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At least 1,585 records · Page 88
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Strength Ranking of Hard-Alloy Cutting Inserts of Different Shape

The stress–strain state of replaceable polyhedral inserts in composite tools is calculated by the finite-element method. The influence of the insert’s design parameter, the basing and attachment configuration, and the load on the stress and strain is established. Besides the strength of the inserts, attention is paid to the positional accuracy in the tool housing. Cutting inserts of maximum strength have been developed and patented.

42 ENGINEERING↗
DOE OSTI2016

Edge flame structure in a turbulent lifted flame: A direct numerical simulation study

This paper presents here a statistical analysis of edge flames in a turbulent lifted flame using direct numerical simulation (DNS). To investigate the dynamics of edge flames, a theoretical framework describing the edge-flame propagation velocity as a function of propagation velocities of mixture-fraction and product-mass fraction iso-surfaces at the flame base is used. The correlations between these propagation velocities and several other variables are then studied, including iso-surface curvatures, iso-surface orientations, strain rates, scalar dissipation rate and gradients of product mass fraction. The contribution of these parameters to the overall behaviour of the edge flame is also investigated using conditional averaging on two-dimensional spatial locations at the flame base. The analysis reveals that the tangential and normal strain rates in addition to the curvatures and scalar dissipation rates have significant contributions to the overall behaviour of the edge flame. The elliptical motion of the flame base described in our earlier study is extended to provide a clearer picture of how these various parameters affect the large fluctuations of edge-flame velocity observed at the flame base.

42 ENGINEERING↗
DOE OSTI2019

Hot Deformation Mechanisms of Ti22Al25Nb Orthorhombic Alloy

In this paper, the hot deformation behavior of Ti22Al25Nb was investigated by hot compression over a range of temperatures (950-1050 °C) and strain rates (0.001-1 s{sup −1}). Considering the adiabatic heating and friction, the original curves were corrected. The friction-corrected data were lower than the measured flow stress data. The flow stress data increased after the temperature correction owing to the elimination of the softening effect. In addition, the work hardening effects on the hot deformation of the normal and multi-peak flow stress curves were compared. A critical dislocation density was proposed to analyze the multi-peak phenomenon. When the dislocation density decreased to a critical value, the work hardening and dynamic recrystallization mechanisms reached a balance. Then, a new work hardening mechanism became dominant, and the flow stress increased. The effect of second-phase particles on the hot deformation mechanisms was investigated. The result showed that second-phase particles led to a high nucleation rate and a low growth rate of new recrystallization grains during the rapid hot deformation.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Synthesis of polyketides from low cost substrates by the thermotolerant yeast Kluyveromyces marxianus

Kluyveromyces marxianus is a promising nonconventional yeast for biobased chemical production due to its rapid growth rate, high TCA cycle flux, and tolerance to low pH and high temperature. Unlike Saccharomyces cerevisiae, K. marxianus grows on low-cost substrates to cell densities that equal or surpass densities in glucose, which can be beneficial for utilization of lignocellulosic biomass (xylose), biofuel production waste (glycerol), and whey (lactose). Additionally, we have evaluated K. marxianus for the synthesis of polyketides, using triacetic acid lactone (TAL) as the product. The 2-pyrone synthase (2-PS) was expressed on a CEN/ARS plasmid in three different strains, and the effects of temperature, carbon source, and cultivation strategy on TAL levels were determined. The highest titer was obtained in defined 1% xylose medium at 37°C, with substantial titers at 41 and 43°C. The introduction of a high-stability 2-PS mutant and a promoter substitution increased titer four-fold. 2-PS expression from a multi-copy pKD1-based plasmid improved TAL titers a further five-fold. Combining the best plasmid, promoter, and strain resulted in a TAL titer of 1.24 g/L and a yield of 0.0295 mol TAL/mol carbon for this otherwise unengineered strain in 3 ml tube culture. This is an excellent titer and yield (on xylose) before metabolic engineering or fed-batch culture relative to other hosts (on glucose), and demonstrates the promise of this rapidly growing and thermotolerant yeast species for polyketide production.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Three-dimensional X-ray diffraction imaging of dislocations in polycrystalline metals under tensile loading

Abstract The nucleation and propagation of dislocations is an ubiquitous process that accompanies the plastic deformation of materials. Consequently, following the first visualization of dislocations over 50 years ago with the advent of the first transmission electron microscopes, significant effort has been invested in tailoring material response through defect engineering and control. To accomplish this more effectively, the ability to identify and characterize defect structure and strain following external stimulus is vital. Here, using X-ray Bragg coherent diffraction imaging, we describe the first direct 3D X-ray imaging of the strain field surrounding a line defect within a grain of free-standing nanocrystalline material following tensile loading. By integrating the observed 3D structure into an atomistic model, we show that the measured strain field corresponds to a screw dislocation.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Emergent multiferroism with magnetodielectric coupling in EuTiO 3 created by a negative pressure control of strong spin-phonon coupling

