Effect Of Line Tension Research Articles

Effect of Groove Shape on the Frictional Hold of a Sheave on Polyester Rope

This paper discusses the effects of sheave groove shape, sheave diameter, and line tension on the frictional hold of polyester rope. A series of tests were conducted using five different sheaves, 5 and 9.2-cm-dia 2-in-1 polyester rope, under both wet and dry conditions. The frictional hold was determined from the difference in rope tension on opposite sides of a rotating sheave. The maximum tension on the high side was 245 kN. It was found that the coefficient of friction between polyester rope and smooth steel sheaves decreases with increase in rope tension for a given rope size. The 70-deg-V groove sheave shape demonstrated approximately 25 percent more frictional hold than the U-groove sheave shape. Holding capacity increases with sheave diameter. Large relative velocity exists between elastic lift line and sheave surface. Data will be used in a traction winch design.

Nucleation at macroscopic steps

The classical heterogeneous nucleation theory is used to study nucleation at macroscopic steps. Line tension effects are included to give a correct description of the phenomena within the known limits of the theory. A criterion of preferential nucleation at steps (decoration criterion) is given. The expected behavior of the system for low macroscopic contact angles is found.

Line effects in disk-shaped heterogeneous nucleation

The classical theory of the heterogeneous nucleation with disk-shaped nuclei is developed and discussed. The nonlinearity of the Pound plot can be understood with the present theory, in which line tension effects play an essential role. Experimental data on the nucleation of zinc depositing on glass is analyzed in the light of the theory; these data can be theoretically fitted for the first time over a full range of temperatures assuming plausible values for the unknown parameters.

Theoretical analysis of heterogeneous nucleation data: Effects of line tension

The classical theory of heterogeneous nucleation is used to analyse experimental nucleation data (water on mercury and chromous iodide on quartz). It is shown that the inclusion of the line tension effects explains these experimental data without the need to assume values for physical variables which are in clear opposition to the experimental evidence. The values obtained for the line tension agree with previous estimations.

Line tension effects in heterogeneous nucleation theory

The classical theory of heterogeneous nucleation is revised including line tension effects. Contrary to what is believed, the uniqueness of the critical nucleation contact angle obtained from experimental data is shown. Besides other physical effects, the critical nucleation contact angle and nucleation barrier are drastically modified by the line tension effect. Experimental data previously used to discard the classical approach can be now satisfactorily explained.

Ectropion after blepharoplasty. Experimental and clinical observations.

Ectropion, or eversion of the lower lid, is the most common serious complication of blepharoplasty. Although many factors can be related to the production of this phenomenon, excess tension on the suture line has been implicated as a causal factor in the past. Because of the lack of instrumentation for measuring suture line tensions during the performance of blepharoplasty, and the relative difficulty in identifying suitable animal models, there has been little investigation of excess suture line tension as a cause of ectropion. This study was designed to establish a technique for measuring suture line tension during the performance of blepharoplasty and evaluating the effects of excessive suture line tension in the experimental production of ectropion in the stump-tailed monkey. In both monkey and human eyelid excisions, suture line tension is evaluated with the use of a fine-balance dynamometer. Suture line tension is shown to be a measurable parameter, and the technique of measurement is described. Excessive suture line tension has been demonstrated in monkeys and humans to be a causal factor in the production of ectropion following eyelid excisions.

Effects of shock loading and cold rolling on the structure and high temperature creep properties of γ′ strengthened Ni-18.6 pct Cr-4.3 pct Al

