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Results for “Dynamics (Mechanics)”

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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS2026

Electromagnetic Melt Processing: A Pathway to New Additive Manufacturing Technologies for Functional High-Performance Thermoplastics

In this study, we apply the electromagnetic (EM) melt processing of thermoplastics on an innovative EM field-driven powder bed fusion additive manufacturing (AM) concept for high-performance functional parts: Selective Microwave Melting/Sintering (SMM/SMS). This technique leverages the EM susceptibility of carbon nanotube-coated polymer micro-pellets to achieve rapid, localized heating and powder fusion. Thus, selective microwave melting (SMM) was used to fabricate multilayer specimens made of recycled polyphenylene sulfide (rPPS) and carbon nanotubes (CNTs). The resulting SMM specimens exhibited very good interlayer integrity, localized fusion at pellet boundaries, and tolerable residual porosity, indicating effective fusion and acceptable consolidation. CNT-rich interphases were retained after irradiation, generating anisotropic electrically active network pathways and enabling conductivity enhancement at low filler content. At only 1.0 wt% CNT, the specimens exhibited electrical conductivity approximately three orders of magnitude higher than neat rPPS. Dynamic mechanical analysis showed improved viscoelastic response relative to neat rPPS, while tensile testing confirmed that the SMM-processed specimens retained practical mechanical integrity despite localized voids. These results demonstrate that SMM can effectively consolidate EM susceptible thermoplastic powder beds while preserving their segregated conductive networks. This may become a scalable route for producing multifunctional thermoplastic parts with low filler loadings, tunable anisotropy, and structured materials and parts. Overall, the findings suggest that EM field-based AM can help overcome key limitations of conventional thermoplastic processing by enabling scalable, energy-efficient fabrication of nanostructured composites and expanding AM to a broader range of resins, including high-performance thermoplastics with customized functional properties.

Powder bed fusion↗
NASA NTRSDate not supplied

Quantum Mechanical Simulations of Dynamics of Electronic Excitations in Low-Dimensional Photovoltaics Materials

Dynamics of electronically excited states including exciton generation and relaxation, exciton-exciton interaction, and charge/energy transfer and transport, are critical to understanding and optimizing photovoltaic materials. Although considerable progress has been made, accurate experimental characterization of such crucial dynamics remains extremely challenging, especially in low-dimensional materials. In this talk, I will discuss how the advancement of quantum mechanical simulations of the dynamics of electronic excitations can reveal the physical mechanisms hindering or improving solar energy harvest. Specifically, we find that surface dangling-bond defects on silicon quantum dots cause rapid charge recombination and low carrier mobility in the inorganic-organic PV cells. Although small quantum dots are essentially free of defects, their optical gaps are too large. To solve this issue, a full-spectrum-light-absorption scheme is computationally designed, taking advantage of complexity and flexibility of low-dimensional materials consisting of different characteristics and dimensions. In this scheme the multifunctional ligands are used to (1) passivate against oxidation, (2) facilitate interfacial charge transfer, and (3) improve both charge transport and optical absorption. A joint theoretical and experimental study has demonstrated the feasibility of this approach. Finally, I will briefly talk about how this scheme and the well-tested quantum mechanical simulations can be employed to help improve energy-conversion efficiency in perovskite photovoltaics including perovskite-based tandem cells.

Zhigang Wu↗
NASA NTRS2000

Coupled Thermo-Mechanical Analyses of Dynamically Loaded Rubber Cylinders

A procedure that models coupled thermo-mechanical deformations of viscoelastic rubber cylinders by employing the ABAQUS finite element code is described. Computational simulations of hysteretic heating are presented for several tall and short rubber cylinders both with and without a steel disk at their centers. The cylinders are compressed axially and are then cyclically loaded about the compressed state. The non-uniform hysteretic heating of the rubber cylinders containing a steel disk is presented. The analyses performed suggest that the coupling procedure should be considered for further development as a design tool for rubber degradation studies.

