Optical Interferometry Technique Research Articles

Behavior of EHL Films in Cyclic Squeeze Motion.

The behavior of elastohydrodynamic lubrication (EHL) films formed between a steel ball and a normally vibrating optical flat is examined by means of the duochromatic optical interferometry technique. The shape of the film entrapped between the ball and Hat plate forms an envelope at the end of the load applying process. The maximum height of the film, which depends on the non-Newtonian response of oils and the squeeze number, stays at a constant value during the cycle. Under conditions of short strokes and high frequency, air bubbles produced in the load removing process result in the collapse of the entrapped EHL film.

Optical Interferometric Observations of the Effects of a Bump on Point Contact EHL

The effects of surface kinematic conditions on micro-elastohydrodynamic lubrication (micro-EHL) are investigated under rolling and/or sliding point contact conditions using the optical interferometry technique. A long bump of chromium sputtered on the surface of a highly polished ball is used as a model asperity. It is shown that the film thickness distribution or the elastic deformation of the bump is influenced significantly by the surface kinematic conditions and the orientation of the bump. An interesting phenomenon is also found when contacting surfaces move with different speeds; the thin film formed on a transversely oriented bump existing at the entrance of the contact travels through the contact region at the average speed of the surfaces. The experimental results obtained qualitatively confirm published numerical simulations.

Behavior of EHL Films in Reciprocating Motion.

The behavior of elastohydrodynamic lubrication (EHL) films formed between a steel ball and an oscillating glass disk is examined by means of the optical interferometry technique, and the results obtained are compared with those of tests conducted under unidirectional conditions. The surface traction is also measured. The film profile in the contact area breathes cyclically because the wedging and squeezing actions are not in phase. In reciprocation under pure sliding, the thick oil film entrapped between both surfaces at the stroke end moves towards the exit side at about half the velocity of the glass disk. Under conditions of a short stroke and a high frequency, air bubbles produced in the downstream result in the oil starvation in the next stroke, so that the EHL film collapses. In the full EHL regime, the central oil film thickness and the surface traction at the stroke center are almost the same as those under unidirectional conditions. It is also found that the oil behaves like a non-Newtonian fluid, and as a result the behavior of EHL films varies with oil and type of motion.

Effects of Elastic Moduli of Contact Surfaces in Elastohydrodynamic Lubrication

Using the optical interferometry technique the film profile in circular elastohydrodynamic contacts is examined with several kinds of fluid under wide ranges of loads and speeds. It is found that under a sliding condition a deep conical depression (dimple) occurs in the contact surface in place of the flat plateau predicted by the EHL theory. This dimple phenomena can be explained by the squeeze film effect acting parallel to the contact plane attributable to the difference in surface deflections of the contact bodies. That is, if the contacting bodies are different in their elastic moduli, EHL film shape is markedly influenced by the slide/roll ratio even if the rolling or entrainment velocity is kept constant. This result suggests that the establishment of a new EHL theory, which takes into consideration the effects of the difference in elastic moduli of the contacting surfaces and surface pressure components parallel to the contact tangent plane, is necessary for deeper understanding of the EHL regime.

Statistical interferometry based on the statistics of speckle phase

A new technique of optical interferometry based on the statistics of the fully developed speckle field is proposed. It is revealed that the complete randomness of the speckle phase can play the role of a standard phase in a statistical sense, and the phase of the object under testing can be derived in a statistical way, in contrast to conventional interferometry. The technique is first described in relation to the phase-shifting interferometry and the compensation problem for the phase-shift error. Next the method is generalized as an independent interferometric technique.

Surface characterization and identification by laser diffraction as a complementary technique to RBS

An optical interferometry technique is presented which can provide information of the surface morphology of remote samples. The technique can be used as a complement to RBS-based techniques or indeed as a substitute when RBS is not practical.

The study of rf plasma activated processes for stannic oxide thin film deposition

The chemical vapour deposition of SnO 2 films in a plasma of SnCl 4 and O 2 has been studied using optical emission spectroscopy and laser interferometry techniques. The Arrhenius equation with an activation energy of 0.25 eV can be used to describe the relationship between increase in the deposition rate and substrate temperature. The deposition rate depends apparently on the flow rate of SnCl 4. Under the experimental conditions the formation of SnO occurs mainly on the substrate surface.

