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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Volatile organic compound emissions from 4D printing: Effects of material composition and external stimulus

4D printing of stimuli-responsive materials extends 3D printing by enabling the fabricated structures to transform their shapes and properties over time in response to external stimuli. Numerous research efforts have been dedicated to developing new smart materials, enhancing material printability, and ensuring time-evolving properties. Meanwhile, the use of smart materials and external stimuli in 4D printing has introduced the possibility of air emissions that can potentially deteriorate the indoor air quality at the workplace and pose continuous health hazards to users during the production and use phases. These potential air emissions caused by 4D printing have not yet been assessed in current literature, leading to unknown occupational hazards and human health effects. This study focuses on stereolithography-based 4D printing with constrained thermo-mechanics and builds an emission model to quantify the volatile organic compound emissions from printing, shape programming, and shape recovery stages. The established model mathematically links the emission characteristics with material compositional design and stimuli-response mechanisms. Additionally, shape fixity and recovery abilities are considered to analyze the trade-off between the air emissions and stimuli-response performance of 4D printed parts. Case study results suggest that the methacrylate-based thermo-responsive material with higher glass transition temperature leads to higher air emissions, surpassing the permissible exposure level in the indoor environment. By altering the thermo-temporal conditions, a 61.29% reduction in emission yield can be achieved while ensuring a satisfactory shape memory performance.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Deep learning–based digital twins for heat pumps

Heat pumps are effective cooling and heating appliances to save energy in buildings. However, traditional heat pump models are challenging to integrate with building demands in a co-simulation environment because of the nonlinear thermodynamics of refrigerants. Developing digital twin representatives for heat pumps capable of faster calculations with good accuracy is desirable. This study aimed to establish a generic deep learning–based digital twin for heat pumps with a large amount of high-fidelity data. Two refrigerants for two different heat pumps were considered: an air source heat pump with refrigerant R-410A, an air source heat pump with refrigerant CO 2 , a water source heat pump with refrigerant R-410A, and a water source heat pump with refrigerant CO 2 . Furthermore, results showed that the deep learning (long short-term memory) models effectively represented these four heat pumps as a digital twin: (a) accuracy for training and testing showed smaller than 0.02 for heating electricity and heating demands, and (b) the digital twins showed good consistency with original data for heating electricity and heating demands (root mean square errors of less than 0.12 W and 0.19 W, respectively). Therefore, deep learning–based heat pump models can be used in the co-simulation of building mechanical systems.

Air source heat pump↗
DOE OSTI2020

Modification to the Hawking temperature of a dynamical black hole by a flow-induced supertranslation

One interesting proposal to solve the black hole information loss paradox without modifying either general relativity or quantum field theory, is the soft hair, a diffeomorphism charge that records the anisotropic radiation in the asymptotic region. This proposal, however, has been challenged, given that away from the source the soft hair behaves as a coordinate transformation that forms an Abelian group, thus unable to store any information. To maintain the spirit of the soft hair but circumvent these obstacles, we consider Hawking radiation as a probe sensitive to the entire history of the black hole evaporation, where the soft hairs on the horizon are induced by the absorption of a null anisotropic flow, generalizing the shock wave considered in [1, 2]. To do so we introduce two different time-dependent extensions of the diffeomorphism associated with the soft hair, where one is the backreaction of the anisotropic null flow, and the other is a coordinate transformation that produces the Unruh effect and a Doppler shift to the Hawking spectrum. Together, they form an exact BMS charge generator on the entire manifold that allows the nonperturbative analysis of the black hole horizon, whose surface gravity, i.e. the Hawking temperature, is found to be modified. The modification depends on an exponential average of the anisotropy of the null flow with a decay rate of 4M, suggesting the emergence of a new 2-D degree of freedom on the horizon, which could be a way out of the information loss paradox.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Effects of deposition and annealing conditions on the crystallisation of NiTi thin films by e-beam evaporation

