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At least 577 records · Page 32

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NASA NTRS2022

Design of Materials with Alchemite

Machine learning models that establish the relationships between materials processing and properties can enable inverse design of materials through active learning. Alchemite is a commercial software that can perform inverse materials design on sparse data. Here we evaluate Alchemite’s performance on a dataset of shape memory alloys and a dataset of heat exchangers compared to baseline random forest models. Alchemite had higher accuracy when making predictions on sparse data and was more accurate or nearly as accurate as random forests on complete datasets while also quantifying uncertainty. The software was also used to suggest processing steps and design parameters to optimize properties and performance; however, physical validation of the suggested design parameters was beyond the scope of this work. Several useful design insights were gained about the impact of the design parameters on properties and performance including the importance of dopant choice and amount for shape memory alloys and the importance of height and weight on the thermal resistance of heat exchangers.

Machine learning↗

NASA NTRS2000

Retraction Assembly for Space Shuttle Extended Nose Landing Gear

As part of a project to encourage the use of shape memory alloy actuators for space actuators, this mechanism uses a nitinol ribbon to provide the necessary motion to help retract the proposed extended nose landing gear (ENLG) for the space shuttle. Initial proof-of-concept design of the ENLG did not include the ability to retract the gear automatically. One proposed actuator for this purpose was designed at Johnson Space Center and uses resistive heating to rotate the ribbon around a cylinder. This rotation then allows the assembly to pull down a wedge that is used to hold the landing gear strut in place, thus returning the landing gear to its previous height before extension. The presentation will follow the design of this assembly from working with the nitinol ribbon to providing mechanical connections and allowing minimal friction for motion of three wraps around a cylinder. Also to be presented is preliminary work on design of a shape memory alloy gripper, a design project to demonstrate uses of NiTi.

Files, Bradley S.↗

NASA NTRS2008

Miniature High-Force, Long-Stroke SMA Linear Actuators

Improved long-stroke shape-memory-alloy (SMA) linear actuators are being developed to exert significantly higher forces and operate at higher activation temperatures than do prior SMA actuators. In these actuators, long linear strokes are achieved through the principle of displacement multiplication, according to which there are multiple stages, each intermediate stage being connected by straight SMA wire segments to the next stage so that relative motions of stages are additive toward the final stage, which is the output stage. Prior SMA actuators typically include polymer housings or shells, steel or aluminum stages, and polymer pads between successive stages of displacement-multiplication assemblies. Typical output forces of prior SMA actuators range from 10 to 20 N, and typical strokes range from 0.5 to 1.5 cm. An important disadvantage of prior SMA wire actuators is relatively low cycle speed, which is related to actuation temperature as follows: The SMA wires in prior SMA actuators are typically made of a durable nickel/titanium alloy that has a shape-memory activation temperature of 80 C. An SMA wire can be heated quickly from below to above its activation temperature to obtain a stroke in one direction, but must then be allowed to cool to somewhat below its activation temperature (typically, less than or equal to 60 C in the case of an activation temperature of 80 C) to obtain a stroke in the opposite direction (return stroke). At typical ambient temperatures, cooling times are of the order of several seconds. Cooling times thus limit cycle speeds. Wires made of SMA alloys having significantly higher activation temperatures [denoted ultra-high-temperature (UHT) SMA alloys] cool to the required lower return-stroke temperatures more rapidly, making it possible to increase cycle speeds. The present development is motivated by a need, in some applications (especially aeronautical and space-flight applications) for SMA actuators that exert higher forces, operate at greater cycle speeds, and have stronger housings that can withstand greater externally applied forces and impacts. The main novel features of the improved SMA actuators are the following: 1) The ends of the wires are anchored in compact crimps made from short steel tubes. Each wire end is inserted in a tube, the tube is flattened between planar jaws to make the tube grip the wire, the tube is compressed to a slight U-cross-section deformation to strengthen the grip, then the crimp is welded onto one of the actuator stages. The pull strength of a typical crimp is about 125 N -- comparable to the strength of the SMA wire and greater than the typical pull strengths of wire-end anchors in prior SMA actuators. Greater pull strength is one of the keys to achievement of higher actuation force; 2) For greater strength and resistance to impacts, housings are milled from aluminum instead of being made from polymers. Each housing is made from two pieces in a clamshell configuration. The pieces are anodized to reduce sliding friction; 3) Stages are made stronger (to bear greater compression loads without excessive flexing) by making them from steel sheets thicker than those used in prior SMA actuators. The stages contain recessed pockets to accommodate the crimps. Recessing the pockets helps to keep overall dimensions as small as possible; and, 4) UHT SMA wires are used to satisfy the higher-speed/higher-temperature requirement.

