662 research outputs found
Methods of Fabricating a Layer of Metallic Glass-Based Material Using Immersion and Pouring Techniques
Systems and methods in accordance with embodiments of the invention implement layers of metallic glass-based materials. In one embodiment, a method of fabricating a layer of metallic glass includes: applying a coating layer of liquid phase metallic glass to an object, the coating layer being applied in a sufficient quantity such that the surface tension of the liquid phase metallic glass causes the coating layer to have a smooth surface; where the metallic glass has a critical cooling rate less than 1000 K/s; and cooling the coating layer of liquid phase metallic glass to form a layer of solid phase metallic glass
Near-threshold fatigue crack growth in bulk metallic glass composites
A major drawback in using bulk metallic glasses (BMGs) as structural materials is their extremely poor fatigue performance. One way to alleviate this problem is through the composite route, in which second phases are introduced into the glass to arrest crack growth. In this paper, the fatigue crack growth behavior of in situ reinforced BMGs with crystalline dendrites, which are tailored to impart significant ductility and toughness to the BMG, was investigated. Three composites, all with equal volume fraction of dendrite phases, were examined to assess the influence of chemical composition on the near-threshold fatigue crack growth characteristics. While the ductility is enhanced at the cost of yield strength vis-Ã -vis that of the fully amorphous BMG, the threshold stress intensity factor range for fatigue crack initiation in composites was found to be enhanced by more than 100%. Crack blunting and trapping by the dendritic phases and constraining of the shear bands within the interdendritic regions are the micromechanisms responsible for this enhanced fatigue crack growth resistance
Compliant morphing structures from twisted bulk metallic glass ribbons
In this work, we investigate the use of pre-twisted metallic ribbons as
building blocks for shape-changing structures. We manufacture these elements by
twisting initially flat ribbons about their (lengthwise) centroidal axis into a
helicoidal geometry, then thermoforming them to make this configuration a
stress-free reference state. The helicoidal shape allows the ribbon to have
preferred bending directions that vary throughout its length. These bending
directions serve as compliant joints and enable several deployed and stowed
configurations that are unachievable without pre-twist, provided that
compaction does not induce material failure. We fabricate these ribbons using a
bulk metallic glass (BMG), for its exceptional elasticity and thermoforming
attributes. Combining numerical simulations, an analytical model based on shell
theory and torsional experiments, we analyze the finite-twisting mechanics of
various ribbon geometries. We find that, in ribbons with undulated edges, the
twisting deformations can be better localized onto desired regions prior to
thermoforming. Finally, we join together multiple ribbons to create deployable
systems. Our work proposes a framework for creating fully metallic, yet
compliant structures that may find application as elements for space structures
and compliant robots
Microgravity metal processing: from undercooled liquids to bulk metallic glasses
Bulk metallic glasses (BMGs) are a novel class of metal alloys that are poised for widespread commercialization. Over 30 years of NASA and ESA (as well as other space agency) funding for both ground-based and microgravity experiments has resulted in fundamental science data that have enabled commercial production. This review focuses on the history of microgravity BMG research, which includes experiments on the space shuttle, the ISS, ground-based experiments, commercial fabrication and currently funded efforts
Systems and Methods for Implementing Bulk Metallic Glass-Based Strain Wave Gears and Strain Wave Gear Components
Bulk metallic glass-based strain wave gears and strain wave gear components. In one embodiment, a strain wave gear includes: a wave generator; a flexspline that itself includes a first set of gear teeth; and a circular spline that itself includes a second set of gear teeth; where at least one of the wave generator, the flexspline, and the circular spline, includes a bulk metallic glass-based material
Systems and Methods for Implementing Bulk Metallic Glass-Based Macroscale Compliant Mechanisms
Systems and methods in accordance with embodiments of the invention implement bulk metallic glass-based macroscale compliant mechanisms. In one embodiment, a bulk metallic glass-based macroscale compliant mechanism includes: a flexible member that is strained during the normal operation of the compliant mechanism; where the flexible member has a thickness of 0.5 mm; where the flexible member comprises a bulk metallic glass-based material; and where the bulk metallic glass-based material can survive a fatigue test that includes 1000 cycles under a bending loading mode at an applied stress to ultimate strength ratio of 0.25
Systems and Methods for Fabricating Structures Including Metallic Glass-Based Materials Using Low Pressure Casting
Systems and methods to fabricate objects including metallic glass-based materials using low-pressure casting techniques are described. In one embodiment, a method of fabricating an object that includes a metallic glass-based material includes: introducing molten alloy into a mold cavity defined by a mold using a low enough pressure such that the molten alloy does not conform to features of the mold cavity that are smaller than 100 microns; and cooling the molten alloy such that it solidifies, the solid including a metallic glass-based material
Systems and Methods for Implementing Tailored Metallic Glass-Based Strain Wave Gears and Strain Wave Gear Components
Systems and methods in accordance with embodiments of the invention implement tailored metallic glass-based strain wave gears and strain wave gear components. In one embodiment, a method of fabricating a flexspline of a strain wave gear includes: forming a MG-based composition into a flexspline using one of a thermoplastic forming technique and a casting technique; where the forming of the MG-based composition results in a formed MG-based material; where the formed flexspline is characterized by: a minimum thickness of greater than approximately 1 mm and a major diameter of less than approximately 4 inches
Systems and Methods for Structurally Interrelating Components Using Inserts Made from Metallic Glass-Based Materials
Systems and methods in accordance with embodiments of the invention operate to structurally interrelate two components using inserts made from metallic glass-based materials. In one embodiment, a method of structurally interrelating two components includes: forming an insert from a metallic glass-based composition; where the formed insert includes a metallic glass-based material; affixing the insert to a first component; and structurally interrelating the second component to the first component using the insert
Bulk Metallic Glasses and Composites for Optical and Compliant Mechanisms
Mechanisms are used widely in engineering applications due to their ability to translate force and movement. They are found in kinematic pairs, gears, cams, linkages, and in flexure mechanisms (also known as compliant mechanisms). Mechanisms and flexures are used widely in spacecraft design, especially in the area of optics, where precise positioning of telescope mirrors requires elastic flexing of elements. A compliant mechanism is generally defined as a flexible mechanism that uses an elastic body deformation to cause a displacement (such as positing a mirror). The mechanisms are usually constructed as a single monolithic piece of material, and contain thin struts to allow for large elastic bending with low input force. This creates the largest problem with developing precise mechanisms; they must be fabricated from a single piece of metal, but are required to have strict accuracy on their dimensions. They are generally required to have high strength, elasticity, and low coefficient of thermal expansion
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