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Results for “Contact angle”

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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Durable Anti-Reflective and Anti-Fog Coatings Produced by Aerosol Impact Driven Assembly

The Exploration Extravehicular Mobility Unit’s (xEMU) helmet is a complex assembly designed to accomplish several tasks to protect and enable astronauts. In addition to maintaining a suitable environment for the wearer, it must also allow for appropriate mobility and provide a wide and undistorted view of the surroundings. A critical component of the helmet’s optical system is the anti-fog coating. While previous versions of the anti-fog coating have provided suitable anti-fog performance, they have been difficult to apply, lacked mechanical or chemical durability, or resulted in unanticipated failures (e.g., outgassing of eye-irritating materials during use). This work describes the use of a new coating technology, aerosol impact-driven assembly (AIDA), to develop a next-generation permanent anti-fog coating for the xEMU helmet. AIDA’s unique ability to tune both the refractive index and surface roughness of films was used to deposit a thin, transparent (>85% transmittance of visible light), and hydrophilic (contact angle <10°) anti-fog coating. The coating’s abrasion resistance and chemical resistance was evaluated and it was found that the coating maintained both its anti-fog and anti-reflective functionally. Finally, the scalability of the process was demonstrated by successfully coating the polycarbonate blanks used to form the helmet’s bubble.

Spacesuit↗
NASA NTRSDate not supplied

Laser Ablative Patterning of B4C and MoAlB Ceramics for Hydrophobic Surfaces

Through a novel laser ablative patterning (LAP) process, the present work reports the increase in wetting contact angle of molybdenum aluminum boride (MoAlB) and the reduction of dust adhesion. The LAP technique employed picosecond laser pulses to form a crosshatch pattern with micropillars on ceramic surfaces. The wetting behavior was successfully transitioned from hydrophilic (θ < 90°) to hydrophobic (θ > 90°), which may be related to Wenzel or Cassie-Baxter mechanisms. Parameters such as laser fluence and number of laser scans were varied to study their effects on ceramic surface characteristics. Dust adhesion experiments were performed on these hydrophobic ceramic surfaces, which showed that the adhesion of lunar soil simulant dust particles was significantly reduced in the patterned MoAlB surface. The patterned MoAlB samples were further examined using the surveying lunar dust influence on device efficacy (SLIDE) testbed to evaluate the wear performance.

Bai Cui↗
NASA NTRS2026

Decoupling Surface Topography from Gravitational Acceleration in Cryogenic Pool Boiling

Boiling heat transfer is governed by a complex interplay between surface conditions and gravitational acceleration. To isolate the sole effects of gravity, we investigated the pool boiling characteristics of liquid nitrogen on atomically smooth silicon dioxide (SiO 2 ) surfaces under terrestrial (1-g) and reduced gravity (0±0.02 g) conditions achieved via parabolic flight. Our results quantify a drastic reduction in the critical heat flux (CHF) in reduced gravity, decreasing from 16.15 W/cm 2 at 1-g to 5−6 W/cm 2 at μ-g due to the suppression of buoyancy. Conversely, we observed a distinct increase in the heat transfer coefficient (HTC) in the reduced gravity condition prior to CHF. By utilizing a surface with a maximum peak-to-valley height of ≈36.7 nm and low contact angle hysteresis (<10°), we confirm this HTC enhancement is an intrinsic response to the gravitational environment, decoupled from surface-defect-induced nucleation. These findings demonstrate that the influence of surface topography is significantly more prominent in reduced gravity than in terrestrial conditions, providing a critical baseline for rationalizing the design of cryogenic thermal management systems in space and quantum applications.