Cummin, Mark A.↗

DOE OSTI2018

A first-principles based description of the Hf-Ni system supported by high-temperature synchrotron experiments

Hf-Ni is an important binary system for high temperature alloys and shape memory alloys which has been investigated several times in the literature but often using samples of Hf contaminated by Zr. The thermodynamics of this system are remodeled in this work based on first-principles calculations and additional experiments using Hf with relatively low Zr contamination (0.25 wt. %). Diffusion couples in the Ni-rich portion of the Hf-Ni system heat treated at 1173, 1273 and 1373 K are used to measure phase stability and Hf solubility in the fcc phase. The solubility observed in fcc Ni from Ni/Ni 50 Hf 50 (at.%) diffusion couples is larger than that observed in previous experiments. These results are the only source fit to during modeling of the fcc solubility to mitigate effects from Zr contamination. Data in the literature suggests that the high temperature crystal structure of the B33 NiHf phase is, in fact, the B2 structure. High temperature synchrotron measurements provide confirmation of this crystal structure. Modeling of the B2 phase was aided by first-principles calculations using special quasi-random structures (SQS). Finally, the present CALPHAD model will prove useful when designing shape memory alloys containing Hf and when modeling the Hf activity in Ni-base high temperature alloys.

36 MATERIALS SCIENCE↗

NASA NTRS2008

Effect of Upper-Cycle Temperature on the Load-Biased, Strain-Temperature Response of NiTi

Over the past decade, interest in shape memory alloy based actuators has increased as the primary benefits of these solid-state devices have become more apparent. However, much is still unknown about the characteristic behavior of these materials when used in actuator applications. Recently we have shown that the maximum temperature reached during thermal cycling under isobaric conditions could significantly affect the observed mechanical response of NiTi (55 wt% Ni), especially the amount of transformation strain available for actuation and thus work output. This investigation extends that original work to ascertain whether further increases in the upper-cycle temperature would produce additional improvement in the work output of the material, which has a stress-free Af of 113 oC, and to determine the optimum cyclic conditions. Thus, isobaric, thermal-cycle experiments were conducted in the aforementioned alloy at various stress levels from 50-300 MPa using upper-cycle temperatures of 165, 200, 230, 260, 290, 320 and 350 oC. The data indicated that the amount of applied stress influenced the transformation strain available in the system, as would be expected. However, the maximum temperature reached during the thermal excursion also plays a role in determining the transformation strain, with the maximum transformation strain being developed by thermal cycling to 290 oC. In situ, neutron diffraction showed that the differences in transformation strain were related to differences in martensite texture within the microstructure when cycling to different upper-cycle temperatures. Hence, understanding this effect is important to optimizing the operation of SMA-based actuators and could lead to new methods for processing and training shape memory alloys for optimal performance.

Padula, Santo, II↗

NASA NTRS2011

Effect of Upper-Cycle Temperature on the Load-Biased, Strain-Temperature Response of NiTi

Over the past decade, interest in shape memory alloy based actuators has increased as the primary benefits of these solid-state devices have become more apparent. However, much is still unknown about the characteristic behavior of these materials when used in actuator applications. Recently we have shown that the maximum temperature reached during thermal cycling under isobaric conditions could significantly affect the observed mechanical response of NiTi (55 wt% Ni), especially the amount of transformation strain available for actuation and thus work output. The investigation we report here extends that original work to ascertain whether further increases in the upper-cycle temperature would produce additional changes in the work output of the material, which has a stress-free austenite finish temperature of 113 C, and to determine the optimum cyclic conditions. Thus, isobaric, thermal-cycle experiments were conducted on the aforementioned alloy at various stresses from 50-300 MPa using upper-cycle temperatures of 165, 200, 230, 260, 290, 320 and 350 C. The data indicated that the amount of applied stress influenced the transformation strain, as would be expected. However, the maximum temperature reached during the thermal excursion also plays an equally significant role in determining the transformation strain, with the maximum transformation strain observed during thermal cycling to 290 C. In situ neutron diffraction at stress and temperature showed that the differences in transformation strain were mostly related to changes in martensite texture when cycling to different upper-cycle temperatures. Hence, understanding this effect is important to optimizing the operation of SMA-based actuators and could lead to new methods for processing and training shape memory alloys for optimal performance.

