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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Shear Band Formation in Plane Strain Experiments of Sand

A series of biaxial (plane strain) experiments were conducted on three sands under low (15 kPa) and high (100 kPa) confining pressure conditions to investigate the effects of specimen density, confining pressure, and sand grain size and shape on the constitutive and stability behavior of granular materials. The three sands used in the experiments were fine-, medium-, and coarse-grained uniform silica sands with rounded, subangular, and angular grains, respectively. Specimen deformation was readily monitored and analyzed with the help of a grid pattern imprinted on the latex membrane. The overall stress-strain behavior is strongly dependent on the specimen density, confining pressure, sand grain texture, and the resulting failure mode(s). That became evident in different degrees of softening responses at various axial strains. The relationship between the constitutive behavior and the specimens' modes of instability is presented. The failure in all specimens was characterized by two distinct and opposite shear bands. It was found that the measured dilatancy angles increase as the sand grains' angularities and sizes increase. The measured shear band inclination angles are also presented and compared with classical Coulomb and Roscoe solutions.

Alshibli, Khalid A.↗
NASA NTRS2000

Assessment of Constitutive and Stability Behavior of Sands Under Plane Strain Condition

A series of biaxial (plane strain) experiments were conducted on three sands under low (15 kPa) and high (100 kPa) confining pressure conditions to investigate the effects of specimen density, confining pressure, and sand grains size and shape on the constitutive and stability behavior of granular materials. The three sands used in the experiments were fine, medium, and coarse-grained uniform silica sands with rounded, sub-angular, and angular grains, respectively. Specimen deformation was readily monitored and analyzed with the help of a grid pattern imprinted on the latex membrane. The overall stress-strain behavior is strongly dependent on the specimen density, confining pressure, sand grain texture, and the resulting failure mode(s). That became evident in different degrees of softening responses at various axial strains. The relationship between the constitutive behavior and the specimens' modes of instability is presented. The failure in all specimens was characterized by two distinct and opposite shear bands. It was found that the measured dilatancy angles increase as the sand grains' angularity and size increase. The measured shear band inclination angles are also presented and compared with classical Coulomb and Roscoe solutions.

Alshibli, Khalid A.↗
NASA NTRS1979

Investigations on the hierarchy of reference frames in geodesy and geodynamics

Problems related to reference directions were investigated. Space and time variant angular parameters are illustrated in hierarchic structures or towers. Using least squares techniques, model towers of triads are presented which allow the formation of linear observation equations. Translational and rotational degrees of freedom (origin and orientation) are discussed along with and the notion of length and scale degrees of freedom. According to the notion of scale parallelism, scale factors with respect to a unit length are given. Three-dimensional geodesy was constructed from the set of three base vectors (gravity, earth-rotation and the ecliptic normal vector). Space and time variations are given with respect to a polar and singular value decomposition or in terms of changes in translation, rotation, deformation (shear, dilatation or angular and scale distortions).

Grafarend, E. W.↗
DOE OSTI2020

Effective field theory for deformed odd-mass nuclei

We develop an effective field theory (EFT) for deformed odd-mass nuclei. These are described as an axially symmetric core to which a nucleon is coupled. In the coordinate system fixed to the core the nucleon is subject to an axially symmetric potential. Power counting is based on the separation of scales between low-lying rotations and higher-lying states of the core. In leading order, core and nucleon are coupled by universal derivative terms. These comprise a covariant derivative and gauge potentials which account for Coriolis forces and relate to Berry-phase phenomena. At leading order, the EFT combines the particle-rotor and Nilsson models. Here, we work out the EFT up to next-to-leading order and illustrate the results in 239 Pu and 187 Os . At leading order, odd-mass nuclei with rotational bandheads that are close in energy and differ by one unit of angular momentum are triaxially deformed. For bandheads that are well separated in energy, triaxiality becomes a subleading effect. The EFT developed in this paper presents a model-independent approach to the particle-rotor system that is capable of systematic improvement.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

The total angular momentum algebra related to the S{sub 3} Dunkl Dirac equation

We consider the symmetry algebra generated by the total angular momentum operators, appearing as constants of motion of the S{sub 3} Dunkl Dirac equation. The latter is a deformation of the Dirac equation by means of Dunkl operators, in our case associated to the root system A{sub 2}, with corresponding Weyl group S{sub 3}, the symmetric group on three elements. The explicit form of the symmetry algebra in this case is a one-parameter deformation of the classical total angular momentum algebra so(3), incorporating elements of S{sub 3}. This was obtained using recent results on the symmetry algebra for a class of Dirac operators, containing in particular the Dirac–Dunkl operator for arbitrary root system. For this symmetry algebra, we classify all finite-dimensional, irreducible representations and determine the conditions for the representations to be unitarizable. The class of unitary irreducible representations admits a natural realization acting on a representation space of eigenfunctions of the Dirac Hamiltonian. Using a Cauchy–Kowalevski extension theorem we obtain explicit expressions for these eigenfunctions in terms of Jacobi polynomials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1990

