Search

An empirical elastohydrodynamic (EHD) film thickness formula for predicting the minimum film thickness occurring within heavily loaded contacts (maximum Hertz stresses above 1.04 × 109 N/m2 (150,000 psi)) was developed. The formula was based upon X-ray film thickness measurements made with synthetic paraffinic, fluorocarbon, Type II ester and polyphenyl ether fluids covering a wide range of test conditions. Comparisons were made between predictions from an isothermal EHD theory and the test data. The deduced relationship was found to adequately reflect the high-load dependence exhibited by the measured data. The effects of contact geometry, material and lubricant properties on the form of the empirical model are also discussed.

Surface cracks initiating flaking failure observed by Sugino in rolling fatigue were further studied. Surface crack initiation was influenced by either running or material conditions, affecting the residual tensile stress just below the rolling contact surface. The fatigue crack is thought to initiate very near the surface by the stress cycle of small tensile residual stress and large compressive contact stress. The amount and direction of the tensile residual stress due to rolling contact varies with the contact geometry, which probably determines the direction of the surface crack and the appearance of flaking. The transition from the surface crack to flaking failure or complete section fracture is material and running condition dependent and is explained by a fracture mechanics concept.

The crystal and molecular structures of dibenzoyldiimide, C6H5CO–N = N–COC6H5, have been determined by SEARCH as part of a study of the solid state photochemistry of α-carbonyl-azo-compounds. Partial three-dimensional data were refined with anisotropic temperature factors of the heavy atoms to r = 0.031 and R = 0.080. The bond lengths and angles have been measured with estimated standard deviations of 0.01 A and 0.6°. As the result of rotation around the C–N bonds, the interplanar distance of the parallel benzoyl groups of the (centro-symmetric) trans-molecule is 1.02 A. Photochemical rearrangement paths are discussed in terms of contact geometry.

It is shown that the compliance of an orthogonal grain-grain contact is so insensitive to the grain geometry in the contact region that this geometry is not at present an important parameter in theories of the speed of propagation of elastic waves in granular media, such as occur in the Earth and in the Moon.

A study was made of solder plated butt contacts to determine the feasibility of designing separable connectors for high reliability low energy circuits without gold or other precious metals. The chemical reactivity of tin-lead and the penetrability of films that formed on it were determined. It is little degraded by sulfur vapor, 0 2 , SO2, H 2 S, CO, and NH3. However, films from NO2 and Cl 2 can grow to large thickness, limited only by time and concentration of the reactant. Corrosion of tin-lead was promoted by a synthetic dust and by salt spray. The penetrability of tin-lead depends on contact pressure, and, owing to creep, on temperature and time. Except at light loads with certain geometries, 0.025 mm (0.001 inch) tin-lead is penetrated nearly to the copper substrate. Reconnection to such spots may be less reliable than to fresh areas, particularly if the contacts are aged between separation and remating. The ability of films on tin-lead to be broken is dependent on contact geometry, load, and wipe. The most effective geometries are cones and short (2.5 ram) wedges having an acute included angle (60°), followed by cones and wedges with an obtuse angle (120°), followed by hemispheres of increasing radius (0.38 to 1.5 mm). The cones and wedges had rounded tips of 0.05 mm radius. The order of merit may be different with thickly plated contacts (much in excess of 0.025 mm); but thick coatings are undesirable on contacts because of their deformability. When good contact is obtained, however, as in the mating of clean surfaces, the ranking of probe geometries in maintaining good contact in aggressive atmospheres is different, with the 1.5 mm radius hemisphere being best. It may be possible to design reliable butt connectors with tin-lead coated contacts for critical applications. However, additional studies need to be undertaken. These include: development of field experience in varied environments, study of long term behavior of mated contacts such as cold welding at elevated temperature, and rematability of contacts that have been aged in corrosive environments between initial use and subsequent matings.

