Volume 16, Issue 6, 01 June 1945
Index of content:
16(1945); http://dx.doi.org/10.1063/1.1707596View Description Hide Description
The analysis of the mechanics of orthogonal cutting with a type 2 chip as presented in the first paper of this series can be extended by introducing those physical properties of the work material which control its plastic behavior. One evident plasticity condition is the equality of the shear stress on the plane of shear to the shear strength of the metal. If it is also assumed that the shear strength of the work material is a constant and is the only quantity controlling its plastic behavior, then a very simple additional plasticity condition is obtained by application of the principle of minimum energy. This condition is 2φ+τ−α=90°, where φ is the shear angle, τ the friction angle, and α the rake angle. This condition, however, is found by experiment to be a poor approximation in the case of polycrystalline metals. A very good approximation is obtained, though, if use is made of the fact that the shear strength of the polycrystalline metal is actually a function of the compressive stress on the shear plane. The resulting plasticity condition is cot (2φ+τ−α)=k, where k is the slope of the linear curve relating shear strength and compressive stress, and is thus a constant of the work material.
Such a plasticity condition establishes a relationship between the force system and the geometry of chip formation, so that, if k and the shear strength be known for a given material, all forces involved in cutting it can be calculated with reasonably good accuracy directly from measurements of chip geometry only, without use of a tool dynamometer. This is of importance in the analysis of practical machining operations.
The Frictional Properties of Some White Metal Bearing Alloys: The Role of the Matrix and the Hard Particles16(1945); http://dx.doi.org/10.1063/1.1707597View Description Hide Description
A previous paper has described an investigation of the frictional properties of alloys of the copper‐lead type which consist of a hard matrix (copper) in which are dispersed particles of a soft material(lead). It was shown that these alloys function by the extrusion and smearing of the soft phase over the hard matrix, so providing metallic‐film lubrication. This paper describes experiments on a typical lead‐base bearing alloy which consists of a soft matrix in which are dispersed numerous hard crystallites. Measurements of the friction were made at room temperature and at elevated temperatures for clean and for lubricated surfaces. Comparison with a special alloy consisting of the matrix material alone, showed that the hard particles played no appreciable part in the basic frictional and wear properties of the bearing alloy. It is suggested that the frictional behaviour of the bearing alloy is determined essentially by the properties of the matrix material itself although in practical running operations there may be other properties which determine the suitability of the alloy for use in bearings. Similar experiments are described on a typical tin‐base bearing alloy and a corresponding tin‐base ``matrix'' alloy.
16(1945); http://dx.doi.org/10.1063/1.1707598View Description Hide Description
A modified Bingham‐type rheometer, designed for operation at temperatures up to 500°F and at pressures up to 2000 p.s.i. is described. Interchangeable orifice plates permit wide variation of shear conditions. With this instrument flow properties may be studied under conditions approximating those encountered in the actual processing of thermoplastics, e.g., by molding or extrusion. Typical results are presented for cellulose acetate, polystyrene, and polyvinyl resin plastics, and correlation with practical experience is pointed out. The instrument is slow, and this limits its usefulness for other than research investigations.
16(1945); http://dx.doi.org/10.1063/1.1707599View Description Hide Description
It is shown that the working properties of a printing ink, i.e., its performance during the printing operation, can be interpreted in terms of the rheological properties as measured in a rotational viscosimeter. The instrument used in this investigation is a viscosimeter of the Stormer type. Data are presented to show that it is necessary to distinguish between time‐dependent and time‐independent flow phenomena. Various theories suggested to explain the time‐independent flow phenomena are discussed briefly. The flow of a printing ink over the main mechanical elements of a typographic printing press is analyzed and correlated with simple flow phenomena which can be measured in a rotational viscosimeter.
16(1945); http://dx.doi.org/10.1063/1.1707600View Description Hide Description
Complete equations below the lowest cut‐off frequency of transverse magnetic type relating the high frequency electric field and magnetic field inside a metallic cylinder excited through a gap and an assumed field at the gap are developed. Curves are calculated based on the equations which can be used to estimate the relative field strength at different points inside the cylinder. Equivalent capacitance due to the energy storage in the cylinder can be calculated and used for estimating the resonant frequency of the associated cavity. The equations can be degenerated to an electrostatic form and used for electron optical calculations.
16(1945); http://dx.doi.org/10.1063/1.1707601View Description Hide Description
The problem is considered of the convection of a fluid through a permeable medium as the result of a vertical temperature‐gradient, the medium being in the shape of a flat layer bounded above and below by perfectly conducting media. It appears that the minimum temperature‐gradient for which convection can occur is approximately 4π2 h 2μ/kg ρ0α D 2, where h 2 is the thermal diffusivity,g is the acceleration of gravity, μ is the viscosity,k is the permeability, α is the coefficient of cubical expansion, ρ0 is the density at zero temperature, and D is the thickness of the layer; this exceeds the limiting gradient found by Rayleigh for a simple fluid by a factor of 16D 2/27π2 k ρ0. A numerical computation of this gradient, based upon the data now available, indicates that convection currents should not occur in such a geological formation as the Woodbine sand of East Texas (west of the Mexia Fault zone); in view of the fact, however, that the distribution of NaCl in this formation seems to require the existence of convection currents, and in view of the approximations involved in applying the present theory, it seems safe tentatively, to conclude that convection currents do exist in this formation and that the expression given above predicts excessive minimum gradients when applied to such a formation.
16(1945); http://dx.doi.org/10.1063/1.1707602View Description Hide Description
A method of preparing a pigment dispersion for electron microscopy is described, wherein the pigment, such as zinc oxide, is first wet with water and is then dispersed in a solution of cellulose acetate. Another method is described in which mechanical or chemical damage of the particles is avoided by the use of an electrostatic dispersion apparatus.