On dynamics and control of multi-link flexible space manipulators

In this paper dynamics, inverse dynamics, and control problems for multi-link flexible space manipulators are presented. In deriving the flexible manipulator dynamics the following are assumed: flexible deformations are relatively small; angular rates of the links are much smaller than their fundamental frequencies; nonlinear terms (centrifugal and Coriolis forces) in the flexible manipulator model are the same as those in the rigid body model. These assumptions are reasonable for large space manipulators, such as the space crane. Flexible displacements are measured with respect to the rigid body configuration, for which a linear time-varying system is obtained. The inverse dynamics problem consists of determination of joint torques, given tip trajectory, such that joint angles in flexible configuration are equal to the angles in the rigid body configuration. The manipulator control system consists of the feedforward compensation and feedback control loops. Simulation results of a two-link space crane with large payload show that the performance of this linearized dynamics and control approach is reasonable and robust subject to parameter variations during slew operations.

Gawronski, W.↗
NASA NTRS2010

Comparative Analysis of the Effects of Severe Plastic Deformation and Thermomechanical Training on the Functional Stability of Ti50.5Ni24.5Pd25 High-Temperature Shape Memory Alloy

We compare the effectiveness of a conventional thermomechanical training procedure and severe plastic deformation via equal channel angular extrusion to achieve improved functional stability in a Ti50.5Ni24.5Pd25 high-temperature shape memory alloy. Thermomechanical testing indicates that both methods result in enhanced shape memory characteristics, such as reduced irrecoverable strain and thermal hysteresis. The mechanisms responsible for the improvements are discussed in light of microstructural findings from transmission electron microscopy.

Atli, K. C.↗
NASA NTRS2011

Shape Memory Characteristics of Ti(sub 49.5)Ni(sub 25)Pd(sub 25)Sc(sub 0.5) High-Temperature Shape Memory Alloy After Severe Plastic Deformation

A Ti(49.5)Ni25Pd25Sc(0.5) high-temperature shape memory alloy is thermomechanically processed to obtain enhanced shape-memory characteristics: in particular, dimensional stability upon repeated thermal cycles under constant loads. This is accomplished using severe plastic deformation via equal channel angular extrusion (ECAE) and post-processing annealing heat treatments. The results of the thermomechanical experiments reveal that the processed materials display enhanced shape memory response, exhibiting higher recoverable transformation and reduced irrecoverable strain levels upon thermal cycling compared with the unprocessed material. This improvement is attributed to the increased strength and resistance of the material against defect generation upon phase transformation as a result of the microstructural refinement due to the ECAE process, as supported by the electron microscopy observations.

Atli, K. C.↗
DOE OSTI2018

Enhanced Impact Toughness at Ambient Temperatures of Ultrafine-Grained Al-26 wt.% Si Alloy Produced by Equal-Channel Angular Pressing

Overcoming general brittleness of hypereutectic Al-Si alloys is in urgent need for expanding their application in automotive, aerospace and construction industries. A unique phenomenon was observed that bulk ultrafine-grained Al-26 wt.% Si alloy, produced by severe plastic deformation via equal-channel angular pressing, exhibited higher toughness at the impact temperature of − 196 ~ 100 °C than the coarse-grained casting alloy. The improvement in impact toughness at all testing temperatures was mainly due to the homogeneous ultrafine-grained structure with the breakage of brittle primary silicon crystals, which generated more and deeper fracture dimples that consumed much higher fracture energy. It indicates the advantage of bulk ultrafine-grained Al-Si alloys and spurs their application interest at various ambient temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Enhanced Hot Tensile Ductility of Mg-3Al-1Zn Alloy Thin-Walled Tubes Processed Via a Combined Severe Plastic Deformation