Elastohydrodynamic Lubrication of Heavily Loaded Circular Contacts

The paper is concerned with theoretical analysis and experimental measurement of lubricant film thickness in heavily loaded elastohydrodynamic contacts in which the area of elastic deformation is approximately circular. The inverse elastohydrodynamic technique for numerical analysis of contacts of this type described by Evans and Snidle(9) has been used to produce solutions covering a wide range of conditions representative of engineering practice. Detailed solutions for film thickness and pressure have been obtained for conditions giving rise to maximum contact pressures of up to 4.1 GPa with steel surfaces and a mineral oil lubricant. On the basis of these results charts for film thickness have been constructed using the non-dimensional groups proposed by Moes and Bosma(12). Experimental measurements of film thickness have been made using the optical interferometry technique. The conditions used in the experiments have been numerically analysed to provide a direct comparison between theory and experiment. The comparison shows excellent agreement between the theoretical predictions and corresponding experimental measurements.

Mechanism of silicon film deposition in the RF plasma reduction of silicon tetrachloride

Plasma-chemical reduction of SiCl4 in mixtures with H2 and Ar has been studied by optical emission spectroscopy (OES) and laser interferometry techniques. It has been found that the Ar:H2 ratio strongly affects the plasma composition as well as the deposition (rD) and etch (rE) rates of Si: H, Cl films and that the electron impact dissociation is the most important channel for the production of SiClx species, which are the precursors of the film growth. Chemisorption of SiClx and the reactive surface reaction SiClx+H→−SiCl(x−1)0+HCl are important steps in the deposition process. The suggested deposition model givesrD ∞ [SiClx][H], in agreement with the experimental data. Etching of Si: H, Cl films occurs at high Ar: H2 ratio when Cl atoms in the gas phase become appreciable and increases with increasing Cl concentration. The etch rate is controlled by the Cl atom chemisorption step.

Superconducting Mbtallic Supkrlattices

ABSTRACTSince the coherence length is of order 50 Å to 1 μm, it is possible to alternately layer thin films of a superconductor with another material to affect the physical properties of the resulting superlattice. A brief description of our sputtering technique used to prepare superlat t ices consisting of Nb/Cu and Ta/Mo is given. Optical interferometry, x-ray diffraction and ion beam analysis techniques independently confirm that control of ±0.3% is achieved over the amount of material deposited in each layer. Results of a study of Josephson tunneling to Nb/Cu metallic super lattices are reviewed. These measurements enable a determination of the London penetration depth to be made as a function of superlattice layer thickness.

Optical Interferometry In Fluid Dynamics Research

Optical interferometry techniques have been applied to the investiga-tion of transonic airfoil flow fields in large-scale wind tunnels. Holographic interferometry techniques were used in the study of two-dimensional sym-metric NACA 64A010 and Douglas Aircraft Company DSMA671 supercritical airfoil performance in the NASA Ames 2 ft X2 ft transonic wind tunnel. Quan-titative data obtained from the interferograms were compared to the surface pressure data. The excellent agreement obtained verified the accuracy of the flow visualization and demonstrated the potential for acquiring quantitative scalar results. Measurements of the inviscid flow speed and the boundary layer and wake velocity profiles were extracted from the interferograms and com-pared to laser Doppler velocimeter measurements. These results were also in good agreement. A method for acquiring real-time interferometric data in large-scale facilities was developed. This method, based on the point diffraction interferometer, was successfully tested in the Ames 2 ft X2 ft transonic wind tunnel. The holographic and real-time interferometry methods were applied to the investigations of circulation control airfoils utilizing the Coanda effect. These results revealed the details of the jet interaction with the trailing edge boundary layer and the other parameters affecting the lift augmentation.