Johnson, Arthur R.↗
NASA NTRS1992

Hardening mechanisms in a dynamic strain aging alloy, Hastelloy X, during isothermal and thermomechanical cyclic deformation

The relative contributions of the hardening mechanisms in Hastelloy X during cyclic deformation were investigated by conducting isothermal cyclic deformation tests within a total strain range of +/-0.3 pct and at several temperatures and strain rates, and thermomechanical tests within several different temperature limits. The results of the TEM examinations and special constant structure tests showed that the precipitation on dislocations of Cr23C6 contributed to hardening, but only after sufficient time above 500 C. Solute drag alone produced very considerable cyclic hardening. Heat dislocation densities, peaking around 10 exp 11 per sq cm, were found to develop at temperatures producing the greatest cyclic hardening.

Miner, R. V.↗
NASA NTRS1966

Mechanism continuously measures static and dynamic cable loads

Pulley mechanism measures the tensile loads on a cable under static and dynamic conditions, without disturbing the continuity of operation of the system. A set of takeoff pulleys are mounted on a pivoted frame that is linked to a strain gage which measures the frame displacement as a function of the static or dynamic tensile load on the cable.

Source record↗
NASA NTRS1989

Probalistic Finite Elements (PFEM) structural dynamics and fracture mechanics

The purpose of this work is to develop computationally efficient methodologies for assessing the effects of randomness in loads, material properties, and other aspects of a problem by a finite element analysis. The resulting group of methods is called probabilistic finite elements (PFEM). The overall objective of this work is to develop methodologies whereby the lifetime of a component can be predicted, accounting for the variability in the material and geometry of the component, the loads, and other aspects of the environment; and the range of response expected in a particular scenario can be presented to the analyst in addition to the response itself. Emphasis has been placed on methods which are not statistical in character; that is, they do not involve Monte Carlo simulations. The reason for this choice of direction is that Monte Carlo simulations of complex nonlinear response require a tremendous amount of computation. The focus of efforts so far has been on nonlinear structural dynamics. However, in the continuation of this project, emphasis will be shifted to probabilistic fracture mechanics so that the effect of randomness in crack geometry and material properties can be studied interactively with the effect of random load and environment.

Liu, Wing-Kam↗
NASA NTRS2002

Thermo-Mechanical Analyses of Dynamically Loaded Rubber Cylinders

Thick rubber components are employed by the Army to carry large loads. In tanks, rubber covers road wheels and track systems to protect roadways. It is difficult for design engineers to simulate the details of the hysteretic heating for large strain viscoelastic deformations. In this study, an approximation to the viscoelastic energy dissipated per unit time is investigated for use in estimating mechanically induced viscoelastic heating. Coupled thermo-mechanical simulations of large cyclic deformations of rubber cylinders are presented. The cylinders are first compressed axially and then cyclically loaded about the compressed state. Details of the algorithm and some computational issues are discussed. The coupled analyses are conducted for tall and short rubber cylinders both with and without imbedded metal disks.

Johnson, Arthur R.↗
NASA NTRS1977

Dynamics and certain mechanisms in the changes of the skeletal-muscular system of man under bedrest conditions

Bed rest conditions evaluated varied in the longitudinal axis of the body, perpendicular to the vector gravitational forces, and the cranial portion of the body inclined from the horizontal. The duration of bed rest fluctuated in various experiments from 30 to 182 days. The state of muscle and neuromuscular system was judged on the basis of the recording of various functional indices, as well as by certain results of morphological and biochemical studies and data from the study of motor functions.

Oganov, V. G.↗
NASA NTRS1983

Structures and Dynamics Division: Research and technology plans for FY 1983 and accomplishments for FY 1982

The objectives, expected results, approach, and milestones for research projects of the IPAD Project Office and the impact dynamics, structural mechanics, and structural dynamics branches of the Structures and Dynamics Division are presented. Research facilities are described. Topics covered include computer aided design; general aviation/transport crash dynamics; aircraft ground performance; composite structures; failure analysis, space vehicle dynamics; and large space structures.