Padula, Santo, II↗

NASA NTRS2014

Locomotion of Amorphous Surface Robots

An amorphous robot includes a compartmented bladder containing fluid, a valve assembly, and an outer layer encapsulating the bladder and valve assembly. The valve assembly draws fluid from a compartment(s) and discharges the drawn fluid into a designated compartment to displace the designated compartment with respect to the surface. Another embodiment includes elements each having a variable property, an outer layer that encapsulates the elements, and a control unit. The control unit energizes a designated element to change its variable property, thereby moving the designated element. The elements may be electromagnetic spheres with a variable polarity or shape memory polymers with changing shape and/or size. Yet another embodiment includes an elongated flexible tube filled with ferrofluid, a moveable electromagnet, an actuator, and a control unit. The control unit energizes the electromagnet and moves the electromagnet via the actuator to magnetize the ferrofluid and lengthen the flexible tube.

Bradley, Arthur T.↗

NASA NTRS2016

Locomotion of Amorphous Surface Robots

Bradley, Arthur T.↗

NASA NTRS2018

Locomotion of Amorphous Surface Robots

Bradley, Arthur T.↗

DOE OSTI2022

Effect of laser scanning speed on the microstructure, phase transformation and mechanical property of NiTi alloys fabricated by $\mathrm{LPBF}$

This study investigated the effects of laser scanning speed on the microstructure, phase transformation and properties of NiTi alloys fabricated by laser powder bed fusion (LPBF). In this study, the contributions of metallurgical factors under different scanning speeds, such as Ni evaporation, Ni4Ti3 precipitation, dislocations and internal stress, to the transformation temperature and transformation latent heat were clarified through specially designed experiments. Ni evaporation is found to have the most profound effect, followed by precipitation. Increasing scanning speed is found to reduce Ni loss, thus cause less increase in the transformation temperature and transformation heat of the LPBF-NiTi alloys. Increasing scanning speed also increases the microstructure non-uniformity and thus widens the transformation temperature interval. The orientations of residual stress exhibit strong crystallographic stiffness dependence. The LPBF-NiTi alloys with different scanning speeds all exhibited high strains (>13.4%) and excellent shape memory effect. A LPBF-NiTi honeycomb structure exhibited 96% shape recovery rate after a 60% pre-compressive deformation. Besides, there is an optimum scanning speed for minimum porosity and smallest average pore size. However, the pore structure is found to have weak influence on the tensile behaviour of the LPBF-NiTi alloys, possibly due to the high defect tolerance of the martensitic transformation.

36 MATERIALS SCIENCE↗

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 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↗

NASA NTRS2016

Shape Morphing Adaptive Radiator Technology (SMART) for Variable Heat Rejection

The proposed technology leverages the temperature dependent phase change of shape memory alloys (SMAs) to drive the shape of a flexible radiator panel. The opening/closing of the radiator panel, as a function of temperature, passively adapts the radiator's rate of heat rejection in response to a vehicle's needs.