Electron microscopy is used to study the contact zones between small metal powders agglomerated together without any external loads or restraints. It is observed that strain field fringe patterns form at the contacting regions due to attractive forces which effectively pull the particles elastically together. Image matching techniques are employed to analyse the elastic deformations observed and it is found that the junctions formed are due to metallic bonding forces. It is confirmed that the size of the junctions depends on an energy balance between the loss of surface due to the contact, the formation of a grain boundary between the particles and stored elastic energy in the particles. On the basis of this simple relationship between energy and contact geometry, it is shown that the surface energy of particles can be estimated directly from the lateral spread of the fringes (as measured on the micrographs) and knowledge of the elastic modulus of the metal. It is also shown that small changes induced in the contact geometry between the metal surfaces (e.g. due to plastic deformation) can substantially increase the adhesion at the junction. This is the basis of such well known metallurgical phenomena as dry friction between metals, the high strength of pressed weld junctions, the green strength of cold-pressed powder compacts, etc.

Approximate solutions valid for different time domains are found for the problem of transient heat flow between contacting solids. The parameters governing the heat flow and the applicability of the different solutions are given in terms of the contact geometry.

Experimental studies were made wherein contact fatigue was brought about by a cyclic variation of normal load applied to the contact between a ball and a flat specimen. Curves of flat-specimen temperature versus time showed that a rapid temperature rise occurred in the initial stage of crack formation rather than after the appearance of fully developed spalls; thus the temperature criterion appeared to provide an early indication of fatigue. Fatigue failure was observed in unlubricated as well as lubricated contact, but with much longer life when unlubricated. Toroidal rings of hardened and softened material were noted both on and below the contact surface. These hardness variations bore symmetrical relationship to the contact geometry and were apparently related to the stress pattern. It was found that the fatigue cracks did not initiate in the most severely hardened material but in the material adjacent to it. Further, the slope of the cracks tended to follow the boundary of the hardened region in gener...

The variations of the contact resistance and temperature distribution in the vicinity of an electric contact are shown for different types of right-circular conicoid contacts. The limiting cases of such contact geometry are the circle and the hemisphere. The paper shows how the resistance and temperature-distribution are relatively affected by the conception of a simplified geometric shape for the contact area. To determine the effect of the elongation of an area on the contact resistance, new form-factor curves are given which are applicable for all contact materials, pressures, and temperatures. Graphs are also given showing the relation between the maximum temperature and the interface temperature in various bimetal contacts which are in common use.

This paper considers a conicoid contact as a general case of contact geometry and derives the resistance of the contact when heated by the passage of an electric current. The expressions for the resistance of circular and hemispherical contacts are shown to be particular cases of this phenomenon. The analysis includes bimetal contacts and the impedance of a contact to alternating current. The paper further endeavors to explain low-voltage coherer action in copper contacts in terms of the softening of the parent metal. Experimental results are given to show that, after the rupture of the oxide film, the contact resistance of copper follows a metallic characteristic until melting occurs. Experimental results are also given for the resistance of carbon contacts carrying direct and alternating current.

Existing torque analyses of drum brakes, based on the assumption that the shoe and drum are rigid, fail to predict torques accurately, especially when the lining makes non-uniform contact with the drum. An analysis has been made therefore of a floating shoe brake in which the elastic deflections of the shoe and the drum have been included. The analysis has been verified by measuring the torque developed by a standard two-leading shoe brake on an inertia dynamometer under different contact conditions. The agreement between the theoretical and observed torques was found to be better than ± 10 per cent even under extreme contact conditions and much better under more moderate conditions. Some consequences of the theory are discussed because of their practical importance.

A method of relating the geometry of contacting surfaces to motion capability in the joints of spatial linkages is presented. Ball's screw system and reciprocal screw system are used to provide this relationship which is then converted into algebraic form. A differential equation which must be satisfied by the surface at points of contact is derived and used to prove several theorems relating to contact geometry.

This paper deals with optimization of the contact geometry of hydrodynamic lip seals with beams moulded on the air side. Seals for both unidirectional and bidirectional rotation are studied. The liquid to be sealed is assumed to be Newtonian and incompressible and the viscosity variations within the film are neglected. Subatmospheric pressures are also neglected. Tests were carried out with an optimum unidirectional metal seal in order to verify the theory, and additional tests were made with synthetic rubber seals. Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE International Lubrication Conference held in New York City, October 9–12, 1972

Planar Gunn diodes made from epitazial GaAs on insulating substrates having a contact geometry which results in an ideal electric field distribution are described. The current density is uniform along the diodes, and no high-field regions appear at the contacts. The lengths of the Gunn diodes varied from over 1000 to less than 100 µ.