Bales, K. S.↗
NASA NTRS1987

A substructure technique for dynamics of flexible mechanical systems with contact-impact

A substructure synthesis method is proposed to account for contact-impact effects in flexible components of mechanical systems. Components that may come into contact is divided into substructures, on each of which local deformation modes are defined to described deformation fields of components. Constraint modes and fixed interface normal modes are used to account for elastic deformation within each substructure. A constraint addition-deletion technique is used to account for contact between impacting bodies. Lagrange multipliers associated with the constraints, which represent constraint forces, are used to determine separation of contacting nodes. Use of the method is illustrated on problems of longitudinal and transverse impact of bodies.

Wu, S.-C.↗
NASA NTRS1988

Computational structural mechanics and fluid dynamics: Advances and trends; Proceedings of the Symposium, Washington, DC, Oct. 17-19, 1988

Recent advances in computational structural and fluid dynamics are discussed in reviews and reports. Topics addressed include fluid-structure interaction and aeroelasticity, CFD techniques for reacting flows, micromechanics, stability and eigenproblems, probabilistic methods and chaotic dynamics, and perturbation and spectral methods. Consideration is given to finite-element, finite-volume, and boundary-element methods; adaptive methods; parallel processing machines and applications; and visualization, mesh generation, and AI interfaces.

Noor, Ahmed K.↗
NASA NTRS1990

Dayside auroral particle acceleration mechanisms derived from Dynamics Explorer data

The characteristics of dayside electron acceleration regions, or inverted V's, and the nature of the field-aligned currents flowing in their vicinity are studied by using data from Dynamics Explorer hot-plasma and magnetic-field instruments. It is shown that dayside inverted-V events are common features of the mid-altitude extension of the boundary layer, which lies equatorward of the cusp. Upward-accelerated ionospheric electron beams are found to be carriers of downward region-1 currents even in regions of downward electron acceleration. It is not clear, however, how the upward-accelerated cold electron beams can exist above an apparent upward parallel electric field, since such a potential different would tend to confine the cold ionospheric electrons to low altitudes.

Burch, J. L.↗
NASA NTRS1992

A low-altitude mechanism for mesoscale dynamics, structure, and current filamentation in the discrete aurora

The 2D nonlinear evolution of the ionization-driven adiabatic auroral arc instability is studied. We find: (1) the adiabatic auroral arc instability can fully develop on time scales of tens to hundreds of seconds and on spatial scales of tens to hundreds of kilometers; (2) the evolution of this instability leads to nonlinear 'hook-shaped' conductivity structures: (3) this instability can lead to parallel current filamentation over a wide range of scale sizes; and (4) the k-spectra of the density, electric field, and parallel current develop into inverse power laws in agreement with satellite observations. Comparison with mesoscale auroral phenomenology and current filamentation structures is made.

Keskinen, M. J.↗
NASA NTRS1972

Dynamics of the molecular and atomic mechanisms for the hydrogen-iodine exchange reaction.

The molecular and atomic mechanisms for the hydrogen-iodine exchange reaction are treated theoretically by means of extensive classical trajectories calculated on a reasonable potential energy surface on which the single adjustable parameter is the iodine-core effective charge. The analysis shows the molecular mechanism to be dynamically forbidden, but gives an over-all rate constant for the atomic mechanism that is in agreement with the experimental values. It is indicated that the formation of a weak H2I complex plays an important dynamical role if the atomic mechanism is limited to reactions with collision complexes involving no more than two hydrogen atoms and two iodine atoms. Excellent agreement with experiment is obtained for the rate constant for the recombination I+I+H2 yields I2+H2 and its negative temperature coefficient.

Raff, L. M.↗