Negative pressure has emerged as a powerful tool to tailor the physical properties of functional materials. However, a negative pressure control of spin-phonon coupling for engineering magnetism and multiferroicity has not been explored to date. Here, using uniform three-dimensional strain-induced negative pressure in nanocomposite films of (EuTiO 3 ) 0.5 :(MgO) 0.5 , we demonstrate an emergent multiferroicity with magnetodielectric coupling in EuTiO 3 , matching exactly with density functional theory calculations. Density functional theory calculations are further used to explore the underlying physics of antiferromagnetic-paraelectric to ferromagnetic-ferroelectric phase transitions, the spin-phonon coupling, and its correlation with negative pressures. The observation of magnetodielectric coupling in the EuTiO 3 reveals that an enhanced spin-phonon coupling originates from a negative pressure induced by uniform three-dimensional strain. Our work provides a route to creating multiferroicity and magnetoelectric coupling in single-phase oxides using a negative pressure approach.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Interleaved bond frustration in a triangular lattice antiferromagnet

Frustration of long-range order via lattice geometry amplifies fluctuations and generates ground states that are highly sensitive to perturbations. Traditionally, geometric frustration is used to engineer unconventional magnetic states; however, the charge degree of freedom and bond order can be similarly frustrated. Finding materials that host both frustrated magnetic and bond networks holds promise for engineering structural and magnetic states with the potential of coupling to one another via either magnetic or strain fields. Here we identify an unusual instance of this coexistence in the triangular lattice antiferromagnets LnCd 3 P 3 (Ln = lanthanides). These compounds feature two-dimensional planes of unique trigonal planar CdP 3 units with an underlying bond instability that is frustrated via emergent kagome ice correlations. This bond instability is interleaved in between layers of frustrated magnetic moments. Furthermore, our results establish LnCd 3 P 3 as a rare materials class in which frustrated magnetism is embedded within a dopable semiconductor with a frustrated bond order instability.

Gomez Alvarado, S. J. [University of California, S↗
DOE OSTI2019

Making metals linear super-elastic with ultralow modulus and nearly zero hysteresis

We demonstrate a novel materials design approach to achieve unprecedented properties by utilizing nanoscale chemo-mechanical coupling. In particular, by using computer simulations we demonstrate how to engineer ultralow modulus (12 GPa), nearly hysteresisfree, and linear super-elastic metals with a giant elastic strain limit (2.7%) by creating appropriate concentration modulations (CMs) at the nanoscale in the parent phase and by pre-straining to regulate the stress-induced martensitic transformation (MT). The nanoscale CMs created via spinodal decomposition produce corresponding phase stability modulations, suppress autocatalysis in nucleation, impose nano-confinements on growth, and hinder long-range ordering of transformation strain during the MT, which changes the otherwise sharp first-order transition into a smeared, macroscopically continuous transition over a large stress range. The pre-straining generates retained martensitic particles that are stable at the test temperature after unloading and act as operational nuclei in subsequent load cycles, eliminating the stress–strain hysteresis and offering an ultralow apparent Young’s modulus. Materials with a high strength and an ultralow apparent Young’s modulus have great potential for application in orthopaedic implants.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Engineered Root Bacteria Release Plant-Available Phosphate from Phytate

Phosphate fertilizers are essential for high-yield agriculture yet are costly and environmentally damaging. Microbes that release soluble phosphate from naturally occurring sources in the soil are appealing, as they may reduce the need for such fertilizers. In this study, we used synthetic biology approaches to create a collection of engineered root-associated microbes with the ability to release phosphate from phytate. We demonstrate that these strains improve plant growth under phosphorus-limited conditions. This represents a first step in the development of phosphate-mining bacteria for future use in crop systems.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2012

Clostridium thermocellum ATCC27405 transcriptomic, metabolomic and proteomic profiles after ethanol stress

Clostridium thermocellum is a candidate consolidated bioprocessing biocatalyst, which is a microorganism that expresses enzymes for both cellulose hydrolysis and its fermentation to produce fuels such as lignocellulosic ethanol. However, C. thermocellum is relatively sensitive to ethanol compared to ethanologenic microorganisms such as yeast and Zymomonas mobilis that are used in industrial fermentations but do not possess native enzymes for industrial cellulose hydrolysis. In this study, C. thermocellum was grown to mid-exponential phase and then treated with ethanol to a final concentration of 3.9 g/L to investigate its physiological and regulatory responses to ethanol stress. Samples were taken pre-shock and 2, 12, 30, 60, 120, and 240 min post-shock, and from untreated control fermentations for systems biology analyses. Cell growth was arrested by ethanol supplementation with intracellular accumulation of carbon sources such as cellobiose, and sugar phosphates, including fructose-6-phosphate and glucose-6-phosphate. The largest response of C. thermocellum to ethanol shock treatment was in genes and proteins related to nitrogen uptake and metabolism, which is likely important for redirecting the cells physiology to overcome inhibition and allow growth to resume. This study suggests possible avenues for metabolic engineering and provides comprehensive, integrated systems biology datasets that will be useful for future metabolic modeling and strain development endeavors.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