Erickson, Lisa↗

NASA NTRS2021

Adaptive Aerostructures for Revolutionary Civil Supersonic Transportation

To enable commercially viable civil supersonic transport (SST) aircraft, innovative solutions must be developed to meet noise and efficiency requirements for overland flight. This research effort consists of a multidisciplinary team of academic and industrial experts exploring for the first time the potential of small real-time geometric outer mold line (OML) reconfigurations to minimize sonic boom signatures and aircraft drag in response to changing ambient conditions, thereby enabling noise-compliant overland supersonic flight. The team utilizes recent advances in supersonic computational fluid dynamic (CFD) methods, new noise prediction tools, and new design approaches to consider embedded highly energy-dense shape memory alloy (SMA) actuators for local shape modifications to an SST aircraft leading to optimal low boom signature and low drag in different environments. This university-led program will provide strategic leadership toward technology convergence that advances NASA's Aerospace Research Mission Directorate's (ARMD) research objectives with regard to Thrust 2: “Innovation in Commercial Supersonic Aircraft” by exploring for the first time enabling low-boom operation across a range of flight conditions via structural adaptivity, and will promote education of the next generation of engineers. The overall research strategy is to pursue three critical areas: the design of configurations for reducing boom, SMA material development and modeling, and technology feasibility demonstration in a relevant environment. Initially, the team will identify potential applications where structure or geometry adaptivity provides a benefit in noise or drag across the entire flight envelope. For selected applications/structural locations, required OML geometry changes will be determined based on analysis of sonic boom ground signature and drag reduction using new design tools, trade studies, and atmospheric sensing techniques. Designs will be developed and evaluated against requirements on loading, stroke length, and operational temperature. New alloy formulations will be developed tailored for both autonomous and controlled actuation modes. As the SMA material development matures, integrated system-level factors will be investigated. Optimized designs for small-scale distributed adaptivity applications of maximum benefit will then be matured and tested, moving toward demonstration of the innovative technology approaches at a TRL 4-5 and showing that sonic booms can be reduced by reconfiguration on demand.

Koushik Datta↗

DOE OSTI2019

Contact Load in a Tight Thermomechanical Pipeline Joint

The contact problem for pipeline connection by means of a connector with shape memory is solved. In the solution, the actual deformation of the pipe is taken into account on the basis of the thermomechanical diagram. The thermal shape recovery of the connector is modeled. The conditions in which this approach may be employed are formulated. As an example, the contact load in a joint is determined.

42 ENGINEERING↗

NASA NTRS2024

Thermal Sensitivity Study of Lunar Terrain Vehicle Wheels

Since the early development of lunar vehicles for the Apollo program, designing a wheel capable of functioning in the harsh equatorial lunar environment was identified as a uniquely difficult engineering challenge. The Lunar Terrain Vehicle (LTV) must contend with many of the same challenges encountered during the Apollo missions, but with the addition of colder, more complex thermal environments at the lunar south pole and longer Artemis mission timelines. A full thermal assessment of LTV wheels should capture these and other details to assess heat leak through the wheels and extreme hot and cold temperatures. The goals of this study are to provide bounding lunar south pole thermal environments; to define sensitivity to interactions between the wheel and the lunar surface in different operation modes, such as parked and traversing; and to identify thermal performance concerns related to the use of shape memory alloys.

Lunar Terrain Vehicle↗

DOE OSTI2016

POLYMERIC MULTIFERROIC, COLLABORATIVE RESEARCH BETWEEN UNIVERSITY OF MARYLAND AND KANSAS UNIVERSITY

The research was directed towards finding new functional materials, mainly polymeric. Main accomplishment consisit of indentifying mulktiferroic polymers and a shape memory alloy featuring an ultralong fatigue life of 10 million cycles.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Microstructure of selective laser melted nickel–titanium

In selective laser melting, the layer-wise local melting of metallic powder by means of a scanning focused laser beam leads to anisotropic microstructures, which reflect the pathway of the laser beam. We studied the impact of laser power, scanning speed, and laser path onto the microstructure of NiTi cylinders. Here, we varied the laser power from 56 to 100 W and the scanning speed from about 100 to 300 mm/s. In increasing the laser power, the grain width and length increased from (33 ± 7) to (90 ± 15) μm and from (60 ± 20) to (600 ± 200) μm, respectively. Also, the grain size distribution changed from uni- to bimodal. Ostwald-ripening of the crystallites explains the distinct bimodal size distributions. Decreasing the scanning speed did not alter the microstructure but led to increased phase transformation temperatures of up to 40 K. This was experimentally determined using differential scanning calorimetry and explained as a result of preferential nickel evaporation during the fabrication process. During selective laser melting of the NiTi shape memory alloy, the control of scanning speed allows restricted changes of the transformation temperatures, whereas controlling the laser power and scanning path enables us to tailor the microstructure, i.e. the crystallite shapes and arrangement, the extent of the preferred crystallographic orientation and the grain size distribution. - Highlights: • Higher laser powers during selective laser melting of NiTi lead to larger grains. • Selective laser melting of NiTi gives rise to preferred <111> orientation. • The observed Ni/Ti ratio depends on the exposure time. • Ostwald ripening explains the bimodal grain size distribution.

36 MATERIALS SCIENCE↗