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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

An extremum principle for computation of the zone of tooth contact and generalized transmission error of spiral bevel gears

For a given set of forces transmitted by the gears, each of the three components of the generalized transmission error of spiral bevel gears is shown to be stationary with respect to small independent variations in the positions of the endpoints of the lines of tooth contact about their true values. The tangential generalized transmission error component is shown to take on a minimum value at the true endpoint positions. A computational procedure based on the method of steepest descent is described for computing the true line of contact endpoint positions and the three components of the generalized transmission error. A method for computing the Fourier series coefficients of the tooth meshing harmonics of the three generalized transmission error components also is provided.

Mark, W. D.↗
NASA NTRS1990

Transmission errors and bearing contact of spur, helical and spiral bevel gears

An investigation of transmission errors and bearing contact of spur, helical and spiral bevel gears was performed. Modified tooth surfaces for these gears have been proposed in order to absorb linear transmission errors caused by gear misalignment and to localize the bearing contact. Numerical examples for spur, helical, and spiral bevel gears are presented to illustrate the behavior of the modified gear surfaces with respect to misalignment and errors of assembly. The numerical results indicate that the modified surfaces will perform with a low level of transmission error in non-ideal operating environments.

F. L. Litvin↗
NASA NTRS1989

Elasto-plastic finite element analyses of two-dimensional rolling and sliding contact deformation of bearing steel

An elastoplastic finite element analysis of repeated rolling-plus-sliding contact is presented for the elastic-linear-kinematic hardening-plastic properties of hardened bearing steel at room temperature. Contacts in the absence of frictional heating are found to produce peak cyclic strain ranges and residual stresses that are similar to the values obtained for pure rolling. For the cases considered, the energy dissipated as heat by plastic deformation is found to be 3-15 percent of the energy dissipated at the surface by friction.

Kumar, A. M.↗
NASA NTRS1988

Crowned spur gears - Methods for generation and Tooth Contact Analysis. II - Generation of the pinion tooth surface by a surface of revolution

A method for generation of crowned pinion tooth surfaces using a surface of revolution is developed. The crowned pinion meshes with a regular involute gear and has a prescribed parabolic type of transmission errors when the gears operate in the aligned mode. When the gears are misaligned the transmission error remains parabolic with the maximum level still remaining very small (less than 0.34 arc second for the numerical examples). Tooth Contact Analysis (TCA) is used to simulate the conditions of meshing, determine the transmission error, and the bearing contact.

Litvin, F. L.↗
NASA NTRS1989

The physics of positively biased conductors surrounded by dielectrics in contact with a plasma

The physics of a positively biased conductor surrounded by dielectrics in contact with plasma is investigated. It is shown that because of the presence of secondary emission from the surrounding dielectrics, the voltage of the surfaces near the conductor has three solutions. The high- and low-voltage solutions are stable, while the intermediate-voltage solution is unstable. This theory is applied to explain the snapover effect observed on high-voltage solar arrays that involve the use of highly biased surfaces in contact with the space environment.

Hastings, Daniel E.↗
NASA NTRS1990

Rolling-Contact Spalling In Bearings

Report describes experimental and theoretical studies of effects of thermal and mechanical contact stresses and attendant plastic deformations responsible for rolling-contact spalling of the 440C-steel bearings in high-pressure-oxygen turbopump.

Kumar, A. M.↗
NASA NTRS1989

Generation and tooth contact analysis of spiral bevel gears with predesigned parabolic functions of transmission errors

A new approach for determination of machine-tool settings for spiral bevel gears is proposed. The proposed settings provide a predesigned parabolic function of transmission errors and the desired location and orientation of the bearing contact. The predesigned parabolic function of transmission errors is able to absorb piece-wise linear functions of transmission errors that are caused by the gear misalignment and reduce gear noise. The gears are face-milled by head cutters with conical surfaces or surfaces of revolution. A computer program for simulation of meshing, bearing contact and determination of transmission errors for misaligned gear has been developed.

Litvin, Faydor L.↗
NASA NTRS1990

On the numerical solution of the dynamically loaded hydrodynamic lubrication of the point contact problem

The transient analysis of hydrodynamic lubrication of a point-contact is presented. A body-fitted coordinate system is introduced to transform the physical domain to a rectangular computational domain, enabling the use of the Newton-Raphson method for determining pressures and locating the cavitation boundary, where the Reynolds boundary condition is specified. In order to obtain the transient solution, an explicit Euler method is used to effect a time march. The transient dynamic load is a sinusoidal function of time with frequency, fractional loading, and mean load as parameters. Results include the variation of the minimum film thickness and phase-lag with time as functions of excitation frequency. The results are compared with the analytic solution to the transient step bearing problem with the same dynamic loading function. The similarities of the results suggest an approximate model of the point contact minimum film thickness solution.

Lim, Sang G.↗
NASA NTRS1990

An analysis of the contact sintering process in III-V solar cells

The possibility of eliminating the gross mechanical changes that take place during sintering while retaining the processes that reduce contact resistivity is investigated. Before considering the electrical aspects, however, it is necessary to understand the relevant metallurgy. As the sintering process proceeds in the InP-Au system, dramatic color changes occur that enable a precise measurement of the kinetics of each step. A detailed insight into the processes that control each stage in the InP-Au interaction has resulted. It is shown that contact sintering in the InP-Au system consists of three consecutive stages, each of which is controlled by a separate mechanism.

Weizer, Victor G.↗
NASA NTRS1989

On the simulation of space based manipulators with contact

An efficient method of simulating the motion of space based manipulators is presented. Since the manipulators will come into contact with different objects in their environment while carrying out different tasks, an important part of the simulation is the modeling of those contacts. An inverse dynamics controller is used to control a two armed manipulator whose task is to grasp an object floating in space. Simulation results are presented and an evaluation is made of the performance of the controller.

