rutile, and in one case rutile needles bond to the adhesive more strongly than to the substrate. Surface roughness is shown to enhance bond strength.

Static and fatigue tests have been carried out at several principal stress ratios on thin-walled tubes fabricated from “E” glass chopped strand mat and a polyester resin. Corresponding data have been obtained from flat laminates under axial tension, axial compression, and in-plane shear loading. The onset of debonding, and resin cracking were observed as well as rupture. The results have been compared with predictions based on the theories of failure for anisotropic materials. Only those theories which include the results of a complex stress test gave safe predictions. The fatigue results for cylinders gave failures at much lower stresses than would have been expected from corresponding axial stress data and further work is required to explain the anomaly.

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Metals reinforced with continuous graphite (Type I) fibres are prone to compatibility and oxidation problems when they are subjected to high temperature treatments. To prevent such interactions, the feasibility of using evaporated barrier layers has been examined in a nickel matrix. A number of techniques, e.g., tensile testing, thermal-balance determinations and microscopy have been employed to test the usefulness of this approach. Results have shown that 1 µm thick metal coatings either react vigorously with the fibre or allow diffusion of oxygen or carbon to take place sufficiently quickly so as to delay fibre degradation by only a short time interval. Whilst chemically stable nonmetallic coatings tend to prevent diffusion of both carbon and oxygen, they are extremely susceptible to brittle cracking due to differential thermal expansion effects. In this respect, zirconium carbide and boron nitride seem to be affected to a lesser degree than other carbides, nitrides and oxides, and can provide protection over a limited temperature range.

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A wide range of binary Co, Fe, Ni alloys has been prepared by electrodeposition on to cube-textured copper substrates. The alloys, after removal from the substrate were examined by transmission electron microscopy. All alloys were found to be of either b.c.c., f.c.c. or c.p.h. structure according to their composition. The interface crystallography of these alloys is discussed in terms of the relationships between prominent directions in the iron-group alloys, and the direction of the copper face diagonals in the cube-textured substrate.

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Atomic forces at the interface constitute the major factor responsible for friction and adhesion between unlubricated surfaces. For non-metals these are basically the van der Waals dispersion forces, though in special cases electrostatic forces may be involved. Some recent work on van der Waals forces at very small separations will be described. These forces provide a fairly direct measure of the adhesion between soft rubber-like materials and between polymeric solids. With polymers, such interfacial forces are sufficient to transfer portions of the polymer from one surface to the other when they are placed in contact or slid over one another. Frictional transfer occurs even for materials such as P.T.F.E.With metal surfaces, van der Waals forces are overtaken by metallic bonding when the regions of contact are separated by distances comparable with atomic dimensions. This leads to very strong adhesion between metals which are atomically clean. By contrast, very small quantities of active vapours adsorbed at the interface can produce a drastic reduction in adhesion. Another factor which greatly influences the adhesion of a metal is its ductility: metals which have a limited number of slip planes usually show smaller adhesion.The importance of ductility is also shown in the behaviour of very hard materials such as TiC or diamond in ultra high vacuum. Intimate contact is restricted to individual asperities, and the adhesion for very clean surfaces is far less than might be expected from calculations based on surface forces. This is partly because the area of real contact is very small; partly because of the brittleness of these materials. If one of the surfaces is soft or ductile adhesion may be quite strong. For example the adhesion of clean TiC to TiC is extremely small; of clean copper to TiC extremely large. Here again surface films can greatly reduce the adhesive strength.

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