This Letter demonstrates the effects of deposition and annealing conditions on the crystallisation of nickel–titanium (NiTi) thin films deposited by the e-beam evaporation. NiTi thin films of 0.5 μm thick are fabricated on P-type (110) silicon substrates using the e-beam evaporation technique. We find that with the characterisations using the X-ray diffraction method, the results indicate that low e-beam deposition rate and argon employed annealing procedures can be beneficial to the formation of NiTi crystalline structure. Additionally, the as-deposited NiTi thin films without annealing procedures are amorphous, when deposited on the substrates at low temperatures. The differential scanning calorimetry studies show NiTi thin films formed by the e-beam evaporation are Ni-rich. Furthermore, SEM images illustrate that high-precision patterned NiTi thin film microstructures can be fabricated by combining with the e-beam evaporation and lift-off resist methods, without any wet or dry etching procedures. The proposed fabrication process for NiTi thin film microstructures shows great potential for application in shape memory alloy medical devices, as well as the micro-robotics.

36 MATERIALS SCIENCE↗
DOE OSTI2023

NMR study of Ni 50+x ⁢Ti 50-x strain glasses

Here, we studied Ni 50+x ⁢Ti 50-x with compositions up to x = 2, performing 47 Ti and 49 Ti nuclear magnetic resonance (NMR) measurements from 4 to 400 K. For large x in this system, a strain glass appears in which frozen ferroelastic nanodomains replace the displacive martensite structural transition. Here, we demonstrate that NMR can provide an extremely effective probe of the strain-glass freezing process, with large changes in NMR line shape due to the effects of random strains which become motionally narrowed at high temperatures. At the same time with high-resolution x-ray diffraction we confirm the lack of structural changes in x ≥ 1.2 samples, while we show that there is little change in the electronic behavior across the strain-glass freezing temperature. NMR spin-lattice relaxation time (T 1 ) measurements provide a further measure of the dynamics of the freezing process, and indicate a predominantly thermally activated behavior both above and below the strain-glass freezing temperature. We show that the strain-glass results are consistent with a very small density of critically divergent domains undergoing a Vogel-Fulcher-type freezing process, coexisting with domains exhibiting faster dynamics and stronger pinning.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Development and Evaluation of a Novel Curved Biopsy Device for CT-Guided Biopsy of Lesions Unreachable Using Standard Straight Needle Trajectories

PurposeTo evaluate the feasibility of a novel curved CT-guided biopsy needle prototype with shape memory to access otherwise not accessible biopsy targets.Methods and MaterialsA biopsy needle curved by 90° with specific radius was designed. It was manufactured using nitinol to acquire shape memory, encased in a straight guiding trocar to be driven out for access of otherwise inaccessible targets. Fifty CT-guided punctures were conducted in a biopsy phantom and 10 CT-guided punctures in a swine corpse. Biposies from porcine liver and muscle tissue were separately gained using the biopsy device, and histological examination was performed subsequently.ResultsMean time for placement of the trocar and deployment of the inner biopsy needle was ~205 ± 69 and ~93 ± 58 s, respectively, with a mean of ~4.5 ± 1.3 steps to reach adequate biopsy position. Mean distance from the tip of the needle to the target was ~0.7 ± 0.8 mm. CT-guided punctures in the swine corpse took relatively longer and required more biopsy steps (~574 ± 107 and ~380 ± 148 s, 8 ± 2.6 steps). Histology demonstrated appropriate tissue samples in nine out of ten cases (90%).ConclusionsTargets that were otherwise inaccessible via standard straight needle trajectories could be successfully reached with the curved biopsy needle prototype. Shape memory and preformed size with specific radius of the curved needle simplify the target accessibility with a low risk of injuring adjacent structures.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

Magnetic and Transport Properties of Mn{sub 2}Ni{sub 1.8}In{sub 0.2} Alloy

The structural, magnetic, and transport properties of the Mn{sub 2}Ni{sub 1.8}In{sub 0.2} alloy have been presented. It was observed to form in tetragonal structure. Multiple magnetic phase transitions have been detected in magnetization data over the temperature range from 2 to 350 K. From the resistivity, ac susceptibility, and heat capacity data, the superconducting transition are observed at T = 5.6 K. The alloy is considered to be one of the potential candidates from the Mn-rich alloys, which has shown both magnetic and superconducting properties, which can be useful from application point of view.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