Liquid nitrogen↗
NASA NTRS1991

Effects of bolt-hole contact on bearing-bypass damage-onset strength

A combined experimental and analytical study was conducted to investigate the effects of bolt-hole contact on the bearing bypass strength of a graphite-epoxy laminate. Tests were conducted on specimens consisting of 16-ply quasi-isotropic T300/5208 laminates with a centrally located hole. Bearing loads were applied through a clearance-fit steel bolt. Damage onset strength and damage mode were determined for each test case. A finite element procedure was used to calculate the bolt-hole stresses and bolt contact for each test case. A finite element procedure was used to calculate the bolt-hole stresses and bolt contact for each measured damage-onset strength. For the tension bearing-bypass cases tested, the bolt contact half-angle was approximately 60 degrees at damage onset. For compression, the contact angle was 20 degrees as the bypass load increased. A corresponding decrease in the bearing damage onset strength was attributed to the decrease in contact angle which made the bearing loads more severe. Hole boundary stresses were also computed by superimposing stresses for separate bearing and bypass loading. Stresses at the specimen net section were accurately approximated by the superposition procedure. However, the peak bearing stresses had large errors because the bolt contact angles were not represented correctly. For compression, peak bearing stress errors of nearly 50 percent were calculated.

Crews, John H., Jr.↗
NASA NTRS1986

Investigation of non-linear contact for a clearance-fit bolt in a graphite/epoxy laminate

Numerous analytical studies have been published for the nonlinear load-contact variations in clearance-fit bolted joints. In these studies, stress distributions have been obtained and failure predictions have been made. However, very little experimental work has been reported regarding the contact or the stresses. This paper describes a fiber-optic technique for measuring the angle of contact in a clearance-fit bolt-loaded hole. Measurements of the contact angle have been made in a quasi-isotropic graphite-epoxy laminate by the optical as well as an electrical technique, and the results have been compared with those obtained from a finite-element analysis. The results from the two experimental techniques show excellent agreement; the finite-element results show some discrepancy, probably due to the interfacial frictions.

Prabhakaran, R.↗
NASA NTRS2017

Growth Angle: A Microscopic View

A microscopic continuum mechanical model of the growth angle is proposed. It is based on the van der Waals type framework that is used for surface force phenomena. The obtained augmented Laplace type integro-differential equations are, in general, difficult to analyze. Here we focused primarily on the particular case of equal melt and crystal surface energies. We derived an approximate equation for the meniscus shape, and obtained an analytical relationship between the contact and the growth angle. Interestingly, the same result can be obtained using the macroscopic model of Herring. The case of a macroscopically sharp corner is also considered. For this case, the macroscopic angle is not defined and it can be any angle between the contact angles of both flat surfaces. The microscopic model yields the smooth shape for the meniscus that also is not unique, but depends on the initial position of the meniscus.

Mazuruk, Konstantin↗
NASA NTRS1995

Hydrodynamics of coalescing binary neutron stars: Ellipsoidal treatment

We employ an approximate treatment of dissipative hydrodynamics in three dimensions to study the coalescence of binary neutron stars driven by the emission of gravitational waves. The stars are modeled as compressible ellipsoids obeying a polytropic equation of state; all internal fluid velocities are assumed to be linear functions of the coordinates. The hydrodynamics equations then reduce to a set of coupled ordinary differential equations for the evolution of the principal axes of the ellipsoids, the internal velocity parameters, and the binary orbital parameters. Gravitational radiation reaction and viscous dissipation are both incorporated. We set up exact initial binary equilibrium configurations and follow the transition from the quasi-static, secular decay of the orbit at large separation to the rapid dynamical evolution of the configurations just prior to contact. A hydrodynamical instability resulting from tidal interactions significantly accelerates the coalescence at small separation, leading to appreciable radial infall velocity and tidal lag angles near contact. This behavior is reflected in the gravitational waveforms and may be observable by gravitational wave detectors under construction. In cases where the neutron stars have spins which are not aligned with the orbital angular momentum, the spin-induced quadrupole moment can lead to precession of the orbital plane and therefore modulation of the gravitational wave amplitude even at large orbital radius. However, the amplitude of the modulation is small for typical neutron star binaries with spins much smaller than the orbital angular momentum.

Lai, Dong↗
NASA NTRS1996

Three-dimensional roller locking sprags

A torque coupling sprag system which provides contact between the sides of at least one groove and at least two contact surfaces angled with respect to the central axial direction of at least one rotatable 3-D sprag member located between a drive member and a reaction member. The surface contacts between the members include various combinations of surface segments arranged in a predetermined manner to define a desired configuration. The contact radius of the 3-D sprag member is significantly larger than its rolling radius; however, radii can be varied in size and shape independently of each other, particularly the contact radius.

