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RESEARCH PAPERS

J. Basic Eng. 1963;85(4):481-485. doi:10.1115/1.3656883.

An apparatus is described for bringing a rider specimen and a slider specimen into continuous sliding contact so that significant temperatures at the interface are achievable. The design is such that the flow fields of heat in the specimens would be at most two-dimensional, i.e., within engineering approximations; this fact makes possible the measurement of temperatures of the specimens without disrupting the flow fields of heat. Typical data are presented of speed, normal load, frictional resistance, and temperatures at strategic locations on the specimens. Using the heat-equation solutions obtained previously for the configurations concerned, contact-surface temperature distributions of both specimens are calculated from experimental data. Results give the pointwise, temperature juncture condition at the interface.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1963;85(4):488-493. doi:10.1115/1.3656886.

A comparison has been made of the friction and wear characteristics of carbons of high (p = 0.1) and low (p = 0.9) graphiticity (hereafter referred to as graphitic and nongraphitic) in vacuo, air, and CO2 at ambient room temperature. The friction of nongraphitic carbon can be just as low as graphitic carbon and it is similarly affected by absorbed gases. It is different, however, in that it periodically exhibits a substantial increase of friction which is not normally observed with graphitic carbon. The surface orientation produced by rubbing is also quite different and so is the mode of wear. These differences have been investigated and are explained in terms of the different physical properties associated with the structures of the two materials. On the basis of this work a critical assessment has been made of the various theories concerning the mechanism of the friction of graphitic carbon. The results are in accord with the view that the low friction of graphitic carbon (and of nongraphitic carbon) is due to low adhesion between crystallites, not to the low shear strength nor to the separation of the surfaces by rolled up crystallites.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1963;85(4):495-502. doi:10.1115/1.3656890.

Application of the flow theory of Laub and Norton [1] and the stability theory of Licht, Fuller, and Sternlicht [2] is made to the design of externally pressurized spherical gas bearings. Analytical results are presented in the form of “stability maps” (stability limits) and were confirmed by experimental data. The double-valuedness of stable loading for a constant supply pressure is predicted. The design procedure presented appears to be a dependable method for assuring stable operation of spherical gas bearings.

Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. Basic Eng. 1963;85(4):513-517. doi:10.1115/1.3656894.

This paper deals with a perfectly cylindrical, self-acting, gas-lubricated, and unloaded journal bearing. Complete stability criteria for the translational mode of oscillation are formulated and a method is given by which the ultimate stable operating speed may be found for arbitrary ambient pressure, viscosity, and bearing geometry. The nature of the stable motion is indicated. In addition, a simplified criterion and bearing motion are given for low-speed operation. Graphs which show the effect of design parameters on bearing forces are included as an aid in numerical calculations.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1963;85(4):519-525. doi:10.1115/1.3656897.

The crack extension in a large plate subjected to general plane loading is examined theoretically and experimentally. It is found that under skew-symmetric plane loading of brittle materials the “sliding” or the crack extension in its own plane does not take place, instead crack grows in the direction approximately 70 deg from the plane of the crack. This is very nearly the direction perpendicular to the maximum tangential stress at the crack tip, which is 70.5 deg. The hypothesis that the crack will grow in the direction perpendicular to the largest tension at the crack tip seems to be verified also by cracked plates under combined tension and shear. In spite of the fact that “sliding” and “tearing” modes of crack extension do not take place in brittle materials it is shown that one can still talk about critical stress intensity factors in plane shear and transverse bending of plates. It is also shown that, in general plane loading, the fracture criterion in terms of stress intensity factors is an ellipse.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1963;85(4):528-533. doi:10.1115/1.3656900.
FREE TO VIEW

The practice of attempting validation of crack-propagation laws (i.e., the laws of Head, Frost and Dugdale, McEvily and Illg, Liu, and Paris) with a small amount of data, such as a few single specimen test results, is questioned. It is shown that all the laws, though they are mutually contradictory, can be in agreement with the same small sample of data. It is suggested that agreement with a wide selection of data from many specimens and over many orders of magnitudes of crack-extension rates may be necessary to validate crack-propagation laws. For such a wide comparison of data a new simple empirical law is given which fits the broad trend of the data.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1963;85(4):535-538. doi:10.1115/1.3656904.

Experimental results are presented for fatigue failure of mild steel specimens under repeated application of lateral impulses; the cumulative damage effect as a result of stresses arising from free-damped vibration of the specimen in the intervals between the repeated impulses is studied. A discussion on the conformity of these results with Miner’s hypothesis is given.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1963;85(4):539-545. doi:10.1115/1.3656905.