High Damping of Lightweight TiNi-Ti{sub 2}Ni Shape Memory Composites for Wide Temperature Range Usage

A bimodal porous TiNi-Ti{sub 2}Ni shape memory alloy composite (SMAC) with 59% porosity was fabricated by sintering Ti-46at.%Ni elemental powders with pore-forming agent. The porous TiNi-Ti{sub 2}Ni SMAC contains two irregular pores of about 400 and 120 μm. We investigated the microstructure and pore morphology correlated with the mechanical properties and damping capacities of the SMAC. Ti{sub 2}Ni intermetallic phases with size of 1-3 μm were homogeneously distributed in the TiNi matrix. The porous TiNi-Ti{sub 2}Ni SMAC exhibits exceptionally high inverse mechanical quality factor (Q{sup −1}) of ~0.25 at < 40 °C, which is among the highest value reported for porous/dense shape memory alloys or composites to best of our knowledge, and it shows very high compressive fracture strain of about 25%. Moreover, the fabricated porous SMAC at relatively low strain amplitude can exhibit considerable high Q{sup −1} of 0.06 ~ 0.11 for a wide range of temperature between − 90 and 200 °C, which is attributed to the stress concentration distribution provided by the bimodal structure of pores and the massive interfaces between pore/matrix and TiNi/Ti{sub 2}Ni. These porous SMACs can be an ideal candidate for using as a lightweight damping material in the energy-saving applications.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Atomic Layer-Deposited TiO{sub 2} Coatings on NiTi Surface

NiTi shape-memory alloys may release poisonous Ni ions at the alloys’ surface. In an attempt to prepare a well-performing surface layer on an NiTi sample, the thermally grown TiO{sub 2} layer, which formed during the heat treatment of NiTi, was removed and replaced with a new TiO{sub 2} layer prepared using the atomic layer deposition (ALD) method. Using x-ray photoelectron spectroscopy, it was found that the ALD layer prepared at as low a temperature as 100 °C contained Ti in oxidation states + 4 and + 3. As for static corrosion properties of the ALD-coated NiTi samples, they further improved compared to those covered by thermally grown oxide. The corrosion rate of samples with thermally grown oxide was 1.05 × 10{sup −5} mm/year, whereas the corrosion rate of the ALD-coated samples turned out to be about five times lower. However, cracking of the ALD coating occurred at about 1.5% strain during the superelastic mechanical loading in tension taking place via the propagation of a localized martensite band.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Compressive Deformation Behavior of Open-Cell Cu-Zn-Al Alloy Foam Made Through P/M Route Using Mechanically Alloyed Powder

Cu-Zn-Al foams of varying porosity fractions using mechanical alloyed powder have been made through powder metallurgy route. Here, NH{sub 4} (HCO{sub 3}) was used as a space holder. Mechanically alloyed Cu-Zn-Al is made using a planetary ball mill taking the ratio of Cu/Zn/Al = 70:25:5 (by weight ratio). The ball/powder ratios were varied in the four ranges 10:1, 15:1, 20:1, and 25:1. Green compacts of milled powder and space holder samples were sintered at three stages at three different temperatures 350, 550, and 850 °C for 1 h at each stage. The crystalline size and particle size as a function of ball/powder ratios were examined. The compressive deformation responses of foams are varied with relative density and the ball/powder ratio. The plateau stress and energy absorption of these foams increase with an increase in relative density but decreases with increase in ball/powder ratio, even though crystalline size decreases. This has further been explained on the basis of particle morphology as a function of ball/powder ratio.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructures, Martensitic Transformation, and Mechanical Behavior of Rapidly Solidified Ti-Ni-Hf and Ti-Ni-Si Shape Memory Alloys

In this work, the microstructure and mechanical properties of rapidly solidified Ti{sub 50−x/2}Ni{sub 50−x/2}Hf{sub x} (x = 0, 2, 4, 6, 8, 10, and 12 at.%) and Ti{sub 50−y/2}Ni{sub 50−y/2}Si{sub y} (y = 1, 2, 3, 5, 7, and 10 at.%) shape memory alloys (SMAs) were investigated. The sequence of the phase formation and transformations in dependence on the chemical composition is established. Rapidly solidified Ti-Ni-Hf or Ti-Ni-Si SMAs are found to show relatively high yield strength and large ductility for specific Hf or Si concentrations, which is due to the gradual disappearance of the phase transformation from austenite to twinned martensite and the predominance of the phase transformation from twinned martensite to detwinned martensite during deformation as well as to the refinement of dendrites and the precipitation of brittle intermetallic compounds.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Fabrication and Properties of Composite Artificial Muscles Based on Nylon and a Shape Memory Alloy