Vranish, John M.↗
NASA NTRS1974

Effect of gravity on liquid phase sintering

The unique conditions offered by the earth orbital environment in material processing involving both solid and liquid phases, such as liquid phase sintering, were studied. An experimental development program involving both test and theoretical work was initiated. Experimental work using material combinations selected such that maximum information about the effect of gravity can be derived has been conducted. Wetting of the solid phase by the liquid during sintering is an important phenomenon in liquid phase sintering, and gravity has influence on both capillary phenomenon and density segregation; hence, material combinations were selected such that these two effects can be suitably studies. The experimental work is meant to form the basis for similar comparative work done under low-g conditions. The part of the model dealing with the capillary phenomenon, as related to liquid phase sintering and the effect of gravity on it, suggest that gravity will have negligible effect on the Bond number and that the cohesive force is dependent on both the amount of liquid phase and the angle of contact.

Mookherji, T.↗
NASA NTRS1980

Methods for an investigation of the effect of material components on the mechanical characteristics of glass-fiber-reinforced plastics

The materials used in the production of glass reinforced plastics are discussed. Specific emphasis is given to matrix polyester materials, the reinforcing glass materials, and aspects of specimen preparation. Various methods of investigation are described, giving attention to optical impregnation and wetting measurements and the gravimetric determination of the angle of contact. Deformation measurements and approaches utilizing a piezoelectric device are also considered.

Willax, H. O.↗
NASA NTRS1982

The stability of the axially symmetric pendent drop

The axially symmetric pendent drop as it occurs in three different physical settings is analyzed: Problem A with constant pressure and a fixed circular opening (the siphon); Problem B with constant volume and a fixed circular opening (the medicine dropper); and Problem C with prescribed volume and a constant angle of contact with a horizontal plate. As examples, the results are verified. For Problem B it is shown that if the opening is small enough to support a stable pendent drop with a bulge, then as the exposed volume is increased, stable pendent drops with both a neck and a bulge will be formed. For Problem C it is shown that with increasing volume the profile curves for the family of stable pendent drops will develop an inflection point before instability arises.

Wente, H. C.↗
NASA NTRS1985

The determination of minority carrier lifetimes in direct band-gap semiconductors by monitoring intensity-modulated luminescence radiation

When an extrinsic, direct band-gap semiconductor sample is irradiated by photons of an energy higher than the energy of the band gap between valence and conduction bands, excess electron-hole pairs are generated which, while diffusing through the sample, produce luminescence via radiative recombination. If, furthermore, the intensity of the impinging beam of photons is modulated sinusoidally, the luminescence radiation escaping from the sample will be phase shifted with respect to the original photon beam in a characteristic way. It will be shown that by measuring the phase shift at different modulation frequencies, the Shockley-Read-Hall lifetime of minority carriers may be ascertained. The method is nondestructive inasmuch as there is no need to fabricate p-n junctions or Ohmic contacts, nor is it necessary to remove already existing Ohmic contacts of angle lap the surface, etc., procedures often needed when determining lifetimes with the scanning electron microscope (in which case a p-n junction must be present).

Von Roos, O.↗
NASA NTRS1988

Application of optical and photomechanical techniques in the study of mechanical joints

A fiber-optic technique and the conventional photoelastic technique were applied to the investigation of pin-loaded specimens which simulate pin joints and bolted joints. The angle of contact between the pin and the hole was measured by these techniques and compared with finite element results. The stress distributions obtained form the otoelastic response were also compared with the finite element results. Such comparisons are needed to verify the finite element model and to assess the role of important joint variables such as friction.