Strain-controlled tension-compression fatigue tests were performed on the ASTM pressure vessel steels, A302 and A225, to study the damage processes that lead to failure in low cycle fatigue. The measurements of static property changes in partially cycled specimens, and hysteresis loop effects obtained during cycling, were utilized to reflect the pattern of damage accumulation. In addition, strain cycling tests were conducted on these materials to assess the applicability of the relationship

Nf = εF − ε0εTR2
as proposed by Manson [4] and Coffin [5] and modified by Sachs, et al. [6]. The experimental data obtained were in good agreement with the failure life and the effect of mean strain as predicted by the foregoing equation. Accordingly, a positive mean strain (prestrain in tension) reduces fatigue life, since the fracture strain available for cycling is reduced by the amount of the prestrain. The damage studies indicated, however, that this equation cannot be used to describe the progress of damage during strain cycling. Rather, it appears that damage is governed by at least two, possibly interdependent, processes; namely, the loss of available ductility due to strain hardening and the formation and growth of cracks which finally determine failure. Both processes are reflected in the remaining ductility after partial cycling. At present, it is not clear how the two processes combine to yield the experimentally confirmed relationship,
Nf = εF − ε0εTR2.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1963;85(4):548-554. doi:10.1115/1.3656909.

Dimensional changes in the form of necking and bulging occur in the shape of cylindrical and hourglass commercially pure aluminum specimens subjected to axial push-pull cyclic loading. The present report deals with the effect of these changes on the resistance to deformation and fracture by fatigue. It is found that the change in shape due to instability affects the stress range response of the material during cycling. The control of shape permits a steady-state response with cycling regardless of the prior state of strain in the material. With an appropriate correction for the shape constraint effect, the steady-state stress range achieved is the same with or without shape control. Frequent removal of the surface material to control the specimen profile during cycling leads to a stabilized hysteresis loop and an indeterminate extension in the fatigue life.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1963;85(4):555-565. doi:10.1115/1.3656910.

Thick-walled cylinder fatigue data due to cyclic internal pressure for open-end cylinders in the range of 103 to 105 cycles to failure and having a diameter ratio of 1.4 to 2.0 at a nominal yield strength of 160,000 pounds per square inch is presented. Discussed and also presented are the effects of autofrettage on the fatigue characteristics of thick-walled cylinders. Autofrettage substantially enhances fatigue characteristics at stress levels below the corresponding overstrain pressure, the degree of improvement increasing the decreasing stress levels. The rate of improvement in fatigue characteristics increases significantly with diameter ratio in autofrettaged cylinders up to a diameter ratio of 1.8–2.0 and to a much smaller degree in the nonautofrettaged condition. The rate of improvement of fatigue characteristics above 2.0 is the same for both the autofrettaged and nonautofrettaged cases. It is shown that thermal treatment of 675 F for 6 hours after autofrettage does not affect fatigue characteristics and that there is a correlation between the cyclic-stress level and the area and depth of the fatigue crack to the point of ductile rupture. The depth of the fatigue crack decreases with increasing cyclic-stress level. A means for using data from a unidirectional tensile fatigue test to predict the fatigue characteristics of thick-walled cylinders is discussed.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1963;85(4):566-568. doi:10.1115/1.3656911.

Predictions of thermal stresses in various shape flat plates with a parabolic temperature field applied in one direction were found to yield good agreement with photothermoelastic analysis. A theory based upon an analog was found to agree with experiments on rectangular plates better than two other methods of analysis. The analog procedure was utilized for analysis of a circular plate, to the results of which an engineering modification was applied to obtain theoretical data for comparison with experiments on a hexagonal plate with and without a central circular hole.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1963;85(4):569-578. doi:10.1115/1.3656912.

Four by six-in. transversely anisotropic plates of 1/8 and 1/4 -in-thick pyrolytic graphite were subjected to transient heating in an oxyacetylene flame apparatus. At temperatures up to 1500 deg F, the temperature and thermal strain distributions were determined over the length and thickness of the plates. The thermal strains measured with an optical gauge and the analytically determined strains calculated from the three-dimensional thermoelasticity equations for a two-dimensional temperature distribution were found to be in good agreement. The calculated stress distribution indicates that maximum compressive stresses of −1400 psi and −3000 psi were produced in the 1/8-in. and 1/4-in. pyrolytic-graphite plates, respectively.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1963;85(4):579-584. doi:10.1115/1.3656913.

A method is described for determining the thermal stresses in plane systems with free boundaries. The method makes use of the analogy between the problems of the bending stresses in clamped plates and those of plane thermoelasticity. The analogy is illustrated for both simply and multiply connected regions. The method allows the simple solution of thermal stress problems for which the analogous plate bending problem has already been solved; and provides a means of easily visualizing the distribution and magnitude of thermal stresses in terms more familiar to many engineers.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1963;85(4):585-591. doi:10.1115/1.3656914.