This paper focuses on the design, fabrication and investigation of the mechanical properties of new artificial muscles formed by twisting and annealing. The artificial muscles designed by twisting nylon have become a popular topic in the field of smart materials due to their high mechanical performance with a large deformation and power density. However, the complexity of the heating and cooling system required to control the nylon muscle is a disadvantage, so we have proposed a composite artificial muscle for providing a direct electricity-driven actuation by integrating nylon and a shape memory alloy (SMA). In this paper, the design and fabrication process of these composite artificial muscles are introduced before their mechanical properties, which include the deformation, stiffness, load and response, are investigated. The results show that these composite artificial muscles that integrate nylon and a SMA provide better mechanical properties and yield up to a 44.1% deformation and 3.43 N driving forces. The good performance and direct electro-thermal actuation make these composite muscles ideal for driving robots in a method similar to human muscles.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Experimental Validation of Numerical Simulations of a New-Generation NiTi Endodontic File Under Bending

The superelasticity of NiTi shape memory alloy has been used in endodontics since the 1990s. To study the mechanical behavior of endodontic instruments, a traditional approach consists in experimental investigations. However, finite element analysis constitutes another way to assess their mechanical behavior and to facilitate their design. The main aim of this study is to compare experimental and numerical bending results on different structures (NiTi wire, spreader, and instruments) to estimate the reliability of the finite element simulations. These investigations were carried out as follows. Firstly, experimental material parameters identification was performed using NiTi wires. These parameters were implemented in an appropriate NiTi model. Bending was numerically applied to the meshed structures generated by the finite element method. Experimental tests were performed on real structures under bending, with exactly the same loading, in order to compare experimental and numerical results. These results were in good agreement for each of the considered structures. This enabled the validation of the simulation results and the use of simulations to design new endodontic instruments.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Stability of Phase Transformation Temperatures During Cycling of Ti-15.8Nb-4.94Al-0.06Sc Shape Memory Alloy

The active ω phase formation decreases the martensitic transformation temperatures sharply and can even suppress the martensitic transformation during thermal cycling in Ti-Nb-based alloys. No ω phase is observed in the present Ti-15.8Nb-4.94Al-0.06Sc alloy when it is annealed at 650 °C for 4 h or subsequently aged at 200 and 250 °C for 2 h. The exclusion of ω phase remarkably improves the stability of phase transformation temperatures during thermal cycling. The martensitic transformation start temperature of the present alloy decreases by 30 °C but tends to be stable gradually during the 20 thermal cycles, owing to the saturation of lattice defects.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Acoustic emission analysis of cyclically loaded superelastic shape memory alloy fiber reinforced mortar beams

Superelastic shape memory alloys (SMAs) are metallic alloys that can recover their nonlinear deformations upon unloading. The use of SMAs in cementitious composites as fibers can enable crack recovery and re-centering capabilities. In this study, the crack recovery characteristics of SMA fiber reinforced mortar specimens subjected to flexural cyclic loading are studied through acoustic emission analysis. SMA fiber reinforced mortar specimens with fiber volume ratios of 0.3%, 0.5% and 1.0% are tested under cyclic flexural loads. Acoustic emissions (AE) signals are captured and analyzed to characterize the crack formation and crack width development at each cycle of loading. In addition, the crack width propagation of the specimens is monitored by Digital Image Correlation measurement system and is used as a basis in AE analyses. Results show that the SMA fiber reinforced mortars exhibit considerable re-centering and crack recovery characteristics at large deformation amplitudes.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Characterization of the microstructures and the shape memory properties of the Fe-Mn-Si-Cr-Ni-C shape memory alloy after severe plastic deformation by differential speed rolling and subsequent annealing