In the current study, combined parallel tubular channel angular pressing (PTCAP) and tube backward extrusion (TBE), as a recently developed severe plastic deformation (SPD) method, were applied at 300 °C on a commercial Mg-3Al-1Zn alloy tubes to achieve an ultrafine grained structure. Then, the microstructure, hardness, tensile properties, and fractography evaluations were done at room temperature on the SPD-processed samples. Also, to study the hot tensile ductility of the SPD-processed samples, tensile testing was performed at an elevated temperature of 400 °C, and then, the fractured surface of the tensile samples was studied. It was observed that a bimodal microstructure, with large gains surrounded by many tiny ones, was created in the sample processed by PTCAP followed by TBE. This microstructure led to reach higher hardness and higher strength at room temperature and also led to reach very high elongation to failure (~ 181%) at 400 °C. Also, the value of elongation to failure for this sample was ~ 14.1% at room temperature. The fractographic SEM images showed the occurrence of predominately ductile fracture in the samples pulled at 400 °C. This was mostly due to the nucleation of microvoids and their subsequent growth and coalescence with each other.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Process–structure–property relationships in bimodal machined microstructures using robust structure descriptors

Machining is a severe plastic deformation process that subjects materials to high rates of deformation and elevated temperatures. Dynamic recrystallization during severe plastic deformation drives grain refinement into the sub-micron range but the ductility and thermal stability of these structures is poor. In contrast, bimodal microstructures consisting of both fine and coarse grains have been shown to exhibit attractive strength and ductility properties at these temperatures. In this paper, we study the process–structure–property relationships for pure copper subject to a machining process where the cutting speeds are varied. Further, we investigate the role of thermal effects by varying the post-deformation cooling rates. Microstructures generated under these deformation conditions are quantified using angularly resolved chord length statistics. The derived metrics are found to be robust descriptors of the studied microstructures as they automatically capture complex features such as unimodal and bimodal distributions of grain structure, grain constituent length scales, and morphological anisotropy induced by shear deformation. The uniaxial equivalent yield strength of the generated structures are estimated using spherical nanoindentation and inverse modeling techniques. Lastly, we present a methodology for identifying the constrained property-process inverse mapping for machining using a Bayesian framework and the established forward process–structure–property mapping.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Comparison of the Thermal Stability in Equal‐Channel‐Angular‐Pressed and High‐Pressure‐Torsion‐Processed Fe–21Cr–5Al Alloy

Nanostructured steels are expected to have enhanced irradiation tolerance and improved strength. However, they suffer from poor microstructural stability at elevated temperatures. In this study, Fe–21Cr–5Al–0.026C (wt%) Kanthal D (KD) alloy belonging to a class of (FeCrAl) alloys considered for accident‐tolerant fuel cladding in light‐water reactors is nanostructured using two severe plastic deformation techniques of equal‐channel angular pressing (ECAP) and high‐pressure torsion (HPT), and their thermal stability between 500–700 °C is studied and compared. ECAP KD is found to be thermally stable up to 500 °C, whereas HPT KD is unstable at 500 °C. Microstructural characterization reveals that ECAP KD undergoes recovery at 550 °C and recrystallization above 600 °C, while HPT KD shows continuous grain growth after annealing above 500 °C. Enhanced thermal stability of ECAP KD is from significant fraction (>50%) of low‐angle grain boundaries (GBs) (misorientation angle 2–15°) stabilizing the microstructure due to their low mobility. Small grain sizes, a high fraction (>80%) of high‐angle GBs (misorientation angle >15°) and accordingly a large amount of stored GB energy, serve as the driving force for HPT KD to undergo grain growth instead of recrystallization driven by excess stored strain energy.

Arivu, Maalavan↗
DOE OSTI2017

Influence of alloying element Zn on the microstructural, mechanical and corrosion properties of binary Mg-Zn alloys after severe plastic deformation

Highlights: • Mg-Zn alloys are processed by equal channel angular pressing with back-pressure. • The α-Mg matrix consists of highly deformed and partially recrystallized areas. • Zn concentration varies in the α-Mg matrix by up to 2 at.%. • The alloys exhibit mechanical anisotropy and a significant increase in strength. • Equal channel angular pressing increases corrosion rate of Mg-Zn alloys. - Abstract: This work presents an analysis of the microstructural, mechanical and corrosion properties of two binary Mg-Zn alloys. Mg-6 wt%Zn and Mg-12 wt%Zn cast alloys were subjected to annealing followed by quenching and processed via equal channel angular pressing with applied back-pressure (ECAP-BP). After ECAP-BP, both alloys were thoroughly examined and showed partially recrystallized and highly deformed areas. High-angle annular dark-field imaging revealed a difference in Zn content across the α-Mg matrix of the Mg-12 wt%Zn after ECAP-BP due to the growth of MgZn{sub 2} nanoparticles. Electron energy-loss spectroscopy (EELS) was carried out to qualify an average Zn content in these areas, and a variation in Zn content up to 2 at.% was found. Compression tests revealed mechanical anisotropy and a significant increase in the strength of both alloys after ECAP-BP. The yield strength, σ{sub 02}, was in the range from 269 to 385 MPa depending on the composition and compression axis. The initial state alloys showed yield strengths, σ{sub 02}, of only 75–150 MPa but improved ductility. The corrosion rates of the Mg-Zn alloys in the initial state, evaluated using a hydrogen evolution method in NaCl solution, were higher for Mg-12 wt%Zn. The corrosion rates of both alloys after ECAP-BP were higher than those of the initial state. Light microscopy observations did not reveal any preference for corrosion propagation, including transcrystalline, intercrystalline or interphase corrosion, in any of the materials.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Angular Momentum in Rotating Superfluid Droplets