The development of plastic strain is followed from the elastic through the partially plastic to the fully plastic condition for a nonstrainhardening material. Adjacent to the zone of deformation in the fully plastic case is a region of limited plastic deformation. The growth of the plastic zone is compared with predictions based on the elastic-plastic solution for a semi-infinite solid and the elastic solution for a plate. Agreement is good at low stress levels. At high stress levels, a relatively simple semiempirical equation is proposed. Predictions based on elasticity theory alone are shown to be seriously in error.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1963;85(4):595-600. doi:10.1115/1.3656918.

The scatter of results in long time creep or rupture tests is such that the strongest sample can sustain a stress at least 50 percent higher than the weakest sample. A large part of this scatter is associated with metallurgical variations in steel. Starting with the assumption that a pure metal of given grain size has a clearly defined shape of creep curve at a given stress and temperature, it is shown that strain aging and precipitation phenomena complicate the shape of the creep curve. A number of examples of these phenomena are discussed showing the great importance of strain age hardening in relation to scatter.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1963;85(4):601-607. doi:10.1115/1.3656919.

Viscosities of twenty well-defined, representative mineral-oil fractions have been determined at temperatures from 25 to 90 deg C (77 to 194 deg F) and at pressures up to about 1000 atmospheres (15,000 psi) with the aid of a falling-needle viscometer. An analysis has been made of both the present measurements and reliable data from literature, which chiefly concern mineral oils and pure hydrocarbons, but also include some silicones, fatty oils, and alcohols. Many literature data cover ranges of viscosity, temperature, and pressure that are more extensive than those of the authors. Newly developed empirical formulas are presented for the isobaric viscosity-temperature relationship, the isothermal viscosity-pressure relationship, and the complete viscosity-temperature-pressure relationship. The formulas have been found to be satisfactorily applicable to all the aforementioned liquids in a wide range, that is, generally, from about 20 to 150 deg C (68 to 302 deg F) and up to pressures of at least 3000 atmospheres (44,000 psi). Diagrams derived from these formulas have proved particularly suitable for a systematic study of the correlation between, on the one hand, the temperature and pressure variation of viscosity of the liquids concerned and, on the other hand, their chemical constitution. This is exemplified by the results for the mineral oils investigated. In fact, it proved possible, presumably for the first time, to establish for mineral oils a really satisfactory quantitative correlation between their viscosity-temperature-pressure dependence and their chemical constitution; the latter has been characterized by the carbon distribution according to the “Waterman analysis” in the form of the so-called n-d-M method.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1963;85(4):611-618. doi:10.1115/1.3656925.

The linearized ph approximation to the time dependent Reynolds equation is solved simultaneously with the equations of motion for a rotating journal shaft supported by a rigidly mounted bearing sleeve. Given the two bearing parameters

Λ = 6μωR2paC2
and
Ω = MCω2πpaDL
a critical operating eccentricity ratio is determined below which the bearing is unstable and above which the bearing is stable. Whirl frequency at the threshold point is computed to be equal to or slightly less than one-half rotor speed.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1963;85(4):620-622. doi:10.1115/1.3656928.

A relatively simple expression is derived for the flow through round wire screens by considering the screen to be made up of a number of noninteracting cylinders and using classical data on the drag coefficient of a cylinder at various Reynolds numbers and Mach numbers. The theory is found to agree closely with the result of some recent experiments for low solidity screens (0.5 or less). At Knudsen numbers higher than 0.01 the screen passes more mass than would be predicted by the theory. This is attributed to slip.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1963;85(4):625-630. doi:10.1115/1.3656933.

Severe sustained vibration of a closed hydraulic-turbine penstock valve was associated with accidentally inadequate inflation of the valve service seal. The vibration stopped when the valve bypass was opened or full seal pressure was applied. Theory indicates that intermittent valve leakage and corresponding oscillating penstock pressure can be self-sustaining in some instances, and that opening a bypass around the leaking valve can suppress them. Field tests were performed to confirm the general theory and prove the reliability of utilizing the bypass to prevent future vibration.

Commentary by Dr. Valentin Fuster
J. Basic Eng. 1963;85(4):631-640. doi:10.1115/1.3656934.

The opinion has been expressed that—in the past thirty years—the most severe and spectacular accidents have been caused by resonance in power conduits. If this appraisal is true, then there is a gap in our knowledge to be filled. The purpose of this paper is to summarize the actual knowledge of this particular chapter of practical fluid mechanics and to open the way to more advanced research.

Commentary by Dr. Valentin Fuster

DISCUSSIONS

Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster

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