Highlights: • The Fe-SMA was subjected to severe plastic deformation and then annealed. • Recovery strain increased with increasing grain size. • An optimum grain size existed for the largest recovery stress. • Grain reduction is useful for having a high recovery stress. - Abstract: The Fe-13.51Mn-4.82Si-8.32Cr-3.49Ni-0.15C shape memory alloy was subjected to severe plastic deformation by high-ratio differential speed rolling and subsequent annealing (between 873 and 1373 K) to find the factors that affect recovery stress and recovery strain. As the annealing temperature increased (i. e., as grain size increased), the recovery strain increased. This was attributed to decrease in the density of grain boundaries and the density of twins with increasing grain size. The recovery stress, however, showed a different behavior. It increased with annealing temperature up to 973 K, at which an ultrafine grain size near 1.6 μm was obtained, and then decreased with further increase in the temperature. The difference between the recovery strain and the plastic strain induced by recovery stress under constrained displacement during cooling was proposed to determine the amount of recovery stress. There was an optimum grain size for the largest difference between the recovery strain and the plastic strain. The current study shows that grain-size reduction is not good for having a high recovery strain but it is beneficial for having a high recovery stress in the Fe-Mn-Si shape memory alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The shape recovery conditions for Fe–Mn–Si alloys: An interplay between martensitic transformation and plasticity

Highlights: • Fe15Mn5Si9Cr5Ni samples were rolled at 800 °C and annealed at 650 (C1) and 1000 °C (C2). • TEM analysis was performed. • High density of stacking faults and appropriate density of dislocation appears in C1. • Complex dislocation arrays due to plastic deformation are observed in C2. • Shape memory properties depend on the thermomechanical treatment. - Abstract: This work analyses the improvement of the shape memory properties of Fe-Mn-Si based alloys, and expands upon and deepens recently published developments concerning this topic. We prepared TEM specimens from a Fe-15Mn-5Si-9Cr-5Ni sheet rolled at 800 °C and annealed at 650 °C–92% shape recovery – and from another sheet annealed at 1000 °C–45% shape recovery. Here, we analyse the development of microstructure during the γ ↔ ε martensitic transformation and correlate it with the shape memory behaviour. Among the observed microstructural features, the introduction of complex dislocation arrays due to plastic deformation appears to be critical for shape memory development, since they can arrest the backward movement of Shockley partial dislocations over the original path. Tailoring the microstructure in order to introduce a high stacking-fault density accompanied by an appropriate dislocation density remains a key issue in the design of these kinds of functional materials.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Recrystallization and martensitic transformation in nanometric grain size Cu-Al-Ni thin films grown by DC sputtering at room temperature

Highlights: • Polycrystalline Cu-Al-Ni thin films with nanometric grain size are grown by DC sputtering. • Influence of thermal annealing process at low temperatures on the microstructure is analyzed. • Strained martensitic transformation is observed for films with grain size average of 30 nm. - Abstract: We report the recrystallization of metastable hexagonal and body centered cubic BCC phase in free-standing 6 μm thick Cu-Al-Ni films grown by DC sputtering at room temperature. The results show that the BCC phase recrystallizes to L2{sub 1} at around 533 K together with precipitation of γ{sub 2}-phase. Annealing temperatures (533 K–623 K) at short times (0–30 min) produce systematic increment of the fraction of γ{sub 2}-phase. Films with phase coexistence of hexagonal, γ{sub 2} and L2{sub 1} structure display temperature driven martensitic transformation. This transformation is observed for samples with austenite grain size of around 30 nm. In all cases, the martensitic transformation temperature (M{sub S}) notoriously decreases (compared to bulk) and systematically increases with the annealing temperatures and annealing time. In addition, the films display extended transformation and retransformation ranges along with asymmetric hysteresis, which may be associated to restitutive forces due to elastic deformations at martensite – martensite and martensite – austenite interfaces. Annealing temperatures above 623 K produce fast precipitation to equilibrium α- and γ{sub 2}-phases. The austenitic phase can be recovered after annealing over 1000 K and fast quenching in ice-water.

77 NANOSCIENCE AND NANOTECHNOLOGY↗