Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Analytical thermo-mechanics 3D model of friction pendulum bearings: Analytical Thermo-mechanics 3D Model of FP Bearings

Among the most effective seismic protection devices, friction pendulum (FP), whose conceptual basis lies in the pendulum motion and its simple analytical description, has now gained a widespread acceptance. All the studies carried out so far have explored almost all the remarkable features of this device. Among the most appealing are constant stiffness, constant oscillation period, and recentering capability. These studies - and the authors found no exception - have systematically made reference to the classical gravity pendulum equation, whose motion occurs only in one dimension (1D), according to one DOF: the polar angle $θ$. When the presence of bi-directional seismic excitation required a 2D model, authors have resorted to the vector combination of the response of two orthogonal 1D pendulums, which we refer to as '1.5D' pendulum. Actually, FP is more correctly described as a 2D spherical pendulum, consisting of a mass moving on a sphere with friction, according to two DOFs: the polar angle θ and the azimuth angle φ. The relevant analytical equations of motion are presented in this paper, also accounting for thermo-mechanical coupling, to model the friction-induced temperature on the contact surface. The so-developed equations have been the object of an ample parametric study. This has allowed to observe some - sometimes notable - features in the FP response, both in free oscillation state and under bi-directional or tri-directional earthquake-like action, which in some cases lead to a different response with respect to what is generally computed - and designed - under the simplified assumptions of 1D or '1.5D' pendulum motion.

42 ENGINEERING↗
DOE OSTI2015

Evaluation of the Mechanical Properties of Naturally Grown Multilayered Oxides Formed on HCM12A Using Small Scale Mechanical Testing

The microstructure and mechanical integrity of protective multilayered oxide films grown in liquid metal on F/M steel HCM12A was investigated utilizing Raman spectroscopy, nanoindentation and micro-cantilever testing methods. Here, the Raman spectra showed a Fe3O4 outer layer and a Cr-rich spinel structure inner layer. The nanoindentation results showed a higher hardness value for the inner layer than for the outer layer. In addition, the hardness of the diffusion layer in between the inner layer and the bulk steel was measured. Quantitative fracture properties were obtained of the steel/oxide interface and within the oxide layers utilizing microcantilever testing. Furthermore the strength and elastic properties of the multilayered oxide film were measured and it was found that the porous structure in the inner Fe–Cr oxide limits the integrity of the steel/oxide interface.

14 SOLAR ENERGY↗
DOE OSTI2018

Regularities and Mechanisms of Formation of Submicro-, Nano-, and Ultrafine-Grained Structures and Mechanical Properties of Metals and Alloys Under Different Treatments

An overview of our original studies and the results reported in the literature on the investigation of variations in structure, phase composition, mechanical and other properties of metallic materials under external impacts is made, including their high-pressure processing by large (severe) plastic and megaplastic deformation, explosion loading, and irradiation with ultra-short laser pulses.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Mechanisms of Hydrogen-Assisted Magnesiothermic Reduction of TiO{sub 2}

Direct reduction of TiO{sub 2} powder has been attempted for decades by researchers in an effort to decrease titanium (Ti) metal production costs. The main objective has been to avoid energy-intensive steps involved in production of primary Ti by the Kroll process. The emerging hydrogen-assisted magnesiothermic reduction process, which uses Mg to directly reduce TiO{sub 2} powder under a H{sub 2} atmosphere, has been shown to have the potential to compete directly with the Kroll process. The present studies represent an effort to understand the reduction reaction mechanisms of this process. Phase transformations and the reaction pathways are examined by SEM/EDX analysis of partially reduced powder cross-sectional, X-ray diffraction, and other analytical techniques. The results show important morphological changes, the prominent intermediate and final phases under the H{sub 2} atmosphere, as well as the local deposition behavior of the MgO byproduct. The effect of the specific surface areas of the initial particles is also discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Development and Mechanical Properties of In Situ Al{sub 3}Ti-Reinforced Nanostructured AA6061 via Mechanical Alloying

Mechanical alloying (MA) was used to disperse 10 wt.% titanium powder in AA6061 powder. The resultant powder was degassed, and differential scanning calorimetry was performed to determine the temperature for formation of titanium aluminide (Al{sub 3}Ti). The MA powder was characterized by field emission scanning electron microscopy, x-ray diffraction (XRD) and transmission electron microscopy (TEM). Subsequently, the MA powder was consolidated by spark plasma sintering (SPS) at 500 °C under a pressure of 50 MPa. XRD and x-ray energy-dispersive spectroscopy of spark plasma sintered compact revealed in situ formation of Al{sub 3}Ti. TEM micrographs of spark plasma sintered sample exhibited Al nanograins (average size 50 nm) in the AA6061 matrix along with the dispersed Al{sub 3}Ti (average size 200 nm). Hardness, yield strength and compressive strength of the SPSed samples were also evaluated and compared with AA6061.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Role of Si in the Surface Damage Mechanism of RB-SiC/Si Under Mechanical Loading

Indentation test (Nanoindentation and Vickers indentation), diamond scratching and high spindle speed grinding are conducted to investigate the role of silicon (Si) in the surface damage behavior of reaction-bonded SiC/Si composites (RB-SiC/Si). Even though the addition of Si contributes to densifying the bulk materials and improving the toughness, the indentation and diamond scratching results firstly indicate that the cracks initiate at the SiC/Si interfaces due to the non-uniform deformation caused by the existence of Si, and the phase transformation of Si also leads to the pop-out effect during the nanoindentation and the diamond scratching test. The ground surface of RB-SiC/Si is characterized by scratching grooves and brittle fracture, indicating the ductile material removal mode and brittle material removal mode for RB-SiC/Si, respectively, and the surface reliefs form on the ground surface due to the different hardness between Si and SiC phases. Moreover, the phase transformation of Si contributes to the easy fracture of phase boundaries under the mechanical loading, and the accompanied volume change also results in the dislodgement of hard particles and the generation of surface burs on the ground surface.

36 MATERIALS SCIENCE↗
DOE OSTI2021

AFRL Additive Manufacturing Modeling Series: Challenge 4, In Situ Mechanical Test of an IN625 Sample with Concurrent High-Energy Diffraction Microscopy Characterization

In this work, we describe 3D characterization of an additively manufactured Inconel 625 nickel-base superalloy specimen conducted during a uniaxial tension test using a suite of nondestructive x-ray techniques. High-energy diffraction microscopy in both near- and far-field modalities are employed in situ to track evolution of the material orientation and stress–strain fields at six points during the mechanical test, and these data streams are registered with micro-computed tomography reconstructions which probe the material density. This data volume was matched to a multi-modal serial sectioning characterization of the specimen taken after loading, described in this article’s companion. Twenty-eight grains which were monitored throughout the experiment were selected to form the basis for AFRL AM Modeling Series Challenge 4, Microscale Structure-to-Properties.

36 MATERIALS SCIENCE↗