The effects of shock loading and cold rolling on the structure and high temperature creep properties of precipitation strengthened Ni-18.6 pct Cr-4.3 pct Al have been investigated. The creep properties of this alloy depend on whether the testing is conducted in forming gas (90 pct N2 + 10 pct H2) or in vacuum. It is found that cold rolling invariably increases the creep rate and decreases the creep life when testing is conducted in forming gas. This unexpected result is believed to be caused by strain concentrations at grain boundaries which are associated with cold rolling and which contribute to creep by promoting premature intergranular fracture. In order to minimize the effects of intergranular fracture and to determine the intrinsic effects of prestraining it is necessary to conduct creep tests in vacuum. Taking this precaution, we find that the creep strength of this alloy can be enhanced only slightly by cold rolling a few percent. Cold rolling by a greater amount or shock loading to about 70 kbar (6.99 × 109 Pa) results in higher creep rates than the asaged condition. It is shown that these unexpected weakening effects can be correlated with, and are probably caused by, the presence of misshaped γ′ precipitate particles. The irregular shapes of these precipitates are believed to be caused by the line tension effects of surrounding dislocations.

The strength of brittle materials containing second phase dispersions

Abstract Cracks in brittle materials can be impeded by obstacles in the form of second phase dispersions. The crack tends to bow out between obstacles forming secondary semi-elliptical flaws. The strength is determined by the stress to propagate these secondary cracks. Stress calculations show that this depends on the ratios of the obstacle dimensions and the obstacle spacing and, except for large relative obstacle spacings, the stress is larger than the stress to extend the primary crack. Second phase dispersions will usually increase strength, therefore, through an effect equivalent to the ‘line tension effect’ observed for dislocation motion. A comparison of the calculated ‘line tension effect’ with observed increases in strength in brittle matrix composites shows that line tension is the major contribution to the strength increase for brittle obstacles, but only a minor contribution for fibre composites, and probably a minor contribution for ductile obstacles.

The dynamics and thermodynamics of solid-fluid-fluid three-phase contact

This paper is an attempt to clarify the dynamics and thermodynamics of solid-fluid-fluid three-phase contact. We demonstrate that the thermodynamic Laplace and Young equations, even in conjunction with a knowledge of temperature, partial potentials, phase mass, and solid surface configuration, do not provide a complete characterization of equilibrium. Dynamic Laplace and Young equations are derived which appear to indicate that spreading is a dissipative process. Finally, it is demonstrated that the effect of line tension on contact angle depends not only on line curvature but also on the relative orientation of the line with respect to the solid surface.

Dislocation Vibration: Effective Mass and Line Tension

The equation of motion of a dislocation is derived on the basis of the Peierls model. From the equation the mass of a kink is calculated and the interaction between kinks is obtained including the effect of retardation. The mass and the line tension of a vibrating dislocation of infinite length are found to depend on both the frequency and the wave length. It is shown that a resonance scattering takes place for a transverse phonon incident obliquely on a screw dislocation. For a pinned dislocation the use of the concepts of the line tension and the mass is not justified near the pinning points.

Line-Tension Effect in a Surface Energy Model of a Cap-Shaped Condensed Phase

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The line-tension effect in heterogeneous nucleation

The theory of heterogeneous vapor-solid nucleation is reformulated to include the line-tension contribution to the free energy of formation of a nucleus. The nucleation theory used is based on the Pound description which employs a cap-shaped model of the critical nucleus. The line-tension effect has been shown to increase the contact angle for small crystals above that of the macroscopic contact angle that would obtain between the phases considered. The role of the contact angle in achieving solutions to the nucleation rate equation is considered in detail. It is shown that in the absence of line-tension there exists one and only one physically real contact angle that satisfies the nucleation equation. However, the nucleation rate equation becomes multivalued in respect to its dependence on contact angle if the line-tension effect is considered. The resultant contact angle derived from the nucleation data need not be the macroscopic contact angle. A general method is derived for plotting nucleation data in which three nucleation effects may be readily distinguished: (1) a mechanism involving direct addition of atoms from the vapor to the critical nucleus, (2) a mechanism involving addition of atoms to the critical nucleus via surface diffusion on the substrate, and (3) the occurrence of the line-tension effect in heterogeneous nucleation. These predictions are compared with data available in the literature. The Zeldovich factor which depends very strongly on contact angle for values less than 60° is found to not affect the conclusions.

Effective Line Tension of a Dislocation

Effective Line Tension of a Dislocation