A Platform for Genome-Scale Design, Redesign, and Optimization of Bacterial Systems

This project was a collaboration between the Gill and Knight labs at University of Colorado Boulder, the Arkin lab at University of California Berkeley, and the Maness group at the National Renewable Energy Laboratory. There were two main objectives for this project: Objective 1: Integrated, genome-scale strategy for “chassis” strain design and construction. Objective 2: Genome “re-design” framework using multiplex synbio and genome-engineering technologies.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1978

Thermal-structural mission analyses of air-cooled gas turbine blades

Cyclic temperature and stress-strain states in cooled turbine blades were calculated for a simulated mission of an advanced technology aircraft engine. TACT1 (three dimensional heat transfer) and MARC (nonlinear structural analysis) computer programs were used to analyze impingement cooled airfoils, with and without leading-edge film cooling. Creep was the predominant damage mode, particularly around film cooling holes. Radially angled holes exhibited less creep than holes normal to surface. Beam-type analyses of all-impingement cooled airfoils gave fair agreement with MARC results for initial creep.

Kaufman, A.↗
NASA NTRS1979

Thermal-structural mission analyses of air-cooled gas turbine blades

Cyclic temperature and stress-strain states in cooled turbine blades were calculated for a simulated mission of an advanced technology aircraft engine. TACTl (three dimensional heat transfer) and MARC (nonlinear structural analysis) computer programs were used to analyze impingement cooled airfoils, with and without leading-edge film cooling. Creep was the predominant damage mode, particularly around film cooling holes. Radially angled holes exhibited less creep than holes normal to surface. Beam-type analyses of all-impingement cooled airfoils gave fair agreement with MARC results for initial creep.

Kaufman, A.↗
NASA NTRS1988

Evaluation of structural analysis methods for life prediction

The utility of advanced constitutive models and structural analysis methods are evaluated for predicting the cyclic life of an air-cooled turbine blade for a gas turbine aircraft engine. Structural analysis methods of various levels of sophistication were exercised to obtain the cyclic stress-strain response at the critical airfoil location. Calculated strain ranges and mean stresses from the stress-strain cycles were used to predict crack initiation lives by using the total strain version of the strain range partitioning life prediction method. The major results are given and discussed.

Kaufman, A.↗
NASA NTRS1994

Long duration biaxial cylinder testing of balloon grade polyethylene films with emphasis on automated data acquisition and control

Characterization of a 2-dimensional material constitutive model in the practical biaxial state for engineering utility of balloon envelope structural analysis is achievable with laboratory cylinder tests. Hoop (circumferential, and longitudinal strains are time-wise measured on axially loaded pressurized cylinders. Pre-programmed ramped loading changes as well as precise long term pressure control are achieved through cascaded proportional, integral derivative (PID) flow control loops that are part of an integrated data acquisition and process control system. Real time data reduction and analysis allow monitoring of unattended tests that have durations of up to a month. Measured and controlled parameters and variables are discussed; date analysis techniques are reviewed.

Martone, Michael↗
NASA NTRS1995

Finite-Element Modeling For Structural Analysis

Report presents study of finite-element mathematical modeling as used in analyzing stresses and strains at joints between thin, shell-like components (e.g., ducts) and thicker components (e.g., flanges or engine blocks). First approach uses global/local model to evaluate system. Provides correct total response and correct representation of stresses away from any discontinuities. Second approach involves development of special transition finite elements to model transitions between shells and thicker structural components.

Min, J. B.↗
NASA NTRS1999

Neural-Net Processing of Characteristic Patterns From Electronic Holograms of Vibrating Blades

Finite-element-model-trained artificial neural networks can be used to process efficiently the characteristic patterns or mode shapes from electronic holograms of vibrating blades. The models used for routine design may not yet be sufficiently accurate for this application. This document discusses the creation of characteristic patterns; compares model generated and experimental characteristic patterns; and discusses the neural networks that transform the characteristic patterns into strain or damage information. The current potential to adapt electronic holography to spin rigs, wind tunnels and engines provides an incentive to have accurate finite element models lor training neural networks.

Decker, Arthur J.↗