Walker, Michael W.↗
NASA NTRS1988

Contact formation in gallium arsenide solar cells

Gold and gold-based alloys, commonly used as solar cell contact materials, are known to react readily with gallium arsenide. Experiments were performed to identify the mechanisms involved in these GaAs-metal interactions. It is shown that the reaction of GaAs with gold takes place via a dissociative diffusion process. It is shown further that the GaAs-metal reaction rate is controlled to a very great extent by the condition of the free surface of the contact metal, an interesting example of which is the previously unexplained increase in the reaction rate that has been observed for samples annealed in a vacuum environment as compared to those annealed in a gaseous ambient. A number of other hard-to-explain observations, such as the low-temperature formation of voids in the gold lattice and crystallite growth on the gold surface, are explained by invoking this mechanism.

Weizer, Victor G.↗
NASA NTRS1991

Flange Correction For Metal-To-Metal Contacts

Improved mathematical model provides correction for flange effect in estimating resistance of square contact between two metal layers from standard four-terminal measurements. Extended version of one developed previously for contact between metal layer and semiconductor layer, wherein flange effect important in semiconductor layer only. Here flange effect in both metal layers significant. Interfacial resistances extracted more accurately.

Lieneweg, Udo↗
NASA NTRS1990

Contact angle determination procedure and detection of an invisible surface film

The contact angle value, i.e., the tangent angle of liquid resting on a planar solid surface, is a basic parameter which can be applied to a wide range of applications. The goal is to provide a basic understanding of the contact angle measurement technique and to present a simple illustration that can be applied as a quality control method; namely, detection of a surface contaminant which exists on a surface that appears clean to the unaided eye. The equipment and experimental procedures are detailed.

Meyer, G.↗
NASA NTRS1991

Contact stresses in gear teeth: A new method of analysis

A new, innovative procedure called point load superposition for determining the contact stresses in mating gear teeth. It is believed that this procedure will greatly extend both the range of applicability and the accuracy of gear contact stress analysis. Point load superposition is based upon fundamental solutions from the theory of elasticity. It is an iterative numerical procedure which has distinct advantages over the classical Hertz method, the finite element method, and over existing applications with the boundary element method. Specifically, friction and sliding effects, which are either excluded from or difficult to study with the classical methods, are routinely handled with the new procedure. Presented here are the basic theory and the algorithms. Several examples are given. Results are consistent with those of the classical theories. Applications to spur gears are discussed.

Somprakit, Paisan↗
NASA NTRS1991

Elasto-plastic coupled temperature-displacement finite element analysis of two-dimensional rolling-sliding contact with a translating heat source

The present paper describes a transient translating elastoplastic thermomechanical finite element model to study two-dimensional frictional rolling contact. Frictional two-dimensional contact is simulated by repeatedly translating a nonuniform thermomechanical distribution across the surface of an elastoplastic half space. The half space is represented by a two-dimensional finite element mesh with appropriate boundaries. Calculations are for an elastic-perfectly plastic material and the selected thermophysical properties are assumed to be temperature independent. The paper presents temperature variations, stress and plastic strain distributions and deformations. Residual tensile stresses are observed. The magnitude and depth of these stresses depends on (1) the temperature gradients and (2) the magnitudes of the normal and tangential tractions.

Rubin, C. A.↗
NASA NTRS1990

Monitoring of contact stresses in advanced propulsion systems

This paper discusses a new and innovative numerical procedure for evaluating and monitoring contact stresses in the mating surfaces of propulsion systems. The procedure is intended to extend the range of applicability and the accuracy of contact stress analyses. Originally proposed by Burton Paul, et. al., (1981) the procedure is based upon fundamental solutions from the theory of elasticity. It is an iterative numerical procedure. It is believed that the method has distinct advantages over the classical Hertz method, the finite-element method and over existing approaches with the boundary element method. Several examples are discussed. Favorable comparisons are obtained with classical results. Applications with mating element of propulsion systems are discussed.

Somprakit, Paisan↗
NASA NTRS1990

A contact stress model for multifingered grasps of rough objects

The model developed utilizes a contact-stress analysis of an arbitrarily shaped object in a multifingered grasp. The fingers and the object are all treated as elastic bodies, and the region of contact is modeled as a deformable surface patch. The relationship between the friction and normal forces is nonlocal and nonlinear in nature and departs from the Coulomb approximation. The nature of the constraints arising out of conditions for compatibility and static equilibrium motivated the formulation of the model as a nonlinear constrained minimization problem. The model is able to predict the magnitude of the inwardly directed normal forces and both the magnitude and direction of the tangential (friction) forces at each finger-object interface for grasped objects in static equilibrium.

Sinha, Pramath Raj↗
NASA NTRS1991

Contact stresses in gear teeth - A new method of analysis

A new, innovative procedure called point load superposition for determining the contact stresses in mating gear teeth is presented. It is believed that this procedure will greatly extend both the range of applicability and the accuracy of gear contact stress analysis. Point load superposition is based upon fundamental solutions from the theory of elasticity. It is an iterative numerical procedure which has distinct advantages over the classical Hertz method, the finite element method, and over existing applications with the boundary element method. Specifically, friction and sliding effects, which are either excluded from or difficult to study with the classical methods, are routinely handled with the new procedure. Presented here are the basic theory and the algorithms. Several examples are given. Results are consistent with those of the classical theories. Applications to spur gears are discussed.

Somprakit, Paisan↗