An Experimental Evaluation of the Hamrock and Dowson Minimum Film Thickness Equation for Fully Flooded EHD Point Contacts

Fifty-seven measurements of the minimum lubricant film thickness separating the elastohydrodynamically lubricated point contact of a steel crowned roller and a flat sapphire disk were made by an optical interferometry technique. The data collected were used to evaluate the Hamrock and Dowson minimum EHD film thickness model over a practical range of contact ellipticity ratio where the major axis of the contact ellipse is aligned both parallel and perpendicular to the direction of motion. A statistical analysis of the measured film thickness data showed that the experimental data averaged 30 percent greater film thickness than the Hamrock and Dowson model predicts.

Crack-tip damage and fracture toughness of borsic/titanium composite

The fracture behavior of center-notched unidirectional borsic/titanium composites under uniaxial tensile loading has been investigated. Load-crack-opening displacement (COD) curves were obtained for crack length-to-width ratios ranging from 0.05 to 0.5. The COD was measured across the crack surfaces by means of laser interferometric displacement gage (gage length of 500 μm). As expected, the interferometric displacement gage (IDG) was very sensitive to the appearance of damage at the crack tip, yielding nonlinear load-COD curves. The crack-tip damage in borsic/titanium was found to grow coplanarly with the original crack and consist of fiber breaks and matrix plastic deformation, the former preceding the latter. The failure mode and the crack-tip-damage growth were found to be different from those observed in unidirectional boron/aluminum and these differences are discussed. The examination techniques include radiography, SEM, photomicrographs, interference microscope and optical-interferometry technique. It was found that the fracture strengths and crack-tip-damage growth can be analyzed by the analytical models proposed in the literature. The resistance-curve method was also tried and found to be applicable. A correlation has been established among the fracture strength, crack-opening displacement and failure mode.

On the variation of fatigue-crack-opening load with measurement location

The work presented here evaluates the vlidity of using the load at the point of linearity on the displacement-load curve, as suggested by Elber, as an experimental measure of the crack-tip-opening load. Displacement-load behavior was investigated for a fatigue-cracked modified compact specimen of a nickel-base superally. Displacements were determined at the notch mouth using a standard clip-on gage, along the crack surface using a laser-interferometric displacement gage and, in the plastic zone ahead of the crack, using an optical-interferometry technique. Acoustic-emission monitoring was employed as a means to detect potential crack extension during measurement-load cycles and to detect physical-crack closure.The magnitude of the crack-tip-opening load, as determined from these measurmeents, is dependent on the distance from the crack tip at which the measurmenet is made. As an additional means of evaluating the crack-tip-opening load, crack-surface profiles are constructed from the displacement-load measurmeents made behind the crack tip. A discussion is given concerning the significance o these results in evaluating the validity of using the load at the point of linearity as a parameter to quantify crack closure.

Crack-Tip Damage and Fracture Toughness of Boron/Aluminum Composites

The fracture behavior of center notched unidirectional boron/aluminum composite under tensile loading has been investigated. Load-crack opening displacement (COD) curves were obtained for crack length-to-width ratios varying from 0.05 to 0.5. The COD was measured across the crack surfaces by means of the laser interferometric technique (gage length of 500 μm). As expected, the interferometric displacement gage (IDG) was found to be very sensitive to the appearance of damage at the crack tip, resulting in highly nonlinear load-COD curves. The damage at the crack-tip has been carefully examined by radiographs, SEM, photomicrographs, interfero metric miscroscope and optical interferometry technique. Fracture strength results and experimental load-COD curves were compared with analytical predictions and an excellent agreement has been established. The resistance curve method has also been tried and found to be non- applicable. An understanding of the correlation between the observed failure modes and deformation characteristics has been achieved.

Underwater optical holographic interferometry

Time-average optical holographic interferometry techniques have been used to obtain measurements of an array of sonar transducer elements operating underwater in a 15-m-diam 30-m-deep tank. Holograms were made from outside the tank through a pair of portholes using an argon-ion laser. Measurements were made to provide experimental verification of predicted acoustically induced mutual coupling effects. The quality of the hologram reconstructions was sufficient to resolve fringes spaced 1 mm apart from a viewing distance of 7.5 m.