Prabhakaran, R.↗
NASA NTRS2017

An Evaluation of Structural Analysis Methodologies for Space Deployable Structures

Benchmarks are introduced for evaluating the performance of numerical simulations of space deployable structures. These benchmarks embody the key challenges of interest to future large space deployable structures, including large angle motion, contact between flexible bodies, and the presence of both soft and stiff mechanical components. The benchmarks were used in companion studies to evaluate the ADAMS multibody dynamics code, the LS-Dyna nonlinear finite element code, and the Sierra large-scale parallel nonlinear finite element code. In the past, only multibody codes would have been considered for this application. This study found that all three codes could be used for these benchmarks, a finding that may lead to larger scale, higher fidelity simulations in the future.

Mobrem, Mehran↗
NASA NTRS2019

The Unrealized Potential of Superhydrophobic Substrates in Advanced Life Support Systems

Nearly all water processing equipment aboard spacecraft is to a large extent controlled by capillary forces arising from substrate wetting conditions. Superhydrophobic wetting conditions provide an essentially passive means to keep water away from certain substrates providing a level of no-moving-parts phase separation and control. This work presents a host of non-wetting aqueous microgravity capillary fluidics phenomena arising from interactions with easily fabricated superhydrophobic substrates. The value of such phenomena for potential life support applications aboard spacecraft is clear, especially for substrate properties that are thermally robust, corrosion resistant, and self-cleaning for both long- and short term applications. Large length scale low-g demonstrations of the phenomena are provided in HD video format for the extensive drop tower tests conducted. The broader crosscutting impacts to numerous fluids processing operations for life support are discussed. Current practical applications addressed in light of superhydrophobicity include urine-processing, water recovery, fire safety, and others.

Superhydrophoic↗
NASA NTRSDate not supplied

Materials for Cryogenic Propellant Dewetting

The purpose of this experiment campaign is to find materials or surface coatings that repel ("dewet") cryogenic propellants. This presentation summarizes progress up to this point.

contact angle↗
NASA NTRS1989

Recursive forward dynamics for multiple robot arms moving a common task object

Recursive forward dynamics algorithms are developed and presented for an arbitrary number of robot arms moving a commonly held object. The multiarm forward dynamics problem is to find the angular accelerations at the joints and the contact forces that the arms impart to the task object. The problem also involves finding the acceleration of this object. The multiarm forward dynamics solutions provide a thorough physical and mathematical understanding of the way several arms behave in response to a set of applied joint moments. Such an understanding simplifies and guides the subsequent control design and experimentation process. The forward dynamics algorithms also provide the necessary analytical foundation for conducting analysis and simulation studies. The multiarm algorithms are based on the filtering and smoothing approach recently advanced for single-arm dynamics, and they can be built up modularly from the single-arm algorithms. The algorithms compute recursively the joint angle accelerations, the contact forces, and the task-object accelerations. Algorithms are also developed to evaluate in closed form the linear transformations from the active joint moments to the joint angle accelerations, to the task object accelerations, and to the task-object contact forces. A possible computing architecture is presented as a precursor to a more complete investigation of the computational performance of the dynamics algorithms.

Rodriguez, Guillermo↗
NASA NTRS1988

Recursive forward dynamics for multiple robot arms moving a common task object

Recursive forward dynamics algorithms are developed for an arbitrary number of robot arms moving a commonly held object. The multiarm forward dynamics problem is to find the angular accelerations at the joints and the contact forces that the arms impart to the task object. The problem also involves finding the acceleration of this object. The multiarm forward dynamics solutions provide a thorough physical and mathematical understanding of the way several arms behave in response to a set of applied joint moments. Such an understanding simplifies and guides the subsequent control design and experimentation process. The forward dynamics algorithms also provide the necessary analytical foundation for conducting analysis and simulation studies. The multiarm algorithms are based on the filtering and smoothing approach recently advanced for single-arm dynamics, and they can be built up modularly from the single-arm algorithms. The algorithms compute recursively the joint-angle accelerations, the contact forces, and the task-object accelerations. Algorithms are also developed to evaluate in closed form the linear transformations from the active joint moments to the joint-angle accelerations, to the task-object accelerations., and to the task-object contact forces. A possible computing architecture is presented as a precursor to a more complete investigation of the computational performance of the dynamics algorithms.

Rodriguez, G.↗