The angular momentum of rotating superfluid droplets originates from quantized vortices and capillary waves, the interplay between which remains to be uncovered. Here, the rotation of isolated submicrometer superfluid 4 He droplets is studied by ultrafast x-ray diffraction using a free electron laser. The diffraction patterns provide simultaneous access to the morphology of the droplets and the vortex arrays they host. In capsule-shaped droplets, vortices form a distorted triangular lattice, whereas they arrange along elliptical contours in ellipsoidal droplets. The combined action of vortices and capillary waves results in droplet shapes close to those of classical droplets rotating with the same angular velocity. The findings are corroborated by density functional theory calculations describing the velocity fields and shape deformations of a rotating superfluid cylinder.

O'Connell, Sean M.O.↗
DOE OSTI2018

Apparatus for deformation of solid sections

An equal channel angular extrusion tool comprising a punch assembly, a die set assembly, a base assembly, and a bottom slider assembly. The punch assembly comprises a punch, a punch nose, and a punch trolley. The die set assembly comprises an inlet channel and a removable core. The base assembly comprises a lifting mechanism which further comprises a die lift cylinder and a hold down ram. The bottom slider assembly comprises an ejection ram. The tool also includes a billet. The billet may be disposed in the bottom slider assembly. Severe plastic deformation is applied to the billet in the bottom slider assembly.

Barber, Robert E.↗
DOE OSTI2019

High Resolution Mapping of Orientation and Strain Gradients in Metals by Synchrotron 3D X-ray Laue Microdiffraction

Synchrotron 3D X-ray Laue microdiffraction, available at beamline 34-ID-E at Advanced Photon Source in Argonne National Laboratory, is a powerful tool for 3D non-destructive mapping of local orientations and strains at sub-micron scale in the bulk. With this technique, it is possible to study local residual stresses developed during manufacturing or while in service due to interactions between, for example, different phases and/or grains with different orientations in materials containing multiple or single phase(s). Such information is essential for understanding mechanical properties and designing advanced materials, but is largely non-existent in the current generation of materials models. In the present paper, the principle and experimental set-up of the 3D microdiffraction are introduced, followed by a description of a method for quantification of the local plastic deformation based on high-angular-resolution orientation maps. The quantification of local residual stresses in two model materials, ductile cast iron (two phases) and partially recrystallized pure nickel (single phase), using 3D microdiffraction will then be presented. The results show that 3D microdiffraction is important for understanding the origin of local residual stresses and to relate them to the microstructural evolution. Finally, the limitations of the 3D microdiffraction on the current generation synchrotron source and new possibilities after the synchrotron upgrade are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Formation Mechanism of Nanoscale Al{sub 3}Fe Phase in Al-Fe Alloy During Semisolid Forming Process

The formation mechanism of nanoscale Al{sub 3}Fe phase in Al-1Fe (wt pct) alloy during rheo-extrusion was investigated, and the mechanical property of the prepared alloy was also measured. The results show that the average length of Al{sub 3}Fe phase in Al-1Fe alloy prepared by rheo-extrusion is 300 nm, which is much more refined than the needlelike Al{sub 3}Fe phase in as-cast Al-1Fe alloy (50 μm). In rheo-extrusion, Al{sub 3}Fe phase formed by eutectic reaction is bonelike, but it could be continuously refined by the shear deformation in the wheel groove, in equal channel angular flow, and in expansion extrusion mold. The total equivalent strain of the shear deformation is higher than 4.82. The tensile strength and elongation of Al-1Fe alloy prepared by rheo-extrusion are 135 MPa and 30 pct, respectively. The tensile strength of Al-1Fe alloy prepared by rheo-extrusion is 58.8 pct higher than that of as-cast Al-1Fe alloy, and the elongation is 19 pct higher than that of as-cast Al-1Fe alloy. Compared with as-cast Al-1Fe alloy, the improvements of tensile strength and elongation caused by shear deformation in rheo-extrusion are higher than the reported improvements induced by rare earth modification.

36 MATERIALS SCIENCE↗